Cache result of isCheckJsEnabledForFile in getSemanticDiagnosticsForFile

Author: sandersn

src/compiler/program.ts

@@ -1273,15 +1273,16 @@ namespace ts {
 
                 Debug.assert(!!sourceFile.bindDiagnostics);
 
+                const isCheckJs = isCheckJsEnabledForFile(sourceFile, options);
                 // By default, only type-check .ts, .tsx, and 'External' files (external files are added by plugins)
                 const includeBindAndCheckDiagnostics = sourceFile.scriptKind === ScriptKind.TS || sourceFile.scriptKind === ScriptKind.TSX ||
-                    sourceFile.scriptKind === ScriptKind.External || isCheckJsEnabledForFile(sourceFile, options);
+                    sourceFile.scriptKind === ScriptKind.External || isCheckJs;
                 const bindDiagnostics = includeBindAndCheckDiagnostics ? sourceFile.bindDiagnostics : emptyArray;
                 const checkDiagnostics = includeBindAndCheckDiagnostics ? typeChecker.getDiagnostics(sourceFile, cancellationToken) : emptyArray;
                 const fileProcessingDiagnosticsInFile = fileProcessingDiagnostics.getDiagnostics(sourceFile.fileName);
                 const programDiagnosticsInFile = programDiagnostics.getDiagnostics(sourceFile.fileName);
                 let diagnostics = bindDiagnostics.concat(checkDiagnostics, fileProcessingDiagnosticsInFile, programDiagnosticsInFile);
-                if (isCheckJsEnabledForFile(sourceFile, options)) {
+                if (isCheckJs) {
                     diagnostics = concatenate(diagnostics, sourceFile.jsDocDiagnostics);
                 }
                 return filter(diagnostics, shouldReportDiagnostic);