Filter out self-fulfilling completions (#35709)

Author: andrewbranch

src/services/completions.ts

@@ -2540,18 +2540,30 @@ namespace ts.Completions {
     }
 
     function getPropertiesForObjectExpression(contextualType: Type, baseConstrainedType: Type | undefined, obj: ObjectLiteralExpression | JsxAttributes, checker: TypeChecker): Symbol[] {
-        const type = baseConstrainedType && !(baseConstrainedType.flags & TypeFlags.AnyOrUnknown)
-            ? checker.getUnionType([contextualType, baseConstrainedType])
+        const hasBaseType = baseConstrainedType && baseConstrainedType !== contextualType;
+        const type = hasBaseType && !(baseConstrainedType!.flags & TypeFlags.AnyOrUnknown)
+            ? checker.getUnionType([contextualType, baseConstrainedType!])
             : contextualType;
 
-        return type.isUnion()
+        const properties = type.isUnion()
             ? checker.getAllPossiblePropertiesOfTypes(type.types.filter(memberType =>
                 // If we're providing completions for an object literal, skip primitive, array-like, or callable types since those shouldn't be implemented by object literals.
                 !(memberType.flags & TypeFlags.Primitive ||
                     checker.isArrayLikeType(memberType) ||
                     typeHasCallOrConstructSignatures(memberType, checker) ||
                     checker.isTypeInvalidDueToUnionDiscriminant(memberType, obj))))
             : type.getApparentProperties();
+
+        return hasBaseType ? properties.filter(hasDeclarationOtherThanSelf) : properties;
+
+        // Filter out members whose only declaration is the object literal itself to avoid
+        // self-fulfilling completions like:
+        //
+        // function f<T>(x: T) {}
+        // f({ abc/**/: "" }) // `abc` is a member of `T` but only because it declares itself
+        function hasDeclarationOtherThanSelf(member: Symbol) {
+            return some(member.declarations, decl => decl.parent !== obj);
+        }
     }
 
     /**

tests/cases/fourslash/completionsSelfDeclaring1.ts

@@ -0,0 +1,23 @@
+/// <reference path="fourslash.ts" />
+
+////interface Test {
+////  keyPath?: string;
+////  autoIncrement?: boolean;
+////}
+////
+////function test<T extends Record<string, Test>>(opt: T) { }
+////
+////test({
+////  a: {
+////    keyPath: '',
+////    a/**/
+////  }
+////})
+
+verify.completions({
+  marker: "",
+  exact: [{
+    name: "autoIncrement",
+    sortText: completion.SortText.OptionalMember
+  }]
+});

tests/cases/fourslash/completionsSelfDeclaring2.ts

@@ -0,0 +1,18 @@
+/// <reference path="fourslash.ts" />
+
+////function f1<T>(x: T) {}
+////f1({ abc/*1*/ });
+////
+////function f2<T extends { xyz: number }>(x: T) {}
+////f2({ x/*2*/ });
+
+
+verify.completions({
+  marker: "1",
+  exact: []
+});
+
+verify.completions({
+  marker: "2",
+  exact: ["xyz"]
+});

tests/cases/fourslash/completionsSelfDeclaring3.ts

@@ -0,0 +1,25 @@
+/// <reference path="fourslash.ts" />
+
+////function f<T extends { x: number }>(p: T & (T extends { hello: string } ? { goodbye: number } : {})) {}
+////f({ x/*x*/: 0, hello/*hello*/: "", goodbye/*goodbye*/: 0, abc/*abc*/: "" })
+
+
+verify.completions({
+  marker: "x",
+  exact: ["x"]
+});
+
+verify.completions({
+  marker: "hello",
+  exact: []
+});
+
+verify.completions({
+  marker: "goodbye",
+  exact: ["goodbye"]
+});
+
+verify.completions({
+  marker: "abc",
+  exact: []
+});