module: do not warn when require(esm) comes from node_modules

Some packages have been using try-catch to load require(esm)
in environments that are available. In 23, where require(esm)
is unflagged, we emit an experimental warning when require()
is used to load ESM. To backport require(esm) to older LTS
releases, however, this could break existing CLI output.
To reduce the disruption for LTS, on older release lines,
this commit is applied to skip the warning if require(esm)
comes from node_modules. This warning will be eventually
removed when require(esm) becomes stable.

Author: joyeecheung

lib/internal/modules/cjs/loader.js

@@ -124,6 +124,7 @@ const { pathToFileURL, fileURLToPath, isURL } = require('internal/url');
 const {
   pendingDeprecate,
   emitExperimentalWarning,
+  isInsideNodeModules,
   isUnderNodeModules,
   kEmptyObject,
   setOwnProperty,
@@ -1351,6 +1352,7 @@ let resolvedArgv;
 let hasPausedEntry = false;
 /** @type {import('vm').Script} */
 
+let emittedRequireModuleWarning = false;
 /**
  * Resolve and evaluate it synchronously as ESM if it's ESM.
  * @param {Module} mod CJS module instance
@@ -1374,11 +1376,27 @@ function loadESMFromCJS(mod, filename) {
     // ESM won't be accessible via process.mainModule.
     setOwnProperty(process, 'mainModule', undefined);
   } else {
-    emitExperimentalWarning('Support for loading ES Module in require()');
+    const parent = mod[kModuleParent];
+    if (!emittedRequireModuleWarning) {
+      let shouldEmitWarning = false;
+      // Check if the require() comes from node_modules.
+      if (parent) {
+        shouldEmitWarning = !isUnderNodeModules(parent.filename);
+      } else if (mod[kIsCachedByESMLoader]) {
+        // It comes from the require() built for `import cjs` and doesn't have a parent recorded
+        // in the CJS module instance. Inspect the stack trace to see if the require()
+        // comes from node_modules.
+        shouldEmitWarning = !isInsideNodeModules();
+      }
+      if (shouldEmitWarning) {
+        emitExperimentalWarning('Support for loading ES Module in require()');
+        emittedRequireModuleWarning = true;
+      }
+    }
     const {
       wrap,
       namespace,
-    } = cascadedLoader.importSyncForRequire(mod, filename, source, isMain, mod[kModuleParent]);
+    } = cascadedLoader.importSyncForRequire(mod, filename, source, isMain, parent);
     // Tooling in the ecosystem have been using the __esModule property to recognize
     // transpiled ESM in consuming code. For example, a 'log' package written in ESM:
     //

test/es-module/test-require-node-modules-warning.js

@@ -0,0 +1,59 @@
+'use strict';
+
+// This checks the experimental warning for require(esm) is disabled when the
+// require() comes from node_modules.
+require('../common');
+const { spawnSyncAndAssert } = require('../common/child_process');
+const fixtures = require('../common/fixtures');
+
+const warningRE = /ExperimentalWarning: Support for loading ES Module in require\(\)/;
+
+// The fixtures are placed in a directory that includes "node_modules" in its name
+// to check false negatives.
+
+// require() in non-node_modules -> esm in node_modules should warn.
+spawnSyncAndAssert(
+  process.execPath,
+  [fixtures.path('es-modules', 'test_node_modules', 'require-esm.js')],
+  {
+    trim: true,
+    stderr: warningRE,
+    stdout: 'world',
+  }
+);
+
+// require() in non-node_modules -> require() in node_modules -> esm in node_modules
+// should not warn.
+spawnSyncAndAssert(
+  process.execPath,
+  [fixtures.path('es-modules', 'test_node_modules', 'require-require-esm.js')],
+  {
+    trim: true,
+    stderr: '',
+    stdout: 'world',
+  }
+);
+
+// Import in non-node_modules -> require() in node_modules -> esm in node_modules
+// should not warn.
+spawnSyncAndAssert(
+  process.execPath,
+  [fixtures.path('es-modules', 'test_node_modules', 'import-require-esm.mjs')],
+  {
+    trim: true,
+    stderr: '',
+    stdout: 'world',
+  }
+);
+
+// Import in non-node_modules -> import in node_modules ->
+// require() in node_modules -> esm in node_modules should not warn.
+spawnSyncAndAssert(
+  process.execPath,
+  [fixtures.path('es-modules', 'test_node_modules', 'import-import-require-esm.mjs')],
+  {
+    trim: true,
+    stderr: '',
+    stdout: 'world',
+  }
+);