Handle strict flag when writing tsbuildinfo (#44394)

* Add test showing how setting strict is not preserved in tsbuildinfo
Test for #44305

* Handle strict flag when writing tsbuildinfo
Fixes #44305

* Apply suggestions from code review

Co-authored-by: Daniel Rosenwasser <DanielRosenwasser@users.noreply.github.com>

Co-authored-by: Daniel Rosenwasser <DanielRosenwasser@users.noreply.github.com>

src/compiler/builder.ts

@@ -853,8 +853,14 @@ namespace ts {
         const { optionsNameMap } = getOptionsNameMap();
 
         for (const name of getOwnKeys(options).sort(compareStringsCaseSensitive)) {
-            const optionInfo = optionsNameMap.get(name.toLowerCase());
-            if (optionInfo?.affectsEmit || optionInfo?.affectsSemanticDiagnostics || name === "skipLibCheck" || name === "skipDefaultLibCheck") {
+            const optionKey = name.toLowerCase();
+            const optionInfo = optionsNameMap.get(optionKey);
+            if (optionInfo?.affectsEmit || optionInfo?.affectsSemanticDiagnostics ||
+                // We need to store `strict`, even though it won't be examined directly, so that the
+                // flags it controls (e.g. `strictNullChecks`) will be retrieved correctly from the buildinfo
+                optionKey === "strict" ||
+                // We need to store these to determine whether `lib` files need to be rechecked.
+                optionKey === "skiplibcheck" || optionKey === "skipdefaultlibcheck") {
                 (result ||= {})[name] = convertToReusableCompilerOptionValue(
                     optionInfo,
                     options[name] as CompilerOptionsValue,

src/compiler/commandLineParser.ts

@@ -566,6 +566,8 @@ namespace ts {
         {
             name: "strict",
             type: "boolean",
+            // Though this affects semantic diagnostics, affectsSemanticDiagnostics is not set here
+            // The value of each strictFlag depends on own strictFlag value or this and never accessed directly.
             showInSimplifiedHelpView: true,
             category: Diagnostics.Type_Checking,
             description: Diagnostics.Enable_all_strict_type_checking_options

src/testRunner/unittests/tsc/incremental.ts

@@ -400,5 +400,23 @@ declare global {
                 },
             ]
         });
+
+
+        verifyTscSerializedIncrementalEdits({
+            scenario: "incremental",
+            subScenario: "when project has strict true",
+            commandLineArgs: ["-noEmit", "-p", `src/project`],
+            fs: () => loadProjectFromFiles({
+                "/src/project/tsconfig.json": JSON.stringify({
+                    compilerOptions: {
+                        incremental: true,
+                        strict: true,
+                    },
+                }),
+                "/src/project/class1.ts": `export class class1 {}`,
+            }),
+            incrementalScenarios: noChangeOnlyRuns,
+            baselinePrograms: true
+        });
     });
 }