From 69bd2e7320430cd468f744d9b085e2abfc450828 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Wed, 22 Feb 2023 16:04:05 -0800
Subject: [PATCH 1/2] Add links to github above big var blocks

---
 src/compiler/binder.ts    | 1 +
 src/compiler/checker.ts   | 1 +
 src/compiler/emitter.ts   | 2 ++
 src/compiler/parser.ts    | 1 +
 src/compiler/scanner.ts   | 1 +
 src/compiler/sourcemap.ts | 1 +
 src/compiler/utilities.ts | 2 ++
 7 files changed, 9 insertions(+)

diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index a6e497fc8a414..af5b5afbf9534 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -501,6 +501,7 @@ export function bindSourceFile(file: SourceFile, options: CompilerOptions) {
 }
 
 function createBinder(): (file: SourceFile, options: CompilerOptions) => void {
+    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var file: SourceFile;
     var options: CompilerOptions;
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index c0b9802d4021b..bf70ed08408d9 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -1378,6 +1378,7 @@ export function isInstantiatedModule(node: ModuleDeclaration, preserveConstEnums
 
 /** @internal */
 export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
+    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var getPackagesMap = memoize(() => {
         // A package name maps to true when we detect it has .d.ts files.
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index fe198d629533c..449b979ec82e8 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -737,6 +737,7 @@ export function getFirstProjectOutput(configFile: ParsedCommandLine, ignoreCase:
 /** @internal */
 // targetSourceFile is when users only want one file in entire project to be emitted. This is used in compileOnSave feature
 export function emitFiles(resolver: EmitResolver, host: EmitHost, targetSourceFile: SourceFile | undefined, { scriptTransformers, declarationTransformers }: EmitTransformers, emitOnly?: boolean | EmitOnly, onlyBuildInfo?: boolean, forceDtsEmit?: boolean): EmitResult {
+    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var compilerOptions = host.getCompilerOptions();
     var sourceMapDataList: SourceMapEmitResult[] | undefined = (compilerOptions.sourceMap || compilerOptions.inlineSourceMap || getAreDeclarationMapsEnabled(compilerOptions)) ? [] : undefined;
@@ -1358,6 +1359,7 @@ export const createPrinterWithRemoveCommentsNeverAsciiEscape = /* @__PURE__ */ m
 export const createPrinterWithRemoveCommentsOmitTrailingSemicolon = /* @__PURE__ */ memoize(() => createPrinter({ removeComments: true, omitTrailingSemicolon: true }));
 
 export function createPrinter(printerOptions: PrinterOptions = {}, handlers: PrintHandlers = {}): Printer {
+    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var {
         hasGlobalName,
diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
index 9bcf3c8c7dd53..aad830d02c28f 100644
--- a/src/compiler/parser.ts
+++ b/src/compiler/parser.ts
@@ -1401,6 +1401,7 @@ export function parseJSDocTypeExpressionForTests(content: string, start?: number
 // parser instances can actually be expensive enough to impact us on projects with many source
 // files.
 namespace Parser {
+    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
 
     // Share a single scanner across all calls to parse a source file.  This helps speed things
diff --git a/src/compiler/scanner.ts b/src/compiler/scanner.ts
index 554800e28b9bb..3798b8a3ab2bb 100644
--- a/src/compiler/scanner.ts
+++ b/src/compiler/scanner.ts
@@ -961,6 +961,7 @@ export function createScanner(languageVersion: ScriptTarget,
     start?: number,
     length?: number): Scanner {
 
+    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var text = textInitial!;
 
diff --git a/src/compiler/sourcemap.ts b/src/compiler/sourcemap.ts
index 8921bdfeba7de..b8be16a174a36 100644
--- a/src/compiler/sourcemap.ts
+++ b/src/compiler/sourcemap.ts
@@ -35,6 +35,7 @@ export interface SourceMapGeneratorOptions {
 
 /** @internal */
 export function createSourceMapGenerator(host: EmitHost, file: string, sourceRoot: string, sourcesDirectoryPath: string, generatorOptions: SourceMapGeneratorOptions): SourceMapGenerator {
+    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var { enter, exit } = generatorOptions.extendedDiagnostics
         ? performance.createTimer("Source Map", "beforeSourcemap", "afterSourcemap")
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 774b3fb2212a7..1c92025b6ed5b 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -596,6 +596,7 @@ export function isTransientSymbol(symbol: Symbol): symbol is TransientSymbol {
 const stringWriter = createSingleLineStringWriter();
 
 function createSingleLineStringWriter(): EmitTextWriter {
+    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var str = "";
     /* eslint-enable no-var */
@@ -5812,6 +5813,7 @@ export function isNightly() {
 
 /** @internal */
 export function createTextWriter(newLine: string): EmitTextWriter {
+    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var output: string;
     var indent: number;

From f298e242661a369effe41bb6be16cdd9d191e920 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Wed, 22 Feb 2023 16:29:41 -0800
Subject: [PATCH 2/2] Update all comments

---
 src/compiler/binder.ts    | 3 ++-
 src/compiler/checker.ts   | 3 ++-
 src/compiler/emitter.ts   | 6 ++++--
 src/compiler/parser.ts    | 3 ++-
 src/compiler/scanner.ts   | 3 ++-
 src/compiler/sourcemap.ts | 3 ++-
 src/compiler/utilities.ts | 6 ++++--
 7 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index af5b5afbf9534..78bf9e1f3a682 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -501,7 +501,8 @@ export function bindSourceFile(file: SourceFile, options: CompilerOptions) {
 }
 
 function createBinder(): (file: SourceFile, options: CompilerOptions) => void {
-    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
+    // Why var? It avoids TDZ checks in the runtime which can be costly.
+    // See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var file: SourceFile;
     var options: CompilerOptions;
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index bf70ed08408d9..beb75fd16d2dc 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -1378,7 +1378,8 @@ export function isInstantiatedModule(node: ModuleDeclaration, preserveConstEnums
 
 /** @internal */
 export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
-    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
+    // Why var? It avoids TDZ checks in the runtime which can be costly.
+    // See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var getPackagesMap = memoize(() => {
         // A package name maps to true when we detect it has .d.ts files.
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index 449b979ec82e8..05f117fdcfa12 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -737,7 +737,8 @@ export function getFirstProjectOutput(configFile: ParsedCommandLine, ignoreCase:
 /** @internal */
 // targetSourceFile is when users only want one file in entire project to be emitted. This is used in compileOnSave feature
 export function emitFiles(resolver: EmitResolver, host: EmitHost, targetSourceFile: SourceFile | undefined, { scriptTransformers, declarationTransformers }: EmitTransformers, emitOnly?: boolean | EmitOnly, onlyBuildInfo?: boolean, forceDtsEmit?: boolean): EmitResult {
-    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
+    // Why var? It avoids TDZ checks in the runtime which can be costly.
+    // See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var compilerOptions = host.getCompilerOptions();
     var sourceMapDataList: SourceMapEmitResult[] | undefined = (compilerOptions.sourceMap || compilerOptions.inlineSourceMap || getAreDeclarationMapsEnabled(compilerOptions)) ? [] : undefined;
@@ -1359,7 +1360,8 @@ export const createPrinterWithRemoveCommentsNeverAsciiEscape = /* @__PURE__ */ m
 export const createPrinterWithRemoveCommentsOmitTrailingSemicolon = /* @__PURE__ */ memoize(() => createPrinter({ removeComments: true, omitTrailingSemicolon: true }));
 
 export function createPrinter(printerOptions: PrinterOptions = {}, handlers: PrintHandlers = {}): Printer {
-    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
+    // Why var? It avoids TDZ checks in the runtime which can be costly.
+    // See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var {
         hasGlobalName,
diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
index aad830d02c28f..e157e0cebd413 100644
--- a/src/compiler/parser.ts
+++ b/src/compiler/parser.ts
@@ -1401,7 +1401,8 @@ export function parseJSDocTypeExpressionForTests(content: string, start?: number
 // parser instances can actually be expensive enough to impact us on projects with many source
 // files.
 namespace Parser {
-    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
+    // Why var? It avoids TDZ checks in the runtime which can be costly.
+    // See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
 
     // Share a single scanner across all calls to parse a source file.  This helps speed things
diff --git a/src/compiler/scanner.ts b/src/compiler/scanner.ts
index 3798b8a3ab2bb..e517b18e685f8 100644
--- a/src/compiler/scanner.ts
+++ b/src/compiler/scanner.ts
@@ -961,7 +961,8 @@ export function createScanner(languageVersion: ScriptTarget,
     start?: number,
     length?: number): Scanner {
 
-    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
+    // Why var? It avoids TDZ checks in the runtime which can be costly.
+    // See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var text = textInitial!;
 
diff --git a/src/compiler/sourcemap.ts b/src/compiler/sourcemap.ts
index b8be16a174a36..14b106b70a318 100644
--- a/src/compiler/sourcemap.ts
+++ b/src/compiler/sourcemap.ts
@@ -35,7 +35,8 @@ export interface SourceMapGeneratorOptions {
 
 /** @internal */
 export function createSourceMapGenerator(host: EmitHost, file: string, sourceRoot: string, sourcesDirectoryPath: string, generatorOptions: SourceMapGeneratorOptions): SourceMapGenerator {
-    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
+    // Why var? It avoids TDZ checks in the runtime which can be costly.
+    // See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var { enter, exit } = generatorOptions.extendedDiagnostics
         ? performance.createTimer("Source Map", "beforeSourcemap", "afterSourcemap")
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 1c92025b6ed5b..af4730f848460 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -596,7 +596,8 @@ export function isTransientSymbol(symbol: Symbol): symbol is TransientSymbol {
 const stringWriter = createSingleLineStringWriter();
 
 function createSingleLineStringWriter(): EmitTextWriter {
-    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
+    // Why var? It avoids TDZ checks in the runtime which can be costly.
+    // See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var str = "";
     /* eslint-enable no-var */
@@ -5813,7 +5814,8 @@ export function isNightly() {
 
 /** @internal */
 export function createTextWriter(newLine: string): EmitTextWriter {
-    // Why var? See: https://github.com/microsoft/TypeScript/issues/52924
+    // Why var? It avoids TDZ checks in the runtime which can be costly.
+    // See: https://github.com/microsoft/TypeScript/issues/52924
     /* eslint-disable no-var */
     var output: string;
     var indent: number;