JSON.stringify can return undefined

src/harness/fourslash.ts

@@ -1518,7 +1518,7 @@ Actual: ${stringify(fullActual)}`);
 
         public printCurrentParameterHelp() {
             const help = this.languageService.getSignatureHelpItems(this.activeFile.fileName, this.currentCaretPosition, /*options*/ undefined);
-            Harness.IO.log(stringify(help));
+            Harness.IO.log(stringify(help)!);
         }
 
         public printCurrentQuickInfo() {
@@ -3565,7 +3565,7 @@ ${code}
         };
     }
 
-    function stringify(data: any, replacer?: (key: string, value: any) => any): string {
+    function stringify<T>(data: T, replacer?: (key: string, value: any) => any) {
         return JSON.stringify(data, replacer, 2);
     }
 

src/lib/es5.d.ts

@@ -1029,6 +1029,8 @@ interface URIErrorConstructor {
 
 declare const URIError: URIErrorConstructor;
 
+type StringifyReturnType<T> = T extends undefined ? string | undefined : string;
+
 interface JSON {
     /**
       * Converts a JavaScript Object Notation (JSON) string into an object.
@@ -1043,14 +1045,14 @@ interface JSON {
       * @param replacer A function that transforms the results.
       * @param space Adds indentation, white space, and line break characters to the return-value JSON text to make it easier to read.
       */
-    stringify(value: any, replacer?: (this: any, key: string, value: any) => any, space?: string | number): string;
+    stringify<T>(value: T, replacer?: (this: any, key: string, value: any) => any, space?: string | number): StringifyReturnType<T>;
     /**
       * Converts a JavaScript value to a JavaScript Object Notation (JSON) string.
       * @param value A JavaScript value, usually an object or array, to be converted.
       * @param replacer An array of strings and numbers that acts as a approved list for selecting the object properties that will be stringified.
       * @param space Adds indentation, white space, and line break characters to the return-value JSON text to make it easier to read.
       */
-    stringify(value: any, replacer?: (number | string)[] | null, space?: string | number): string;
+    stringify<T>(value: T, replacer?: (number | string)[] | null, space?: string | number): StringifyReturnType<T>;
 }
 
 /**

src/services/shims.ts

@@ -77,7 +77,7 @@ namespace ts {
         useCaseSensitiveFileNames?(): boolean;
 
         getTypeRootsVersion?(): number;
-        readDirectory(rootDir: string, extension: string, basePaths?: string, excludeEx?: string, includeFileEx?: string, includeDirEx?: string, depth?: number): string;
+        readDirectory(rootDir: string, extension?: string, basePaths?: string, excludeEx?: string, includeFileEx?: string, includeDirEx?: string, depth?: number): string;
         readFile(path: string, encoding?: string): string | undefined;
         fileExists(path: string): boolean;
 

src/testRunner/unittests/config/convertCompilerOptionsFromJson.ts

@@ -38,7 +38,7 @@ namespace ts {
         }
 
         function assertCompilerOptionsWithJsonNode(json: any, configFileName: string, expectedResult: ExpectedResultWithParsingSuccess) {
-            assertCompilerOptionsWithJsonText(JSON.stringify(json), configFileName, expectedResult);
+            assertCompilerOptionsWithJsonText(JSON.stringify(json)!, configFileName, expectedResult);
         }
 
         function assertCompilerOptionsWithJsonText(fileText: string, configFileName: string, expectedResult: ExpectedResult) {

src/testRunner/unittests/config/convertTypeAcquisitionFromJson.ts

@@ -36,7 +36,7 @@ namespace ts {
         }
 
         function assertTypeAcquisitionWithJsonNode(json: any, configFileName: string, expectedResult: ExpectedResult) {
-            const fileText = JSON.stringify(json);
+            const fileText = JSON.stringify(json)!;
             const result = parseJsonText(configFileName, fileText);
             assert(!result.parseDiagnostics.length);
             assert(!!result.endOfFileToken);

src/testRunner/unittests/config/matchFiles.ts

@@ -108,7 +108,7 @@ namespace ts {
 
     function validateMatches(expected: ParsedCommandLine, json: any, host: ParseConfigHost, basePath: string, existingOptions?: CompilerOptions, configFileName?: string, resolutionStack?: Path[]) {
         {
-            const jsonText = JSON.stringify(json);
+            const jsonText = JSON.stringify(json)!;
             const result = parseJsonText(caseInsensitiveTsconfigPath, jsonText);
             const actual = parseJsonSourceFileConfigFileContent(result, host, basePath, existingOptions, configFileName, resolutionStack);
             for (const error of expected.errors) {

src/testRunner/unittests/tsbuildWatchMode.ts

@@ -982,7 +982,7 @@ export function gfoo() {
                                     const cTsConfigJson = JSON.parse(cTsconfig.content);
                                     host.ensureFileOrFolder(nrefs);
                                     cTsConfigJson.compilerOptions.paths = { "@ref/*": nrefsPath };
-                                    host.writeFile(cTsconfig.path, JSON.stringify(cTsConfigJson));
+                                    host.writeFile(cTsconfig.path, JSON.stringify(cTsConfigJson)!);
                                 },
                                 emptyArray,
                                 expectedProgramFiles.map(nrefReplacer),
@@ -1015,7 +1015,7 @@ export function gfoo() {
                                     const bTsConfigJson = JSON.parse(bTsconfig.content);
                                     host.ensureFileOrFolder(nrefs);
                                     bTsConfigJson.compilerOptions.paths = { "@ref/*": nrefsPath };
-                                    host.writeFile(bTsconfig.path, JSON.stringify(bTsConfigJson));
+                                    host.writeFile(bTsconfig.path, JSON.stringify(bTsConfigJson)!);
                                 },
                                 emptyArray,
                                 expectedProgramFiles,

src/testRunner/unittests/tscWatch/emit.ts

@@ -214,7 +214,7 @@ namespace ts.tscWatch {
             (configObj.compilerOptions || (configObj.compilerOptions = {})).listEmittedFiles = true;
             const configFile = getFileOrFolderEmit({
                 path: configFilePath,
-                content: JSON.stringify(configObj)
+                content: JSON.stringify(configObj)!
             });
 
             const files = [moduleFile1, file1Consumer1, file1Consumer2, globalFile3, moduleFile2, configFile, libFile, ...additionalFiles];

src/testRunner/unittests/tscWatch/watchApi.ts

@@ -11,7 +11,7 @@ namespace ts.tscWatch {
         };
         const config: File = {
             path: `${projectRoot}/tsconfig.json`,
-            content: JSON.stringify(configFileJson)
+            content: JSON.stringify(configFileJson)!
         };
         const settingsJson: File = {
             path: `${projectRoot}/settings.json`,

src/testRunner/unittests/tsserver/events/projectUpdatedInBackground.ts

@@ -172,7 +172,7 @@ namespace ts.projectSystem {
                     const additionalFiles = getAdditionalFileOrFolder ? getAdditionalFileOrFolder() : [];
                     const configFile = {
                         path: configFilePath,
-                        content: JSON.stringify(configObj || { compilerOptions: {} })
+                        content: JSON.stringify(configObj || { compilerOptions: {} })!
                     };
 
                     const files: File[] = [file1Consumer1, moduleFile1, file1Consumer2, moduleFile2, ...additionalFiles, globalFile3, libFile, configFile];
@@ -525,7 +525,7 @@ namespace ts.projectSystem {
                 };
 
                 function eventToString(event: server.ProjectsUpdatedInBackgroundEvent) {
-                    return JSON.stringify(event && { eventName: event.eventName, data: event.data });
+                    return JSON.stringify(event && { eventName: event.eventName, data: event.data })!;
                 }
 
                 function eventsToString(events: ReadonlyArray<server.ProjectsUpdatedInBackgroundEvent>) {

src/testRunner/unittests/tsserver/metadataInResponse.ts

@@ -10,7 +10,7 @@ namespace ts.projectSystem {
         function verifyCommandWithMetadata<T extends server.protocol.Request, U = undefined>(session: TestSession, host: TestServerHost, command: Partial<T>, expectedResponseBody: U) {
             command.seq = session.getSeq();
             command.type = "request";
-            session.onMessage(JSON.stringify(command));
+            session.onMessage(JSON.stringify(command)!);
             verifyOutput(host, expectedResponseBody ?
                 { seq: 0, type: "response", command: command.command!, request_seq: command.seq, success: true, body: expectedResponseBody, metadata } :
                 { seq: 0, type: "response", command: command.command!, request_seq: command.seq, success: false, message: "No content available." }

tests/baselines/reference/json.stringify.errors.txt

@@ -0,0 +1,24 @@
+tests/cases/compiler/json.stringify.ts(8,7): error TS2322: Type 'string | undefined' is not assignable to type 'string'.
+  Type 'undefined' is not assignable to type 'string'.
+tests/cases/compiler/json.stringify.ts(9,7): error TS2322: Type 'string | undefined' is not assignable to type 'string'.
+  Type 'undefined' is not assignable to type 'string'.
+
+
+==== tests/cases/compiler/json.stringify.ts (2 errors) ====
+    var value = null;
+    JSON.stringify(value, undefined, 2);
+    JSON.stringify(value, null, 2);
+    JSON.stringify(value, ["a", 1], 2);
+    JSON.stringify(value, (k) => undefined, 2);
+    JSON.stringify(value, undefined, 2);
+
+    const isUndefined: string = JSON.stringify(undefined);
+          ~~~~~~~~~~~
+!!! error TS2322: Type 'string | undefined' is not assignable to type 'string'.
+!!! error TS2322:   Type 'undefined' is not assignable to type 'string'.
+    const maybeUndefined: string = JSON.stringify("apple" as string | undefined);
+          ~~~~~~~~~~~~~~
+!!! error TS2322: Type 'string | undefined' is not assignable to type 'string'.
+!!! error TS2322:   Type 'undefined' is not assignable to type 'string'.
+    const isNotUndefined: string = JSON.stringify("banana");
+

tests/baselines/reference/json.stringify.js

@@ -4,7 +4,12 @@ JSON.stringify(value, undefined, 2);
 JSON.stringify(value, null, 2);
 JSON.stringify(value, ["a", 1], 2);
 JSON.stringify(value, (k) => undefined, 2);
-JSON.stringify(value, undefined, 2);
+JSON.stringify(value, undefined, 2);
+
+const isUndefined: string = JSON.stringify(undefined);
+const maybeUndefined: string = JSON.stringify("apple" as string | undefined);
+const isNotUndefined: string = JSON.stringify("banana");
+
 
 //// [json.stringify.js]
 var value = null;
@@ -13,3 +18,6 @@ JSON.stringify(value, null, 2);
 JSON.stringify(value, ["a", 1], 2);
 JSON.stringify(value, function (k) { return undefined; }, 2);
 JSON.stringify(value, undefined, 2);
+var isUndefined = JSON.stringify(undefined);
+var maybeUndefined = JSON.stringify("apple");
+var isNotUndefined = JSON.stringify("banana");

tests/baselines/reference/json.stringify.symbols

@@ -36,3 +36,22 @@ JSON.stringify(value, undefined, 2);
 >value : Symbol(value, Decl(json.stringify.ts, 0, 3))
 >undefined : Symbol(undefined)
 
+const isUndefined: string = JSON.stringify(undefined);
+>isUndefined : Symbol(isUndefined, Decl(json.stringify.ts, 7, 5))
+>JSON.stringify : Symbol(JSON.stringify, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>JSON : Symbol(JSON, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>stringify : Symbol(JSON.stringify, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>undefined : Symbol(undefined)
+
+const maybeUndefined: string = JSON.stringify("apple" as string | undefined);
+>maybeUndefined : Symbol(maybeUndefined, Decl(json.stringify.ts, 8, 5))
+>JSON.stringify : Symbol(JSON.stringify, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>JSON : Symbol(JSON, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>stringify : Symbol(JSON.stringify, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+const isNotUndefined: string = JSON.stringify("banana");
+>isNotUndefined : Symbol(isNotUndefined, Decl(json.stringify.ts, 9, 5))
+>JSON.stringify : Symbol(JSON.stringify, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>JSON : Symbol(JSON, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>stringify : Symbol(JSON.stringify, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+