moduleDetection: auto makes cjs files parse as modules, module: node sets moduleDetection: force (#49268)

Author: weswigham

src/compiler/binder.ts

@@ -2834,12 +2834,14 @@ namespace ts {
         }
 
         function setCommonJsModuleIndicator(node: Node) {
-            if (file.externalModuleIndicator) {
+            if (file.externalModuleIndicator && file.externalModuleIndicator !== true) {
                 return false;
             }
             if (!file.commonJsModuleIndicator) {
                 file.commonJsModuleIndicator = node;
-                bindSourceFileAsExternalModule();
+                if (!file.externalModuleIndicator) {
+                    bindSourceFileAsExternalModule();
+                }
             }
             return true;
         }

src/compiler/checker.ts

@@ -2747,7 +2747,7 @@ namespace ts {
                 return hasExportAssignmentSymbol(moduleSymbol);
             }
             // JS files have a synthetic default if they do not contain ES2015+ module syntax (export = is not valid in js) _and_ do not have an __esModule marker
-            return !file.externalModuleIndicator && !resolveExportByName(moduleSymbol, escapeLeadingUnderscores("__esModule"), /*sourceNode*/ undefined, dontResolveAlias);
+            return typeof file.externalModuleIndicator !== "object" && !resolveExportByName(moduleSymbol, escapeLeadingUnderscores("__esModule"), /*sourceNode*/ undefined, dontResolveAlias);
         }
 
         function getTargetOfImportClause(node: ImportClause, dontResolveAlias: boolean): Symbol | undefined {

src/compiler/utilities.ts

@@ -6302,8 +6302,9 @@ namespace ts {
      */
     function isFileForcedToBeModuleByFormat(file: SourceFile): true | undefined {
         // Excludes declaration files - they still require an explicit `export {}` or the like
-        // for back compat purposes.
-        return file.impliedNodeFormat === ModuleKind.ESNext && !file.isDeclarationFile ? true : undefined;
+        // for back compat purposes. The only non-declaration files _not_ forced to be a module are `.js` files
+        // that aren't esm-mode (meaning not in a `type: module` scope).
+        return (file.impliedNodeFormat === ModuleKind.ESNext || (fileExtensionIsOneOf(file.fileName, [Extension.Cjs, Extension.Cts]))) && !file.isDeclarationFile ? true : undefined;
     }
 
     export function getSetExternalModuleIndicator(options: CompilerOptions): (file: SourceFile) => void {
@@ -6312,7 +6313,7 @@ namespace ts {
             case ModuleDetectionKind.Force:
                 // All non-declaration files are modules, declaration files still do the usual isFileProbablyExternalModule
                 return (file: SourceFile) => {
-                    file.externalModuleIndicator = !file.isDeclarationFile || isFileProbablyExternalModule(file);
+                    file.externalModuleIndicator = isFileProbablyExternalModule(file) || !file.isDeclarationFile || undefined;
                 };
             case ModuleDetectionKind.Legacy:
                 // Files are modules if they have imports, exports, or import.meta
@@ -6372,7 +6373,8 @@ namespace ts {
     }
 
     export function getEmitModuleDetectionKind(options: CompilerOptions) {
-        return options.moduleDetection || ModuleDetectionKind.Auto;
+        return options.moduleDetection ||
+            (getEmitModuleKind(options) === ModuleKind.Node16 || getEmitModuleKind(options) === ModuleKind.NodeNext ? ModuleDetectionKind.Force : ModuleDetectionKind.Auto);
     }
 
     export function hasJsonModuleEmitEnabled(options: CompilerOptions) {

tests/baselines/reference/moduleResolutionWithoutExtension8.js

@@ -3,5 +3,7 @@
 import("./foo").then(x => x); // should error, ask for extension
 
 //// [bar.cjs]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
 // Extensionless relative path dynamic import in a cjs module
 import("./foo").then(x => x); // should error, ask for extension

tests/baselines/reference/nodeModulesAllowJsExportAssignment(module=node16).js

@@ -34,6 +34,8 @@ module.exports = a;
 const a = {};
 module.exports = a;
 //// [file.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
 // cjs format file
 const a = {};
 module.exports = a;

tests/baselines/reference/nodeModulesAllowJsExportAssignment(module=nodenext).js

@@ -34,6 +34,8 @@ module.exports = a;
 const a = {};
 module.exports = a;
 //// [file.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
 // cjs format file
 const a = {};
 module.exports = a;

tests/baselines/reference/nodeModulesAllowJsExportlessJsModuleDetectionAuto(module=node16).js

@@ -0,0 +1,13 @@
+//// [tests/cases/conformance/node/allowJs/nodeModulesAllowJsExportlessJsModuleDetectionAuto.ts] ////
+
+//// [foo.cjs]
+// this file is a module despite having no imports
+//// [bar.js]
+// however this file is _not_ a module
+
+//// [foo.cjs]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+// this file is a module despite having no imports
+//// [bar.js]
+// however this file is _not_ a module

tests/baselines/reference/nodeModulesAllowJsExportlessJsModuleDetectionAuto(module=node16).symbols

@@ -0,0 +1,5 @@
+=== tests/cases/conformance/node/allowJs/foo.cjs ===
+// this file is a module despite having no imports
+No type information for this code.=== tests/cases/conformance/node/allowJs/bar.js ===
+// however this file is _not_ a module
+No type information for this code.

tests/baselines/reference/nodeModulesAllowJsExportlessJsModuleDetectionAuto(module=node16).types

@@ -0,0 +1,5 @@
+=== tests/cases/conformance/node/allowJs/foo.cjs ===
+// this file is a module despite having no imports
+No type information for this code.=== tests/cases/conformance/node/allowJs/bar.js ===
+// however this file is _not_ a module
+No type information for this code.

tests/baselines/reference/nodeModulesAllowJsExportlessJsModuleDetectionAuto(module=nodenext).js

@@ -0,0 +1,13 @@
+//// [tests/cases/conformance/node/allowJs/nodeModulesAllowJsExportlessJsModuleDetectionAuto.ts] ////
+
+//// [foo.cjs]
+// this file is a module despite having no imports
+//// [bar.js]
+// however this file is _not_ a module
+
+//// [foo.cjs]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+// this file is a module despite having no imports
+//// [bar.js]
+// however this file is _not_ a module