24542 - bad error message for import *-ing an export=

src/compiler/checker.ts

@@ -2408,11 +2408,18 @@ namespace ts {
         // combine other declarations with the module or variable (e.g. a class/module, function/module, interface/variable).
         function resolveESModuleSymbol(moduleSymbol: Symbol | undefined, referencingLocation: Node, dontResolveAlias: boolean): Symbol | undefined {
             const symbol = resolveExternalModuleSymbol(moduleSymbol, dontResolveAlias);
+
             if (!dontResolveAlias && symbol) {
                 if (!(symbol.flags & (SymbolFlags.Module | SymbolFlags.Variable)) && !getDeclarationOfKind(symbol, SyntaxKind.SourceFile)) {
-                    error(referencingLocation, Diagnostics.Module_0_resolves_to_a_non_module_entity_and_cannot_be_imported_using_this_construct, symbolToString(moduleSymbol!));
+                    const compilerOptionName = moduleKind >= ModuleKind.ES2015
+                        ? "allowSyntheticDefaultImports"
+                        : "esModuleInterop";
+
+                    error(referencingLocation, Diagnostics.This_module_can_only_be_referenced_with_ECMAScript_imports_Slashexports_by_turning_on_the_0_flag_and_referencing_its_default_export, compilerOptionName);
+
                     return symbol;
                 }
+
                 if (compilerOptions.esModuleInterop) {
                     const referenceParent = referencingLocation.parent;
                     if (

src/compiler/diagnosticMessages.json

@@ -1776,7 +1776,7 @@
         "category": "Error",
         "code": 2496
     },
-    "Module '{0}' resolves to a non-module entity and cannot be imported using this construct.": {
+    "This module can only be referenced with ECMAScript imports/exports by turning on the '{0}' flag and referencing its default export.": {
         "category": "Error",
         "code": 2497
     },

tests/baselines/reference/es6ExportEqualsInterop.errors.txt

@@ -11,24 +11,24 @@ tests/cases/compiler/main.ts(33,8): error TS1192: Module '"function"' has no def
 tests/cases/compiler/main.ts(34,8): error TS1192: Module '"function-module"' has no default export.
 tests/cases/compiler/main.ts(35,8): error TS1192: Module '"class"' has no default export.
 tests/cases/compiler/main.ts(36,8): error TS1192: Module '"class-module"' has no default export.
-tests/cases/compiler/main.ts(39,21): error TS2497: Module '"interface"' resolves to a non-module entity and cannot be imported using this construct.
-tests/cases/compiler/main.ts(45,21): error TS2497: Module '"function"' resolves to a non-module entity and cannot be imported using this construct.
-tests/cases/compiler/main.ts(47,21): error TS2497: Module '"class"' resolves to a non-module entity and cannot be imported using this construct.
+tests/cases/compiler/main.ts(39,21): error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
+tests/cases/compiler/main.ts(45,21): error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
+tests/cases/compiler/main.ts(47,21): error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
 tests/cases/compiler/main.ts(50,1): error TS2693: 'y1' only refers to a type, but is being used as a value here.
 tests/cases/compiler/main.ts(56,4): error TS2339: Property 'a' does not exist on type '() => any'.
 tests/cases/compiler/main.ts(58,4): error TS2339: Property 'a' does not exist on type 'typeof Foo'.
 tests/cases/compiler/main.ts(62,10): error TS2305: Module '"interface"' has no exported member 'a'.
-tests/cases/compiler/main.ts(62,25): error TS2497: Module '"interface"' resolves to a non-module entity and cannot be imported using this construct.
+tests/cases/compiler/main.ts(62,25): error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
 tests/cases/compiler/main.ts(68,10): error TS2305: Module '"function"' has no exported member 'a'.
-tests/cases/compiler/main.ts(68,25): error TS2497: Module '"function"' resolves to a non-module entity and cannot be imported using this construct.
+tests/cases/compiler/main.ts(68,25): error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
 tests/cases/compiler/main.ts(70,10): error TS2305: Module '"class"' has no exported member 'a'.
-tests/cases/compiler/main.ts(70,25): error TS2497: Module '"class"' resolves to a non-module entity and cannot be imported using this construct.
+tests/cases/compiler/main.ts(70,25): error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
 tests/cases/compiler/main.ts(85,10): error TS2305: Module '"interface"' has no exported member 'a'.
-tests/cases/compiler/main.ts(85,25): error TS2497: Module '"interface"' resolves to a non-module entity and cannot be imported using this construct.
+tests/cases/compiler/main.ts(85,25): error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
 tests/cases/compiler/main.ts(91,10): error TS2305: Module '"function"' has no exported member 'a'.
-tests/cases/compiler/main.ts(91,25): error TS2497: Module '"function"' resolves to a non-module entity and cannot be imported using this construct.
+tests/cases/compiler/main.ts(91,25): error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
 tests/cases/compiler/main.ts(93,10): error TS2305: Module '"class"' has no exported member 'a'.
-tests/cases/compiler/main.ts(93,25): error TS2497: Module '"class"' resolves to a non-module entity and cannot be imported using this construct.
+tests/cases/compiler/main.ts(93,25): error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
 tests/cases/compiler/main.ts(97,15): error TS2498: Module '"interface"' uses 'export =' and cannot be used with 'export *'.
 tests/cases/compiler/main.ts(98,15): error TS2498: Module '"variable"' uses 'export =' and cannot be used with 'export *'.
 tests/cases/compiler/main.ts(99,15): error TS2498: Module '"interface-variable"' uses 'export =' and cannot be used with 'export *'.
@@ -108,19 +108,19 @@ tests/cases/compiler/main.ts(106,15): error TS2498: Module '"class-module"' uses
     // namespace import
     import * as y1 from "interface";
                         ~~~~~~~~~~~
-!!! error TS2497: Module '"interface"' resolves to a non-module entity and cannot be imported using this construct.
+!!! error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
     import * as y2 from "variable";
     import * as y3 from "interface-variable";
     import * as y4 from "module";
     import * as y5 from "interface-module";
     import * as y6 from "variable-module";
     import * as y7 from "function";
                         ~~~~~~~~~~
-!!! error TS2497: Module '"function"' resolves to a non-module entity and cannot be imported using this construct.
+!!! error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
     import * as y8 from "function-module";
     import * as y9 from "class";
                         ~~~~~~~
-!!! error TS2497: Module '"class"' resolves to a non-module entity and cannot be imported using this construct.
+!!! error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
     import * as y0 from "class-module";
 
     y1.a;
@@ -145,7 +145,7 @@ tests/cases/compiler/main.ts(106,15): error TS2498: Module '"class-module"' uses
              ~
 !!! error TS2305: Module '"interface"' has no exported member 'a'.
                             ~~~~~~~~~~~
-!!! error TS2497: Module '"interface"' resolves to a non-module entity and cannot be imported using this construct.
+!!! error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
     import { a as a2 } from "variable";
     import { a as a3 } from "interface-variable";
     import { a as a4 } from "module";
@@ -155,13 +155,13 @@ tests/cases/compiler/main.ts(106,15): error TS2498: Module '"class-module"' uses
              ~
 !!! error TS2305: Module '"function"' has no exported member 'a'.
                             ~~~~~~~~~~
-!!! error TS2497: Module '"function"' resolves to a non-module entity and cannot be imported using this construct.
+!!! error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
     import { a as a8 } from "function-module";
     import { a as a9 } from "class";
              ~
 !!! error TS2305: Module '"class"' has no exported member 'a'.
                             ~~~~~~~
-!!! error TS2497: Module '"class"' resolves to a non-module entity and cannot be imported using this construct.
+!!! error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
     import { a as a0 } from "class-module";
 
     a1;
@@ -180,7 +180,7 @@ tests/cases/compiler/main.ts(106,15): error TS2498: Module '"class-module"' uses
              ~
 !!! error TS2305: Module '"interface"' has no exported member 'a'.
                             ~~~~~~~~~~~
-!!! error TS2497: Module '"interface"' resolves to a non-module entity and cannot be imported using this construct.
+!!! error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
     export { a as a2 } from "variable";
     export { a as a3 } from "interface-variable";
     export { a as a4 } from "module";
@@ -190,13 +190,13 @@ tests/cases/compiler/main.ts(106,15): error TS2498: Module '"class-module"' uses
              ~
 !!! error TS2305: Module '"function"' has no exported member 'a'.
                             ~~~~~~~~~~
-!!! error TS2497: Module '"function"' resolves to a non-module entity and cannot be imported using this construct.
+!!! error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
     export { a as a8 } from "function-module";
     export { a as a9 } from "class";
              ~
 !!! error TS2305: Module '"class"' has no exported member 'a'.
                             ~~~~~~~
-!!! error TS2497: Module '"class"' resolves to a non-module entity and cannot be imported using this construct.
+!!! error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
     export { a as a0 } from "class-module";
 
     // export-star

tests/baselines/reference/es6ImportEqualsExportModuleCommonJsError.errors.txt

@@ -0,0 +1,15 @@
+tests/cases/compiler/main.ts(1,20): error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
+
+
+==== tests/cases/compiler/a.ts (0 errors) ====
+    class a { }
+    export = a;
+
+==== tests/cases/compiler/main.ts (1 errors) ====
+    import * as a from "./a";
+                       ~~~~~
+!!! error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'esModuleInterop' flag and referencing its default export.
+    a;
+
+
+

tests/baselines/reference/es6ImportEqualsExportModuleCommonJsError.js

@@ -0,0 +1,26 @@
+//// [tests/cases/compiler/es6ImportEqualsExportModuleCommonJsError.ts] ////
+
+//// [a.ts]
+class a { }
+export = a;
+
+//// [main.ts]
+import * as a from "./a";
+a;
+
+
+
+
+//// [a.js]
+"use strict";
+var a = /** @class */ (function () {
+    function a() {
+    }
+    return a;
+}());
+module.exports = a;
+//// [main.js]
+"use strict";
+exports.__esModule = true;
+var a = require("./a");
+a;

tests/baselines/reference/es6ImportEqualsExportModuleCommonJsError.symbols

@@ -0,0 +1,16 @@
+=== tests/cases/compiler/a.ts ===
+class a { }
+>a : Symbol(a, Decl(a.ts, 0, 0))
+
+export = a;
+>a : Symbol(a, Decl(a.ts, 0, 0))
+
+=== tests/cases/compiler/main.ts ===
+import * as a from "./a";
+>a : Symbol(a, Decl(main.ts, 0, 6))
+
+a;
+>a : Symbol(a, Decl(main.ts, 0, 6))
+
+
+

tests/baselines/reference/es6ImportEqualsExportModuleCommonJsError.types

@@ -0,0 +1,16 @@
+=== tests/cases/compiler/a.ts ===
+class a { }
+>a : a
+
+export = a;
+>a : a
+
+=== tests/cases/compiler/main.ts ===
+import * as a from "./a";
+>a : typeof a
+
+a;
+>a : typeof a
+
+
+

tests/baselines/reference/es6ImportEqualsExportModuleEs2015Error.errors.txt

@@ -0,0 +1,18 @@
+tests/cases/compiler/a.ts(2,1): error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
+tests/cases/compiler/main.ts(1,20): error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'allowSyntheticDefaultImports' flag and referencing its default export.
+
+
+==== tests/cases/compiler/a.ts (1 errors) ====
+    class a { }
+    export = a;
+    ~~~~~~~~~~~
+!!! error TS1203: Export assignment cannot be used when targeting ECMAScript modules. Consider using 'export default' or another module format instead.
+
+==== tests/cases/compiler/main.ts (1 errors) ====
+    import * as a from "./a";
+                       ~~~~~
+!!! error TS2497: This module can only be referenced with ECMAScript imports/exports by turning on the 'allowSyntheticDefaultImports' flag and referencing its default export.
+    a;
+
+
+

tests/baselines/reference/es6ImportEqualsExportModuleEs2015Error.js

@@ -0,0 +1,22 @@
+//// [tests/cases/compiler/es6ImportEqualsExportModuleEs2015Error.ts] ////
+
+//// [a.ts]
+class a { }
+export = a;
+
+//// [main.ts]
+import * as a from "./a";
+a;
+
+
+
+
+//// [a.js]
+var a = /** @class */ (function () {
+    function a() {
+    }
+    return a;
+}());
+//// [main.js]
+import * as a from "./a";
+a;

tests/baselines/reference/es6ImportEqualsExportModuleEs2015Error.symbols

@@ -0,0 +1,16 @@
+=== tests/cases/compiler/a.ts ===
+class a { }
+>a : Symbol(a, Decl(a.ts, 0, 0))
+
+export = a;
+>a : Symbol(a, Decl(a.ts, 0, 0))
+
+=== tests/cases/compiler/main.ts ===
+import * as a from "./a";
+>a : Symbol(a, Decl(main.ts, 0, 6))
+
+a;
+>a : Symbol(a, Decl(main.ts, 0, 6))
+
+
+

tests/baselines/reference/es6ImportEqualsExportModuleEs2015Error.types

@@ -0,0 +1,16 @@
+=== tests/cases/compiler/a.ts ===
+class a { }
+>a : a
+
+export = a;
+>a : a
+
+=== tests/cases/compiler/main.ts ===
+import * as a from "./a";
+>a : typeof a
+
+a;
+>a : typeof a
+
+
+

tests/cases/compiler/es6ImportEqualsExportModuleCommonJsError.ts

@@ -0,0 +1,11 @@
+// @module: commonjs
+
+// @filename: a.ts
+class a { }
+export = a;
+
+// @filename: main.ts
+import * as a from "./a";
+a;
+
+

tests/cases/compiler/es6ImportEqualsExportModuleEs2015Error.ts

@@ -0,0 +1,11 @@
+// @module: es2015
+
+// @filename: a.ts
+class a { }
+export = a;
+
+// @filename: main.ts
+import * as a from "./a";
+a;
+
+