Merge pull request #7567 from Microsoft/contextual-type-parameters

show completion in destructured parameter if containing function was contextually typed

Author: vladima

src/services/services.ts

@@ -3504,7 +3504,18 @@ namespace ts {
                         // We don't want to complete using the type acquired by the shape
                         // of the binding pattern; we are only interested in types acquired
                         // through type declaration or inference.
-                        if (rootDeclaration.initializer || rootDeclaration.type) {
+                        // Also proceed if rootDeclaration is parameter and if its containing function expression\arrow function is contextually typed -
+                        // type of parameter will flow in from the contextual type of the function
+                        let canGetType = !!(rootDeclaration.initializer || rootDeclaration.type);
+                        if (!canGetType && rootDeclaration.kind === SyntaxKind.Parameter) {
+                            if (isExpression(rootDeclaration.parent)) {
+                                canGetType = !!typeChecker.getContextualType(<Expression>rootDeclaration.parent);
+                            }
+                            else if (rootDeclaration.parent.kind === SyntaxKind.MethodDeclaration || rootDeclaration.parent.kind === SyntaxKind.SetAccessor) {
+                                canGetType = isExpression(rootDeclaration.parent.parent) && !!typeChecker.getContextualType(<Expression>rootDeclaration.parent.parent);
+                            }
+                        }
+                        if (canGetType) {
                             typeForObject = typeChecker.getTypeAtLocation(objectLikeContainer);
                             existingMembers = (<BindingPattern>objectLikeContainer).elements;
                         }

tests/cases/fourslash/objectLiteralBindingInParameter.ts

@@ -0,0 +1,35 @@
+/// <reference path="fourslash.ts"/>
+
+////interface I { x1: number; x2: string }
+////function f(cb: (ev: I) => any) { }
+////f(({/*1*/}) => 0);
+
+////[<I>null].reduce(({/*2*/}, b) => b);
+
+////interface Foo {
+////    m(x: { x1: number, x2: number }): void;
+////    prop: I;
+////}
+////let x: Foo = {
+////    m({ /*3*/ }) {
+////    },
+////    get prop(): I { return undefined; },
+////    set prop({ /*4*/ }) {
+////    }
+////};
+
+goTo.marker("1");
+verify.completionListContains("x1");
+verify.completionListContains("x2");
+
+goTo.marker("2");
+verify.completionListContains("x1");
+verify.completionListContains("x2");
+
+goTo.marker("3");
+verify.completionListContains("x1");
+verify.completionListContains("x2");
+
+goTo.marker("4");
+verify.completionListContains("x1");
+verify.completionListContains("x2");