From 0b71f5f6617f0a421f0c3d2c7fa009c5c0923faa Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Tue, 23 Aug 2016 13:38:39 -0700
Subject: [PATCH 1/3] An import ending in "/" is always an import of a
 directory.

---
 src/compiler/core.ts                          | 14 ++++++++++++-
 src/compiler/program.ts                       |  2 +-
 ...gBasedModuleResolution7_classic.trace.json |  6 +++---
 ...pingBasedModuleResolution7_node.trace.json |  6 +++---
 .../reference/relativeModuleWithoutSlash.js   |  8 ++++----
 .../relativeModuleWithoutSlash.symbols        | 12 +++++------
 .../relativeModuleWithoutSlash.trace.json     | 18 +++++++++--------
 .../relativeModuleWithoutSlash.types          | 20 +++++++++----------
 .../compiler/relativeModuleWithoutSlash.ts    |  4 ++--
 9 files changed, 52 insertions(+), 38 deletions(-)

diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 27b27bc6532..a0c869e612a 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -829,8 +829,20 @@ namespace ts {
     export function normalizePath(path: string): string {
         path = normalizeSlashes(path);
         const rootLength = getRootLength(path);
+        const root = path.substr(0, rootLength);
         const normalized = getNormalizedParts(path, rootLength);
-        return path.substr(0, rootLength) + normalized.join(directorySeparator);
+        if (normalized.length) {
+            const joinedParts = root + normalized.join(directorySeparator);
+            return isPathToDirectory(path) ? joinedParts + "/" : joinedParts;
+        }
+        else {
+            return root;
+        }
+    }
+
+    /** A path ending with '/' refers to a directory only, never a file. */
+    export function isPathToDirectory(path: string): boolean {
+        return path.charCodeAt(path.length - 1) === CharacterCodes.slash;
     }
 
     export function getDirectoryPath(path: Path): Path;
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index f099d858119..ca756b6f1dd 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -646,7 +646,7 @@ namespace ts {
             trace(state.host, Diagnostics.Loading_module_as_file_Slash_folder_candidate_module_location_0, candidate);
         }
 
-        const resolvedFileName = loadModuleFromFile(candidate, supportedExtensions, failedLookupLocations, onlyRecordFailures, state);
+        const resolvedFileName = !isPathToDirectory(candidate) && loadModuleFromFile(candidate, supportedExtensions, failedLookupLocations, onlyRecordFailures, state);
 
         return resolvedFileName || loadNodeModuleFromDirectory(supportedExtensions, candidate, failedLookupLocations, onlyRecordFailures, state);
     }
diff --git a/tests/baselines/reference/pathMappingBasedModuleResolution7_classic.trace.json b/tests/baselines/reference/pathMappingBasedModuleResolution7_classic.trace.json
index 2d72108210e..a8cadb8f067 100644
--- a/tests/baselines/reference/pathMappingBasedModuleResolution7_classic.trace.json
+++ b/tests/baselines/reference/pathMappingBasedModuleResolution7_classic.trace.json
@@ -14,7 +14,7 @@
     "======== Module name './project/file2' was successfully resolved to 'c:/root/generated/src/project/file2.ts'. ========",
     "======== Resolving module 'module3' from 'c:/root/src/file1.ts'. ========",
     "Module resolution kind is not specified, using 'Classic'.",
-    "'baseUrl' option is set to 'c:/root', using this value to resolve non-relative module name 'module3'",
+    "'baseUrl' option is set to 'c:/root/', using this value to resolve non-relative module name 'module3'",
     "'paths' option is specified, looking for a pattern to match module name 'module3'.",
     "Module name 'module3', matched pattern '*'.",
     "Trying substitution '*', candidate module location: 'module3'.",
@@ -32,7 +32,7 @@
     "======== Module name 'module3' was successfully resolved to 'c:/module3.d.ts'. ========",
     "======== Resolving module 'module1' from 'c:/root/generated/src/project/file2.ts'. ========",
     "Module resolution kind is not specified, using 'Classic'.",
-    "'baseUrl' option is set to 'c:/root', using this value to resolve non-relative module name 'module1'",
+    "'baseUrl' option is set to 'c:/root/', using this value to resolve non-relative module name 'module1'",
     "'paths' option is specified, looking for a pattern to match module name 'module1'.",
     "Module name 'module1', matched pattern '*'.",
     "Trying substitution '*', candidate module location: 'module1'.",
@@ -44,7 +44,7 @@
     "======== Module name 'module1' was successfully resolved to 'c:/shared/module1.d.ts'. ========",
     "======== Resolving module 'templates/module2' from 'c:/root/generated/src/project/file2.ts'. ========",
     "Module resolution kind is not specified, using 'Classic'.",
-    "'baseUrl' option is set to 'c:/root', using this value to resolve non-relative module name 'templates/module2'",
+    "'baseUrl' option is set to 'c:/root/', using this value to resolve non-relative module name 'templates/module2'",
     "'paths' option is specified, looking for a pattern to match module name 'templates/module2'.",
     "Module name 'templates/module2', matched pattern 'templates/*'.",
     "Trying substitution 'generated/src/templates/*', candidate module location: 'generated/src/templates/module2'.",
diff --git a/tests/baselines/reference/pathMappingBasedModuleResolution7_node.trace.json b/tests/baselines/reference/pathMappingBasedModuleResolution7_node.trace.json
index 6be7d349fed..48633c85e3b 100644
--- a/tests/baselines/reference/pathMappingBasedModuleResolution7_node.trace.json
+++ b/tests/baselines/reference/pathMappingBasedModuleResolution7_node.trace.json
@@ -22,7 +22,7 @@
     "======== Module name './project/file2' was successfully resolved to 'c:/root/generated/src/project/file2.ts'. ========",
     "======== Resolving module 'module3' from 'c:/root/src/file1.ts'. ========",
     "Module resolution kind is not specified, using 'NodeJs'.",
-    "'baseUrl' option is set to 'c:/root', using this value to resolve non-relative module name 'module3'",
+    "'baseUrl' option is set to 'c:/root/', using this value to resolve non-relative module name 'module3'",
     "'paths' option is specified, looking for a pattern to match module name 'module3'.",
     "Module name 'module3', matched pattern '*'.",
     "Trying substitution '*', candidate module location: 'module3'.",
@@ -79,7 +79,7 @@
     "======== Module name 'module3' was successfully resolved to 'c:/node_modules/module3.d.ts'. ========",
     "======== Resolving module 'module1' from 'c:/root/generated/src/project/file2.ts'. ========",
     "Module resolution kind is not specified, using 'NodeJs'.",
-    "'baseUrl' option is set to 'c:/root', using this value to resolve non-relative module name 'module1'",
+    "'baseUrl' option is set to 'c:/root/', using this value to resolve non-relative module name 'module1'",
     "'paths' option is specified, looking for a pattern to match module name 'module1'.",
     "Module name 'module1', matched pattern '*'.",
     "Trying substitution '*', candidate module location: 'module1'.",
@@ -104,7 +104,7 @@
     "======== Module name 'module1' was successfully resolved to 'c:/shared/module1/index.d.ts'. ========",
     "======== Resolving module 'templates/module2' from 'c:/root/generated/src/project/file2.ts'. ========",
     "Module resolution kind is not specified, using 'NodeJs'.",
-    "'baseUrl' option is set to 'c:/root', using this value to resolve non-relative module name 'templates/module2'",
+    "'baseUrl' option is set to 'c:/root/', using this value to resolve non-relative module name 'templates/module2'",
     "'paths' option is specified, looking for a pattern to match module name 'templates/module2'.",
     "Module name 'templates/module2', matched pattern 'templates/*'.",
     "Trying substitution 'generated/src/templates/*', candidate module location: 'generated/src/templates/module2'.",
diff --git a/tests/baselines/reference/relativeModuleWithoutSlash.js b/tests/baselines/reference/relativeModuleWithoutSlash.js
index f83406499d4..e52d0cd19ed 100644
--- a/tests/baselines/reference/relativeModuleWithoutSlash.js
+++ b/tests/baselines/reference/relativeModuleWithoutSlash.js
@@ -11,13 +11,13 @@ export default { aIndex: 0 };
 import a from ".";
 import aIndex from "./";
 a.a;
-aIndex.a; //aIndex.aIndex; See GH#9690
+aIndex.aIndex;
 
 //// [test.ts]
 import a from "..";
 import aIndex from "../";
 a.a;
-aIndex.a; //aIndex.aIndex;
+aIndex.aIndex;
 
 
 //// [a.js]
@@ -33,10 +33,10 @@ exports["default"] = { aIndex: 0 };
 var _1 = require(".");
 var _2 = require("./");
 _1["default"].a;
-_2["default"].a; //aIndex.aIndex; See GH#9690
+_2["default"].aIndex;
 //// [test.js]
 "use strict";
 var __1 = require("..");
 var _1 = require("../");
 __1["default"].a;
-_1["default"].a; //aIndex.aIndex;
+_1["default"].aIndex;
diff --git a/tests/baselines/reference/relativeModuleWithoutSlash.symbols b/tests/baselines/reference/relativeModuleWithoutSlash.symbols
index 8c54a0682c7..4a9f8b41569 100644
--- a/tests/baselines/reference/relativeModuleWithoutSlash.symbols
+++ b/tests/baselines/reference/relativeModuleWithoutSlash.symbols
@@ -19,10 +19,10 @@ a.a;
 >a : Symbol(a, Decl(test.ts, 0, 6))
 >a : Symbol(a, Decl(a.ts, 1, 16))
 
-aIndex.a; //aIndex.aIndex; See GH#9690
->aIndex.a : Symbol(a, Decl(a.ts, 1, 16))
+aIndex.aIndex;
+>aIndex.aIndex : Symbol(aIndex, Decl(index.ts, 0, 16))
 >aIndex : Symbol(aIndex, Decl(test.ts, 1, 6))
->a : Symbol(a, Decl(a.ts, 1, 16))
+>aIndex : Symbol(aIndex, Decl(index.ts, 0, 16))
 
 === /a/b/test.ts ===
 import a from "..";
@@ -36,8 +36,8 @@ a.a;
 >a : Symbol(a, Decl(test.ts, 0, 6))
 >a : Symbol(a, Decl(a.ts, 1, 16))
 
-aIndex.a; //aIndex.aIndex;
->aIndex.a : Symbol(a, Decl(a.ts, 1, 16))
+aIndex.aIndex;
+>aIndex.aIndex : Symbol(aIndex, Decl(index.ts, 0, 16))
 >aIndex : Symbol(aIndex, Decl(test.ts, 1, 6))
->a : Symbol(a, Decl(a.ts, 1, 16))
+>aIndex : Symbol(aIndex, Decl(index.ts, 0, 16))
 
diff --git a/tests/baselines/reference/relativeModuleWithoutSlash.trace.json b/tests/baselines/reference/relativeModuleWithoutSlash.trace.json
index cee5b060676..3c99d4eb6a0 100644
--- a/tests/baselines/reference/relativeModuleWithoutSlash.trace.json
+++ b/tests/baselines/reference/relativeModuleWithoutSlash.trace.json
@@ -7,10 +7,11 @@
     "======== Module name '.' was successfully resolved to '/a.ts'. ========",
     "======== Resolving module './' from '/a/test.ts'. ========",
     "Explicitly specified module resolution kind: 'NodeJs'.",
-    "Loading module as file / folder, candidate module location '/a'.",
-    "File '/a.ts' exist - use it as a name resolution result.",
-    "Resolving real path for '/a.ts', result '/a.ts'",
-    "======== Module name './' was successfully resolved to '/a.ts'. ========",
+    "Loading module as file / folder, candidate module location '/a/'.",
+    "File '/a/package.json' does not exist.",
+    "File '/a/index.ts' exist - use it as a name resolution result.",
+    "Resolving real path for '/a/index.ts', result '/a/index.ts'",
+    "======== Module name './' was successfully resolved to '/a/index.ts'. ========",
     "======== Resolving module '..' from '/a/b/test.ts'. ========",
     "Explicitly specified module resolution kind: 'NodeJs'.",
     "Loading module as file / folder, candidate module location '/a'.",
@@ -19,8 +20,9 @@
     "======== Module name '..' was successfully resolved to '/a.ts'. ========",
     "======== Resolving module '../' from '/a/b/test.ts'. ========",
     "Explicitly specified module resolution kind: 'NodeJs'.",
-    "Loading module as file / folder, candidate module location '/a'.",
-    "File '/a.ts' exist - use it as a name resolution result.",
-    "Resolving real path for '/a.ts', result '/a.ts'",
-    "======== Module name '../' was successfully resolved to '/a.ts'. ========"
+    "Loading module as file / folder, candidate module location '/a/'.",
+    "File '/a/package.json' does not exist.",
+    "File '/a/index.ts' exist - use it as a name resolution result.",
+    "Resolving real path for '/a/index.ts', result '/a/index.ts'",
+    "======== Module name '../' was successfully resolved to '/a/index.ts'. ========"
 ]
\ No newline at end of file
diff --git a/tests/baselines/reference/relativeModuleWithoutSlash.types b/tests/baselines/reference/relativeModuleWithoutSlash.types
index 796ef714dd9..b84b57814be 100644
--- a/tests/baselines/reference/relativeModuleWithoutSlash.types
+++ b/tests/baselines/reference/relativeModuleWithoutSlash.types
@@ -16,32 +16,32 @@ import a from ".";
 >a : { a: number; }
 
 import aIndex from "./";
->aIndex : { a: number; }
+>aIndex : { aIndex: number; }
 
 a.a;
 >a.a : number
 >a : { a: number; }
 >a : number
 
-aIndex.a; //aIndex.aIndex; See GH#9690
->aIndex.a : number
->aIndex : { a: number; }
->a : number
+aIndex.aIndex;
+>aIndex.aIndex : number
+>aIndex : { aIndex: number; }
+>aIndex : number
 
 === /a/b/test.ts ===
 import a from "..";
 >a : { a: number; }
 
 import aIndex from "../";
->aIndex : { a: number; }
+>aIndex : { aIndex: number; }
 
 a.a;
 >a.a : number
 >a : { a: number; }
 >a : number
 
-aIndex.a; //aIndex.aIndex;
->aIndex.a : number
->aIndex : { a: number; }
->a : number
+aIndex.aIndex;
+>aIndex.aIndex : number
+>aIndex : { aIndex: number; }
+>aIndex : number
 
diff --git a/tests/cases/compiler/relativeModuleWithoutSlash.ts b/tests/cases/compiler/relativeModuleWithoutSlash.ts
index 42b328e1175..a5bceff8b13 100644
--- a/tests/cases/compiler/relativeModuleWithoutSlash.ts
+++ b/tests/cases/compiler/relativeModuleWithoutSlash.ts
@@ -11,10 +11,10 @@ export default { aIndex: 0 };
 import a from ".";
 import aIndex from "./";
 a.a;
-aIndex.a; //aIndex.aIndex; See GH#9690
+aIndex.aIndex;
 
 // @Filename: /a/b/test.ts
 import a from "..";
 import aIndex from "../";
 a.a;
-aIndex.a; //aIndex.aIndex;
+aIndex.aIndex;

From f0a532dac9fdc53e2b4af8f493be6fc47ee47a03 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Tue, 30 Aug 2016 07:45:51 -0700
Subject: [PATCH 2/3] Improve tests

---
 ...outSlash.js => importWithTrailingSlash.js} |  2 +-
 ...race.json => importWithTrailingSlash.json} |  0
 ...ymbols => importWithTrailingSlash.symbols} |  0
 .../importWithTrailingSlash.trace.json        | 28 +++++++++++++++++++
 ...sh.types => importWithTrailingSlash.types} |  0
 ...portWithTrailingSlash_noResolve.errors.txt |  9 ++++++
 .../importWithTrailingSlash_noResolve.js      |  7 +++++
 ...portWithTrailingSlash_noResolve.trace.json | 10 +++++++
 ...outSlash.ts => importWithTrailingSlash.ts} |  0
 .../importWithTrailingSlash_noResolve.ts      |  5 ++++
 10 files changed, 60 insertions(+), 1 deletion(-)
 rename tests/baselines/reference/{relativeModuleWithoutSlash.js => importWithTrailingSlash.js} (87%)
 rename tests/baselines/reference/{relativeModuleWithoutSlash.trace.json => importWithTrailingSlash.json} (100%)
 rename tests/baselines/reference/{relativeModuleWithoutSlash.symbols => importWithTrailingSlash.symbols} (100%)
 create mode 100644 tests/baselines/reference/importWithTrailingSlash.trace.json
 rename tests/baselines/reference/{relativeModuleWithoutSlash.types => importWithTrailingSlash.types} (100%)
 create mode 100644 tests/baselines/reference/importWithTrailingSlash_noResolve.errors.txt
 create mode 100644 tests/baselines/reference/importWithTrailingSlash_noResolve.js
 create mode 100644 tests/baselines/reference/importWithTrailingSlash_noResolve.trace.json
 rename tests/cases/compiler/{relativeModuleWithoutSlash.ts => importWithTrailingSlash.ts} (100%)
 create mode 100644 tests/cases/compiler/importWithTrailingSlash_noResolve.ts

diff --git a/tests/baselines/reference/relativeModuleWithoutSlash.js b/tests/baselines/reference/importWithTrailingSlash.js
similarity index 87%
rename from tests/baselines/reference/relativeModuleWithoutSlash.js
rename to tests/baselines/reference/importWithTrailingSlash.js
index e52d0cd19ed..7118dd95bb8 100644
--- a/tests/baselines/reference/relativeModuleWithoutSlash.js
+++ b/tests/baselines/reference/importWithTrailingSlash.js
@@ -1,4 +1,4 @@
-//// [tests/cases/compiler/relativeModuleWithoutSlash.ts] ////
+//// [tests/cases/compiler/importWithTrailingSlash.ts] ////
 
 //// [a.ts]
 
diff --git a/tests/baselines/reference/relativeModuleWithoutSlash.trace.json b/tests/baselines/reference/importWithTrailingSlash.json
similarity index 100%
rename from tests/baselines/reference/relativeModuleWithoutSlash.trace.json
rename to tests/baselines/reference/importWithTrailingSlash.json
diff --git a/tests/baselines/reference/relativeModuleWithoutSlash.symbols b/tests/baselines/reference/importWithTrailingSlash.symbols
similarity index 100%
rename from tests/baselines/reference/relativeModuleWithoutSlash.symbols
rename to tests/baselines/reference/importWithTrailingSlash.symbols
diff --git a/tests/baselines/reference/importWithTrailingSlash.trace.json b/tests/baselines/reference/importWithTrailingSlash.trace.json
new file mode 100644
index 00000000000..3c99d4eb6a0
--- /dev/null
+++ b/tests/baselines/reference/importWithTrailingSlash.trace.json
@@ -0,0 +1,28 @@
+[
+    "======== Resolving module '.' from '/a/test.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/a'.",
+    "File '/a.ts' exist - use it as a name resolution result.",
+    "Resolving real path for '/a.ts', result '/a.ts'",
+    "======== Module name '.' was successfully resolved to '/a.ts'. ========",
+    "======== Resolving module './' from '/a/test.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/a/'.",
+    "File '/a/package.json' does not exist.",
+    "File '/a/index.ts' exist - use it as a name resolution result.",
+    "Resolving real path for '/a/index.ts', result '/a/index.ts'",
+    "======== Module name './' was successfully resolved to '/a/index.ts'. ========",
+    "======== Resolving module '..' from '/a/b/test.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/a'.",
+    "File '/a.ts' exist - use it as a name resolution result.",
+    "Resolving real path for '/a.ts', result '/a.ts'",
+    "======== Module name '..' was successfully resolved to '/a.ts'. ========",
+    "======== Resolving module '../' from '/a/b/test.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/a/'.",
+    "File '/a/package.json' does not exist.",
+    "File '/a/index.ts' exist - use it as a name resolution result.",
+    "Resolving real path for '/a/index.ts', result '/a/index.ts'",
+    "======== Module name '../' was successfully resolved to '/a/index.ts'. ========"
+]
\ No newline at end of file
diff --git a/tests/baselines/reference/relativeModuleWithoutSlash.types b/tests/baselines/reference/importWithTrailingSlash.types
similarity index 100%
rename from tests/baselines/reference/relativeModuleWithoutSlash.types
rename to tests/baselines/reference/importWithTrailingSlash.types
diff --git a/tests/baselines/reference/importWithTrailingSlash_noResolve.errors.txt b/tests/baselines/reference/importWithTrailingSlash_noResolve.errors.txt
new file mode 100644
index 00000000000..780e1d2f1bc
--- /dev/null
+++ b/tests/baselines/reference/importWithTrailingSlash_noResolve.errors.txt
@@ -0,0 +1,9 @@
+/a.ts(2,17): error TS2307: Cannot find module './foo/'.
+
+
+==== /a.ts (1 errors) ====
+    
+    import foo from "./foo/";
+                    ~~~~~~~~
+!!! error TS2307: Cannot find module './foo/'.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/importWithTrailingSlash_noResolve.js b/tests/baselines/reference/importWithTrailingSlash_noResolve.js
new file mode 100644
index 00000000000..b523c76af3b
--- /dev/null
+++ b/tests/baselines/reference/importWithTrailingSlash_noResolve.js
@@ -0,0 +1,7 @@
+//// [a.ts]
+
+import foo from "./foo/";
+
+
+//// [a.js]
+"use strict";
diff --git a/tests/baselines/reference/importWithTrailingSlash_noResolve.trace.json b/tests/baselines/reference/importWithTrailingSlash_noResolve.trace.json
new file mode 100644
index 00000000000..e010603106f
--- /dev/null
+++ b/tests/baselines/reference/importWithTrailingSlash_noResolve.trace.json
@@ -0,0 +1,10 @@
+[
+    "======== Resolving module './foo/' from '/a.ts'. ========",
+    "Explicitly specified module resolution kind: 'NodeJs'.",
+    "Loading module as file / folder, candidate module location '/foo/'.",
+    "File '/foo/package.json' does not exist.",
+    "File '/foo/index.ts' does not exist.",
+    "File '/foo/index.tsx' does not exist.",
+    "File '/foo/index.d.ts' does not exist.",
+    "======== Module name './foo/' was not resolved. ========"
+]
\ No newline at end of file
diff --git a/tests/cases/compiler/relativeModuleWithoutSlash.ts b/tests/cases/compiler/importWithTrailingSlash.ts
similarity index 100%
rename from tests/cases/compiler/relativeModuleWithoutSlash.ts
rename to tests/cases/compiler/importWithTrailingSlash.ts
diff --git a/tests/cases/compiler/importWithTrailingSlash_noResolve.ts b/tests/cases/compiler/importWithTrailingSlash_noResolve.ts
new file mode 100644
index 00000000000..95541adfb11
--- /dev/null
+++ b/tests/cases/compiler/importWithTrailingSlash_noResolve.ts
@@ -0,0 +1,5 @@
+// @traceResolution: true
+// @moduleResolution: node
+
+// @Filename: /a.ts
+import foo from "./foo/";

From 0f51bdbb4ff76697d72497a0fc229aaefc7dd4c0 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Wed, 14 Sep 2016 06:21:07 -0700
Subject: [PATCH 3/3] Rename function and use `directorySeparator` variables

---
 src/compiler/core.ts    | 9 +++++----
 src/compiler/program.ts | 2 +-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index eb90b5f5ec5..8c0ca87d862 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -1018,7 +1018,8 @@ namespace ts {
         return 0;
     }
 
-    export let directorySeparator = "/";
+    export const directorySeparator = "/";
+    const directorySeparatorCharCode = CharacterCodes.slash;
     function getNormalizedParts(normalizedSlashedPath: string, rootLength: number) {
         const parts = normalizedSlashedPath.substr(rootLength).split(directorySeparator);
         const normalized: string[] = [];
@@ -1047,7 +1048,7 @@ namespace ts {
         const normalized = getNormalizedParts(path, rootLength);
         if (normalized.length) {
             const joinedParts = root + normalized.join(directorySeparator);
-            return isPathToDirectory(path) ? joinedParts + "/" : joinedParts;
+            return pathEndsWithDirectorySeparator(path) ? joinedParts + directorySeparator : joinedParts;
         }
         else {
             return root;
@@ -1055,8 +1056,8 @@ namespace ts {
     }
 
     /** A path ending with '/' refers to a directory only, never a file. */
-    export function isPathToDirectory(path: string): boolean {
-        return path.charCodeAt(path.length - 1) === CharacterCodes.slash;
+    export function pathEndsWithDirectorySeparator(path: string): boolean {
+        return path.charCodeAt(path.length - 1) === directorySeparatorCharCode;
     }
 
     export function getDirectoryPath(path: Path): Path;
diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 94f87700d99..ab306e90f3a 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -670,7 +670,7 @@ namespace ts {
             trace(state.host, Diagnostics.Loading_module_as_file_Slash_folder_candidate_module_location_0, candidate);
         }
 
-        const resolvedFileName = !isPathToDirectory(candidate) && loadModuleFromFile(candidate, supportedExtensions, failedLookupLocations, onlyRecordFailures, state);
+        const resolvedFileName = !pathEndsWithDirectorySeparator(candidate) && loadModuleFromFile(candidate, supportedExtensions, failedLookupLocations, onlyRecordFailures, state);
 
         return resolvedFileName || loadNodeModuleFromDirectory(supportedExtensions, candidate, failedLookupLocations, onlyRecordFailures, state);
     }