From c8c042816266f4ccd2fc8495c70a1e86bd7642df Mon Sep 17 00:00:00 2001
From: Ron Buckton <ron.buckton@microsoft.com>
Date: Wed, 20 Jun 2018 18:24:12 -0700
Subject: [PATCH] Cleanup, remove some unneeded dependencies, make it easier to
 add gulp.watch support later

---
 Gulpfile.js                  | 122 +++--
 package-lock.json            | 111 ++---
 package.json                 |   2 +-
 scripts/build/chalk.js       |   5 +
 scripts/build/colors.js      |  20 -
 scripts/build/diagnostics.js |  31 +-
 scripts/build/exec.js        |   4 +-
 scripts/build/gulp.js        |   7 +
 scripts/build/lib.js         |  33 +-
 scripts/build/pass.js        |  11 -
 scripts/build/prepend.js     |  14 -
 scripts/build/project.js     | 847 ++++++++++++++++-------------------
 scripts/build/upToDate.js    |   4 +-
 src/compiler/tsbuild.ts      |   6 -
 14 files changed, 539 insertions(+), 678 deletions(-)
 create mode 100644 scripts/build/chalk.js
 delete mode 100644 scripts/build/colors.js
 delete mode 100644 scripts/build/pass.js
 delete mode 100644 scripts/build/prepend.js

diff --git a/Gulpfile.js b/Gulpfile.js
index c2b5627b749..1ba05048578 100644
--- a/Gulpfile.js
+++ b/Gulpfile.js
@@ -24,12 +24,13 @@ const getDirSize = require("./scripts/build/getDirSize");
 const project = require("./scripts/build/project");
 const replace = require("./scripts/build/replace");
 const convertConstEnums = require("./scripts/build/convertConstEnum");
-const makeLibraryTargets = require("./scripts/build/lib");
 const needsUpdate = require("./scripts/build/needsUpdate");
 const getDiffTool = require("./scripts/build/getDiffTool");
 const baselineAccept = require("./scripts/build/baselineAccept");
 const cmdLineOptions = require("./scripts/build/options");
 const exec = require("./scripts/build/exec");
+const _debugMode = require("./scripts/build/debugMode");
+const { libraryTargets, generateLibs } = require("./scripts/build/lib");
 const { runConsoleTests, cleanTestDirs, writeTestConfigFile, refBaseline, localBaseline, refRwcBaseline, localRwcBaseline } = require("./scripts/build/tests");
 
 Error.stackTraceLimit = 1000;
@@ -37,11 +38,10 @@ Error.stackTraceLimit = 1000;
 // Constants
 const host = cmdLineOptions.host;
 const copyright = "CopyrightNotice.txt";
-const libraryTargets = makeLibraryTargets([copyright]);
 
-// Compile using the LKG compiler
 project.addTypeScript("lkg", "./lib/typescript.js");
-project.addTypeScript("default", "lkg");
+project.addTypeScript("built", "./built/local/typescriptServices.js");
+project.addTypeScript("default", "lkg"); // Compile using the LKG compiler by default
 
 const scriptsProject = "scripts/tsconfig.json";
 const configurePrereleaseJs = "scripts/configurePrerelease.js";
@@ -50,7 +50,7 @@ const generateLocalizedDiagnosticMessagesJs = "scripts/generateLocalizedDiagnost
 const buildProtocolJs = "scripts/buildProtocol.js";
 const produceLKGJs = "scripts/produceLKG.js";
 const word2mdJs = "scripts/word2md.js";
-gulp.task("scripts", /*help*/ false, [project(scriptsProject)], undefined, {
+gulp.task("scripts", /*help*/ false, () => project.compile(scriptsProject), {
     aliases: [
         configurePrereleaseJs, 
         processDiagnosticMessagesJs,
@@ -60,7 +60,7 @@ gulp.task("scripts", /*help*/ false, [project(scriptsProject)], undefined, {
         word2mdJs
     ]
 });
-gulp.task("clean-scripts", /*help*/ false, [project.clean(scriptsProject)]);
+gulp.task("clean-scripts", /*help*/ false, () => project.clean(scriptsProject));
 
 // Nightly management tasks
 gulp.task(
@@ -78,8 +78,8 @@ gulp.task(
 
 const importDefinitelyTypedTestsProject = "scripts/importDefinitelyTypedTests/tsconfig.json";
 const importDefinitelyTypedTestsJs = "scripts/importDefinitelyTypedTests/importDefinitelyTypedTests.js";
-gulp.task(importDefinitelyTypedTestsJs, /*help*/ false, [project(importDefinitelyTypedTestsProject)]);
-gulp.task("clean:" + importDefinitelyTypedTestsJs, /*help*/ false, [project.clean(importDefinitelyTypedTestsProject)]);
+gulp.task(importDefinitelyTypedTestsJs, /*help*/ false, () => project.compile(importDefinitelyTypedTestsProject));
+gulp.task("clean:" + importDefinitelyTypedTestsJs, /*help*/ false, () => project.clean(importDefinitelyTypedTestsProject));
 
 gulp.task(
     "importDefinitelyTypedTests",
@@ -90,7 +90,7 @@ gulp.task(
 gulp.task(
     "lib",
     "Builds the library targets",
-    libraryTargets);
+    () => generateLibs([copyright]));
 
 // The generated diagnostics map; built for the compiler and for the "generate-diagnostics" task
 const diagnosticInformationMapTs = "src/compiler/diagnosticInformationMap.generated.ts";
@@ -145,20 +145,18 @@ gulp.task(typescriptServicesProject, /*help*/ false, () => {
     // NOTE: flatten services so that we can properly strip @internal
     project.flatten("src/services/tsconfig.json", typescriptServicesProject, {
         compilerOptions: {
+            "removeComments": true,
             "stripInternal": true,
             "outFile": "typescriptServices.js"
         }
     });
-})
+});
 
 const typescriptServicesJs = "built/local/typescriptServices.js";
 const typescriptServicesDts = "built/local/typescriptServices.d.ts";
-const typescriptServicesProjectTask = project.defer(typescriptServicesProject, {
-    dts: files => files.pipe(convertConstEnums()),
-    release: { compilerOptions: { removeComments: true } }
-});
-
-gulp.task(typescriptServicesJs, /*help*/ false, ["lib", "generate-diagnostics", typescriptServicesProject], typescriptServicesProjectTask, { aliases: [typescriptServicesDts] });
+gulp.task(typescriptServicesJs, /*help*/ false, ["lib", "generate-diagnostics", typescriptServicesProject], () => 
+    project.compile(typescriptServicesProject, { dts: convertConstEnums() }), 
+    { aliases: [typescriptServicesDts] });
 
 const typescriptJs = "built/local/typescript.js";
 gulp.task(typescriptJs, /*help*/ false, [typescriptServicesJs], () =>
@@ -186,28 +184,25 @@ gulp.task(typescriptStandaloneDts, /*help*/ false, [typescriptServicesDts], () =
 // build all 'typescriptServices'-related outputs
 gulp.task("typescriptServices", /*help*/ false, [typescriptServicesJs, typescriptServicesDts, typescriptJs, typescriptDts, typescriptStandaloneDts]);
 
-// Add the "built" compiler with a dependency on the built version of the compiler.
-project.addTypeScript("built", "./built/local/typescriptServices.js", [typescriptServicesJs]);
-
 const tscProject = "src/tsc/tsconfig.json";
 const tscJs = "built/local/tsc.js";
-gulp.task(tscJs, /*help*/ false, [project(tscProject, { typescript: "built", release: { compilerOptions: { removeComments: true } } })]);
+gulp.task(tscJs, /*help*/ false, [typescriptServicesJs], () => project.compile(tscProject, { typescript: "built" }));
 
 const cancellationTokenProject = "src/cancellationToken/tsconfig.json";
 const cancellationTokenJs = "built/local/cancellationToken.js";
-gulp.task(cancellationTokenJs, /*help*/ false, [project(cancellationTokenProject, { typescript: "built", release: { compilerOptions: { removeComments: true } } })]);
+gulp.task(cancellationTokenJs, /*help*/ false, [typescriptServicesJs], () => project.compile(cancellationTokenProject, { typescript: "built" }));
 
 const typingsInstallerProject = "src/typingsInstaller/tsconfig.json";
 const typingsInstallerJs = "built/local/typingsInstaller.js";
-gulp.task(typingsInstallerJs, /*help*/ false, [project(typingsInstallerProject, { typescript: "built", release: { compilerOptions: { removeComments: true } } })]);
+gulp.task(typingsInstallerJs, /*help*/ false, [typescriptServicesJs], () => project.compile(typingsInstallerProject, { typescript: "built" }));
 
 const tsserverProject = "src/tsserver/tsconfig.json";
 const tsserverJs = "built/local/tsserver.js";
-gulp.task(tsserverJs, /*help*/ false, [project(tsserverProject, { typescript: "built", release: { compilerOptions: { removeComments: true } } })]);
+gulp.task(tsserverJs, /*help*/ false, [typescriptServicesJs], () => project.compile(tsserverProject, { typescript: "built" }));
 
 const watchGuardProject = "src/watchGuard/tsconfig.json";
 const watchGuardJs = "built/local/watchGuard.js";
-gulp.task(watchGuardJs, /*help*/ false, [project(watchGuardProject, { typescript: "built", release: { compilerOptions: { removeComments: true } } })]);
+gulp.task(watchGuardJs, /*help*/ false, [typescriptServicesJs], () => project.compile(watchGuardProject, { typescript: "built" }));
 
 const typesMapJson = "built/local/typesMap.json";
 gulp.task(typesMapJson, /*help*/ false, [], () =>
@@ -249,42 +244,43 @@ gulp.task(
     "Generates a Markdown version of the Language Specification", 
     [specMd]);
 
+gulp.task("produce-LKG", /*help*/ false, ["scripts", "local", cancellationTokenJs, typingsInstallerJs, watchGuardJs], () => {
+    const expectedFiles = [
+        tscJs, 
+        typescriptServicesJs, 
+        tsserverJs, 
+        typescriptJs, 
+        typescriptDts, 
+        typescriptServicesDts, 
+        tsserverlibraryDts, 
+        tsserverlibraryDts, 
+        typingsInstallerJs, 
+        cancellationTokenJs
+    ].concat(libraryTargets);
+    const missingFiles = expectedFiles
+        .concat(localizationTargets)
+        .filter(f => !fs.existsSync(f));
+    if (missingFiles.length > 0) {
+        throw new Error("Cannot replace the LKG unless all built targets are present in directory 'built/local/'. The following files are missing:\n" + missingFiles.join("\n"));
+    }
+    const sizeBefore = getDirSize("lib");
+    return exec(host, [produceLKGJs]).then(() => {
+        const sizeAfter = getDirSize("lib");
+        if (sizeAfter > (sizeBefore * 1.10)) {
+            throw new Error("The lib folder increased by 10% or more. This likely indicates a bug.");
+        }
+    });
+});
+
 gulp.task(
     "LKG", 
     "Makes a new LKG out of the built js files", 
-    () => runSequence("clean-built", "dontUseDebugMode", ["scripts", "local", cancellationTokenJs, typingsInstallerJs, watchGuardJs], 
-        () => {
-            const expectedFiles = [
-                tscJs, 
-                typescriptServicesJs, 
-                tsserverJs, 
-                typescriptJs, 
-                typescriptDts, 
-                typescriptServicesDts, 
-                tsserverlibraryDts, 
-                tsserverlibraryDts, 
-                typingsInstallerJs, 
-                cancellationTokenJs
-            ].concat(libraryTargets);
-            const missingFiles = expectedFiles
-                .concat(localizationTargets)
-                .filter(f => !fs.existsSync(f));
-            if (missingFiles.length > 0) {
-                throw new Error("Cannot replace the LKG unless all built targets are present in directory 'built/local/'. The following files are missing:\n" + missingFiles.join("\n"));
-            }
-            const sizeBefore = getDirSize("lib");
-            return exec(host, [produceLKGJs]).then(() => {
-                const sizeAfter = getDirSize("lib");
-                if (sizeAfter > (sizeBefore * 1.10)) {
-                    throw new Error("The lib folder increased by 10% or more. This likely indicates a bug.");
-                }
-            });
-        }));
+    () => runSequence("clean-built", "dontUseDebugMode", "produce-LKG"));
 
 // Task to build the tests infrastructure using the built compiler
 const testRunnerProject = "src/testRunner/tsconfig.json";
 const runJs = "built/local/run.js";
-gulp.task(runJs, /*help*/ false, [project(testRunnerProject, { typescript: "built", deps: [tsserverlibraryDts] })]);
+gulp.task(runJs, /*help*/ false, [typescriptServicesJs, tsserverlibraryDts], () => project.compile(testRunnerProject, { typescript: "built" }));
 
 gulp.task(
     "tests",
@@ -310,8 +306,8 @@ gulp.task(
 
 const webTestServerProject = "tests/webTestServer.tsconfig.json";
 const webTestServerJs = "tests/webTestServer.js";
-gulp.task(webTestServerJs, /*help*/ false, [project(webTestServerProject, { typescript: "built", release: { compilerOptions: { removeComments: true } } })])
-gulp.task("clean:" + webTestServerJs, /*help*/ false, [project.clean(webTestServerProject, { typescript: "built" })])
+gulp.task(webTestServerJs, /*help*/ false, [typescriptServicesJs], () => project.compile(webTestServerProject, { typescript: "built" }));
+gulp.task("clean:" + webTestServerJs, /*help*/ false, () => project.clean(webTestServerProject));
 
 const bundlePath = path.resolve("built/local/bundle.js");
 
@@ -447,8 +443,8 @@ gulp.task(
 // Webhost
 const webtscProject = "tests/webhost/webtsc.tsconfig.json";
 const webtscJs = "tests/webhost/webtsc.js";
-gulp.task(webtscJs, /*help*/ false, [project(webtscProject, { typescript: "built", release: { compilerOptions: { removeComments: true } } })]);
-gulp.task("clean:" + webtscJs, /*help*/ false, [project.clean(webtscProject, { typescript: "built" })]);
+gulp.task(webtscJs, /*help*/ false, [typescriptServicesJs], () => project.compile(webtscProject, { typescript: "built" }));
+gulp.task("clean:" + webtscJs, /*help*/ false, () => project.clean(webtscProject));
 
 gulp.task("webhost", "Builds the tsc web host", [webtscJs], () =>
     gulp.src("built/local/lib.d.ts")
@@ -457,8 +453,8 @@ gulp.task("webhost", "Builds the tsc web host", [webtscJs], () =>
 // Perf compiler
 const perftscProject = "tests/perftsc.tsconfig.json";
 const perftscJs = "built/local/perftsc.js";
-gulp.task(perftscJs, /*help*/ false, [project(perftscProject, { typescript: "built", release: { compilerOptions: { removeComments: true } } })]);
-gulp.task("clean:" + perftscJs, /*help*/ false, [project.clean(perftscProject, { typescript: "built" })]);
+gulp.task(perftscJs, /*help*/ false, [typescriptServicesJs], () => project.compile(perftscProject, { typescript: "built" }));
+gulp.task("clean:" + perftscJs, /*help*/ false, () => project.clean(perftscProject));
 
 gulp.task(
     "perftsc",
@@ -477,8 +473,8 @@ gulp.task(loggedIOJs, /*help*/ false, [], (done) => {
 
 const instrumenterProject = "src/instrumenter/tsconfig.json";
 const instrumenterJs = "built/local/instrumenter.js";
-gulp.task(instrumenterJs, /*help*/ false, [project(instrumenterProject)]);
-gulp.task("clean:" + instrumenterJs, /*help*/ false, [project.clean(instrumenterProject)]);
+gulp.task(instrumenterJs, /*help*/ false, () => project.compile(instrumenterProject));
+gulp.task("clean:" + instrumenterJs, /*help*/ false, () => project.clean(instrumenterProject));
 
 gulp.task(
     "tsc-instrumented",
@@ -497,9 +493,9 @@ gulp.task(
 gulp.task(
     "build-rules",
     "Compiles tslint rules to js",
-    [project("scripts/tslint/tsconfig.json")]);
+    () => project.compile("scripts/tslint/tsconfig.json"));
 
-gulp.task("clean-rules", /*help*/ false, [project.clean("scripts/tslint/tsconfig.json")]);
+gulp.task("clean-rules", /*help*/ false, () => project.clean("scripts/tslint/tsconfig.json"));
 
 gulp.task(
     "lint",
diff --git a/package-lock.json b/package-lock.json
index 53cf762c995..ff52eb7be20 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11,7 +11,7 @@
             "dev": true,
             "requires": {
                 "acorn": "5.7.1",
-                "css": "2.2.1",
+                "css": "2.2.3",
                 "normalize-path": "2.1.1",
                 "source-map": "0.5.7",
                 "through2": "2.0.3"
@@ -408,6 +408,7 @@
             "version": "0.1.1",
             "resolved": "https://registry.npmjs.org/ansi-gray/-/ansi-gray-0.1.1.tgz",
             "integrity": "sha1-KWLPVOyXksSFEKPetSRDaGHvclE=",
+            "dev": true,
             "requires": {
                 "ansi-wrap": "0.1.0"
             }
@@ -439,7 +440,8 @@
         "ansi-wrap": {
             "version": "0.1.0",
             "resolved": "https://registry.npmjs.org/ansi-wrap/-/ansi-wrap-0.1.0.tgz",
-            "integrity": "sha1-qCJQ3bABXponyoLoLqYDu/pF768="
+            "integrity": "sha1-qCJQ3bABXponyoLoLqYDu/pF768=",
+            "dev": true
         },
         "append-buffer": {
             "version": "1.0.2",
@@ -468,7 +470,8 @@
         "arr-diff": {
             "version": "4.0.0",
             "resolved": "https://registry.npmjs.org/arr-diff/-/arr-diff-4.0.0.tgz",
-            "integrity": "sha1-1kYQdP6/7HHn4VI1dhoyml3HxSA="
+            "integrity": "sha1-1kYQdP6/7HHn4VI1dhoyml3HxSA=",
+            "dev": true
         },
         "arr-flatten": {
             "version": "1.1.0",
@@ -479,7 +482,8 @@
         "arr-union": {
             "version": "3.1.0",
             "resolved": "https://registry.npmjs.org/arr-union/-/arr-union-3.1.0.tgz",
-            "integrity": "sha1-45sJrqne+Gao8gbiiK9jkZuuOcQ="
+            "integrity": "sha1-45sJrqne+Gao8gbiiK9jkZuuOcQ=",
+            "dev": true
         },
         "array-differ": {
             "version": "1.0.0",
@@ -584,7 +588,8 @@
         "assign-symbols": {
             "version": "1.0.0",
             "resolved": "https://registry.npmjs.org/assign-symbols/-/assign-symbols-1.0.0.tgz",
-            "integrity": "sha1-WWZ/QfrdTyDMvCu5a41Pf3jsA2c="
+            "integrity": "sha1-WWZ/QfrdTyDMvCu5a41Pf3jsA2c=",
+            "dev": true
         },
         "astw": {
             "version": "2.2.0",
@@ -1171,7 +1176,8 @@
         "color-support": {
             "version": "1.1.3",
             "resolved": "https://registry.npmjs.org/color-support/-/color-support-1.1.3.tgz",
-            "integrity": "sha512-qiBjkpbMLO/HL68y+lh4q0/O1MZFj2RX6X/KmMa3+gJD3z+WwI1ZzDHysvqHGS3mP6mznPckpXmw1nI9cJjyRg=="
+            "integrity": "sha512-qiBjkpbMLO/HL68y+lh4q0/O1MZFj2RX6X/KmMa3+gJD3z+WwI1ZzDHysvqHGS3mP6mznPckpXmw1nI9cJjyRg==",
+            "dev": true
         },
         "combine-source-map": {
             "version": "0.8.0",
@@ -1353,23 +1359,17 @@
             }
         },
         "css": {
-            "version": "2.2.1",
-            "resolved": "https://registry.npmjs.org/css/-/css-2.2.1.tgz",
-            "integrity": "sha1-c6TIHehdtmTU7mdPfUcIXjstVdw=",
+            "version": "2.2.3",
+            "resolved": "https://registry.npmjs.org/css/-/css-2.2.3.tgz",
+            "integrity": "sha512-0W171WccAjQGGTKLhw4m2nnl0zPHUlTO/I8td4XzJgIB8Hg3ZZx71qT4G4eX8OVsSiaAKiUMy73E3nsbPlg2DQ==",
             "dev": true,
             "requires": {
                 "inherits": "2.0.3",
                 "source-map": "0.1.43",
-                "source-map-resolve": "0.3.1",
+                "source-map-resolve": "0.5.1",
                 "urix": "0.1.0"
             },
             "dependencies": {
-                "atob": {
-                    "version": "1.1.3",
-                    "resolved": "https://registry.npmjs.org/atob/-/atob-1.1.3.tgz",
-                    "integrity": "sha1-lfE2KbEsOlGl0hWr3OKqnzL4B3M=",
-                    "dev": true
-                },
                 "source-map": {
                     "version": "0.1.43",
                     "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.1.43.tgz",
@@ -1378,24 +1378,6 @@
                     "requires": {
                         "amdefine": "1.0.1"
                     }
-                },
-                "source-map-resolve": {
-                    "version": "0.3.1",
-                    "resolved": "https://registry.npmjs.org/source-map-resolve/-/source-map-resolve-0.3.1.tgz",
-                    "integrity": "sha1-YQ9hIqRFuN1RU1oqcbeD38Ekh2E=",
-                    "dev": true,
-                    "requires": {
-                        "atob": "1.1.3",
-                        "resolve-url": "0.2.1",
-                        "source-map-url": "0.3.0",
-                        "urix": "0.1.0"
-                    }
-                },
-                "source-map-url": {
-                    "version": "0.3.0",
-                    "resolved": "https://registry.npmjs.org/source-map-url/-/source-map-url-0.3.0.tgz",
-                    "integrity": "sha1-fsrxO1e80J2opAxdJp2zN5nUqvk=",
-                    "dev": true
                 }
             }
         },
@@ -1405,7 +1387,7 @@
             "integrity": "sha1-dUu1v+VUUdpppYuU1F9MWwRi1Y8=",
             "dev": true,
             "requires": {
-                "es5-ext": "0.10.42"
+                "es5-ext": "0.10.45"
             }
         },
         "date-now": {
@@ -1632,12 +1614,6 @@
             "integrity": "sha512-jnjyiM6eRyZl2H+W8Q/zLMA481hzi0eszAaBUzIVnmYVDBbnLxVNnfu1HgEBvCbL+71FrxMl3E6lpKH7Ge3OXA==",
             "dev": true
         },
-        "duplexer": {
-            "version": "0.1.1",
-            "resolved": "https://registry.npmjs.org/duplexer/-/duplexer-0.1.1.tgz",
-            "integrity": "sha1-rOb/gIwc5mtX0ev5eXessCM0z8E=",
-            "dev": true
-        },
         "duplexer2": {
             "version": "0.1.4",
             "resolved": "https://registry.npmjs.org/duplexer2/-/duplexer2-0.1.4.tgz",
@@ -1706,9 +1682,9 @@
             }
         },
         "es5-ext": {
-            "version": "0.10.42",
-            "resolved": "https://registry.npmjs.org/es5-ext/-/es5-ext-0.10.42.tgz",
-            "integrity": "sha512-AJxO1rmPe1bDEfSR6TJ/FgMFYuTBhR5R57KW58iCkYACMyFbrkqVyzXSurYoScDGvgyMpk7uRF/lPUPPTmsRSA==",
+            "version": "0.10.45",
+            "resolved": "https://registry.npmjs.org/es5-ext/-/es5-ext-0.10.45.tgz",
+            "integrity": "sha512-FkfM6Vxxfmztilbxxz5UKSD4ICMf5tSpRFtDNtkAhOxZ0EKtX6qwmXNyH/sFyIbX2P/nU5AMiA9jilWsUGJzCQ==",
             "dev": true,
             "requires": {
                 "es6-iterator": "2.0.3",
@@ -1723,7 +1699,7 @@
             "dev": true,
             "requires": {
                 "d": "1.0.0",
-                "es5-ext": "0.10.42",
+                "es5-ext": "0.10.45",
                 "es6-symbol": "3.1.1"
             }
         },
@@ -1757,7 +1733,7 @@
             "dev": true,
             "requires": {
                 "d": "1.0.0",
-                "es5-ext": "0.10.42"
+                "es5-ext": "0.10.45"
             }
         },
         "es6-weak-map": {
@@ -1767,7 +1743,7 @@
             "dev": true,
             "requires": {
                 "d": "1.0.0",
-                "es5-ext": "0.10.42",
+                "es5-ext": "0.10.45",
                 "es6-iterator": "2.0.3",
                 "es6-symbol": "3.1.1"
             }
@@ -1828,7 +1804,7 @@
             "dev": true,
             "requires": {
                 "d": "1.0.0",
-                "es5-ext": "0.10.42"
+                "es5-ext": "0.10.45"
             }
         },
         "events": {
@@ -1916,6 +1892,7 @@
             "version": "3.0.2",
             "resolved": "https://registry.npmjs.org/extend-shallow/-/extend-shallow-3.0.2.tgz",
             "integrity": "sha1-Jqcarwc7OfshJxcnRhMcJwQCjbg=",
+            "dev": true,
             "requires": {
                 "assign-symbols": "1.0.0",
                 "is-extendable": "1.0.1"
@@ -1925,6 +1902,7 @@
                     "version": "1.0.1",
                     "resolved": "https://registry.npmjs.org/is-extendable/-/is-extendable-1.0.1.tgz",
                     "integrity": "sha512-arnXMxT1hhoKo9k1LZdmlNyJdDDfy2v0fXjFlmok4+i8ul/6WlbVge9bhM74OpNPQPMGUToDtz+KXa1PneJxOA==",
+                    "dev": true,
                     "requires": {
                         "is-plain-object": "2.0.4"
                     }
@@ -2000,6 +1978,7 @@
             "version": "1.3.2",
             "resolved": "https://registry.npmjs.org/fancy-log/-/fancy-log-1.3.2.tgz",
             "integrity": "sha1-9BEl49hPLn2JpD0G2VjI94vha+E=",
+            "dev": true,
             "requires": {
                 "ansi-gray": "0.1.1",
                 "color-support": "1.1.3",
@@ -2760,7 +2739,7 @@
                 "@gulp-sourcemaps/map-sources": "1.0.0",
                 "acorn": "5.7.1",
                 "convert-source-map": "1.5.1",
-                "css": "2.2.1",
+                "css": "2.2.3",
                 "debug-fabulous": "1.1.0",
                 "detect-newline": "2.1.0",
                 "graceful-fs": "4.1.11",
@@ -3406,6 +3385,7 @@
             "version": "2.0.4",
             "resolved": "https://registry.npmjs.org/is-plain-object/-/is-plain-object-2.0.4.tgz",
             "integrity": "sha512-h5PpgXkWitc38BBMYawTYMWJHFZJVnBquFE57xFpjB8pJFiF6gZ+bU+WyI/yqXiFR5mdLsgYNaPe8uao6Uv9Og==",
+            "dev": true,
             "requires": {
                 "isobject": "3.0.1"
             }
@@ -3473,7 +3453,8 @@
         "isobject": {
             "version": "3.0.1",
             "resolved": "https://registry.npmjs.org/isobject/-/isobject-3.0.1.tgz",
-            "integrity": "sha1-TkMekrEalzFjaqH5yNHMvP2reN8="
+            "integrity": "sha1-TkMekrEalzFjaqH5yNHMvP2reN8=",
+            "dev": true
         },
         "istanbul": {
             "version": "0.4.5",
@@ -3672,15 +3653,6 @@
             "dev": true,
             "optional": true
         },
-        "lazypipe": {
-            "version": "1.0.1",
-            "resolved": "https://registry.npmjs.org/lazypipe/-/lazypipe-1.0.1.tgz",
-            "integrity": "sha1-FHGu9rN6NA1Rw030Rpnc7wZMGUA=",
-            "dev": true,
-            "requires": {
-                "stream-combiner": "0.2.2"
-            }
-        },
         "lazystream": {
             "version": "1.0.0",
             "resolved": "https://registry.npmjs.org/lazystream/-/lazystream-1.0.0.tgz",
@@ -3902,7 +3874,7 @@
             "integrity": "sha1-Jzi9nw089PhEkMVzbEhpmsYyzaM=",
             "dev": true,
             "requires": {
-                "es5-ext": "0.10.42"
+                "es5-ext": "0.10.45"
             }
         },
         "make-iterator": {
@@ -3955,7 +3927,7 @@
             "dev": true,
             "requires": {
                 "d": "1.0.0",
-                "es5-ext": "0.10.42",
+                "es5-ext": "0.10.45",
                 "es6-weak-map": "2.0.2",
                 "event-emitter": "0.3.5",
                 "is-promise": "2.1.0",
@@ -4657,6 +4629,7 @@
             "version": "1.0.1",
             "resolved": "https://registry.npmjs.org/plugin-error/-/plugin-error-1.0.1.tgz",
             "integrity": "sha512-L1zP0dk7vGweZME2i+EeakvUNqSrdiI3F91TwEoYiGrAfUXmVv6fJIq4g82PAXxNsWOp0J7ZqQy/3Szz0ajTxA==",
+            "dev": true,
             "requires": {
                 "ansi-colors": "1.1.0",
                 "arr-diff": "4.0.0",
@@ -4668,6 +4641,7 @@
                     "version": "1.1.0",
                     "resolved": "https://registry.npmjs.org/ansi-colors/-/ansi-colors-1.1.0.tgz",
                     "integrity": "sha512-SFKX67auSNoVR38N3L+nvsPjOE0bybKTYbkf5tRvushrAPQ9V75huw0ZxBkKVeRU9kqH3d6HA4xTckbwZ4ixmA==",
+                    "dev": true,
                     "requires": {
                         "ansi-wrap": "0.1.0"
                     }
@@ -5478,16 +5452,6 @@
                 "readable-stream": "2.3.6"
             }
         },
-        "stream-combiner": {
-            "version": "0.2.2",
-            "resolved": "https://registry.npmjs.org/stream-combiner/-/stream-combiner-0.2.2.tgz",
-            "integrity": "sha1-rsjLrBd7Vrb0+kec7YwZEs7lKFg=",
-            "dev": true,
-            "requires": {
-                "duplexer": "0.1.1",
-                "through": "2.3.8"
-            }
-        },
         "stream-combiner2": {
             "version": "1.1.1",
             "resolved": "https://registry.npmjs.org/stream-combiner2/-/stream-combiner2-1.1.1.tgz",
@@ -5712,7 +5676,8 @@
         "time-stamp": {
             "version": "1.1.0",
             "resolved": "https://registry.npmjs.org/time-stamp/-/time-stamp-1.1.0.tgz",
-            "integrity": "sha1-dkpaEa9QVhkhsTPztE5hhofg9cM="
+            "integrity": "sha1-dkpaEa9QVhkhsTPztE5hhofg9cM=",
+            "dev": true
         },
         "timers-browserify": {
             "version": "1.4.2",
@@ -5729,7 +5694,7 @@
             "integrity": "sha512-tsEStd7kmACHENhsUPaxb8Jf8/+GZZxyNFQbZD07HQOyooOa6At1rQqjffgvg7n+dxscQa9cjjMdWhJtsP2sxg==",
             "dev": true,
             "requires": {
-                "es5-ext": "0.10.42",
+                "es5-ext": "0.10.45",
                 "next-tick": "1.0.0"
             }
         },
diff --git a/package.json b/package.json
index ae87651d6c1..37e4cc663d6 100644
--- a/package.json
+++ b/package.json
@@ -61,8 +61,8 @@
         "chalk": "latest",
         "convert-source-map": "latest",
         "del": "latest",
-        "fs-extra": "^6.0.1",
         "fancy-log": "latest",
+        "fs-extra": "^6.0.1",
         "gulp": "3.X",
         "gulp-clone": "latest",
         "gulp-concat": "latest",
diff --git a/scripts/build/chalk.js b/scripts/build/chalk.js
new file mode 100644
index 00000000000..149c8ea1533
--- /dev/null
+++ b/scripts/build/chalk.js
@@ -0,0 +1,5 @@
+// @ts-check
+
+// this just fixes the incorrect types for chalk :/
+const chalk = /**@type {import("chalk").Chalk}*/(require("chalk").default || require("chalk"));
+module.exports = chalk;
\ No newline at end of file
diff --git a/scripts/build/colors.js b/scripts/build/colors.js
deleted file mode 100644
index 91619364120..00000000000
--- a/scripts/build/colors.js
+++ /dev/null
@@ -1,20 +0,0 @@
-// @ts-check
-const chalk = /**@type {import("chalk").Chalk}*/(require("chalk").default || require("chalk"));
-
-exports.useColors = process.stdout.isTTY;
-for (const arg of process.argv) {
-    if (arg === "--no-color") exports["useColors"] = false;
-    else if (arg === "--color") exports["useColors"] = true;
-}
-
-/**
- * @param {string} message 
- * @param {import("chalk").Chalk} color 
- */
-function addColor(message, color) {
-    return exports.useColors ? color(message) : message;
-}
-exports.addColor = addColor;
-
-/** @type {{[P in Exclude<keyof import("chalk").Chalk, "constructor" | "enabled" | "level">]: import("chalk").Chalk[P]}} */
-exports.color = chalk;
\ No newline at end of file
diff --git a/scripts/build/diagnostics.js b/scripts/build/diagnostics.js
index dee74192875..5ca51c572ea 100644
--- a/scripts/build/diagnostics.js
+++ b/scripts/build/diagnostics.js
@@ -11,20 +11,37 @@ const formatDiagnosticsHost = exports.formatDiagnosticsHost = {
 
 /**
  * @param {Diagnostic[]} diagnostics
- * @param {boolean} [pretty]
+ * @param {{ cwd?: string, pretty?: boolean }} [options]
  */
-function formatDiagnostics(diagnostics, pretty) {
-    return pretty ? ts.formatDiagnosticsWithColorAndContext(diagnostics, formatDiagnosticsHost) :
-        ts.formatDiagnostics(diagnostics, formatDiagnosticsHost);
+function formatDiagnostics(diagnostics, options) {
+    return options && options.pretty 
+        ? ts.formatDiagnosticsWithColorAndContext(diagnostics, getFormatDiagnosticsHost(options && options.cwd)) 
+        : ts.formatDiagnostics(diagnostics, getFormatDiagnosticsHost(options && options.cwd));
 }
 exports.formatDiagnostics = formatDiagnostics;
 
-/** @param {Diagnostic[]} diagnostics */
-function reportDiagnostics(diagnostics) {
-    log(formatDiagnostics(diagnostics, process.stdout.isTTY));
+/** 
+ * @param {Diagnostic[]} diagnostics 
+ * @param {{ cwd?: string }} [options]
+ */
+function reportDiagnostics(diagnostics, options) {
+    log(formatDiagnostics(diagnostics, { cwd: options && options.cwd, pretty: process.stdout.isTTY }));
 }
 exports.reportDiagnostics = reportDiagnostics;
 
+/**
+ * @param {string | undefined} cwd 
+ * @returns {FormatDiagnosticsHost}
+ */
+function getFormatDiagnosticsHost(cwd) {
+    if (!cwd || cwd === process.cwd()) return formatDiagnosticsHost;
+    return {
+        getCanonicalFileName: formatDiagnosticsHost.getCanonicalFileName,
+        getCurrentDirectory: () => cwd,
+        getNewLine: formatDiagnosticsHost.getNewLine
+    };
+}
+
 /**
  * @typedef {import("../../lib/typescript").FormatDiagnosticsHost} FormatDiagnosticsHost
  * @typedef {import("../../lib/typescript").Diagnostic} Diagnostic
diff --git a/scripts/build/exec.js b/scripts/build/exec.js
index a7839cf1cb4..ca7c6e3f6c9 100644
--- a/scripts/build/exec.js
+++ b/scripts/build/exec.js
@@ -2,7 +2,7 @@
 const cp = require("child_process");
 const log = require("fancy-log"); // was `require("gulp-util").log (see https://github.com/gulpjs/gulp-util)
 const isWin = /^win/.test(process.platform);
-const { addColor, color } = require("./colors");
+const chalk = require("./chalk");
 
 module.exports = exec;
 
@@ -15,7 +15,7 @@ module.exports = exec;
  */
 function exec(cmd, args, options = {}) {
     return /**@type {Promise<{exitCode: number}>}*/(new Promise((resolve, reject) => {
-        log(addColor(`${cmd} ${args.join(" ")}`, color.gray));
+        log(`> ${chalk.green(cmd)} ${args.join(" ")}`);
         // TODO (weswig): Update child_process types to add windowsVerbatimArguments to the type definition
         const subshellFlag = isWin ? "/c" : "-c";
         const command = isWin ? [possiblyQuote(cmd), ...args] : [`${cmd} ${args.join(" ")}`];
diff --git a/scripts/build/gulp.js b/scripts/build/gulp.js
index 9aaa70d4eef..40f27b9526e 100644
--- a/scripts/build/gulp.js
+++ b/scripts/build/gulp.js
@@ -1 +1,8 @@
+// @ts-check
+/**
+ * @typedef {import("gulp").Gulp} Gulp
+ * @typedef {import("gulp-help").GulpHelp} GulpHelp
+ * @typedef {GulpHelp & { Gulp: new () => Gulp }} DotGulpModule
+ * @type {DotGulpModule}
+ */
 module.exports = require("gulp-help")(require("gulp"));
\ No newline at end of file
diff --git a/scripts/build/lib.js b/scripts/build/lib.js
index 297b1db9bdd..f8dac7529e0 100644
--- a/scripts/build/lib.js
+++ b/scripts/build/lib.js
@@ -4,26 +4,27 @@ const path = require("path");
 const gulp = require("./gulp");
 const newer = require("gulp-newer");
 const concat = require("gulp-concat");
-
-module.exports = exports = makeLibraryTargets;
+const merge2 = require("merge2");
 
 /** @type {{ libs: string[], paths?: Record<string, string>, sources?: Record<string, string[]> }} */
 const libraries = readJson("./src/lib/libs.json");
+const libs = libraries.libs.map(lib => {
+    const relativeSources = ["header.d.ts"].concat(libraries.sources && libraries.sources[lib] || [lib + ".d.ts"]);
+    const relativeTarget = libraries.paths && libraries.paths[lib] || ("lib." + lib + ".d.ts");
+    const sources = relativeSources.map(s => path.posix.join("src/lib", s));
+    const target = `built/local/${relativeTarget}`;
+    return { target, relativeTarget, sources };
+});
+exports.libraryTargets = libs.map(lib => lib.target);
 
 /**
  * @param {string[]} prepends 
  */
-function makeLibraryTargets(prepends) {
-    return libraries.libs.map(lib => {
-        const relativeSources = ["header.d.ts"].concat(libraries.sources && libraries.sources[lib] || [lib + ".d.ts"]);
-        const relativeTarget = libraries.paths && libraries.paths[lib] || ("lib." + lib + ".d.ts");
-        const sources = prepends.concat(relativeSources.map(s => path.posix.join("src/lib", s)));
-        const target = `built/local/${relativeTarget}`;
-        gulp.task(target, /*help*/ false, [], () =>
-            gulp.src(sources)
-                .pipe(newer(target))
-                .pipe(concat(relativeTarget, { newLine: "\n\n" }))
-                .pipe(gulp.dest("built/local")));
-        return target;
-    });
-}
\ No newline at end of file
+function generateLibs(prepends) {
+    return merge2(libs.map(({ sources, target, relativeTarget }) => 
+        gulp.src(prepends.concat(sources))
+            .pipe(newer(target))
+            .pipe(concat(relativeTarget, { newLine: "\n\n" }))
+            .pipe(gulp.dest("built/local"))));
+}
+exports.generateLibs = generateLibs;
\ No newline at end of file
diff --git a/scripts/build/pass.js b/scripts/build/pass.js
deleted file mode 100644
index bc3c5ee84d8..00000000000
--- a/scripts/build/pass.js
+++ /dev/null
@@ -1,11 +0,0 @@
-// @ts-check
-const { PassThrough } = require("stream");
-
-/**
- * @returns {NodeJS.ReadWriteStream}
- */
-function pass() {
-    return new PassThrough({ objectMode: true });
-}
-
-module.exports = pass;
\ No newline at end of file
diff --git a/scripts/build/prepend.js b/scripts/build/prepend.js
deleted file mode 100644
index 8c44d329112..00000000000
--- a/scripts/build/prepend.js
+++ /dev/null
@@ -1,14 +0,0 @@
-// @ts-check
-const fs = require("fs");
-const insert = require("gulp-insert");
-const pass = require("./pass");
-
-/**
- * @param {(() => string[] | undefined) | string[]} [prepends]
- * @returns {NodeJS.ReadWriteStream}
- */
-function prepend(prepends) {
-    if (typeof prepends === "function") prepends = prepends();
-    return (prepends || []).reduce((stream, file) => stream.pipe(insert.prepend(fs.readFileSync(file))), pass());
-}
-module.exports = prepend;
\ No newline at end of file
diff --git a/scripts/build/project.js b/scripts/build/project.js
index 69a45e9d32e..f4c2b819c17 100644
--- a/scripts/build/project.js
+++ b/scripts/build/project.js
@@ -2,8 +2,6 @@
 const path = require("path");
 const fs = require("fs");
 const gulp = require("./gulp");
-const PluginError = require("plugin-error");
-const log = require("fancy-log"); // was `require("gulp-util").log (see https://github.com/gulpjs/gulp-util)
 const gulpif = require("gulp-if");
 const sourcemaps = require("gulp-sourcemaps");
 const merge2 = require("merge2");
@@ -11,105 +9,140 @@ const tsc = require("gulp-typescript");
 const tsc_oop = require("./gulp-typescript-oop");
 const upToDate = require("./upToDate");
 const ts = require("../../lib/typescript");
-const debugMode = require("./debugMode");
 const del = require("del");
 const needsUpdate = require("./needsUpdate");
 const mkdirp = require("./mkdirp");
+const { reportDiagnostics } = require("./diagnostics");
+const { PassThrough } = require("stream");
 
-module.exports = exports = project;
+class CompilationGulp extends gulp.Gulp {
+    /**
+     * @param {import("gulp-help").GulpHelp | import("gulp").Gulp} gulp
+     */
+    constructor(gulp) {
+        super();
+        // forward notifications to the outer gulp.
+        this.on("task_start", e => gulp.emit("task_start", e));
+        this.on("task_stop", e => gulp.emit("task_stop", e));
+        this.on("task_err", e => gulp.emit("task_err", e));
+        this.on("task_not_found", e => gulp.emit("task_not_found", e));
+        this.on("task_recursion", e => gulp.emit("task_recursion", e));
+        this.on("err", e => gulp.emit("err", e));
+    }
 
-/** @type {Map<string, Map<string, ResolvedProject>>} */
-const typescriptProjects = new Map();
-
-/** @type {Record<string, { typescript: string, deps?: string[] }>} */
-const typescriptRegistry = { };
-
-/**
- * Defines a series of gulp tasks for a TypeScript project, returning the root task name.
- * @param {string} projectSpec
- * @param {ProjectOptions} [options]
- * @param {(project: ParsedCommandLine, destPath: string, options: ResolvedProjectOptions) => NodeJS.ReadWriteStream} [task]
- */
-function project(projectSpec, options, task) {
-    return makeProject(projectSpec, resolveProjectOptions(options), /*referer*/ undefined, task).taskName;
+    dispose() {
+        this.removeAllListeners();
+        this.reset();
+    }
+    
+    // Do not reset tasks when `gulp.start()` is called
+    _resetAllTasks() {}
+    _resetSpecificTasks() {}
+    _resetTask() {}
 }
-exports.project = project;
+
+// internal `Gulp` instance for compilation artifacts.
+const compilationGulp = new CompilationGulp(gulp);
+
+/** @type {Map<ResolvedProjectSpec, ProjectGraph>} */
+const projectGraphCache = new Map();
+
+/** @type {Map<string, { typescript: string, alias: string, paths: ResolvedPathOptions }>} */
+const typescriptAliasMap = new Map();
 
 /**
- * Defines a deferred gulp pipeline for a TypeScript project.
- * @param {string} projectSpec
- * @param {ProjectOptions} [options]
- * @param {(project: ParsedCommandLine, destPath: string, options: ResolvedProjectOptions) => NodeJS.ReadWriteStream} [task]
+ * Defines a gulp orchestration for a TypeScript project, returning a callback that can be used to trigger compilation.
+ * @param {string} projectSpec The path to a tsconfig.json file or its containing directory.
+ * @param {ProjectOptions} [options] Project compilation options.
+ * @returns {() => Promise<void>}
  */
-function defer(projectSpec, options, task) {
+function createCompiler(projectSpec, options) {
     const resolvedOptions = resolveProjectOptions(options);
-    resolvedOptions.defer = true;
-    const resolvedProject = prepareProject(projectSpec, resolvedOptions, /*referer*/ undefined, task);
-    return getProjectTaskFunction(resolvedProject);
+    const resolvedProjectSpec = resolveProjectSpec(projectSpec, resolvedOptions.paths, /*referrer*/ undefined);
+    const taskName = compileTaskName(ensureCompileTask(getOrCreateProjectGraph(resolvedProjectSpec, resolvedOptions.paths), resolvedOptions), resolvedOptions.typescript);
+    return () => new Promise((resolve, reject) => compilationGulp.start(taskName, err => err ? reject(err) : resolve(err)));
 }
-exports.defer = defer;
+exports.createCompiler = createCompiler;
 
 /**
- * Defines a series of gulp tasks to clean the outputs of a TypeScript project, returning the root task name.
- * @param {string} projectSpec
- * @param {CleanOptions} [options]
+ * Defines and executes a gulp orchestration for a TypeScript project.
+ * @param {string} projectSpec The path to a tsconfig.json file or its containing directory.
+ * @param {ProjectOptions} [options] Project compilation options.
+ * @returns {Promise<void>}
+ * 
+ * @typedef ProjectOptions
+ * @property {string} [cwd] The path to use for the current working directory. Defaults to `process.cwd()`.
+ * @property {string} [base] The path to use as the base for relative paths. Defaults to `cwd`.
+ * @property {string} [typescript] A module specifier or path (relative to gulpfile.js) to the version of TypeScript to use.
+ * @property {Hook} [js] Pipeline hook for .js file outputs. For multiple steps, use `stream-combiner`.
+ * @property {Hook} [dts] Pipeline hook for .d.ts file outputs. For multiple steps, use `stream-combiner`.
+ * @property {boolean} [verbose] Indicates whether verbose logging is enabled.
+ * @property {boolean} [force] Force recompilation (no up-to-date check).
+ * @property {boolean} [inProcess] Indicates whether to run gulp-typescript in-process or out-of-process (default).
+ * 
+ * @typedef {NodeJS.ReadWriteStream | (() => NodeJS.ReadWriteStream)} Hook
+ */
+function compile(projectSpec, options) {
+    const compiler = createCompiler(projectSpec, options);
+    return compiler();
+}
+exports.compile = compile;
+
+/**
+ * Defines a gulp orchestration to clean the outputs of a TypeScript project, returning a callback that can be used to trigger compilation.
+ * @param {string} projectSpec The path to a tsconfig.json file or its containing directory.
+ * @param {PathOptions} [options] Project clean options.
+ */
+function createCleaner(projectSpec, options) {
+    const paths = resolvePathOptions(options);
+    const resolvedProjectSpec = resolveProjectSpec(projectSpec, paths, /*referrer*/ undefined);
+    const taskName = cleanTaskName(ensureCleanTask(getOrCreateProjectGraph(resolvedProjectSpec, paths)));
+    return () => new Promise((resolve, reject) => compilationGulp.start(taskName, err => err ? reject(err) : resolve(err)));
+}
+exports.createCleaner = createCleaner;
+
+/**
+ * Defines and executes a gulp orchestration to clean the outputs of a TypeScript project.
+ * @param {string} projectSpec The path to a tsconfig.json file or its containing directory.
+ * @param {PathOptions} [options] Project clean options.
  */
 function clean(projectSpec, options) {
-    return makeClean(projectSpec, resolveCleanOptions(options), /*referer*/ undefined);
+    const cleaner = createCleaner(projectSpec, options);
+    return cleaner();
 }
 exports.clean = clean;
 
-/**
- * Defines the default task behavior.
- * @param {ParsedCommandLine} parsedProject
- * @param {string} destPath
- * @param {ResolvedTaskConfiguration} options
- */
-function defaultTask(parsedProject, destPath, options) {
-    const { sourceMap, inlineSourceMap, inlineSources = false, sourceRoot, declarationMap } = parsedProject.options;
-    const configFilePath = parsedProject.options.configFilePath;
-    const sourceMapPath = inlineSourceMap ? undefined : ".";
-    const sourceMapOptions = { includeContent: inlineSources, sourceRoot, destPath };
-    const project = options.inProcess
-        ? tsc.createProject(configFilePath, Object.assign({}, options.compilerOptions, { typescript: require(options.typescript)}))
-        : tsc_oop.createProject(configFilePath, Object.assign({}, options.compilerOptions), { typescript: options.typescript });
-    const stream = project.src()
-        .pipe(gulpif(!options.force, upToDate(parsedProject, { verbose: options.verbose })))
-        .pipe(gulpif(sourceMap || inlineSourceMap, sourcemaps.init()))
-        .pipe(project());
-    const js = stream.js
-        .pipe(gulpif(sourceMap || inlineSourceMap, sourcemaps.write(sourceMapPath, sourceMapOptions)));
-    const dts = stream.dts
-        .pipe(gulpif(declarationMap, sourcemaps.write(sourceMapPath, sourceMapOptions)));
-    return merge2([options.js ? options.js(js) : js, options.dts ? options.dts(dts) : dts])
-        .pipe(gulp.dest(destPath));
-}
-exports.defaultTask = defaultTask;
-
 /**
  * Adds a named alias for a TypeScript language service path
- * @param {string} alias 
- * @param {string} typescript 
- * @param {string[]} [deps] 
+ * @param {string} alias An alias for a TypeScript version.
+ * @param {string} typescript An alias or module specifier for a TypeScript version.
+ * @param {PathOptions} [options] Options used to resolve the path to `typescript`.
  */
-function addTypeScript(alias, typescript, deps) {
-    typescriptRegistry[alias] = { typescript, deps };
+function addTypeScript(alias, typescript, options) {
+    const paths = resolvePathOptions(options);
+    typescriptAliasMap.set(alias, { typescript, alias, paths });
 }
 exports.addTypeScript = addTypeScript;
 
 /**
  * Flattens a project with project references into a single project.
- * @param {string} projectSpec
- * @param {string} flattenedProjectSpec
- * @param {FlattenOptions} [options]
+ * @param {string} projectSpec The path to a tsconfig.json file or its containing directory.
+ * @param {string} flattenedProjectSpec The output path for the flattened tsconfig.json file.
+ * @param {FlattenOptions} [options] Options used to flatten a project hierarchy.
+ * 
+ * @typedef FlattenOptions
+ * @property {string} [cwd] The path to use for the current working directory. Defaults to `process.cwd()`.
+ * @property {CompilerOptions} [compilerOptions] Compiler option overrides.
+ * @property {boolean} [force] Forces creation of the output project.
  */
 function flatten(projectSpec, flattenedProjectSpec, options = {}) {
+    const paths = resolvePathOptions(options);
     const files = [];
-    const resolvedOutputSpec = path.resolve(flattenedProjectSpec);
+    const resolvedOutputSpec = path.resolve(paths.cwd, flattenedProjectSpec);
     const resolvedOutputDirectory = path.dirname(resolvedOutputSpec);
-    const resolvedProjectSpec = resolveProjectSpec(projectSpec);
-    const parsedProject = ts.getParsedCommandLineOfConfigFile(resolvedProjectSpec, {}, parseConfigFileHost);
-    recur(parsedProject);
+    const resolvedProjectSpec = resolveProjectSpec(projectSpec, paths, /*referrer*/ undefined);
+    const projectGraph = getOrCreateProjectGraph(resolvedProjectSpec, paths);
+    recur(projectGraph);
 
     const config = {
         extends: normalizeSlashes(path.relative(resolvedOutputDirectory, resolvedProjectSpec)),
@@ -123,418 +156,384 @@ function flatten(projectSpec, flattenedProjectSpec, options = {}) {
     }
 
     /**
-     * @param {ParsedCommandLine} parsedProject 
+     * @param {ProjectGraph} projectGraph 
      */
-    function recur(parsedProject) {
-        if (parsedProject.projectReferences) {
-            for (const ref of parsedProject.projectReferences) {
-                const resolvedProjectSpec = resolveProjectSpec(ref.path, parsedProject);
-                const referencedProject = ts.getParsedCommandLineOfConfigFile(resolvedProjectSpec, {}, parseConfigFileHost);
-                recur(referencedProject);
-            }
+    function recur(projectGraph) {
+        for (const ref of projectGraph.references) {
+            recur(ref.target);
         }
-        for (const file of parsedProject.fileNames) {
-            files.push(normalizeSlashes(path.relative(resolvedOutputDirectory, path.resolve(file))));
+        for (const file of projectGraph.project.fileNames) {
+            files.push(normalizeSlashes(path.relative(resolvedOutputDirectory, path.resolve(projectGraph.projectDirectory, file))));
         }
     }
 }
 exports.flatten = flatten;
 
 /**
- * @param {string} typescript 
+ * Resolve a TypeScript specifier into a fully-qualified module specifier and any requisite dependencies.
+ * @param {string} typescript An unresolved module specifier to a TypeScript version.
+ * @param {ResolvedPathOptions} paths Paths used to resolve `typescript`.
+ * @returns {ResolvedTypeScript}
+ * 
+ * @typedef {string & {_isResolvedTypeScript: never}} ResolvedTypeScriptSpec
+ * 
+ * @typedef ResolvedTypeScript
+ * @property {ResolvedTypeScriptSpec} typescript
+ * @property {string} [alias]
  */
-function resolveTypeScript(typescript) {
-    /** @type {string[] | undefined} */
-    let deps;
-    while (typescript in typescriptRegistry) {
-        const entry = typescriptRegistry[typescript];
-        typescript = entry.typescript;
-        if (!deps) deps = entry.deps;
+function resolveTypeScript(typescript, paths) {
+    let alias;
+    while (typescriptAliasMap.has(typescript)) {
+        ({ typescript, alias, paths } = typescriptAliasMap.get(typescript));
     }
 
     if (typescript === "default") {
         typescript = require.resolve("../../lib/typescript");
     }
     else if (isPath(typescript)) {
-        typescript = path.resolve(process.cwd(), typescript);
+        typescript = path.resolve(paths.cwd, typescript);
     }
 
-    return { typescript, deps };
+    return { typescript: /**@type {ResolvedTypeScriptSpec}*/(normalizeSlashes(typescript)), alias };
+}
+
+/**
+ * Gets a suffix to append to Gulp task names that vary by TypeScript version.
+ * @param {ResolvedTypeScript} typescript A resolved module specifier to a TypeScript version.
+ * @param {ResolvedPathOptions} paths Paths used to resolve a relative reference to `typescript`.
+ */
+function getTaskNameSuffix(typescript, paths) {
+    return typescript.typescript === resolveTypeScript("default", paths).typescript ? "" :
+        typescript.alias ? `@${typescript.alias}` :
+        isPath(typescript.typescript) ? `@${normalizeSlashes(path.relative(paths.base, typescript.typescript))}` :
+        `@${typescript}`;
+}
+
+/** @type {ResolvedPathOptions} */
+const defaultPaths = { cwd: process.cwd(), base: process.cwd() };
+
+/**
+ * @param {PathOptions | undefined} options Path options to resolve and normalize.
+ * @returns {ResolvedPathOptions}
+ * 
+ * @typedef PathOptions
+ * @property {string} [cwd] The path to use for the current working directory. Defaults to `process.cwd()`.
+ * @property {string} [base] The path to use as the base for relative paths. Defaults to `cwd`.
+ * 
+ * @typedef ResolvedPathOptions
+ * @property {string} cwd The path to use for the current working directory. Defaults to `process.cwd()`.
+ * @property {string} base The path to use as the base for relative paths. Defaults to `cwd`.
+ */
+function resolvePathOptions(options) {
+    const cwd = options && options.cwd ? path.resolve(process.cwd(), options.cwd) : process.cwd();
+    const base = options && options.base ? path.resolve(cwd, options.base) : cwd;
+    return cwd === defaultPaths.cwd && base === defaultPaths.base ? defaultPaths : { cwd, base };
 }
 
 /**
  * @param {ProjectOptions} [options]
  * @returns {ResolvedProjectOptions}
+ * 
+ * @typedef ResolvedProjectOptions
+ * @property {ResolvedPathOptions} paths
+ * @property {ResolvedTypeScript} typescript A resolved reference to a TypeScript implementation.
+ * @property {Hook} [js] Pipeline hook for .js file outputs.
+ * @property {Hook} [dts] Pipeline hook for .d.ts file outputs.
+ * @property {boolean} [verbose] Indicates whether verbose logging is enabled.
+ * @property {boolean} [force] Force recompilation (no up-to-date check).
+ * @property {boolean} [inProcess] Indicates whether to run gulp-typescript in-process or out-of-process (default).
  */
 function resolveProjectOptions(options = {}) {
-    const resolvedTypeScript = resolveTypeScript(options.typescript || "default");
+    const paths = resolvePathOptions(options);
+    const typescript = resolveTypeScript(options.typescript || "default", paths);
     return {
-        typescript: resolvedTypeScript.typescript,
-        deps: concat(options.deps, resolvedTypeScript.deps),
-        compilerOptions: options.compilerOptions || {},
+        paths,
+        typescript,
         js: options.js,
         dts: options.dts,
-        debug: resolveProjectConfiguration(options.debug),
-        release: resolveProjectConfiguration(options.release),
         verbose: options.verbose || false,
         force: options.force || false,
-        inProcess: options.inProcess || false,
-        defer: false
+        inProcess: options.inProcess || false
     };
 }
 
 /**
- * @param {CleanOptions} [options]
- * @returns {ResolvedCleanOptions}
+ * @param {Hook} hook 
+ * @returns {NodeJS.ReadWriteStream}
  */
-function resolveCleanOptions(options = {}) {
-    const resolvedTypeScript = resolveTypeScript(options.typescript || "default");
-    return { typescript: resolvedTypeScript.typescript };
+function evaluateHook(hook) {
+    return (typeof hook === "function" ? hook() : hook) || new PassThrough({ objectMode: true });
 }
 
 /**
- * @param {ProjectConfiguration} [config]
- * @returns {ResolvedProjectConfiguration}
+ * @param {ResolvedProjectOptions} left
+ * @param {ResolvedProjectOptions} right
+ * @returns {ResolvedProjectOptions}
  */
-function resolveProjectConfiguration(config = {}) {
+function mergeProjectOptions(left, right) {
+    if (left.typescript !== right.typescript) throw new Error("Cannot merge project options targeting different TypeScript packages");
+    if (tryReuseProjectOptions(left, right)) return left;
     return {
-        compilerOptions: config.compilerOptions || {},
-        deps: config.deps,
-        js: config.js,
-        dts: config.dts,
-        force: config.force,
-        inProcess: config.inProcess
+        paths: left.paths,
+        typescript: left.typescript,
+        js: right.js || left.js,
+        dts: right.dts || left.dts,
+        verbose: right.verbose || left.verbose,
+        force: right.force || left.force,
+        inProcess: right.inProcess || left.inProcess
     };
 }
 
 /**
- * @param {ResolvedProjectOptions} a
- * @param {ResolvedProjectOptions} b
+ * @param {ResolvedProjectOptions} left
+ * @param {ResolvedProjectOptions} right
  */
-function mergeProjectOptions(a, b) {
-    return {
-        typescript: a.typescript || b.typescript,
-        deps: distinct(concat(a.deps, b.deps)),
-        compilerOptions: Object.assign({}, a.compilerOptions, b.compilerOptions),
-        js: b.js || a.js,
-        dts: b.dts || a.dts,
-        debug: mergeProjectConfigurations(a.debug, b.debug),
-        release: mergeProjectConfigurations(a.release, b.release),
-        verbose: b.verbose || a.verbose,
-        force: b.force || a.force,
-        inProcess: b.inProcess || a.inProcess,
-        defer: a.defer || b.defer
-    };
+function tryReuseProjectOptions(left, right) {
+    return left === right
+        || left.js === (right.js || left.js)
+        && left.dts === (right.dts || left.dts)
+        && !left.verbose === !(right.verbose || left.verbose)
+        && !left.force === !(right.force || left.force)
+        && !left.inProcess === !(right.inProcess || left.inProcess);
 }
 
 /**
- * @param {ResolvedProjectConfiguration} a
- * @param {ResolvedProjectConfiguration} b
+ * @param {ResolvedProjectSpec} projectSpec
+ * @param {ResolvedPathOptions} paths
+ * @returns {UnqualifiedProjectName}
+ * 
+ * @typedef {string & {_isUnqualifiedProjectName:never}} UnqualifiedProjectName
  */
-function mergeProjectConfigurations(a, b) {
-    return {
-        compilerOptions: Object.assign({}, a.compilerOptions, b.compilerOptions),
-        deps: concat(a.deps, b.deps),
-        js: b.js || a.js,
-        dts: b.dts || a.dts,
-        force: b.force !== undefined ? b.force : a.force,
-        inProcess: b.inProcess !== undefined ? b.inProcess : a.inProcess
-    };
+function getUnqualifiedProjectName(projectSpec, paths) {
+    return /**@type {UnqualifiedProjectName}*/(normalizeSlashes(path.relative(paths.base, projectSpec)));
 }
 
 /**
- * @param {ResolvedProjectOptions} options
- * @returns {ResolvedTaskConfiguration}
+ * @param {UnqualifiedProjectName} projectName
+ * @param {ResolvedPathOptions} paths
+ * @param {ResolvedTypeScript} typescript
+ * @returns {QualifiedProjectName}
+ * 
+ * @typedef {string & {_isQualifiedProjectName:never}} QualifiedProjectName
  */
-function getResolvedTaskConfiguration(options) {
-    const config = debugMode.useDebugMode ? options.debug : options.release
-    return {
-        typescript: options.typescript,
-        compilerOptions: Object.assign({}, options.compilerOptions, config.compilerOptions),
-        deps: concat(options.deps, config.deps),
-        dts: config.dts || options.dts,
-        js: config.js || options.js,
-        verbose: options.verbose,
-        force: config.force !== undefined ? config.force : options.force,
-        inProcess: config.inProcess !== undefined ? config.inProcess : options.inProcess
-    };
+function getQualifiedProjectName(projectName, paths, typescript) {
+    return /**@type {QualifiedProjectName}*/(projectName + getTaskNameSuffix(typescript, paths));
 }
 
-/**
- * @template T
- * @param {T[] | undefined} a 
- * @param {T[] | undefined} b 
- * @returns {T[] | undefined}
+/** 
+ * @typedef {import("../../lib/typescript").ParseConfigFileHost} ParseConfigFileHost
+ * @type {ParseConfigFileHost} 
  */
-function concat(a, b) {
-    return a ? b ? a.concat(b) : a : b;
-}
-
-/**
- * @template T
- * @param {T[] | undefined} ar 
- * @returns {T[] | undefined}
- */
-
-function distinct(ar) {
-    return ar && [...new Set(ar)];
-}
-
-/**
- * @param {string} projectSpec
- * @param {ResolvedProjectOptions} resolvedOptions
- * @param {ParsedCommandLine} [referer]
- * @param {Task} [task]
- */
-function prepareProject(projectSpec, resolvedOptions, referer, task) {
-    const resolvedProject = resolveProject(projectSpec, resolvedOptions, referer);
-    if (resolvedProject.resolvedOptions !== resolvedOptions) {
-        resolvedProject.resolvedOptions = mergeProjectOptions(resolvedProject.resolvedOptions, resolvedOptions);
-    }
-    if (task) resolvedProject.task = task;
-    return resolvedProject;
-}
-
-/**
- * @param {string} projectSpec
- * @param {ResolvedProjectOptions} resolvedOptions
- * @param {ParsedCommandLine} [referer]
- * @param {Task} [task]
- */
-function makeProject(projectSpec, resolvedOptions, referer, task) {
-    const resolvedProject = prepareProject(projectSpec, resolvedOptions, referer, task);
-    if (!resolvedProject.projectTaskCreated || resolvedProject.task) {
-        createProjectTask(resolvedProject);
-    }
-    return resolvedProject;
-}
-
-/**
- * @param {string} projectSpec
- * @param {ResolvedCleanOptions} resolvedOptions
- * @param {ParsedCommandLine} [referer]
- */
-function makeClean(projectSpec, resolvedOptions, referer) {
-    const projects = getProjects(resolvedOptions);
-    const resolvedProjectSpec = resolveProjectSpec(projectSpec, referer, projects);
-    const resolvedProject = projects.get(resolvedProjectSpec);
-    if (!resolvedProject) throw new PluginError("clean", `Project not found: '${projectSpec}'. Add project via 'project()' first.`);
-    if (!resolvedProject.cleanTaskCreated) {
-        createCleanTask(resolvedProject);
-    }
-    return "clean:" + resolvedProject.projectName;
-}
-
-/**
- * @param {ResolvedProjectOptions | ResolvedCleanOptions} resolvedOptions
- */
-function getProjects(resolvedOptions) {
-    let projects = typescriptProjects.get(resolvedOptions.typescript);
-    if (!projects) typescriptProjects.set(resolvedOptions.typescript, projects = new Map());
-    return projects;
-}
-
-/**
- * @param {string} resolvedProjectSpec
- * @param {ResolvedProjectOptions} resolvedOptions
- */
-function getProjectName(resolvedProjectSpec, resolvedOptions) {
-    let projectName = path.relative(process.cwd(), resolvedProjectSpec);
-    if (resolvedOptions.typescript !== resolveTypeScript("default").typescript) {
-        projectName += `@${isPath(resolvedOptions.typescript) ? path.relative(process.cwd(), resolvedOptions.typescript) : resolvedOptions.typescript}`;
-    }
-    return normalizeSlashes(projectName);
-}
-
-/** @type {FormatDiagnosticsHost} */
-const formatDiagnosticsHost = {
-    getCanonicalFileName: fileName => fileName,
-    getCurrentDirectory: () => process.cwd(),
-    getNewLine: () => ts.sys.newLine
-};
-
-/** @type {ParseConfigFileHost} */
 const parseConfigFileHost = {
     useCaseSensitiveFileNames: ts.sys.useCaseSensitiveFileNames,
     fileExists: fileName => ts.sys.fileExists(fileName),
     readFile: fileName => ts.sys.readFile(fileName),
-    getCurrentDirectory: () => ts.sys.getCurrentDirectory(),
+    getCurrentDirectory: () => process.cwd(),
     readDirectory: (rootDir, extensions, exclude, include, depth) => ts.sys.readDirectory(rootDir, extensions, exclude, include, depth),
-    onUnRecoverableConfigFileDiagnostic: diagnostic => {
-        log.warn(ts.formatDiagnosticsWithColorAndContext([diagnostic], formatDiagnosticsHost));
-    }
+    onUnRecoverableConfigFileDiagnostic: diagnostic => reportDiagnostics([diagnostic])
 };
 
 /**
- * @param {string} projectSpec
- * @param {ResolvedProjectOptions} resolvedOptions
- * @param {ParsedCommandLine} [referer]
+ * @param {string} [cwd] 
+ * @returns {ParseConfigFileHost}
  */
-function resolveProject(projectSpec, resolvedOptions, referer) {
-    const projects = getProjects(resolvedOptions);
-    const resolvedProjectSpec = resolveProjectSpec(projectSpec, referer, projects);
-    let resolvedProject = projects.get(resolvedProjectSpec);
-    if (!resolvedProject) {
-        const projectName = getProjectName(resolvedProjectSpec, resolvedOptions);
-        resolvedProject = {
-            resolvedProjectSpec,
-            projectName,
-            taskName: "project:" + projectName,
-            parsedProject: undefined,
-            resolvedOptions,
-            destPath: undefined,
-            projectTaskCreated: false,
-            cleanTaskCreated: false,
-            task: undefined,
-            projectTask: undefined
+function getParseConfigFileHost(cwd) {
+    if (!cwd || cwd === process.cwd()) return parseConfigFileHost;
+    return {
+        useCaseSensitiveFileNames: parseConfigFileHost.useCaseSensitiveFileNames,
+        fileExists: parseConfigFileHost.fileExists,
+        readFile: parseConfigFileHost.readFile,
+        getCurrentDirectory: () => cwd,
+        readDirectory: parseConfigFileHost.readDirectory,
+        onUnRecoverableConfigFileDiagnostic: diagnostic => reportDiagnostics([diagnostic], { cwd })
+    };
+}
+
+/**
+ * @param {ResolvedProjectSpec} projectSpec
+ * @param {ResolvedPathOptions} paths
+ * @returns {ProjectGraph}
+ *
+ * @typedef ProjectGraph
+ * @property {ResolvedProjectSpec} projectSpec The fully qualified path to the tsconfig.json of the project
+ * @property {UnqualifiedProjectName} projectName The relative project name, excluding any TypeScript suffix.
+ * @property {string} projectDirectory The fully qualified path to the project directory.
+ * @property {ParsedCommandLine} project The parsed tsconfig.json file.
+ * @property {ProjectGraphReference[]} references An array of project references.
+ * @property {Map<ResolvedTypeScriptSpec, ProjectGraphConfiguration>} configurations TypeScript-specific configurations for the project.
+ * @property {boolean} cleanTaskCreated A value indicating whether a `clean:` task has been created for this project (not dependent on TypeScript version).
+ * 
+ * @typedef ProjectGraphReference
+ * @property {ProjectGraph} source The referring project.
+ * @property {ProjectGraph} target The referenced project.
+ */
+function getOrCreateProjectGraph(projectSpec, paths) {
+    let projectGraph = projectGraphCache.get(projectSpec);
+    if (!projectGraph) {
+        const project = ts.getParsedCommandLineOfConfigFile(projectSpec, {}, getParseConfigFileHost(paths.cwd));
+        projectGraph = {
+            projectSpec,
+            projectName: getUnqualifiedProjectName(projectSpec, paths),
+            projectDirectory: path.dirname(projectSpec),
+            project,
+            references: [],
+            configurations: new Map(),
+            cleanTaskCreated: false
         };
-        if (!resolvedOptions.defer) {
-            getParsedProject(resolvedProject);
-            getDestPath(resolvedProject);
+        projectGraphCache.set(projectSpec, projectGraph);
+        if (project.projectReferences) {
+            for (const projectReference of project.projectReferences) {
+                const resolvedProjectSpec = resolveProjectSpec(projectReference.path, paths, projectGraph);
+                const referencedProject = getOrCreateProjectGraph(resolvedProjectSpec, paths);
+                const reference = { source: projectGraph, target: referencedProject };
+                projectGraph.references.push(reference);
+            }
         }
-        projects.set(resolvedProjectSpec, resolvedProject);
     }
-    return resolvedProject;
+    return projectGraph;
 }
 
 /**
- * @param {ResolvedProject} resolvedProject 
+ * @param {ProjectGraph} projectGraph
+ * @param {ResolvedProjectOptions} resolvedOptions
+ * @returns {ProjectGraphConfiguration}
+ *
+ * @typedef ProjectGraphConfiguration
+ * @property {QualifiedProjectName} projectName
+ * @property {ResolvedProjectOptions} resolvedOptions
+ * @property {boolean} compileTaskCreated
  */
-function getParsedProject(resolvedProject) {
-    if (!resolvedProject.parsedProject) {
-        resolvedProject.parsedProject = ts.getParsedCommandLineOfConfigFile(
-            resolvedProject.resolvedProjectSpec, 
-            resolvedProject.resolvedOptions.compilerOptions, 
-            parseConfigFileHost);
+function getOrCreateProjectGraphConfiguration(projectGraph, resolvedOptions) {
+    let projectGraphConfig = projectGraph.configurations.get(resolvedOptions.typescript.typescript);
+    if (!projectGraphConfig) {
+        projectGraphConfig = {
+            projectName: getQualifiedProjectName(projectGraph.projectName, resolvedOptions.paths, resolvedOptions.typescript),
+            resolvedOptions,
+            compileTaskCreated: false
+        };
+        projectGraph.configurations.set(resolvedOptions.typescript.typescript, projectGraphConfig);
     }
-    return resolvedProject.parsedProject;
-}
-
-/**
- * @param {ResolvedProject} resolvedProject 
- */
-function getDestPath(resolvedProject) {
-    if (!resolvedProject.destPath) {
-        resolvedProject.destPath = resolveDestPath(getParsedProject(resolvedProject));
-    }
-    return resolvedProject.destPath;
+    return projectGraphConfig;
 }
 
 /**
  * @param {string} projectSpec
- * @param {ParsedCommandLine} [referer]
- * @param {Map<string, ResolvedProject>} [projects]
+ * @param {ResolvedPathOptions} paths
+ * @param {ProjectGraph | undefined} referrer
+ * @returns {ResolvedProjectSpec}
+ * 
+ * @typedef {string & {_isResolvedProjectSpec: never}} ResolvedProjectSpec
  */
-function resolveProjectSpec(projectSpec, referer, projects) {
-    projectSpec = referer ? path.resolve(path.dirname(referer.options.configFilePath), projectSpec) : path.resolve(projectSpec);
-    projectSpec = normalizeSlashes(projectSpec);
-
-    // quick checks for existing project in cache
-    if (projects && projects.has(projectSpec)) return projectSpec;
-
-    const configSpec = normalizeSlashes(path.join(projectSpec, "tsconfig.json"));
-    if (projects && projects.has(configSpec)) return configSpec;
-
-    // slower checks against file system
-    if (fs.existsSync(projectSpec) && fs.statSync(projectSpec).isDirectory()) {
-        return configSpec;
-    }
-
-    return projectSpec;
+function resolveProjectSpec(projectSpec, paths, referrer) {
+    projectSpec = path.resolve(paths.cwd, referrer && referrer.projectDirectory || "", projectSpec);
+    if (!ts.sys.fileExists(projectSpec)) projectSpec = path.join(projectSpec, "tsconfig.json");
+    return /**@type {ResolvedProjectSpec}*/(normalizeSlashes(projectSpec));
 }
 
 /**
- * @param {ParsedCommandLine} parsedProject
+ * @param {ProjectGraph} projectGraph
+ * @param {ResolvedPathOptions} paths
  */
-function resolveDestPath(parsedProject) {
+function resolveDestPath(projectGraph, paths) {
     /** @type {string} */
-    let destPath = path.dirname(parsedProject.options.configFilePath);
-    if (parsedProject.options.outDir) {
-        destPath = path.resolve(destPath, parsedProject.options.outDir);
+    let destPath = projectGraph.projectDirectory;
+    if (projectGraph.project.options.outDir) {
+        destPath = path.resolve(paths.cwd, destPath, projectGraph.project.options.outDir);
     }
-    else if (parsedProject.options.outFile || parsedProject.options.out) {
-        destPath = path.dirname(path.resolve(destPath, parsedProject.options.outFile || parsedProject.options.out));
+    else if (projectGraph.project.options.outFile || projectGraph.project.options.out) {
+        destPath = path.dirname(path.resolve(paths.cwd, destPath, projectGraph.project.options.outFile || projectGraph.project.options.out));
     }
-    return normalizeSlashes(path.relative(process.cwd(), destPath));
+    return normalizeSlashes(path.relative(paths.base, destPath));
 }
 
 /**
- * @param {ResolvedProject} resolvedProject
- */
-function createProjectTask(resolvedProject) {
-    const { parsedProject, resolvedOptions, taskName } = resolvedProject;
-    const deps = makeProjectDeps(parsedProject, resolvedOptions);
-    gulp.task(taskName, /*help*/ false, (resolvedOptions.deps || []).concat(deps), getProjectTaskFunction(resolvedProject));
-    resolvedProject.projectTaskCreated = true;
-}
-
-/**
- * @param {ResolvedProject} resolvedProject
- */
-function getProjectTaskFunction(resolvedProject) {
-    if (!resolvedProject.projectTask) {
-        resolvedProject.projectTask = () => (resolvedProject.task || exports.defaultTask)(
-            getParsedProject(resolvedProject),
-            getDestPath(resolvedProject),
-            getResolvedTaskConfiguration(resolvedProject.resolvedOptions));
-    }
-    return resolvedProject.projectTask;
-}
-
-/**
- * @param {ParsedCommandLine | undefined} parsedProject
+ * @param {ProjectGraph} projectGraph
  * @param {ResolvedProjectOptions} resolvedOptions
  */
-function makeProjectDeps(parsedProject, resolvedOptions) {
-    /** @type {string[]} */
-    const deps = [];
-    if (parsedProject && parsedProject.projectReferences) {
-        for (const projectReference of parsedProject.projectReferences) {
-            const projectReferenceOptions = resolveProjectOptions({
-                typescript: resolvedOptions.typescript,
-                deps: resolvedOptions.deps
-            });
-            deps.push(makeProject(projectReference.path, projectReferenceOptions, parsedProject).taskName);
-        }
+function ensureCompileTask(projectGraph, resolvedOptions) {
+    const projectGraphConfig = getOrCreateProjectGraphConfiguration(projectGraph, resolvedOptions);
+    projectGraphConfig.resolvedOptions = resolvedOptions = mergeProjectOptions(resolvedOptions, resolvedOptions);
+    if (!projectGraphConfig.compileTaskCreated) {
+        const deps = makeProjectReferenceCompileTasks(projectGraph, resolvedOptions.typescript, resolvedOptions.paths);
+        compilationGulp.task(compileTaskName(projectGraph, resolvedOptions.typescript), deps, () => {
+            const destPath = resolveDestPath(projectGraph, resolvedOptions.paths);
+            const { sourceMap, inlineSourceMap, inlineSources = false, sourceRoot, declarationMap } = projectGraph.project.options;
+            const configFilePath = projectGraph.project.options.configFilePath;
+            const sourceMapPath = inlineSourceMap ? undefined : ".";
+            const sourceMapOptions = { includeContent: inlineSources, sourceRoot, destPath };
+            const project = resolvedOptions.inProcess
+                ? tsc.createProject(configFilePath, { typescript: require(resolvedOptions.typescript.typescript) })
+                : tsc_oop.createProject(configFilePath, {}, { typescript: resolvedOptions.typescript.typescript });
+            const stream = project.src()
+                .pipe(gulpif(!resolvedOptions.force, upToDate(projectGraph.project, { verbose: resolvedOptions.verbose })))
+                .pipe(gulpif(sourceMap || inlineSourceMap, sourcemaps.init()))
+                .pipe(project());
+            const js = stream.js
+                .pipe(evaluateHook(resolvedOptions.js))
+                .pipe(gulpif(sourceMap || inlineSourceMap, sourcemaps.write(sourceMapPath, sourceMapOptions)));
+            const dts = stream.dts
+                .pipe(evaluateHook(resolvedOptions.dts))
+                .pipe(gulpif(declarationMap, sourcemaps.write(sourceMapPath, sourceMapOptions)));
+            return merge2([js, dts])
+                .pipe(gulp.dest(destPath));
+        });
+        projectGraphConfig.compileTaskCreated = true;
     }
-    return deps;
+    return projectGraph;
 }
 
 /**
- * @param {ResolvedProject} resolvedProject
+ * @param {ProjectGraph} projectGraph
+ * @param {ResolvedTypeScript} typescript
+ * @param {ResolvedPathOptions} paths
  */
-function createCleanTask(resolvedProject) {
-    const { parsedProject, resolvedOptions, projectName } = resolvedProject;
-    const deps = makeCleanDeps(parsedProject, resolvedOptions);
-    gulp.task("clean:" + projectName, /*help*/ false, deps, () => {
-        let outputs = ts.getAllProjectOutputs(parsedProject);
-        if (!parsedProject.options.inlineSourceMap) {
-            if (parsedProject.options.sourceMap) {
-                outputs = outputs.concat(outputs.filter(file => /\.jsx?$/.test(file)).map(file => file + ".map"));
-            }
-            if (parsedProject.options.declarationMap) {
-                outputs = outputs.concat(outputs.filter(file => /\.d.ts$/.test(file)).map(file => file + ".map"));
-            }
-        }
-        return del(outputs);
-    });
-    resolvedProject.cleanTaskCreated = true;
+function makeProjectReferenceCompileTasks(projectGraph, typescript, paths) {
+    return projectGraph.references.map(({target}) => compileTaskName(ensureCompileTask(target, { paths, typescript }), typescript));
 }
 
 /**
- * @param {ParsedCommandLine} parsedProject
- * @param {ResolvedCleanOptions} resolvedOptions
+ * @param {ProjectGraph} projectGraph
  */
-function makeCleanDeps(parsedProject, resolvedOptions) {
-    /** @type {string[]} */
-    const deps = [];
-    if (parsedProject.projectReferences) {
-        for (const projectReference of parsedProject.projectReferences) {
-            const projectReferenceOptions = resolveCleanOptions({ typescript: resolvedOptions.typescript });
-            deps.push(makeClean(projectReference.path, projectReferenceOptions, parsedProject));
-        }
+function ensureCleanTask(projectGraph) {
+    if (!projectGraph.cleanTaskCreated) {
+        const deps = makeProjectReferenceCleanTasks(projectGraph);
+        compilationGulp.task(cleanTaskName(projectGraph), deps, () => {
+            let outputs = ts.getAllProjectOutputs(projectGraph.project);
+            if (!projectGraph.project.options.inlineSourceMap) {
+                if (projectGraph.project.options.sourceMap) {
+                    outputs = outputs.concat(outputs.filter(file => /\.jsx?$/.test(file)).map(file => file + ".map"));
+                }
+                if (projectGraph.project.options.declarationMap) {
+                    outputs = outputs.concat(outputs.filter(file => /\.d.ts$/.test(file)).map(file => file + ".map"));
+                }
+            }
+            return del(outputs);
+        });
+        projectGraph.cleanTaskCreated = true;
     }
-    return deps;
+    return projectGraph;
+}
+
+/**
+ * @param {ProjectGraph} projectGraph
+ */
+function makeProjectReferenceCleanTasks(projectGraph) {
+    return projectGraph.references.map(({target}) => cleanTaskName(ensureCleanTask(target)));
+}
+
+/**
+ * @param {ProjectGraph} projectGraph 
+ * @param {ResolvedTypeScript} typescript
+ */
+function compileTaskName(projectGraph, typescript) {
+    return `compile:${projectGraph.configurations.get(typescript.typescript).projectName}`;
+}
+
+/**
+ * @param {ProjectGraph} projectGraph 
+ */
+function cleanTaskName(projectGraph) {
+    return `clean:${projectGraph.projectName}`;
 }
 
 /**
@@ -555,83 +554,5 @@ function isPath(moduleSpec) {
 /**
  * @typedef {import("../../lib/typescript").ParsedCommandLine & { options: CompilerOptions }} ParsedCommandLine
  * @typedef {import("../../lib/typescript").CompilerOptions & { configFilePath?: string }} CompilerOptions
- * @typedef {import("../../lib/typescript").ParseConfigFileHost} ParseConfigFileHost
- * @typedef {import("../../lib/typescript").FormatDiagnosticsHost} FormatDiagnosticsHost
- * @typedef {(project: ParsedCommandLine, destPath: string, options: ResolvedTaskConfiguration) => NodeJS.ReadWriteStream} Task
- * 
- * @typedef ProjectOptions
- * @property {string} [typescript] A module specifier or path (relative to gulpfile.js) to the version of TypeScript to use.
- * @property {string[]} [deps] Gulp task dependencies for all tasks created for a project.
- * @property {CompilerOptions} [compilerOptions] Default options to pass to the compiler.
- * @property {(stream: NodeJS.ReadWriteStream) => NodeJS.ReadWriteStream} [js] Pipeline hook for .js file outputs.
- * @property {(stream: NodeJS.ReadWriteStream) => NodeJS.ReadWriteStream} [dts] Pipeline hook for .d.ts file outputs.
- * @property {ProjectConfiguration} [debug] Project option overrides when building a "debug" build.
- * @property {ProjectConfiguration} [release] Project option overrides when building a "release" build.
- * @property {boolean} [verbose] Indicates whether verbose logging is enabled.
- * @property {boolean} [force] Force recompilation (no up-to-date check).
- * @property {boolean} [inProcess] Indicates whether to run gulp-typescript in-process or out-of-process (default).
- *
- * @typedef ProjectConfiguration
- * @property {CompilerOptions} [compilerOptions] Default options to pass to the compiler.
- * @property {string[]} [deps] Gulp task dependencies for all tasks created for a project.
- * @property {(stream: NodeJS.ReadWriteStream) => NodeJS.ReadWriteStream} [js] Pipeline hook for .js file outputs.
- * @property {(stream: NodeJS.ReadWriteStream) => NodeJS.ReadWriteStream} [dts] Pipeline hook for .d.ts file outputs.
- * @property {boolean} [force] Force recompilation (no up-to-date check).
- * @property {boolean} [inProcess] Indicates whether to run gulp-typescript in-process or out-of-process (default).
- *
- * @typedef ResolvedProjectOptions
- * @property {string} typescript A module specifier or path (relative to gulpfile.js) to the version of TypeScript to use.
- * @property {CompilerOptions} compilerOptions Default options to pass to the compiler.
- * @property {string[] | undefined} deps Gulp task dependencies for all tasks created for a project.
- * @property {(stream: NodeJS.ReadWriteStream) => NodeJS.ReadWriteStream | undefined} js Pipeline hook for .js file outputs.
- * @property {(stream: NodeJS.ReadWriteStream) => NodeJS.ReadWriteStream | undefined} dts Pipeline hook for .d.ts file outputs.
- * @property {ResolvedProjectConfiguration} debug Project option overrides when building a "debug" build.
- * @property {ResolvedProjectConfiguration} release Project option overrides when building a "release" build.
- * @property {boolean} verbose Indicates whether verbose logging is enabled.
- * @property {boolean} force Force recompilation (no up-to-date check).
- * @property {boolean} inProcess Indicates whether to run gulp-typescript in-process or out-of-process (default).
- * @property {boolean} defer Defer loading the project until later (not supported for projects with project references).
- *
- * @typedef ResolvedProjectConfiguration
- * @property {CompilerOptions} compilerOptions Project configuration overrides to pass to the compiler.
- * @property {string[] | undefined} deps Gulp task dependencies for all tasks created for a project.
- * @property {(stream: NodeJS.ReadWriteStream) => NodeJS.ReadWriteStream | undefined} js Pipeline hook for .js file outputs.
- * @property {(stream: NodeJS.ReadWriteStream) => NodeJS.ReadWriteStream | undefined} dts Pipeline hook for .d.ts file outputs.
- * @property {boolean | undefined} force Force recompilation (no up-to-date check).
- * @property {boolean | undefined} inProcess Indicates whether to run gulp-typescript in-process or out-of-process (default).
- *
- * @typedef ResolvedTaskConfiguration
- * @property {string} typescript
- * @property {CompilerOptions} compilerOptions Project configuration overrides to pass to the compiler.
- * @property {string[] | undefined} deps Gulp task dependencies for all tasks created for a project.
- * @property {(stream: NodeJS.ReadWriteStream) => NodeJS.ReadWriteStream | undefined} js Pipeline hook for .js file outputs.
- * @property {(stream: NodeJS.ReadWriteStream) => NodeJS.ReadWriteStream | undefined} dts Pipeline hook for .d.ts file outputs.
- * @property {boolean} verbose Indicates whether verbose logging is enabled.
- * @property {boolean} force Force recompilation (no up-to-date check).
- * @property {boolean} inProcess Indicates whether to run gulp-typescript in-process or out-of-process (default).
- *
- * @typedef ResolvedProject
- * @property {string} resolvedProjectSpec
- * @property {string} projectName
- * @property {string} taskName
- * @property {ParsedCommandLine | undefined} parsedProject
- * @property {string | undefined} destPath
- * @property {ResolvedProjectOptions} resolvedOptions
- * @property {Task | undefined} task
- * @property {(() => NodeJS.ReadWriteStream) | undefined} projectTask
- * @property {boolean} projectTaskCreated
- * @property {boolean} cleanTaskCreated
- * 
- * @typedef CleanOptions
- * @property {string} [typescript] A module specifier or path (relative to gulpfile.js) to the version of TypeScript to use.
- * 
- * @typedef ResolvedCleanOptions
- * @property {string | undefined} typescript A module specifier or path (relative to gulpfile.js) to the version of TypeScript to use.
- * 
- * @typedef FlattenOptions
- * @property {CompilerOptions} [compilerOptions]
- * @property {string} [base]
- * @property {boolean} [force]
  */
-void 0;
-
+void 0;
\ No newline at end of file
diff --git a/scripts/build/upToDate.js b/scripts/build/upToDate.js
index 5ba0c80e034..07e5080b576 100644
--- a/scripts/build/upToDate.js
+++ b/scripts/build/upToDate.js
@@ -3,7 +3,7 @@ const path = require("path");
 const log = require("fancy-log"); // was `require("gulp-util").log (see https://github.com/gulpjs/gulp-util)
 const ts = require("../../lib/typescript");
 const { Duplex } = require("stream");
-const { addColor, color } = require("./colors");
+const chalk = require("./chalk");
 const Vinyl = require("vinyl");
 
 /**
@@ -86,7 +86,7 @@ function normalizeSlashes(file) {
  * @private
  */
 function fileName(file) {
-    return addColor(normalizeSlashes(path.relative(process.cwd(), path.resolve(file))), color.cyan);
+    return chalk.cyan(normalizeSlashes(path.relative(process.cwd(), path.resolve(file))));
 }
 
 /**
diff --git a/src/compiler/tsbuild.ts b/src/compiler/tsbuild.ts
index 9055fc1030c..007ec1afc7c 100644
--- a/src/compiler/tsbuild.ts
+++ b/src/compiler/tsbuild.ts
@@ -1016,12 +1016,6 @@ namespace ts {
      * Gets the UpToDateStatus for a project
      */
     export function getUpToDateStatus(host: UpToDateHost, project: ParsedCommandLine | undefined): UpToDateStatus {
-        if (project === undefined) {
-            return {
-                type: UpToDateStatusType.Unbuildable, reason: "File deleted mid-build"
-            };
-        }
-
         if (project === undefined) {
             return { type: UpToDateStatusType.Unbuildable, reason: "File deleted mid-build" };
         }