Infer from context sensitive return expressions

src/compiler/checker.ts

@@ -1339,11 +1339,14 @@ export const enum CheckMode {
     Inferential = 1 << 1,                           // Inferential typing
     SkipContextSensitive = 1 << 2,                  // Skip context sensitive function expressions
     SkipGenericFunctions = 1 << 3,                  // Skip single signature generic functions
-    IsForSignatureHelp = 1 << 4,                    // Call resolution for purposes of signature help
-    RestBindingElement = 1 << 5,                    // Checking a type that is going to be used to determine the type of a rest binding element
+    SkipReturnTypeFromBodyInference = 1 << 4,       // Skip inferring from return types of context sensitive functions
+                                                    //   it's used to prevent inferring within return types of generic functions,
+                                                    //   as that could create overlapping inferences that would interfere with the logic `instantiateTypeWithSingleGenericCallSignature` that handles them better
+    IsForSignatureHelp = 1 << 5,                    // Call resolution for purposes of signature help
+    RestBindingElement = 1 << 6,                    // Checking a type that is going to be used to determine the type of a rest binding element
                                                     //   e.g. in `const { a, ...rest } = foo`, when checking the type of `foo` to determine the type of `rest`,
                                                     //   we need to preserve generic types instead of substituting them for constraints
-    TypeOnly = 1 << 6,                              // Called from getTypeOfExpression, diagnostics may be omitted
+    TypeOnly = 1 << 7,                              // Called from getTypeOfExpression, diagnostics may be omitted
 }
 
 /** @internal */
@@ -39550,7 +39553,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         return getTypeOfSymbol(getSymbolOfDeclaration(node));
     }
 
-    function contextuallyCheckFunctionExpressionOrObjectLiteralMethod(node: FunctionExpression | ArrowFunction | MethodDeclaration, checkMode?: CheckMode) {
+    function contextuallyCheckFunctionExpressionOrObjectLiteralMethod(node: FunctionExpression | ArrowFunction | MethodDeclaration, checkMode = CheckMode.Normal) {
         const links = getNodeLinks(node);
         // Check if function expression is contextually typed and assign parameter types if so.
         if (!(links.flags & NodeCheckFlags.ContextChecked)) {
@@ -39564,11 +39567,12 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 if (!signature) {
                     return;
                 }
-                if (isContextSensitive(node)) {
+                const isNodeContextSensitive = isContextSensitive(node);
+                if (isNodeContextSensitive) {
                     if (contextualSignature) {
                         const inferenceContext = getInferenceContext(node);
                         let instantiatedContextualSignature: Signature | undefined;
-                        if (checkMode && checkMode & CheckMode.Inferential) {
+                        if (checkMode & CheckMode.Inferential) {
                             inferFromAnnotatedParametersAndReturn(signature, contextualSignature, inferenceContext!);
                             const restType = getEffectiveRestType(contextualSignature);
                             if (restType && restType.flags & TypeFlags.TypeParameter) {
@@ -39586,15 +39590,34 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 }
                 else if (contextualSignature && !node.typeParameters && contextualSignature.parameters.length > node.parameters.length) {
                     const inferenceContext = getInferenceContext(node);
-                    if (checkMode && checkMode & CheckMode.Inferential) {
+                    if (checkMode & CheckMode.Inferential) {
                         inferFromAnnotatedParametersAndReturn(signature, contextualSignature, inferenceContext!);
                     }
                 }
                 if (contextualSignature && !getReturnTypeFromAnnotation(node) && !signature.resolvedReturnType) {
-                    const returnType = getReturnTypeFromBody(node, checkMode);
-                    if (!signature.resolvedReturnType) {
-                        signature.resolvedReturnType = returnType;
+                    let contextualReturnType: Type;
+                    let returnType: Type;
+
+                    if (node.typeParameters) {
+                        checkMode |= CheckMode.SkipReturnTypeFromBodyInference;
+                    }
+
+                    if (
+                        isNodeContextSensitive && ((checkMode & (CheckMode.Inferential | CheckMode.SkipReturnTypeFromBodyInference)) === CheckMode.Inferential) &&
+                        couldContainTypeVariables(contextualReturnType = getReturnTypeOfSignature(contextualSignature))
+                    ) {
+                        const inferenceContext = getInferenceContext(node);
+                        const isReturnContextSensitive = !!node.body && (node.body.kind === SyntaxKind.Block ? forEachReturnStatement(node.body as Block, statement => !!statement.expression && isContextSensitive(statement.expression)) : isContextSensitive(node.body));
+                        returnType = getReturnTypeFromBody(node, checkMode | (isReturnContextSensitive ? CheckMode.SkipContextSensitive : 0));
+                        inferTypes(inferenceContext!.inferences, returnType, contextualReturnType);
+                        if (isReturnContextSensitive) {
+                            returnType = getReturnTypeFromBody(node, checkMode);
+                        }
+                    }
+                    else {
+                        returnType = getReturnTypeFromBody(node, checkMode);
                     }
+                    signature.resolvedReturnType ??= returnType;
                 }
                 checkSignatureDeclaration(node);
             }

tests/baselines/reference/InferFromReturnsInContextSensitive1.js

@@ -0,0 +1,295 @@
+//// [tests/cases/conformance/types/typeRelationships/typeInference/InferFromReturnsInContextSensitive1.ts] ////
+
+//// [InferFromReturnsInContextSensitive1.ts]
+// https://github.com/microsoft/TypeScript/issues/60720
+
+type Options<TContext> = {
+  onStart?: () => TContext;
+  onEnd?: (context: TContext) => void;
+};
+
+function create<TContext>(builder: (arg: boolean) => Options<TContext>) {
+  return builder(true);
+}
+
+create((arg) => ({
+  onStart: () => ({ time: new Date() }),
+  onEnd: (context) => {},
+}));
+
+create((arg) => ({
+  onEnd: (context) => {},
+  onStart: () => ({ time: new Date() }),
+}));
+
+// https://github.com/microsoft/TypeScript/issues/57021
+
+type Schema = Record<string, unknown>;
+
+type StepFunction<TSchema extends Schema = Schema> = (anything: unknown) => {
+  readonly schema: TSchema;
+  readonly toAnswers?: (keys: keyof TSchema) => unknown;
+};
+
+function step<TSchema extends Schema = Schema>(
+  stepVal: StepFunction<TSchema>,
+): StepFunction<TSchema> {
+  return stepVal;
+}
+
+const stepResult1 = step((_something) => ({
+  schema: {
+    attribute: "anything",
+  },
+  toAnswers: (keys) => {
+    type Test = string extends typeof keys ? never : "true";
+    const test: Test = "true"; // ok
+    return { test };
+  },
+}));
+
+const stepResult2 = step((_something) => ({
+  toAnswers: (keys) => {
+    type Test = string extends typeof keys ? never : "true";
+    const test: Test = "true"; // ok
+    return { test };
+  },
+  schema: {
+    attribute: "anything",
+  },
+}));
+
+type Fn1<T, T2> = (anything: unknown) => {
+  stuff: T;
+  consume: (arg: T) => (anything: unknown) => {
+    stuff2: T2;
+    consume2: (arg: T2) => void;
+  };
+};
+
+declare function test1<T, T2>(fn: Fn1<T, T2>): [T, T2];
+
+const res1 = test1((_something) => ({
+  stuff: "foo",
+  consume: (arg) => {
+    return (_something) => ({
+      stuff2: 42,
+      consume2: (arg2) => {},
+    });
+  },
+}));
+
+const res2 = test1((_something) => ({
+  consume: (arg) => {
+    return (_something) => ({
+      consume2: (arg2) => {},
+      stuff2: 42,
+    });
+  },
+  stuff: "foo",
+}));
+
+const res3 = test1((_something) => ({
+  stuff: "foo",
+  consume: () => {
+    return (_something) => ({
+      stuff2: 42,
+      consume2: (arg2) => {},
+    });
+  },
+}));
+
+const res4 = test1((_something) => ({
+  consume: () => {
+    return (_something) => ({
+      consume2: (arg2) => {},
+      stuff2: 42,
+    });
+  },
+  stuff: "foo",
+}));
+
+const res5 = test1((_something) => ({
+  stuff: "foo",
+  consume: () => {
+    return () => ({
+      stuff2: 42,
+      consume2: (arg2) => {},
+    });
+  },
+}));
+
+const res6 = test1((_something) => ({
+  consume: () => {
+    return () => ({
+      consume2: (arg2) => {},
+      stuff2: 42,
+    });
+  },
+  stuff: "foo",
+}));
+
+const res7 = test1((_something) => ({
+  stuff: "foo",
+  consume: () => {
+    return () => ({
+      stuff2: 42,
+      consume2: () => {},
+    });
+  },
+}));
+
+const res8 = test1((_something) => ({
+  consume: () => {
+    return () => ({
+      consume2: () => {},
+      stuff2: 42,
+    });
+  },
+  stuff: "foo",
+}));
+
+
+//// [InferFromReturnsInContextSensitive1.js]
+"use strict";
+// https://github.com/microsoft/TypeScript/issues/60720
+function create(builder) {
+    return builder(true);
+}
+create(function (arg) { return ({
+    onStart: function () { return ({ time: new Date() }); },
+    onEnd: function (context) { },
+}); });
+create(function (arg) { return ({
+    onEnd: function (context) { },
+    onStart: function () { return ({ time: new Date() }); },
+}); });
+function step(stepVal) {
+    return stepVal;
+}
+var stepResult1 = step(function (_something) { return ({
+    schema: {
+        attribute: "anything",
+    },
+    toAnswers: function (keys) {
+        var test = "true"; // ok
+        return { test: test };
+    },
+}); });
+var stepResult2 = step(function (_something) { return ({
+    toAnswers: function (keys) {
+        var test = "true"; // ok
+        return { test: test };
+    },
+    schema: {
+        attribute: "anything",
+    },
+}); });
+var res1 = test1(function (_something) { return ({
+    stuff: "foo",
+    consume: function (arg) {
+        return function (_something) { return ({
+            stuff2: 42,
+            consume2: function (arg2) { },
+        }); };
+    },
+}); });
+var res2 = test1(function (_something) { return ({
+    consume: function (arg) {
+        return function (_something) { return ({
+            consume2: function (arg2) { },
+            stuff2: 42,
+        }); };
+    },
+    stuff: "foo",
+}); });
+var res3 = test1(function (_something) { return ({
+    stuff: "foo",
+    consume: function () {
+        return function (_something) { return ({
+            stuff2: 42,
+            consume2: function (arg2) { },
+        }); };
+    },
+}); });
+var res4 = test1(function (_something) { return ({
+    consume: function () {
+        return function (_something) { return ({
+            consume2: function (arg2) { },
+            stuff2: 42,
+        }); };
+    },
+    stuff: "foo",
+}); });
+var res5 = test1(function (_something) { return ({
+    stuff: "foo",
+    consume: function () {
+        return function () { return ({
+            stuff2: 42,
+            consume2: function (arg2) { },
+        }); };
+    },
+}); });
+var res6 = test1(function (_something) { return ({
+    consume: function () {
+        return function () { return ({
+            consume2: function (arg2) { },
+            stuff2: 42,
+        }); };
+    },
+    stuff: "foo",
+}); });
+var res7 = test1(function (_something) { return ({
+    stuff: "foo",
+    consume: function () {
+        return function () { return ({
+            stuff2: 42,
+            consume2: function () { },
+        }); };
+    },
+}); });
+var res8 = test1(function (_something) { return ({
+    consume: function () {
+        return function () { return ({
+            consume2: function () { },
+            stuff2: 42,
+        }); };
+    },
+    stuff: "foo",
+}); });
+
+
+//// [InferFromReturnsInContextSensitive1.d.ts]
+type Options<TContext> = {
+    onStart?: () => TContext;
+    onEnd?: (context: TContext) => void;
+};
+declare function create<TContext>(builder: (arg: boolean) => Options<TContext>): Options<TContext>;
+type Schema = Record<string, unknown>;
+type StepFunction<TSchema extends Schema = Schema> = (anything: unknown) => {
+    readonly schema: TSchema;
+    readonly toAnswers?: (keys: keyof TSchema) => unknown;
+};
+declare function step<TSchema extends Schema = Schema>(stepVal: StepFunction<TSchema>): StepFunction<TSchema>;
+declare const stepResult1: StepFunction<{
+    attribute: string;
+}>;
+declare const stepResult2: StepFunction<{
+    attribute: string;
+}>;
+type Fn1<T, T2> = (anything: unknown) => {
+    stuff: T;
+    consume: (arg: T) => (anything: unknown) => {
+        stuff2: T2;
+        consume2: (arg: T2) => void;
+    };
+};
+declare function test1<T, T2>(fn: Fn1<T, T2>): [T, T2];
+declare const res1: [string, number];
+declare const res2: [string, number];
+declare const res3: [string, number];
+declare const res4: [string, number];
+declare const res5: [string, number];
+declare const res6: [string, number];
+declare const res7: [string, number];
+declare const res8: [string, number];