Improve contextual types using jsdoc tags

src/compiler/checker.ts

@@ -12744,6 +12744,10 @@ namespace ts {
                 if (declaration.type) {
                     return getTypeFromTypeNode(declaration.type);
                 }
+                const jsDocType = isInJavaScriptFile(declaration) && getTypeForDeclarationFromJSDocComment(declaration);
+                if (jsDocType) {
+                    return jsDocType;
+                }
                 if (declaration.kind === SyntaxKind.Parameter) {
                     const type = getContextuallyTypedParameterType(<ParameterDeclaration>declaration);
                     if (type) {
@@ -12816,8 +12820,9 @@ namespace ts {
             // If the containing function has a return type annotation, is a constructor, or is a get accessor whose
             // corresponding set accessor has a type annotation, return statements in the function are contextually typed
             if (functionDecl.type ||
+                (isInJavaScriptFile(functionDecl) && getJSDocReturnType(functionDecl)) ||
                 functionDecl.kind === SyntaxKind.Constructor ||
-                functionDecl.kind === SyntaxKind.GetAccessor && getSetAccessorTypeAnnotationNode(getDeclarationOfKind<SetAccessorDeclaration>(functionDecl.symbol, SyntaxKind.SetAccessor))) {
+                functionDecl.kind === SyntaxKind.GetAccessor && getSetAccessorTypeAnnotationNode(getDeclarationOfKind<SetAccessorDeclaration>(functionDecl.symbol, SyntaxKind.SetAccessor), /*includeJSDocType*/ true)) {
                 return getReturnTypeOfSignature(getSignatureFromDeclaration(functionDecl));
             }
 
@@ -16437,11 +16442,10 @@ namespace ts {
         }
 
         function getReturnTypeFromJSDocComment(func: SignatureDeclaration | FunctionDeclaration): Type {
-            const returnTag = getJSDocReturnTag(func);
-            if (returnTag && returnTag.typeExpression) {
-                return getTypeFromTypeNode(returnTag.typeExpression.type);
+            const jsdocType = getJSDocReturnType(func);
+            if (jsdocType) {
+                return getTypeFromTypeNode(jsdocType);
             }
-
             return undefined;
         }
 

src/compiler/utilities.ts

@@ -1570,6 +1570,11 @@ namespace ts {
         return getFirstJSDocTag(node, SyntaxKind.JSDocReturnTag) as JSDocReturnTag;
     }
 
+    export function getJSDocReturnType(node: Node): JSDocType {
+        const returnTag = getJSDocReturnTag(node);
+        return returnTag && returnTag.typeExpression && returnTag.typeExpression.type;
+    }
+
     export function getJSDocTemplateTag(node: Node): JSDocTemplateTag {
         return getFirstJSDocTag(node, SyntaxKind.JSDocTemplateTag) as JSDocTemplateTag;
     }
@@ -2615,11 +2620,19 @@ namespace ts {
         });
     }
 
-    /** Get the type annotaion for the value parameter. */
-    export function getSetAccessorTypeAnnotationNode(accessor: SetAccessorDeclaration): TypeNode {
+    /** Get the type annotation for the value parameter. */
+    export function getSetAccessorTypeAnnotationNode(accessor: SetAccessorDeclaration, includeJSDocType?: boolean): TypeNode {
         if (accessor && accessor.parameters.length > 0) {
             const hasThis = accessor.parameters.length === 2 && parameterIsThisKeyword(accessor.parameters[0]);
-            return accessor.parameters[hasThis ? 1 : 0].type;
+            const parameter = accessor.parameters[hasThis ? 1 : 0];
+            if (parameter) {
+                if (parameter.type) {
+                    return parameter.type;
+                }
+                if (includeJSDocType && parameter.flags & NodeFlags.JavaScriptFile) {
+                    return getJSDocType(parameter);
+                }
+            }
         }
     }
 

tests/baselines/reference/checkJsdocTypeTag1.types

@@ -61,10 +61,10 @@ x(1);
 /** @type {function (number)} */
 const x1 = (a) => a + 1;
 >x1 : (arg0: number) => any
->(a) => a + 1 : (a: any) => any
->a : any
->a + 1 : any
->a : any
+>(a) => a + 1 : (a: number) => number
+>a : number
+>a + 1 : number
+>a : number
 >1 : 1
 
 x1(0);
@@ -75,10 +75,10 @@ x1(0);
 /** @type {function (number): number} */
 const x2 = (a) => a + 1;
 >x2 : (arg0: number) => number
->(a) => a + 1 : (a: any) => any
->a : any
->a + 1 : any
->a : any
+>(a) => a + 1 : (a: number) => number
+>a : number
+>a + 1 : number
+>a : number
 >1 : 1
 
 x2(0);

tests/baselines/reference/checkJsdocTypeTag2.errors.txt

@@ -4,9 +4,10 @@ tests/cases/conformance/jsdoc/0.js(10,4): error TS2345: Argument of type '"strin
 tests/cases/conformance/jsdoc/0.js(13,7): error TS2451: Cannot redeclare block-scoped variable 'x2'.
 tests/cases/conformance/jsdoc/0.js(17,1): error TS2322: Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/jsdoc/0.js(20,7): error TS2451: Cannot redeclare block-scoped variable 'x2'.
+tests/cases/conformance/jsdoc/0.js(20,21): error TS2339: Property 'concat' does not exist on type 'number'.
 
 
-==== tests/cases/conformance/jsdoc/0.js (6 errors) ====
+==== tests/cases/conformance/jsdoc/0.js (7 errors) ====
     // @ts-check
     /** @type {String} */
     var S = true;
@@ -39,4 +40,6 @@ tests/cases/conformance/jsdoc/0.js(20,7): error TS2451: Cannot redeclare block-s
     const x2 = (a) => a.concat("hi");
           ~~
 !!! error TS2451: Cannot redeclare block-scoped variable 'x2'.
+                        ~~~~~~
+!!! error TS2339: Property 'concat' does not exist on type 'number'.
     x2(0);

tests/baselines/reference/contextualTypeFromJSDoc.symbols

@@ -0,0 +1,12 @@
+=== tests/cases/conformance/types/contextualTypes/jsdoc/index.js ===
+/** @type {Array<[string, {x?:number, y?:number}]>} */
+const arr = [
+>arr : Symbol(arr, Decl(index.js, 1, 5))
+
+    ['a', { x: 1 }],
+>x : Symbol(x, Decl(index.js, 2, 11))
+
+    ['b', { y: 2 }]
+>y : Symbol(y, Decl(index.js, 3, 11))
+
+];

tests/baselines/reference/contextualTypeFromJSDoc.types

@@ -0,0 +1,21 @@
+=== tests/cases/conformance/types/contextualTypes/jsdoc/index.js ===
+/** @type {Array<[string, {x?:number, y?:number}]>} */
+const arr = [
+>arr : [string, { x?: number; y?: number; }][]
+>[    ['a', { x: 1 }],    ['b', { y: 2 }]] : ([string, { x: number; }] | [string, { y: number; }])[]
+
+    ['a', { x: 1 }],
+>['a', { x: 1 }] : [string, { x: number; }]
+>'a' : "a"
+>{ x: 1 } : { x: number; }
+>x : number
+>1 : 1
+
+    ['b', { y: 2 }]
+>['b', { y: 2 }] : [string, { y: number; }]
+>'b' : "b"
+>{ y: 2 } : { y: number; }
+>y : number
+>2 : 2
+
+];

tests/cases/conformance/types/contextualTypes/jsdoc/contextualTypeFromJSDoc.ts

@@ -0,0 +1,10 @@
+// @allowJs: true
+// @checkJs: true
+// @noEmit: true
+// @filename: index.js
+
+/** @type {Array<[string, {x?:number, y?:number}]>} */
+const arr = [
+    ['a', { x: 1 }],
+    ['b', { y: 2 }]
+];