isolatedModules errors for non-literal enum initializers

src/compiler/checker.ts

@@ -719,6 +719,8 @@ import {
     isStringOrNumericLiteralLike,
     isSuperCall,
     isSuperProperty,
+    isSyntacticallyNumeric,
+    isSyntacticallyString,
     isTaggedTemplateExpression,
     isTemplateSpan,
     isThisContainerOrFunctionBlock,
@@ -45518,15 +45520,17 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         if (!(nodeLinks.flags & NodeCheckFlags.EnumValuesComputed)) {
             nodeLinks.flags |= NodeCheckFlags.EnumValuesComputed;
             let autoValue: number | undefined = 0;
+            let previous: EnumMember | undefined;
             for (const member of node.members) {
-                const value = computeMemberValue(member, autoValue);
+                const value = computeMemberValue(member, autoValue, previous);
                 getNodeLinks(member).enumMemberValue = value;
                 autoValue = typeof value === "number" ? value + 1 : undefined;
+                previous = member;
             }
         }
     }
 
-    function computeMemberValue(member: EnumMember, autoValue: number | undefined) {
+    function computeMemberValue(member: EnumMember, autoValue: number | undefined, previous: EnumMember | undefined) {
         if (isComputedNonLiteralName(member.name)) {
             error(member.name, Diagnostics.Computed_property_names_are_not_allowed_in_enums);
         }
@@ -45548,11 +45552,17 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         // If the member is the first member in the enum declaration, it is assigned the value zero.
         // Otherwise, it is assigned the value of the immediately preceding member plus one, and an error
         // occurs if the immediately preceding member is not a constant enum member.
-        if (autoValue !== undefined) {
-            return autoValue;
+        if (autoValue === undefined) {
+            error(member.name, Diagnostics.Enum_member_must_have_initializer);
+            return undefined;
         }
-        error(member.name, Diagnostics.Enum_member_must_have_initializer);
-        return undefined;
+        if (getIsolatedModules(compilerOptions) && previous?.initializer && !isSyntacticallyNumeric(previous.initializer)) {
+            error(
+                member.name,
+                Diagnostics.Enum_member_following_a_non_literal_numeric_member_must_have_an_initializer_when_isolatedModules_is_enabled,
+            );
+        }
+        return autoValue;
     }
 
     function computeConstantValue(member: EnumMember): string | number | undefined {
@@ -45568,6 +45578,12 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                         Diagnostics.const_enum_member_initializer_was_evaluated_to_a_non_finite_value,
                 );
             }
+            else if (getIsolatedModules(compilerOptions) && typeof value === "string" && !isSyntacticallyString(initializer)) {
+                error(
+                    initializer,
+                    Diagnostics.A_string_member_initializer_in_a_enum_declaration_can_only_use_constant_expressions_when_isolatedModules_is_enabled,
+                );
+            }
         }
         else if (isConstEnum) {
             error(initializer, Diagnostics.const_enum_member_initializers_must_be_constant_expressions);

src/compiler/diagnosticMessages.json

@@ -7976,5 +7976,13 @@
     "'await using' statements cannot be used inside a class static block.": {
         "category": "Error",
         "code": 18054
+    },
+    "A string member initializer in a enum declaration can only use constant expressions when 'isolatedModules' is enabled.": {
+        "category": "Error",
+        "code": 18055
+    },
+    "Enum member following a non-literal numeric member must have an initializer when 'isolatedModules' is enabled.": {
+        "category": "Error",
+        "code": 18056
     }
 }

src/compiler/utilities.ts

@@ -10657,3 +10657,17 @@ export function isSyntacticallyString(expr: Expression): boolean {
     }
     return false;
 }
+
+/** @internal */
+export function isSyntacticallyNumeric(expr: Expression): boolean {
+    expr = skipOuterExpressions(expr);
+    switch (expr.kind) {
+        case SyntaxKind.PrefixUnaryExpression:
+            return isSyntacticallyNumeric((expr as PrefixUnaryExpression).operand);
+        case SyntaxKind.BinaryExpression:
+            return isSyntacticallyNumeric((expr as BinaryExpression).left) && isSyntacticallyNumeric((expr as BinaryExpression).right);
+        case SyntaxKind.NumericLiteral:
+            return true;
+    }
+    return false;
+}

tests/baselines/reference/enumNoInitializerFollowsNonLiteralInitializer.errors.txt

@@ -0,0 +1,34 @@
+bad.ts(4,5): error TS18056: Enum member following a non-literal numeric member must have an initializer when 'isolatedModules' is enabled.
+
+
+==== ./helpers.ts (0 errors) ====
+    export const foo = 2;
+
+==== ./bad.ts (1 errors) ====
+    import { foo } from "./helpers";
+    enum A {
+        a = foo,
+        b,
+        ~
+!!! error TS18056: Enum member following a non-literal numeric member must have an initializer when 'isolatedModules' is enabled.
+    }
+
+==== ./good.ts (0 errors) ====
+    import { foo } from "./helpers";
+    enum A {
+        a = foo,
+        b = 3,
+    }
+    enum B {
+        a = 1 + 1,
+        b,
+    }
+    enum C {
+        a = +2,
+        b,
+    }
+    enum D {
+        a = (2),
+        b,
+    }
+

tests/baselines/reference/enumNoInitializerFollowsNonLiteralInitializer.js

@@ -0,0 +1,70 @@
+//// [tests/cases/compiler/enumNoInitializerFollowsNonLiteralInitializer.ts] ////
+
+//// [helpers.ts]
+export const foo = 2;
+
+//// [bad.ts]
+import { foo } from "./helpers";
+enum A {
+    a = foo,
+    b,
+}
+
+//// [good.ts]
+import { foo } from "./helpers";
+enum A {
+    a = foo,
+    b = 3,
+}
+enum B {
+    a = 1 + 1,
+    b,
+}
+enum C {
+    a = +2,
+    b,
+}
+enum D {
+    a = (2),
+    b,
+}
+
+
+//// [helpers.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.foo = void 0;
+exports.foo = 2;
+//// [bad.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+var helpers_1 = require("./helpers");
+var A;
+(function (A) {
+    A[A["a"] = 2] = "a";
+    A[A["b"] = 3] = "b";
+})(A || (A = {}));
+//// [good.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+var helpers_1 = require("./helpers");
+var A;
+(function (A) {
+    A[A["a"] = 2] = "a";
+    A[A["b"] = 3] = "b";
+})(A || (A = {}));
+var B;
+(function (B) {
+    B[B["a"] = 2] = "a";
+    B[B["b"] = 3] = "b";
+})(B || (B = {}));
+var C;
+(function (C) {
+    C[C["a"] = 2] = "a";
+    C[C["b"] = 3] = "b";
+})(C || (C = {}));
+var D;
+(function (D) {
+    D[D["a"] = 2] = "a";
+    D[D["b"] = 3] = "b";
+})(D || (D = {}));

tests/baselines/reference/enumWithNonLiteralStringInitializer.errors.txt

@@ -0,0 +1,24 @@
+bad.ts(3,8): error TS18055: A string member initializer in a enum declaration can only use constant expressions when 'isolatedModules' is enabled.
+
+
+==== ./helpers.ts (0 errors) ====
+    export const foo = 2;
+    export const bar = "bar";
+
+==== ./bad.ts (1 errors) ====
+    import { bar } from "./helpers";
+    enum A {
+       a = bar,
+           ~~~
+!!! error TS18055: A string member initializer in a enum declaration can only use constant expressions when 'isolatedModules' is enabled.
+    }
+
+==== ./good.ts (0 errors) ====
+    import { foo } from "./helpers";
+    enum A {
+       a = `${foo}`,
+       b = "" + 2,
+       c = 2 + "",
+       d = ("foo"),
+    }
+

tests/baselines/reference/enumWithNonLiteralStringInitializer.js

@@ -0,0 +1,47 @@
+//// [tests/cases/compiler/enumWithNonLiteralStringInitializer.ts] ////
+
+//// [helpers.ts]
+export const foo = 2;
+export const bar = "bar";
+
+//// [bad.ts]
+import { bar } from "./helpers";
+enum A {
+   a = bar,
+}
+
+//// [good.ts]
+import { foo } from "./helpers";
+enum A {
+   a = `${foo}`,
+   b = "" + 2,
+   c = 2 + "",
+   d = ("foo"),
+}
+
+
+//// [helpers.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.bar = exports.foo = void 0;
+exports.foo = 2;
+exports.bar = "bar";
+//// [bad.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+var helpers_1 = require("./helpers");
+var A;
+(function (A) {
+    A["a"] = "bar";
+})(A || (A = {}));
+//// [good.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+var helpers_1 = require("./helpers");
+var A;
+(function (A) {
+    A["a"] = "2";
+    A["b"] = "2";
+    A["c"] = "2";
+    A["d"] = "foo";
+})(A || (A = {}));

tests/baselines/reference/isolatedModulesGlobalNamespacesAndEnums.errors.txt

@@ -1,3 +1,4 @@
+enum2.ts(2,9): error TS18055: A string member initializer in a enum declaration can only use constant expressions when 'isolatedModules' is enabled.
 enum2.ts(3,9): error TS1281: Cannot access 'A' from another file without qualification when 'isolatedModules' is enabled. Use 'Enum.A' instead.
 enum2.ts(4,9): error TS1281: Cannot access 'X' from another file without qualification when 'isolatedModules' is enabled. Use 'Enum.X' instead.
 script-namespaces.ts(1,11): error TS1280: Namespaces are not allowed in global script files when 'isolatedModules' is enabled. If this file is not intended to be a global script, set 'moduleDetection' to 'force' or add an empty 'export {}' statement.
@@ -26,9 +27,11 @@ script-namespaces.ts(1,11): error TS1280: Namespaces are not allowed in global s
     declare enum Enum { X = 1_000_000 }
     const d = 'd';
 
-==== enum2.ts (2 errors) ====
+==== enum2.ts (3 errors) ====
     enum Enum {
         D = d,
+            ~
+!!! error TS18055: A string member initializer in a enum declaration can only use constant expressions when 'isolatedModules' is enabled.
         E = A, // error
             ~
 !!! error TS1281: Cannot access 'A' from another file without qualification when 'isolatedModules' is enabled. Use 'Enum.A' instead.

tests/cases/compiler/enumNoInitializerFollowsNonLiteralInitializer.ts

@@ -0,0 +1,31 @@
+// @isolatedModules: true
+// @noTypesAndSymbols: true
+
+// @filename: ./helpers.ts
+export const foo = 2;
+
+// @filename: ./bad.ts
+import { foo } from "./helpers";
+enum A {
+    a = foo,
+    b,
+}
+
+// @filename: ./good.ts
+import { foo } from "./helpers";
+enum A {
+    a = foo,
+    b = 3,
+}
+enum B {
+    a = 1 + 1,
+    b,
+}
+enum C {
+    a = +2,
+    b,
+}
+enum D {
+    a = (2),
+    b,
+}

tests/cases/compiler/enumWithNonLiteralStringInitializer.ts

@@ -0,0 +1,21 @@
+// @isolatedModules: true
+// @noTypesAndSymbols: true
+
+// @filename: ./helpers.ts
+export const foo = 2;
+export const bar = "bar";
+
+// @filename: ./bad.ts
+import { bar } from "./helpers";
+enum A {
+   a = bar,
+}
+
+// @filename: ./good.ts
+import { foo } from "./helpers";
+enum A {
+   a = `${foo}`,
+   b = "" + 2,
+   c = 2 + "",
+   d = ("foo"),
+}