fix(3758): show completion for object literals in an assignment pattern (#40976)

Author: a-tarasyuk

src/services/completions.ts

@@ -1891,10 +1891,12 @@ namespace ts.Completions {
             let existingMembers: readonly Declaration[] | undefined;
 
             if (objectLikeContainer.kind === SyntaxKind.ObjectLiteralExpression) {
-                const instantiatedType = typeChecker.getContextualType(objectLikeContainer);
-                const completionsType = instantiatedType && typeChecker.getContextualType(objectLikeContainer, ContextFlags.Completions);
-                if (!instantiatedType || !completionsType) return GlobalsSearch.Fail;
-                isNewIdentifierLocation = hasIndexSignature(instantiatedType || completionsType);
+                const instantiatedType = tryGetObjectLiteralContextualType(objectLikeContainer, typeChecker);
+                if (instantiatedType === undefined) {
+                    return GlobalsSearch.Fail;
+                }
+                const completionsType = typeChecker.getContextualType(objectLikeContainer, ContextFlags.Completions);
+                isNewIdentifierLocation = hasIndexSignature(completionsType || instantiatedType);
                 typeMembers = getPropertiesForObjectExpression(instantiatedType, completionsType, objectLikeContainer, typeChecker);
                 existingMembers = objectLikeContainer.properties;
             }
@@ -2830,4 +2832,15 @@ namespace ts.Completions {
     function isStaticProperty(symbol: Symbol) {
         return !!(symbol.valueDeclaration && getEffectiveModifierFlags(symbol.valueDeclaration) & ModifierFlags.Static && isClassLike(symbol.valueDeclaration.parent));
     }
+
+    function tryGetObjectLiteralContextualType(node: ObjectLiteralExpression, typeChecker: TypeChecker) {
+        const type = typeChecker.getContextualType(node);
+        if (type) {
+            return type;
+        }
+        if (isBinaryExpression(node.parent) && node.parent.operatorToken.kind === SyntaxKind.EqualsToken) {
+            return typeChecker.getTypeAtLocation(node.parent);
+        }
+        return undefined;
+    }
 }

tests/cases/fourslash/completionListInObjectLiteralAssignmentPattern1.ts

@@ -0,0 +1,7 @@
+
+/// <reference path="fourslash.ts" />
+
+////let x = { a: 1, b: 2 };
+////let y = ({ /**/ } = x, 1);
+
+verify.completions({ marker: "", exact: ["a", "b"] });

tests/cases/fourslash/completionListInObjectLiteralAssignmentPattern2.ts

@@ -0,0 +1,7 @@
+
+/// <reference path="fourslash.ts" />
+
+////let x = { a: 1, b: 2 };
+////let y = ({ a, /**/ } = x, 1);
+
+verify.completions({ marker: "", exact: ["b"] });