Enhance type argument completions

src/compiler/checker.ts

@@ -421,6 +421,7 @@ import {
     hasSyntacticModifier,
     hasSyntacticModifiers,
     hasType,
+    hasTypeArguments,
     HeritageClause,
     hostGetCanonicalFileName,
     Identifier,
@@ -42625,6 +42626,51 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         return undefined;
     }
 
+    /**
+     * Gets generic signatures from the function's/constructor's type.
+     */
+    function getUninstantiatedSignatures(node: CallLikeExpression): readonly Signature[] {
+        switch (node.kind) {
+            case SyntaxKind.CallExpression:
+            case SyntaxKind.Decorator:
+                return getSignaturesOfType(
+                    getTypeOfExpression(node.expression),
+                    SignatureKind.Call,
+                );
+            case SyntaxKind.NewExpression:
+                return getSignaturesOfType(
+                    getTypeOfExpression(node.expression),
+                    SignatureKind.Construct,
+                );
+            case SyntaxKind.JsxSelfClosingElement:
+            case SyntaxKind.JsxOpeningElement:
+                if (isJsxIntrinsicTagName(node.tagName)) return [];
+                return getSignaturesOfType(
+                    getTypeOfExpression(node.tagName),
+                    SignatureKind.Call,
+                );
+            case SyntaxKind.TaggedTemplateExpression:
+                return getSignaturesOfType(
+                    getTypeOfExpression(node.tag),
+                    SignatureKind.Call,
+                );
+            case SyntaxKind.BinaryExpression:
+            case SyntaxKind.JsxOpeningFragment:
+                return [];
+        }
+    }
+
+    function getTypeParameterConstraintForPositionAcrossSignatures(signatures: readonly Signature[], position: number) {
+        const relevantTypeParameterConstraints = flatMap(signatures, signature => {
+            const relevantTypeParameter = signature.typeParameters?.[position];
+            if (relevantTypeParameter === undefined) return [];
+            const relevantConstraint = getConstraintOfTypeParameter(relevantTypeParameter);
+            if (relevantConstraint === undefined) return [];
+            return [relevantConstraint];
+        });
+        return getUnionType(relevantTypeParameterConstraints);
+    }
+
     function checkTypeReferenceNode(node: TypeReferenceNode | ExpressionWithTypeArguments) {
         checkGrammarTypeArguments(node, node.typeArguments);
         if (node.kind === SyntaxKind.TypeReference && !isInJSFile(node) && !isInJSDoc(node) && node.typeArguments && node.typeName.end !== node.typeArguments.pos) {
@@ -42663,12 +42709,59 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     }
 
     function getTypeArgumentConstraint(node: TypeNode): Type | undefined {
-        const typeReferenceNode = tryCast(node.parent, isTypeReferenceType);
-        if (!typeReferenceNode) return undefined;
-        const typeParameters = getTypeParametersForTypeReferenceOrImport(typeReferenceNode);
-        if (!typeParameters) return undefined;
-        const constraint = getConstraintOfTypeParameter(typeParameters[typeReferenceNode.typeArguments!.indexOf(node)]);
-        return constraint && instantiateType(constraint, createTypeMapper(typeParameters, getEffectiveTypeArguments(typeReferenceNode, typeParameters)));
+        let typeArgumentPosition;
+        if (hasTypeArguments(node.parent) && Array.isArray(node.parent.typeArguments)) {
+            typeArgumentPosition = node.parent.typeArguments.indexOf(node);
+        }
+
+        if (typeArgumentPosition !== undefined) {
+            // The node could be a type argument of a call, a `new` expression, a decorator, an
+            // instantiation expression, or a generic type instantiation.
+
+            if (isCallLikeExpression(node.parent)) {
+                return getTypeParameterConstraintForPositionAcrossSignatures(
+                    getUninstantiatedSignatures(node.parent),
+                    typeArgumentPosition,
+                );
+            }
+
+            if (isDecorator(node.parent.parent)) {
+                return getTypeParameterConstraintForPositionAcrossSignatures(
+                    getUninstantiatedSignatures(node.parent.parent),
+                    typeArgumentPosition,
+                );
+            }
+
+            if (isExpressionWithTypeArguments(node.parent) && isExpressionStatement(node.parent.parent)) {
+                const uninstantiatedType = checkExpression(node.parent.expression);
+
+                const callConstraint = getTypeParameterConstraintForPositionAcrossSignatures(
+                    getSignaturesOfType(uninstantiatedType, SignatureKind.Call),
+                    typeArgumentPosition,
+                );
+                const constructConstraint = getTypeParameterConstraintForPositionAcrossSignatures(
+                    getSignaturesOfType(uninstantiatedType, SignatureKind.Construct),
+                    typeArgumentPosition,
+                );
+
+                // An instantiation expression instantiates both call and construct signatures, so
+                // if both exist type arguments must be assignable to both constraints.
+                if (constructConstraint.flags & TypeFlags.Never) return callConstraint;
+                if (callConstraint.flags & TypeFlags.Never) return constructConstraint;
+                return getIntersectionType([callConstraint, constructConstraint]);
+            }
+
+            if (isTypeReferenceType(node.parent)) {
+                const typeParameters = getTypeParametersForTypeReferenceOrImport(node.parent);
+                if (!typeParameters) return undefined;
+                const relevantTypeParameter = typeParameters[typeArgumentPosition];
+                const constraint = getConstraintOfTypeParameter(relevantTypeParameter);
+                return constraint && instantiateType(
+                    constraint,
+                    createTypeMapper(typeParameters, getEffectiveTypeArguments(node.parent, typeParameters)),
+                );
+            }
+        }
     }
 
     function checkTypeQuery(node: TypeQueryNode) {

src/services/completions.ts

@@ -256,7 +256,6 @@ import {
     isTypeOnlyImportDeclaration,
     isTypeOnlyImportOrExportDeclaration,
     isTypeParameterDeclaration,
-    isTypeReferenceType,
     isValidTypeOnlyAliasUseSite,
     isVariableDeclaration,
     isVariableLike,
@@ -3626,17 +3625,20 @@ function getCompletionData(
     }
 
     log("getCompletionData: Semantic work: " + (timestamp() - semanticStart));
-    const contextualType = previousToken && getContextualType(previousToken, position, sourceFile, typeChecker);
+    const contextualTypeOrConstraint = previousToken && (
+        getContextualType(previousToken, position, sourceFile, typeChecker) ??
+            getConstraintOfTypeArgumentProperty(previousToken, typeChecker)
+    );
 
     // exclude literal suggestions after <input type="text" [||] /> (#51667) and after closing quote (#52675)
     // for strings getStringLiteralCompletions handles completions
     const isLiteralExpected = !tryCast(previousToken, isStringLiteralLike) && !isJsxIdentifierExpected;
     const literals = !isLiteralExpected ? [] : mapDefined(
-        contextualType && (contextualType.isUnion() ? contextualType.types : [contextualType]),
+        contextualTypeOrConstraint && (contextualTypeOrConstraint.isUnion() ? contextualTypeOrConstraint.types : [contextualTypeOrConstraint]),
         t => t.isLiteral() && !(t.flags & TypeFlags.EnumLiteral) ? t.value : undefined,
     );
 
-    const recommendedCompletion = previousToken && contextualType && getRecommendedCompletion(previousToken, contextualType, typeChecker);
+    const recommendedCompletion = previousToken && contextualTypeOrConstraint && getRecommendedCompletion(previousToken, contextualTypeOrConstraint, typeChecker);
     return {
         kind: CompletionDataKind.Data,
         symbols,
@@ -5766,11 +5768,13 @@ function tryGetTypeLiteralNode(node: Node): TypeLiteralNode | undefined {
     return undefined;
 }
 
-function getConstraintOfTypeArgumentProperty(node: Node, checker: TypeChecker): Type | undefined {
+/** @internal */
+export function getConstraintOfTypeArgumentProperty(node: Node, checker: TypeChecker): Type | undefined {
     if (!node) return undefined;
 
-    if (isTypeNode(node) && isTypeReferenceType(node.parent)) {
-        return checker.getTypeArgumentConstraint(node);
+    if (isTypeNode(node)) {
+        const constraint = checker.getTypeArgumentConstraint(node);
+        if (constraint) return constraint;
     }
 
     const t = getConstraintOfTypeArgumentProperty(node.parent, checker);
@@ -5779,10 +5783,19 @@ function getConstraintOfTypeArgumentProperty(node: Node, checker: TypeChecker):
     switch (node.kind) {
         case SyntaxKind.PropertySignature:
             return checker.getTypeOfPropertyOfContextualType(t, (node as PropertySignature).symbol.escapedName);
+        case SyntaxKind.ColonToken:
+            if (node.parent.kind === SyntaxKind.PropertySignature) {
+                // The cursor is at a property value location like `Foo<{ x: | }`.
+                // `t` already refers to the appropriate property type.
+                return t;
+            }
+            break;
         case SyntaxKind.IntersectionType:
         case SyntaxKind.TypeLiteral:
         case SyntaxKind.UnionType:
             return t;
+        case SyntaxKind.OpenBracketToken:
+            return checker.getElementTypeOfArrayType(t);
     }
 }
 

src/services/stringCompletions.ts

@@ -3,6 +3,7 @@ import {
     createCompletionDetails,
     createCompletionDetailsForSymbol,
     getCompletionEntriesFromSymbols,
+    getConstraintOfTypeArgumentProperty,
     getDefaultCommitCharacters,
     getPropertiesForObjectExpression,
     Log,
@@ -509,7 +510,12 @@ function getStringLiteralCompletionEntries(sourceFile: SourceFile, node: StringL
 
     function fromUnionableLiteralType(grandParent: Node): StringLiteralCompletionsFromTypes | StringLiteralCompletionsFromProperties | undefined {
         switch (grandParent.kind) {
+            case SyntaxKind.CallExpression:
             case SyntaxKind.ExpressionWithTypeArguments:
+            case SyntaxKind.JsxOpeningElement:
+            case SyntaxKind.JsxSelfClosingElement:
+            case SyntaxKind.NewExpression:
+            case SyntaxKind.TaggedTemplateExpression:
             case SyntaxKind.TypeReference: {
                 const typeArgument = findAncestor(parent, n => n.parent === grandParent) as LiteralTypeNode;
                 if (typeArgument) {
@@ -529,6 +535,8 @@ function getStringLiteralCompletionEntries(sourceFile: SourceFile, node: StringL
                     return undefined;
                 }
                 return stringLiteralCompletionsFromProperties(typeChecker.getTypeFromTypeNode(objectType));
+            case SyntaxKind.PropertySignature:
+                return { kind: StringLiteralCompletionKind.Types, types: getStringLiteralTypes(getConstraintOfTypeArgumentProperty(grandParent, typeChecker)), isNewIdentifier: false };
             case SyntaxKind.UnionType: {
                 const result = fromUnionableLiteralType(walkUpParentheses(grandParent.parent));
                 if (!result) {

tests/cases/fourslash/completionListInTypeLiteralInTypeParameter10.ts

@@ -0,0 +1,38 @@
+/// <reference path="fourslash.ts" />
+
+////interface Foo {
+////    one: string;
+////    two: number;
+////}
+////interface Bar {
+////    three: boolean;
+////    four: {
+////        five: unknown;
+////    };
+////}
+////
+////function a<T extends Foo>() {}
+////a<{/*0*/}>();
+////
+////var b = () => <T extends Foo>() => {};
+////b()<{/*1*/}>();
+////
+////declare function c<T extends Foo>(): void
+////declare function c<T extends Bar>(): void
+////c<{/*2*/}>();
+////
+////function d<T extends Foo, U extends Bar>() {}
+////d<{/*3*/}, {/*4*/}>();
+////d<Foo, { four: {/*5*/} }>();
+////
+////(<T extends Foo>() => {})<{/*6*/}>();
+
+verify.completions(
+    { marker: "0", unsorted: ["one", "two"], isNewIdentifierLocation: true },
+    { marker: "1", unsorted: ["one", "two"], isNewIdentifierLocation: true },
+    { marker: "2", unsorted: ["one", "two", "three", "four"], isNewIdentifierLocation: true },
+    { marker: "3", unsorted: ["one", "two"], isNewIdentifierLocation: true },
+    { marker: "4", unsorted: ["three", "four"], isNewIdentifierLocation: true },
+    { marker: "5", unsorted: ["five"], isNewIdentifierLocation: true },
+    { marker: "6", unsorted: ["one", "two"], isNewIdentifierLocation: true },
+);

tests/cases/fourslash/completionListInTypeLiteralInTypeParameter11.ts

@@ -0,0 +1,32 @@
+/// <reference path="fourslash.ts" />
+
+////interface Foo {
+////    one: string;
+////    two: number;
+////}
+////interface Bar {
+////    three: boolean;
+////    four: symbol;
+////}
+////
+////class A<T extends Foo> {}
+////new A<{/*0*/}>();
+////
+////class B<T extends Foo, U extends Bar> {}
+////new B<{/*1*/}, {/*2*/}>();
+////
+////declare const C: {
+////   new <T extends Foo>(): unknown
+////   new <T extends Bar>(): unknown
+////}
+////new C<{/*3*/}>()
+////
+////new (class <T extends Foo> {})<{/*4*/}>();
+
+verify.completions(
+    { marker: "0", unsorted: ["one", "two"], isNewIdentifierLocation: true },
+    { marker: "1", unsorted: ["one", "two"], isNewIdentifierLocation: true },
+    { marker: "2", unsorted: ["three", "four"], isNewIdentifierLocation: true },
+    { marker: "3", unsorted: ["one", "two", "three", "four"], isNewIdentifierLocation: true },
+    { marker: "4", unsorted: ["one", "two"], isNewIdentifierLocation: true },
+);

tests/cases/fourslash/completionListInTypeLiteralInTypeParameter12.ts

@@ -0,0 +1,25 @@
+/// <reference path="fourslash.ts" />
+
+////interface Foo {
+////    kind: 'foo';
+////    one: string;
+////}
+////interface Bar {
+////    kind: 'bar';
+////    two: number;
+////}
+////
+////declare function a<T extends Foo>(): void
+////declare function a<T extends Bar>(): void
+////a<{ kind: 'bar', /*0*/ }>();
+////
+////declare function b<T extends Foo>(kind: 'foo'): void
+////declare function b<T extends Bar>(kind: 'bar'): void
+////b<{/*1*/}>('bar');
+
+// The completion lists are unfortunately not narrowed here (ideally only
+// properties of `Bar` would be suggested).
+verify.completions(
+  { marker: "0", unsorted: ["one", "two"], isNewIdentifierLocation: true },
+  { marker: "1", unsorted: ["kind", "one", "two"], isNewIdentifierLocation: true },
+);

tests/cases/fourslash/completionListInTypeLiteralInTypeParameter13.ts

@@ -0,0 +1,18 @@
+/// <reference path="fourslash.ts" />
+
+// @jsx: preserve
+// @filename: a.tsx
+////interface Foo {
+////    one: string;
+////    two: number;
+////}
+////
+////const Component = <T extends Foo>() => <></>;
+////
+////<Component<{/*0*/}>></Component>;
+////<Component<{/*1*/}>/>;
+
+verify.completions(
+  { marker: "0", unsorted: ["one", "two"], isNewIdentifierLocation: true },
+  { marker: "1", unsorted: ["one", "two"], isNewIdentifierLocation: true },
+);

tests/cases/fourslash/completionListInTypeLiteralInTypeParameter14.ts

@@ -0,0 +1,10 @@
+/// <reference path="fourslash.ts" />
+
+////interface Foo {
+////   one: string;
+////   two: number;
+////}
+////declare function f<T extends Foo>(x: TemplateStringsArray): void;
+////f<{/*0*/}>``;
+
+verify.completions({ marker: "0", unsorted: ["one", "two"], isNewIdentifierLocation: true });

tests/cases/fourslash/completionListInTypeLiteralInTypeParameter15.ts

@@ -0,0 +1,15 @@
+/// <reference path="fourslash.ts" />
+
+////interface Foo {
+////   one: string;
+////   two: number;
+////}
+////
+////declare function decorator<T extends Foo>(originalMethod: unknown, _context: unknown): never
+////
+////class {
+////   @decorator<{/*0*/}>
+////   method() {}
+////}
+
+verify.completions({ marker: "0", unsorted: ["one", "two"], isNewIdentifierLocation: true });