fixed

Author: ace-tk

src/compiler/checker.ts

@@ -9130,7 +9130,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 return false;
             }
             if ((isPropertySignature(annotatedDeclaration) || isPropertyDeclaration(annotatedDeclaration)) && annotatedDeclaration.questionToken) {
-                return getTypeWithFacts(type, TypeFacts.NEUndefined) === typeFromTypeNode;
+                // When `exactOptionalPropertyTypes` is enabled we interpret optional properties as written,
+                // so reusing the existing annotation even if it doesn't include `undefined` is fine.
+                // When it's disabled, optional properties implicitly include `undefined`, so the annotation
+                // without `| undefined` must *not* be treated as equivalent.
+                return exactOptionalPropertyTypes ? getTypeWithFacts(type, TypeFacts.NEUndefined) === typeFromTypeNode : false;
             }
             if (isParameter(annotatedDeclaration) && hasEffectiveQuestionToken(annotatedDeclaration)) {
                 return getTypeWithFacts(type, TypeFacts.NEUndefined) === typeFromTypeNode;

tests/cases/fourslash/issue63276.ts

@@ -0,0 +1,21 @@
+/// <reference path='fourslash.ts' />
+//
+// Regression test for GH#63276: "Missing undefined for hover".
+//
+// @strict: true
+// @exactOptionalPropertyTypes: false
+
+//// type X/*1*/ = {
+////   a?: A;
+////   b?: A;
+////   c?: A;
+//// };
+////
+//// type A = {};
+
+verify.quickInfoAt("1", `type X = {
+    a?: A | undefined;
+    b?: A | undefined;
+    c?: A | undefined;
+}`);
+