Get return type from @type tag

src/compiler/checker.ts

@@ -7566,12 +7566,21 @@ namespace ts {
                 const setter = getDeclarationOfKind<AccessorDeclaration>(getSymbolOfNode(declaration), SyntaxKind.SetAccessor);
                 return getAnnotatedAccessorType(setter);
             }
-
+            const typeFromTag = getReturnTypeOfTypeTag(declaration);
+            if (typeFromTag) {
+                return typeFromTag;
+            }
             if (nodeIsMissing((<FunctionLikeDeclaration>declaration).body)) {
                 return anyType;
             }
         }
 
+        function getReturnTypeOfTypeTag(node: SignatureDeclaration | JSDocSignature) {
+            const typeTag = isInJavaScriptFile(node) ? getJSDocTypeTag(node) : undefined;
+            const signatures = typeTag && typeTag.typeExpression && getSignaturesOfType(getTypeFromTypeNode(typeTag.typeExpression), SignatureKind.Call);
+            return signatures && signatures.length === 1 ? getReturnTypeOfSignature(signatures[0]) : undefined;
+        }
+
         function containsArgumentsReference(declaration: SignatureDeclaration): boolean {
             const links = getNodeLinks(declaration);
             if (links.containsArgumentsReference === undefined) {
@@ -20521,23 +20530,28 @@ namespace ts {
             return type;
         }
 
+        function getReturnOrPromisedType(node: FunctionLikeDeclaration | MethodSignature, functionFlags: FunctionFlags) {
+            const returnTypeNode = getEffectiveReturnTypeNode(node);
+            return returnTypeNode &&
+                ((functionFlags & FunctionFlags.AsyncGenerator) === FunctionFlags.Async ?
+                 checkAsyncFunctionReturnType(node, returnTypeNode) : // Async function
+                 getTypeFromTypeNode(returnTypeNode)) || // AsyncGenerator function, Generator function, or normal function
+                getReturnTypeOfTypeTag(node); // type from JSDoc @type tag
+        }
+
         function checkFunctionExpressionOrObjectLiteralMethodDeferred(node: ArrowFunction | FunctionExpression | MethodDeclaration) {
             Debug.assert(node.kind !== SyntaxKind.MethodDeclaration || isObjectLiteralMethod(node));
 
             const functionFlags = getFunctionFlags(node);
-            const returnTypeNode = getEffectiveReturnTypeNode(node);
-            const returnOrPromisedType = returnTypeNode &&
-                ((functionFlags & FunctionFlags.AsyncGenerator) === FunctionFlags.Async ?
-                    checkAsyncFunctionReturnType(node) : // Async function
-                    getTypeFromTypeNode(returnTypeNode)); // AsyncGenerator function, Generator function, or normal function
+            const returnOrPromisedType = getReturnOrPromisedType(node, functionFlags);
 
             if ((functionFlags & FunctionFlags.Generator) === 0) { // Async function or normal function
                 // return is not necessary in the body of generators
                 checkAllCodePathsInNonVoidFunctionReturnOrThrow(node, returnOrPromisedType);
             }
 
             if (node.body) {
-                if (!returnTypeNode) {
+                if (!getEffectiveReturnTypeNode(node)) {
                     // There are some checks that are only performed in getReturnTypeFromBody, that may produce errors
                     // we need. An example is the noImplicitAny errors resulting from widening the return expression
                     // of a function. Because checking of function expression bodies is deferred, there was never an
@@ -21989,7 +22003,7 @@ namespace ts {
                         }
                     }
                     else if ((functionFlags & FunctionFlags.AsyncGenerator) === FunctionFlags.Async) {
-                        checkAsyncFunctionReturnType(<FunctionLikeDeclaration>node);
+                        checkAsyncFunctionReturnType(<FunctionLikeDeclaration>node, returnTypeNode);
                     }
                 }
                 if (node.kind !== SyntaxKind.IndexSignature && node.kind !== SyntaxKind.JSDocFunctionType) {
@@ -23049,7 +23063,7 @@ namespace ts {
          *
          * @param node The signature to check
          */
-        function checkAsyncFunctionReturnType(node: FunctionLikeDeclaration | MethodSignature): Type {
+        function checkAsyncFunctionReturnType(node: FunctionLikeDeclaration | MethodSignature, returnTypeNode: TypeNode): Type {
             // As part of our emit for an async function, we will need to emit the entity name of
             // the return type annotation as an expression. To meet the necessary runtime semantics
             // for __awaiter, we must also check that the type of the declaration (e.g. the static
@@ -23074,7 +23088,6 @@ namespace ts {
             //      then<U>(...): Promise<U>;
             //  }
             //
-            const returnTypeNode = getEffectiveReturnTypeNode(node)!; // TODO: GH#18217
             const returnType = getTypeFromTypeNode(returnTypeNode);
 
             if (languageVersion >= ScriptTarget.ES2015) {
@@ -23484,15 +23497,12 @@ namespace ts {
             const body = node.kind === SyntaxKind.MethodSignature ? undefined : node.body;
             checkSourceElement(body);
 
-            const returnTypeNode = getEffectiveReturnTypeNode(node);
             if ((functionFlags & FunctionFlags.Generator) === 0) { // Async function or normal function
-                const returnOrPromisedType = returnTypeNode && (functionFlags & FunctionFlags.Async
-                    ? checkAsyncFunctionReturnType(node) // Async function
-                    : getTypeFromTypeNode(returnTypeNode)); // normal function
+                const returnOrPromisedType = getReturnOrPromisedType(node, functionFlags);
                 checkAllCodePathsInNonVoidFunctionReturnOrThrow(node, returnOrPromisedType);
             }
 
-            if (produceDiagnostics && !returnTypeNode) {
+            if (produceDiagnostics && !getEffectiveReturnTypeNode(node)) {
                 // Report an implicit any error if there is no body, no explicit return type, and node is not a private method
                 // in an ambient context
                 if (noImplicitAny && nodeIsMissing(body) && !isPrivateWithinAmbient(node)) {
@@ -23505,6 +23515,13 @@ namespace ts {
                     // yielded values. The only way to trigger these errors is to try checking its return type.
                     getReturnTypeOfSignature(getSignatureFromDeclaration(node));
                 }
+                // A js function declaration can have a @type tag instead of a return type node, but that type must have a call signature
+                if (isInJavaScriptFile(node)) {
+                    const typeTag = getJSDocTypeTag(node);
+                    if (typeTag && typeTag.typeExpression && !getSignaturesOfType(getTypeFromTypeNode(typeTag.typeExpression), SignatureKind.Call).length) {
+                        error(typeTag, Diagnostics.The_type_of_a_function_declaration_must_be_callable);
+                    }
+                }
             }
         }
 
@@ -24767,7 +24784,7 @@ namespace ts {
                         error(node, Diagnostics.Return_type_of_constructor_signature_must_be_assignable_to_the_instance_type_of_the_class);
                     }
                 }
-                else if (getEffectiveReturnTypeNode(func) || isGetAccessorWithAnnotatedSetAccessor(func)) {
+                else if (getEffectiveReturnTypeNode(func) || isGetAccessorWithAnnotatedSetAccessor(func) || getReturnTypeOfTypeTag(func)) {
                     if (functionFlags & FunctionFlags.Async) { // Async function
                         const promisedType = getPromisedTypeOfPromise(returnType);
                         const awaitedType = checkAwaitedType(exprType, node, Diagnostics.The_return_type_of_an_async_function_must_either_be_a_valid_promise_or_must_not_contain_a_callable_then_member);

src/compiler/diagnosticMessages.json

@@ -4017,6 +4017,10 @@
         "category": "Error",
         "code": 8029
     },
+    "The type of a function declaration must be callable.": {
+        "category": "Error",
+        "code": 8030
+    },
     "Only identifiers/qualified-names with optional type arguments are currently supported in a class 'extends' clause.": {
         "category": "Error",
         "code": 9002

tests/baselines/reference/callbackTag2.types

@@ -43,7 +43,7 @@ var outside = n => n + 1;
 /** @type {Final<{ fantasy }, { heroes }>} */
 var noreturn = (barts, tidus, noctis) => "cecil"
 >noreturn : Final<{ fantasy: any; }, { heroes: any; }>
->(barts, tidus, noctis) => "cecil" : (barts: { fantasy: any; }, tidus: { heroes: any; }, noctis: { heroes: any; } & { fantasy: any; }) => "cecil"
+>(barts, tidus, noctis) => "cecil" : (barts: { fantasy: any; }, tidus: { heroes: any; }, noctis: { heroes: any; } & { fantasy: any; }) => "cecil" | "zidane"
 >barts : { fantasy: any; }
 >tidus : { heroes: any; }
 >noctis : { heroes: any; } & { fantasy: any; }

tests/baselines/reference/callbackTagNamespace.types

@@ -11,7 +11,7 @@ var x = 1;
 
 /** @type {NS.Nested.Inner} */
 function f(space, peace) {
->f : (space: any, peace: any) => string
+>f : (space: any, peace: any) => string | number
 >space : any
 >peace : any
 

tests/baselines/reference/checkJsdocTypeTag1.types

@@ -61,7 +61,7 @@ y(1);
 /** @type {function (number)} */
 const x1 = (a) => a + 1;
 >x1 : (arg0: number) => any
->(a) => a + 1 : (a: number) => number
+>(a) => a + 1 : (a: number) => any
 >a : number
 >a + 1 : number
 >a : number

tests/baselines/reference/checkJsdocTypeTag2.errors.txt

@@ -3,8 +3,7 @@ tests/cases/conformance/jsdoc/0.js(6,5): error TS2322: Type '"hello"' is not ass
 tests/cases/conformance/jsdoc/0.js(10,4): error TS2345: Argument of type '"string"' is not assignable to parameter of type 'number'.
 tests/cases/conformance/jsdoc/0.js(17,1): error TS2322: Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/jsdoc/0.js(20,21): error TS2339: Property 'concat' does not exist on type 'number'.
-tests/cases/conformance/jsdoc/0.js(24,7): error TS2322: Type '(a: number) => number' is not assignable to type '(arg0: number) => string'.
-  Type 'number' is not assignable to type 'string'.
+tests/cases/conformance/jsdoc/0.js(24,19): error TS2322: Type 'number' is not assignable to type 'string'.
 
 
 ==== tests/cases/conformance/jsdoc/0.js (6 errors) ====
@@ -42,7 +41,6 @@ tests/cases/conformance/jsdoc/0.js(24,7): error TS2322: Type '(a: number) => num
 
     /** @type {function (number): string} */
     const x4 = (a) => a + 1;
-          ~~
-!!! error TS2322: Type '(a: number) => number' is not assignable to type '(arg0: number) => string'.
-!!! error TS2322:   Type 'number' is not assignable to type 'string'.
+                      ~~~~~
+!!! error TS2322: Type 'number' is not assignable to type 'string'.
     x4(0);

tests/baselines/reference/checkJsdocTypeTag2.types

@@ -13,7 +13,7 @@ var n = "hello";
 /** @type {function (number)} */
 const x1 = (a) => a + 1;
 >x1 : (arg0: number) => any
->(a) => a + 1 : (a: number) => number
+>(a) => a + 1 : (a: number) => any
 >a : number
 >a + 1 : number
 >a : number
@@ -47,7 +47,7 @@ a = x2(0);
 /** @type {function (number): number} */
 const x3 = (a) => a.concat("hi");
 >x3 : (arg0: number) => number
->(a) => a.concat("hi") : (a: number) => any
+>(a) => a.concat("hi") : (a: number) => number
 >a : number
 >a.concat("hi") : any
 >a.concat : any
@@ -63,7 +63,7 @@ x3(0);
 /** @type {function (number): string} */
 const x4 = (a) => a + 1;
 >x4 : (arg0: number) => string
->(a) => a + 1 : (a: number) => number
+>(a) => a + 1 : (a: number) => string
 >a : number
 >a + 1 : number
 >a : number

tests/baselines/reference/checkJsdocTypeTag5.errors.txt

@@ -4,9 +4,11 @@ tests/cases/conformance/jsdoc/test.js(7,24): error TS2322: Type 'number' is not
 tests/cases/conformance/jsdoc/test.js(10,17): error TS2322: Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/jsdoc/test.js(12,14): error TS2322: Type 'number' is not assignable to type 'string'.
 tests/cases/conformance/jsdoc/test.js(14,24): error TS2322: Type 'number' is not assignable to type 'string'.
+tests/cases/conformance/jsdoc/test.js(34,5): error TS2322: Type '1 | 2' is not assignable to type '2 | 3'.
+  Type '1' is not assignable to type '2 | 3'.
 
 
-==== tests/cases/conformance/jsdoc/test.js (6 errors) ====
+==== tests/cases/conformance/jsdoc/test.js (7 errors) ====
     // all 6 should error on return statement/expression
     /** @type {(x: number) => string} */
     function h(x) { return x }
@@ -33,4 +35,27 @@ tests/cases/conformance/jsdoc/test.js(14,24): error TS2322: Type 'number' is not
     var k = function (x) { return x }
                            ~~~~~~~~
 !!! error TS2322: Type 'number' is not assignable to type 'string'.
+
+
+    /** @typedef {(x: 'hi' | 'bye') => 0 | 1 | 2} Argle */
+    /** @type {Argle} */
+    function blargle(s) {
+        return 0;
+    }
+
+    /** @type {0 | 1 | 2} - assignment should not error */
+    var zeroonetwo = blargle('hi')
+
+    /** @typedef {{(s: string): 0 | 1; (b: boolean): 2 | 3 }} Gioconda */
+
+    /** @type {Gioconda} */
+    function monaLisa(sb) {
+        return typeof sb === 'string' ? 1 : 2;
+    }
+
+    /** @type {2 | 3} - overloads are not supported, so there will be an error */
+    var twothree = monaLisa(false);
+        ~~~~~~~~
+!!! error TS2322: Type '1 | 2' is not assignable to type '2 | 3'.
+!!! error TS2322:   Type '1' is not assignable to type '2 | 3'.
 

tests/baselines/reference/checkJsdocTypeTag5.symbols

@@ -36,3 +36,34 @@ var k = function (x) { return x }
 >x : Symbol(x, Decl(test.js, 13, 18))
 >x : Symbol(x, Decl(test.js, 13, 18))
 
+
+/** @typedef {(x: 'hi' | 'bye') => 0 | 1 | 2} Argle */
+/** @type {Argle} */
+function blargle(s) {
+>blargle : Symbol(blargle, Decl(test.js, 13, 33))
+>s : Symbol(s, Decl(test.js, 18, 17))
+
+    return 0;
+}
+
+/** @type {0 | 1 | 2} - assignment should not error */
+var zeroonetwo = blargle('hi')
+>zeroonetwo : Symbol(zeroonetwo, Decl(test.js, 23, 3))
+>blargle : Symbol(blargle, Decl(test.js, 13, 33))
+
+/** @typedef {{(s: string): 0 | 1; (b: boolean): 2 | 3 }} Gioconda */
+
+/** @type {Gioconda} */
+function monaLisa(sb) {
+>monaLisa : Symbol(monaLisa, Decl(test.js, 23, 30))
+>sb : Symbol(sb, Decl(test.js, 28, 18))
+
+    return typeof sb === 'string' ? 1 : 2;
+>sb : Symbol(sb, Decl(test.js, 28, 18))
+}
+
+/** @type {2 | 3} - overloads are not supported, so there will be an error */
+var twothree = monaLisa(false);
+>twothree : Symbol(twothree, Decl(test.js, 33, 3))
+>monaLisa : Symbol(monaLisa, Decl(test.js, 23, 30))
+

tests/baselines/reference/checkJsdocTypeTag5.types

@@ -40,3 +40,45 @@ var k = function (x) { return x }
 >x : number
 >x : number
 
+
+/** @typedef {(x: 'hi' | 'bye') => 0 | 1 | 2} Argle */
+/** @type {Argle} */
+function blargle(s) {
+>blargle : (s: "hi" | "bye") => 0 | 1 | 2
+>s : "hi" | "bye"
+
+    return 0;
+>0 : 0
+}
+
+/** @type {0 | 1 | 2} - assignment should not error */
+var zeroonetwo = blargle('hi')
+>zeroonetwo : 0 | 1 | 2
+>blargle('hi') : 0 | 1 | 2
+>blargle : (s: "hi" | "bye") => 0 | 1 | 2
+>'hi' : "hi"
+
+/** @typedef {{(s: string): 0 | 1; (b: boolean): 2 | 3 }} Gioconda */
+
+/** @type {Gioconda} */
+function monaLisa(sb) {
+>monaLisa : (sb: any) => 1 | 2
+>sb : any
+
+    return typeof sb === 'string' ? 1 : 2;
+>typeof sb === 'string' ? 1 : 2 : 1 | 2
+>typeof sb === 'string' : boolean
+>typeof sb : "string" | "number" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>sb : any
+>'string' : "string"
+>1 : 1
+>2 : 2
+}
+
+/** @type {2 | 3} - overloads are not supported, so there will be an error */
+var twothree = monaLisa(false);
+>twothree : 2 | 3
+>monaLisa(false) : 1 | 2
+>monaLisa : (sb: any) => 1 | 2
+>false : false
+

tests/baselines/reference/checkJsdocTypeTag6.errors.txt

@@ -0,0 +1,20 @@
+tests/cases/conformance/jsdoc/test.js(1,5): error TS8030: The type of a function declaration must be callable.
+tests/cases/conformance/jsdoc/test.js(7,5): error TS2322: Type '(prop: any) => void' is not assignable to type '{ prop: string; }'.
+  Property 'prop' is missing in type '(prop: any) => void'.
+
+
+==== tests/cases/conformance/jsdoc/test.js (2 errors) ====
+    /** @type {number} */
+        ~~~~~~~~~~~~~~
+!!! error TS8030: The type of a function declaration must be callable.
+    function f() {
+        return 1
+    }
+
+    /** @type {{ prop: string }} */
+    var g = function (prop) {
+        ~
+!!! error TS2322: Type '(prop: any) => void' is not assignable to type '{ prop: string; }'.
+!!! error TS2322:   Property 'prop' is missing in type '(prop: any) => void'.
+    }
+

tests/baselines/reference/checkJsdocTypeTag6.symbols

@@ -0,0 +1,14 @@
+=== tests/cases/conformance/jsdoc/test.js ===
+/** @type {number} */
+function f() {
+>f : Symbol(f, Decl(test.js, 0, 0))
+
+    return 1
+}
+
+/** @type {{ prop: string }} */
+var g = function (prop) {
+>g : Symbol(g, Decl(test.js, 6, 3))
+>prop : Symbol(prop, Decl(test.js, 6, 18))
+}
+

tests/baselines/reference/checkJsdocTypeTag6.types

@@ -0,0 +1,16 @@
+=== tests/cases/conformance/jsdoc/test.js ===
+/** @type {number} */
+function f() {
+>f : () => number
+
+    return 1
+>1 : 1
+}
+
+/** @type {{ prop: string }} */
+var g = function (prop) {
+>g : { prop: string; }
+>function (prop) {} : (prop: any) => void
+>prop : any
+}
+