Improve type checking and inference for Generators and Async Generators

src/compiler/builderState.ts

@@ -427,8 +427,8 @@ namespace ts.BuilderState {
  const references = state.referencedMap.get(path);
  if (references) {
  const iterator = references.keys();
- for (let { value, done } = iterator.next(); !done; { value, done } = iterator.next()) {
- queue.push(value as Path);
+ for (let iterResult = iterator.next(); !iterResult.done; iterResult = iterator.next()) {
+ queue.push(iterResult.value as Path);
  }
  }
  }

src/compiler/commandLineParser.ts

@@ -40,6 +40,7 @@ namespace ts {
  ["es2017.string", "lib.es2017.string.d.ts"],
  ["es2017.intl", "lib.es2017.intl.d.ts"],
  ["es2017.typedarrays", "lib.es2017.typedarrays.d.ts"],
+ ["es2018.asyncgenerator", "lib.es2018.asyncgenerator.d.ts"],
  ["es2018.asynciterable", "lib.es2018.asynciterable.d.ts"],
  ["es2018.intl", "lib.es2018.intl.d.ts"],
  ["es2018.promise", "lib.es2018.promise.d.ts"],
@@ -1899,7 +1900,9 @@ namespace ts {
  case "object":
  return {};
  default:
- return option.type.keys().next().value;
+ const iterResult = option.type.keys().next();
+ if (!iterResult.done) return iterResult.value;
+ return Debug.fail("Expected 'option.type' to have entries.");
  }
  }
 

src/compiler/core.ts

@@ -24,7 +24,6 @@ namespace ts {
  " __sortedArrayBrand": any;
  }
 
-
  /** ES6 Map interface, only read methods included. */
  export interface ReadonlyMap<T> {
  get(key: string): T | undefined;
@@ -45,7 +44,7 @@ namespace ts {
 
  /** ES6 Iterator type. */
  export interface Iterator<T> {
- next(): { value: T, done: false } | { value: never, done: true };
+ next(): { value: T, done?: false } | { value: never, done: true };
  }
 
  /** Array that is only intended to be pushed to, never read. */
@@ -297,12 +296,13 @@ namespace ts {
  forEach(action: (value: T, key: string) => void): void {
  const iterator = this.entries();
  while (true) {
- const { value: entry, done } = iterator.next();
- if (done) {
+ const iterResult = iterator.next();
+ if (iterResult.done) {
  break;
  }
 
- action(entry[1], entry[0]);
+ const [key, value] = iterResult.value;
+ action(value, key);
  }
  }
  };
@@ -346,11 +346,11 @@ namespace ts {
 
  export function firstDefinedIterator<T, U>(iter: Iterator<T>, callback: (element: T) => U | undefined): U | undefined {
  while (true) {
- const { value, done } = iter.next();
- if (done) {
+ const iterResult = iter.next();
+ if (iterResult.done) {
  return undefined;
  }
- const result = callback(value);
+ const result = callback(iterResult.value);
  if (result !== undefined) {
  return result;
  }
@@ -375,7 +375,7 @@ namespace ts {
  return { value: undefined as never, done: true };
  }
  i++;
- return { value: [arrayA[i - 1], arrayB[i - 1]], done: false };
+ return { value: [arrayA[i - 1], arrayB[i - 1]] as [T, U], done: false };
  }
  };
  }
@@ -567,7 +567,7 @@ namespace ts {
  return {
  next() {
  const iterRes = iter.next();
- return iterRes.done ? iterRes : { value: mapFn(iterRes.value), done: false };
+ return iterRes.done ? iterRes as { done: true, value: never } : { value: mapFn(iterRes.value), done: false };
  }
  };
  }
@@ -678,7 +678,7 @@ namespace ts {
  }
  const iterRes = iter.next();
  if (iterRes.done) {
- return iterRes;
+ return iterRes as { done: true, value: never };
  }
  currentIter = getIterator(iterRes.value);
  }
@@ -753,7 +753,7 @@ namespace ts {
  while (true) {
  const res = iter.next();
  if (res.done) {
- return res;
+ return res as { done: true, value: never };
  }
  const value = mapFn(res.value);
  if (value !== undefined) {
@@ -1078,6 +1078,7 @@ namespace ts {
  * @param value The value to append to the array. If `value` is `undefined`, nothing is
  * appended.
  */
+ export function append<TArray extends any[] | undefined, TValue extends NonNullable<TArray>[number] | undefined>(to: TArray, value: TValue): [undefined, undefined] extends [TArray, TValue] ? TArray : NonNullable<TArray>[number][];
  export function append<T>(to: T[], value: T | undefined): T[];
  export function append<T>(to: T[] | undefined, value: T): T[];
  export function append<T>(to: T[] | undefined, value: T | undefined): T[] | undefined;
@@ -1402,8 +1403,8 @@ namespace ts {
  export function arrayFrom<T>(iterator: Iterator<T> | IterableIterator<T>): T[];
  export function arrayFrom<T, U>(iterator: Iterator<T> | IterableIterator<T>, map?: (t: T) => U): (T | U)[] {
  const result: (T | U)[] = [];
- for (let { value, done } = iterator.next(); !done; { value, done } = iterator.next()) {
- result.push(map ? map(value) : value);
+ for (let iterResult = iterator.next(); !iterResult.done; iterResult = iterator.next()) {
+ result.push(map ? map(iterResult.value) : iterResult.value);
  }
  return result;
  }

src/compiler/diagnosticMessages.json

@@ -1764,7 +1764,7 @@
  "category": "Error",
  "code": 2489
  },
- "The type returned by the 'next()' method of an iterator must have a 'value' property.": {
+ "The type returned by the '{0}()' method of an iterator must have a 'value' property.": {
  "category": "Error",
  "code": 2490
  },
@@ -1992,7 +1992,7 @@
  "category": "Error",
  "code": 2546
  },
- "The type returned by the 'next()' method of an async iterator must be a promise for a type with a 'value' property.": {
+ "The type returned by the '{0}()' method of an async iterator must be a promise for a type with a 'value' property.": {
  "category": "Error",
  "code": 2547
  },
@@ -2653,6 +2653,30 @@
  "category": "Error",
  "code": 2762
  },
+ "Cannot iterate value because the 'next' method of its iterator expects type '{1}', but for-of will always send '{0}'.": {
+ "category": "Error",
+ "code": 2763
+ },
+ "Cannot iterate value because the 'next' method of its iterator expects type '{1}', but array spread will always send '{0}'.": {
+ "category": "Error",
+ "code": 2764
+ },
+ "Cannot iterate value because the 'next' method of its iterator expects type '{1}', but array destructuring will always send '{0}'.": {
+ "category": "Error",
+ "code": 2765
+ },
+ "Cannot delegate iteration to value because the 'next' method of its iterator expects type '{1}', but the containing generator will always send '{0}'.": {
+ "category": "Error",
+ "code": 2766
+ },
+ "The '{0}' property of an iterator must be a method.": {
+ "category": "Error",
+ "code": 2767
+ },
+ "The '{0}' property of an async iterator must be a method.": {
+ "category": "Error",
+ "code": 2768
+ },
 
  "Import declaration '{0}' is using private name '{1}'.": {
  "category": "Error",
@@ -4214,7 +4238,7 @@
  "category": "Error",
  "code": 7024
  },
- "Generator implicitly has type '{0}' because it does not yield any values. Consider supplying a return type.": {
+ "Generator implicitly has yield type '{0}' because it does not yield any values. Consider supplying a return type annotation.": {
  "category": "Error",
  "code": 7025
  },
@@ -4336,6 +4360,11 @@
  "category": "Error",
  "code": 7054
  },
+ "'{0}', which lacks return-type annotation, implicitly has an '{1}' yield type.": {
+ "category": "Error",
+ "code": 7055
+ },
+
  "You cannot rename this element.": {
  "category": "Error",
  "code": 8000

src/compiler/sourcemap.ts

@@ -148,7 +148,8 @@ namespace ts {
  const sourceIndexToNewSourceIndexMap: number[] = [];
  let nameIndexToNewNameIndexMap: number[] | undefined;
  const mappingIterator = decodeMappings(map.mappings);
- for (let { value: raw, done } = mappingIterator.next(); !done; { value: raw, done } = mappingIterator.next()) {
+ for (let iterResult = mappingIterator.next(); !iterResult.done; iterResult = mappingIterator.next()) {
+ const raw = iterResult.value;
  if (end && (
  raw.generatedLine > end.line ||
  (raw.generatedLine === end.line && raw.generatedCharacter > end.character))) {

src/compiler/types.ts

@@ -4273,13 +4273,23 @@ namespace ts {
  regularType: ResolvedType; // Regular version of fresh type
  }
 
+ /* @internal */
+ export interface IterationTypes {
+ readonly yieldType: Type;
+ readonly returnType: Type;
+ readonly nextType: Type;
+ }
+
  // Just a place to cache element types of iterables and iterators
  /* @internal */
  export interface IterableOrIteratorType extends ObjectType, UnionType {
- iteratedTypeOfIterable?: Type;
- iteratedTypeOfIterator?: Type;
- iteratedTypeOfAsyncIterable?: Type;
- iteratedTypeOfAsyncIterator?: Type;
+ iterationTypesOfGeneratorReturnType?: IterationTypes;
+ iterationTypesOfAsyncGeneratorReturnType?: IterationTypes;
+ iterationTypesOfIterable?: IterationTypes;
+ iterationTypesOfIterator?: IterationTypes;
+ iterationTypesOfAsyncIterable?: IterationTypes;
+ iterationTypesOfAsyncIterator?: IterationTypes;
+ iterationTypesOfIteratorResult?: IterationTypes;
  }
 
  /* @internal */

src/compiler/utilities.ts

@@ -150,8 +150,8 @@ namespace ts {
  export function forEachEntry<T, U>(map: ReadonlyMap<T>, callback: (value: T, key: string) => U | undefined): U | undefined;
  export function forEachEntry<T, U>(map: ReadonlyUnderscoreEscapedMap<T> | ReadonlyMap<T>, callback: (value: T, key: (string & __String)) => U | undefined): U | undefined {
  const iterator = map.entries();
- for (let { value: pair, done } = iterator.next(); !done; { value: pair, done } = iterator.next()) {
- const [key, value] = pair;
+ for (let iterResult = iterator.next(); !iterResult.done; iterResult = iterator.next()) {
+ const [key, value] = iterResult.value;
  const result = callback(value, key as (string & __String));
  if (result) {
  return result;
@@ -165,8 +165,8 @@ namespace ts {
  export function forEachKey<T>(map: ReadonlyMap<{}>, callback: (key: string) => T | undefined): T | undefined;
  export function forEachKey<T>(map: ReadonlyUnderscoreEscapedMap<{}> | ReadonlyMap<{}>, callback: (key: string & __String) => T | undefined): T | undefined {
  const iterator = map.keys();
- for (let { value: key, done } = iterator.next(); !done; { value: key, done } = iterator.next()) {
- const result = callback(key as string & __String);
+ for (let iterResult = iterator.next(); !iterResult.done; iterResult = iterator.next()) {
+ const result = callback(iterResult.value as string & __String);
  if (result) {
  return result;
  }

src/harness/sourceMapRecorder.ts

@@ -301,7 +301,8 @@ namespace Harness.SourceMapRecorder {
 
  SourceMapSpanWriter.initializeSourceMapSpanWriter(sourceMapRecorder, sourceMapData.sourceMap, currentFile);
  const mapper = ts.decodeMappings(sourceMapData.sourceMap.mappings);
- for (let { value: decodedSourceMapping, done } = mapper.next(); !done; { value: decodedSourceMapping, done } = mapper.next()) {
+ for (let iterResult = mapper.next(); !iterResult.done; iterResult = mapper.next()) {
+ const decodedSourceMapping = iterResult.value;
  const currentSourceFile = ts.isSourceMapping(decodedSourceMapping)
  ? program.getSourceFile(sourceMapData.inputSourceFileNames[decodedSourceMapping.sourceIndex])
  : undefined;
@@ -335,7 +336,8 @@ namespace Harness.SourceMapRecorder {
 
  SourceMapSpanWriter.initializeSourceMapSpanWriter(sourceMapRecorder, sourceMap, currentFile);
  const mapper = ts.decodeMappings(sourceMap.mappings);
- for (let { value: decodedSourceMapping, done } = mapper.next(); !done; { value: decodedSourceMapping, done } = mapper.next()) {
+ for (let iterResult = mapper.next(); !iterResult.done; iterResult = mapper.next()) {
+ const decodedSourceMapping = iterResult.value;
  const currentSourceFile = ts.isSourceMapping(decodedSourceMapping)
  ? getFile(sourceFileAbsolutePaths[decodedSourceMapping.sourceIndex])
  : undefined;

src/harness/vfs.ts

@@ -683,7 +683,7 @@ namespace vfs {
 
  if (isDirectory(node)) throw createIOError("EISDIR");
  if (!isFile(node)) throw createIOError("EBADF");
- node.buffer = Buffer.isBuffer(data) ? data.slice() : ts.sys.bufferFrom!("" + data, encoding || "utf8");
+ node.buffer = Buffer.isBuffer(data) ? data.slice() : ts.sys.bufferFrom!("" + data, encoding || "utf8") as Buffer;
  node.size = node.buffer.byteLength;
  node.mtimeMs = time;
  node.ctimeMs = time;
@@ -1204,7 +1204,7 @@ namespace vfs {
  }
  },
  readFileSync(path: string): Buffer {
- return ts.sys.bufferFrom!(host.readFile(path)!, "utf8"); // TODO: GH#18217
+ return ts.sys.bufferFrom!(host.readFile(path)!, "utf8") as Buffer; // TODO: GH#18217
  }
  };
  }

src/lib/es2015.generator.d.ts

@@ -1,4 +1,12 @@
-interface Generator extends Iterator<any> { }
+/// <reference lib="es2015.iterable" />
+
+interface Generator<T = unknown, TReturn = any, TNext = unknown> extends Iterator<T, TReturn, TNext> {
+ // NOTE: 'next' is defined using a tuple to ensure we report the correct assignability errors in all places.
+ next(...args: [] | [TNext]): IteratorResult<T, TReturn>;
+ return(value: TReturn): IteratorResult<T, TReturn>;
+ throw(e: any): IteratorResult<T, TReturn>;
+ [Symbol.iterator](): Generator<T, TReturn, TNext>;
+}
 
 interface GeneratorFunction {
  /**

src/lib/es2015.iterable.d.ts

@@ -8,15 +8,23 @@ interface SymbolConstructor {
  readonly iterator: symbol;
 }
 
-interface IteratorResult<T> {
- done: boolean;
- value: T;
+interface IteratorYieldResult<TYield> {
+ done?: false;
+ value: TYield;
 }
 
-interface Iterator<T> {
- next(value?: any): IteratorResult<T>;
- return?(value?: any): IteratorResult<T>;
- throw?(e?: any): IteratorResult<T>;
+interface IteratorReturnResult<TReturn> {
+ done: true;
+ value: TReturn;
+}
+
+type IteratorResult<T, TReturn = any> = IteratorYieldResult<T> | IteratorReturnResult<TReturn>;
+
+interface Iterator<T, TReturn = any, TNext = undefined> {
+ // NOTE: 'next' is defined using a tuple to ensure we report the correct assignability errors in all places.
+ next(...args: [] | [TNext]): IteratorResult<T, TReturn>;
+ return?(value?: TReturn): IteratorResult<T, TReturn>;
+ throw?(e?: any): IteratorResult<T, TReturn>;
 }
 
 interface Iterable<T> {