prefer-const

src/compiler/debug.ts

@@ -1,8 +1,10 @@
 /* @internal */
 namespace ts {
     export namespace Debug {
+        /* eslint-disable prefer-const */
         export let currentAssertionLevel = AssertionLevel.None;
         export let isDebugging = false;
+        /* eslint-enable prefer-const */
 
         export function shouldAssert(level: AssertionLevel): boolean {
             return currentAssertionLevel >= level;
@@ -258,4 +260,4 @@ namespace ts {
             isDebugInfoEnabled = true;
         }
     }
-}
+}

src/compiler/program.ts

@@ -709,7 +709,6 @@ namespace ts {
         const { rootNames, options, configFileParsingDiagnostics, projectReferences } = createProgramOptions;
         let { oldProgram } = createProgramOptions;
 
-        let program: Program;
         let processingDefaultLibFiles: SourceFile[] | undefined;
         let processingOtherFiles: SourceFile[] | undefined;
         let files: SourceFile[];
@@ -905,7 +904,7 @@ namespace ts {
         // unconditionally set oldProgram to undefined to prevent it from being captured in closure
         oldProgram = undefined;
 
-        program = {
+        const program: Program = {
             getRootFileNames: () => rootNames,
             getSourceFile,
             getSourceFileByPath,

src/compiler/sys.ts

@@ -635,6 +635,7 @@ namespace ts {
     };
 
     // TODO: GH#18217 this is used as if it's certainly defined in many places.
+    // eslint-disable-next-line prefer-const
     export let sys: System = (() => {
         // NodeJS detects "\uFEFF" at the start of the string and *replaces* it with the actual
         // byte order mark from the specified encoding. Using any other byte order mark does

src/compiler/transformers/generators.ts

@@ -1975,12 +1975,11 @@ namespace ts {
         }
 
         function cacheExpression(node: Expression): Identifier {
-            let temp: Identifier;
             if (isGeneratedIdentifier(node) || getEmitFlags(node) & EmitFlags.HelperName) {
                 return <Identifier>node;
             }
 
-            temp = createTempVariable(hoistVariableDeclaration);
+            const temp = createTempVariable(hoistVariableDeclaration);
             emitAssignment(temp, node, /*location*/ node);
             return temp;
         }

src/compiler/utilities.ts

@@ -4724,7 +4724,7 @@ namespace ts {
         return { span, newLength };
     }
 
-    export let unchangedTextChangeRange = createTextChangeRange(createTextSpan(0, 0), 0);
+    export let unchangedTextChangeRange = createTextChangeRange(createTextSpan(0, 0), 0); // eslint-disable-line prefer-const
 
     /**
      * Called to merge all the changes that occurred across several versions of a script snapshot
@@ -7025,6 +7025,7 @@ namespace ts {
         this.skipTrivia = skipTrivia || (pos => pos);
     }
 
+    // eslint-disable-next-line prefer-const
     export let objectAllocator: ObjectAllocator = {
         getNodeConstructor: () => <any>Node,
         getTokenConstructor: () => <any>Node,

src/harness/harness.ts

@@ -623,8 +623,10 @@ namespace Harness {
     ) => void;
 
     // Settings
+    /* eslint-disable prefer-const */
     export let userSpecifiedRoot = "";
     export let lightMode = false;
+    /* eslint-enable prefer-const */
 
     /** Functionality for compiling TypeScript code */
     export namespace Compiler {

src/harness/harnessLanguageService.ts

@@ -594,15 +594,13 @@ namespace Harness.LanguageService {
         getLanguageService(): ts.LanguageService { return new LanguageServiceShimProxy(this.factory.createLanguageServiceShim(this.host)); }
         getClassifier(): ts.Classifier { return new ClassifierShimProxy(this.factory.createClassifierShim(this.host)); }
         getPreProcessedFileInfo(fileName: string, fileContents: string): ts.PreProcessedFileInfo {
-            let shimResult: {
+            const coreServicesShim = this.factory.createCoreServicesShim(this.host);
+            const shimResult: {
                 referencedFiles: ts.ShimsFileReference[];
                 typeReferenceDirectives: ts.ShimsFileReference[];
                 importedFiles: ts.ShimsFileReference[];
                 isLibFile: boolean;
-            };
-
-            const coreServicesShim = this.factory.createCoreServicesShim(this.host);
-            shimResult = unwrapJSONCallResult(coreServicesShim.getPreProcessedFileInfo(fileName, ts.ScriptSnapshot.fromString(fileContents)));
+            } = unwrapJSONCallResult(coreServicesShim.getPreProcessedFileInfo(fileName, ts.ScriptSnapshot.fromString(fileContents)));
 
             const convertResult: ts.PreProcessedFileInfo = {
                 referencedFiles: [],

src/services/services.ts

@@ -1012,7 +1012,7 @@ namespace ts {
         return sourceFile;
     }
 
-    export let disableIncrementalParsing = false;
+    export let disableIncrementalParsing = false; // eslint-disable-line prefer-const
 
     export function updateLanguageServiceSourceFile(sourceFile: SourceFile, scriptSnapshot: IScriptSnapshot, version: string, textChangeRange: TextChangeRange | undefined, aggressiveChecks?: boolean): SourceFile {
         // If we were given a text change range, and our version or open-ness changed, then

src/services/shims.ts

@@ -14,7 +14,7 @@
 //
 
 /* @internal */
-let debugObjectHost: { CollectGarbage(): void } = (function (this: any) { return this; })();
+let debugObjectHost: { CollectGarbage(): void } = (function (this: any) { return this; })(); // eslint-disable-line prefer-const
 
 // We need to use 'null' to interface with the managed side.
 /* tslint:disable:no-null-keyword */

src/testRunner/runner.ts

@@ -1,5 +1,5 @@
-let runners: RunnerBase[] = [];
-let iterations = 1;
+const runners: RunnerBase[] = [];
+const iterations = 1;
 
 function runTests(runners: RunnerBase[]) {
     for (let i = iterations; i > 0; i--) {
@@ -50,7 +50,7 @@ const mytestconfigFileName = "mytest.config";
 const testconfigFileName = "test.config";
 
 const customConfig = tryGetConfig(Harness.IO.args());
-let testConfigContent =
+const testConfigContent =
     customConfig && Harness.IO.fileExists(customConfig)
         ? Harness.IO.readFile(customConfig)!
         : Harness.IO.fileExists(mytestconfigFileName)

src/testRunner/unittests/services/transpile.ts

@@ -7,15 +7,11 @@ namespace ts {
 
         function transpilesCorrectly(name: string, input: string, testSettings: TranspileTestSettings) {
             describe(name, () => {
-                let justName: string;
-                let transpileOptions: TranspileOptions;
-                let canUseOldTranspile: boolean;
-                let toBeCompiled: Harness.Compiler.TestFile[];
                 let transpileResult: TranspileOutput;
                 let oldTranspileResult: string;
                 let oldTranspileDiagnostics: Diagnostic[];
 
-                transpileOptions = testSettings.options || {};
+                const transpileOptions: TranspileOptions = testSettings.options || {};
                 if (!transpileOptions.compilerOptions) {
                     transpileOptions.compilerOptions = {};
                 }
@@ -33,13 +29,12 @@ namespace ts {
 
                 transpileOptions.reportDiagnostics = true;
 
-                justName = "transpile/" + name.replace(/[^a-z0-9\-. ]/ig, "") + (transpileOptions.compilerOptions.jsx ? Extension.Tsx : Extension.Ts);
-                toBeCompiled = [{
+                const justName = "transpile/" + name.replace(/[^a-z0-9\-. ]/ig, "") + (transpileOptions.compilerOptions.jsx ? Extension.Tsx : Extension.Ts);
+                const toBeCompiled: Harness.Compiler.TestFile[] = [{
                     unitName: transpileOptions.fileName,
                     content: input
                 }];
-
-                canUseOldTranspile = !transpileOptions.renamedDependencies;
+                const canUseOldTranspile = !transpileOptions.renamedDependencies;
 
                 before(() => {
                     transpileResult = transpileModule(input, transpileOptions);