Ensure enum aliases referenced in other enum members do not get marked as referenced

src/compiler/checker.ts

@@ -28942,10 +28942,17 @@ namespace ts {
                 prop = getPropertyOfType(apparentType, right.escapedText);
             }
             // In `Foo.Bar.Baz`, 'Foo' is not referenced if 'Bar' is a const enum or a module containing only const enums.
+            // `Foo` is also not referenced in `enum FooCopy { Bar = Foo.Bar }`, because the enum member value gets inlined
+            // here even if `Foo` is not a const enum.
+            //
             // The exceptions are:
             //   1. if 'isolatedModules' is enabled, because the const enum value will not be inlined, and
             //   2. if 'preserveConstEnums' is enabled and the expression is itself an export, e.g. `export = Foo.Bar.Baz`.
-            if (isIdentifier(left) && parentSymbol && (compilerOptions.isolatedModules || !(prop && isConstEnumOrConstEnumOnlyModule(prop)) || shouldPreserveConstEnums(compilerOptions) && isExportOrExportExpression(node))) {
+            if (isIdentifier(left) && parentSymbol && (
+                compilerOptions.isolatedModules ||
+                !(prop && (isConstEnumOrConstEnumOnlyModule(prop) || prop.flags & SymbolFlags.EnumMember && node.parent.kind === SyntaxKind.EnumMember)) ||
+                shouldPreserveConstEnums(compilerOptions) && isExportOrExportExpression(node)
+            )) {
                 markAliasReferenced(parentSymbol, node);
             }
 
@@ -40215,7 +40222,7 @@ namespace ts {
 
         function isConstantMemberAccess(node: Expression): node is AccessExpression {
             const type = getTypeOfExpression(node);
-            if(type === errorType) {
+            if (type === errorType) {
                 return false;
             }
 

tests/baselines/reference/importElisionEnum.js

@@ -0,0 +1,35 @@
+//// [tests/cases/compiler/importElisionEnum.ts] ////
+
+//// [enum.ts]
+export enum MyEnum {
+  a = 0,
+  b,
+  c,
+  d
+}
+
+//// [index.ts]
+import { MyEnum as MyEnumFromModule } from "./enum";
+
+enum MyEnum {
+  a = MyEnumFromModule.a
+}
+
+//// [enum.js]
+"use strict";
+exports.__esModule = true;
+exports.MyEnum = void 0;
+var MyEnum;
+(function (MyEnum) {
+    MyEnum[MyEnum["a"] = 0] = "a";
+    MyEnum[MyEnum["b"] = 1] = "b";
+    MyEnum[MyEnum["c"] = 2] = "c";
+    MyEnum[MyEnum["d"] = 3] = "d";
+})(MyEnum = exports.MyEnum || (exports.MyEnum = {}));
+//// [index.js]
+"use strict";
+exports.__esModule = true;
+var MyEnum;
+(function (MyEnum) {
+    MyEnum[MyEnum["a"] = 0] = "a";
+})(MyEnum || (MyEnum = {}));

tests/baselines/reference/importElisionEnum.symbols

@@ -0,0 +1,31 @@
+=== tests/cases/compiler/enum.ts ===
+export enum MyEnum {
+>MyEnum : Symbol(MyEnum, Decl(enum.ts, 0, 0))
+
+  a = 0,
+>a : Symbol(MyEnum.a, Decl(enum.ts, 0, 20))
+
+  b,
+>b : Symbol(MyEnum.b, Decl(enum.ts, 1, 8))
+
+  c,
+>c : Symbol(MyEnum.c, Decl(enum.ts, 2, 4))
+
+  d
+>d : Symbol(MyEnum.d, Decl(enum.ts, 3, 4))
+}
+
+=== tests/cases/compiler/index.ts ===
+import { MyEnum as MyEnumFromModule } from "./enum";
+>MyEnum : Symbol(MyEnumFromModule, Decl(enum.ts, 0, 0))
+>MyEnumFromModule : Symbol(MyEnumFromModule, Decl(index.ts, 0, 8))
+
+enum MyEnum {
+>MyEnum : Symbol(MyEnum, Decl(index.ts, 0, 52))
+
+  a = MyEnumFromModule.a
+>a : Symbol(MyEnum.a, Decl(index.ts, 2, 13))
+>MyEnumFromModule.a : Symbol(MyEnumFromModule.a, Decl(enum.ts, 0, 20))
+>MyEnumFromModule : Symbol(MyEnumFromModule, Decl(index.ts, 0, 8))
+>a : Symbol(MyEnumFromModule.a, Decl(enum.ts, 0, 20))
+}

tests/baselines/reference/importElisionEnum.types

@@ -0,0 +1,32 @@
+=== tests/cases/compiler/enum.ts ===
+export enum MyEnum {
+>MyEnum : MyEnum
+
+  a = 0,
+>a : MyEnum.a
+>0 : 0
+
+  b,
+>b : MyEnum.b
+
+  c,
+>c : MyEnum.c
+
+  d
+>d : MyEnum.d
+}
+
+=== tests/cases/compiler/index.ts ===
+import { MyEnum as MyEnumFromModule } from "./enum";
+>MyEnum : typeof MyEnumFromModule
+>MyEnumFromModule : typeof MyEnumFromModule
+
+enum MyEnum {
+>MyEnum : MyEnum
+
+  a = MyEnumFromModule.a
+>a : MyEnum
+>MyEnumFromModule.a : MyEnumFromModule.a
+>MyEnumFromModule : typeof MyEnumFromModule
+>a : MyEnumFromModule.a
+}

tests/cases/compiler/importElisionEnum.ts

@@ -0,0 +1,14 @@
+// @Filename: enum.ts
+export enum MyEnum {
+  a = 0,
+  b,
+  c,
+  d
+}
+
+// @Filename: index.ts
+import { MyEnum as MyEnumFromModule } from "./enum";
+
+enum MyEnum {
+  a = MyEnumFromModule.a
+}