Fix issue with case sensitivity of noUnusedVariable rule on Windows (#…

…2819)

When TSLint is being used to provide as-you-type linting as in Angular
IDE, incorrect configuration of program created in
makeUnusedCheckedProgram function is causing whole functionality to blow
up. The core of the issue is that SourceFiles are being assigned case
sensitive path when program is recreated for TSLint validation, which
later causes that wrong path to stick and file not found problems appear
in whole IDE.

src/rules/noUnusedVariableRule.ts

@@ -368,22 +368,26 @@ function getUnusedCheckedProgram(program: ts.Program, checkParameters: boolean):
 
 function makeUnusedCheckedProgram(program: ts.Program, checkParameters: boolean): ts.Program {
     const options = { ...program.getCompilerOptions(), noUnusedLocals: true, ...(checkParameters ? { noUnusedParameters: true } : null) };
-    const sourceFilesByName = new Map<string, ts.SourceFile>(program.getSourceFiles().map<[string, ts.SourceFile]>((s) => [s.fileName, s]));
+    const sourceFilesByName = new Map<string, ts.SourceFile>(
+        program.getSourceFiles().map<[string, ts.SourceFile]>((s) => [getCanonicalFileName(s.fileName), s]));
+
     // tslint:disable object-literal-sort-keys
     return ts.createProgram(Array.from(sourceFilesByName.keys()), options, {
-        fileExists: (f) => sourceFilesByName.has(f),
-        readFile(f) {
-            const s = sourceFilesByName.get(f)!;
-            return s.text;
-        },
-        getSourceFile: (f) => sourceFilesByName.get(f)!,
+        fileExists: (f) => sourceFilesByName.has(getCanonicalFileName(f)),
+        readFile: (f) => sourceFilesByName.get(getCanonicalFileName(f))!.text,
+        getSourceFile: (f) => sourceFilesByName.get(getCanonicalFileName(f))!,
         getDefaultLibFileName: () => ts.getDefaultLibFileName(options),
         writeFile: () => {}, // tslint:disable-line no-empty
         getCurrentDirectory: () => "",
         getDirectories: () => [],
-        getCanonicalFileName: (f) => f,
-        useCaseSensitiveFileNames: () => true,
+        getCanonicalFileName,
+        useCaseSensitiveFileNames: () => ts.sys.useCaseSensitiveFileNames,
         getNewLine: () => "\n",
     });
     // tslint:enable object-literal-sort-keys
+
+    // We need to be careful with file system case sensitivity
+    function getCanonicalFileName(fileName: string): string {
+        return ts.sys.useCaseSensitiveFileNames ? fileName : fileName.toLowerCase();
+    }
 }