esm: fix emit deprecation on legacy main resolve

lib/internal/modules/esm/resolve.js

@@ -30,7 +30,7 @@ const { getOptionValue } = require('internal/options');
 const policy = getOptionValue('--experimental-policy') ?
   require('internal/process/policy') :
   null;
-const { sep, relative, toNamespacedPath } = require('path');
+const { sep, relative, toNamespacedPath, resolve } = require('path');
 const preserveSymlinks = getOptionValue('--preserve-symlinks');
 const preserveSymlinksMain = getOptionValue('--preserve-symlinks-main');
 const experimentalNetworkImports =
@@ -101,7 +101,7 @@ function emitInvalidSegmentDeprecation(target, request, match, pjsonUrl, interna
  * @param {URL} url
  * @param {URL} packageJSONUrl
  * @param {string | URL | undefined} base
- * @param {string} main
+ * @param {string} [main]
  * @returns {void}
  */
 function emitLegacyIndexDeprecation(url, packageJSONUrl, base, main) {
@@ -111,17 +111,7 @@ function emitLegacyIndexDeprecation(url, packageJSONUrl, base, main) {
   const path = fileURLToPath(url);
   const pkgPath = fileURLToPath(new URL('.', packageJSONUrl));
   const basePath = fileURLToPath(base);
-  if (main)
-    process.emitWarning(
-      `Package ${pkgPath} has a "main" field set to ${JSONStringify(main)}, ` +
-      `excluding the full filename and extension to the resolved file at "${
-        StringPrototypeSlice(path, pkgPath.length)}", imported from ${
-        basePath}.\n Automatic extension resolution of the "main" field is ` +
-      'deprecated for ES modules.',
-      'DeprecationWarning',
-      'DEP0151',
-    );
-  else
+  if (!main) {
     process.emitWarning(
       `No "main" or "exports" field defined in the package.json for ${pkgPath
       } resolving the main entry point "${
@@ -130,6 +120,17 @@ function emitLegacyIndexDeprecation(url, packageJSONUrl, base, main) {
       'DeprecationWarning',
       'DEP0151',
     );
+  } else if (resolve(pkgPath, main) !== path) {
+    process.emitWarning(
+      `Package ${pkgPath} has a "main" field set to "${main}", ` +
+      `excluding the full filename and extension to the resolved file at "${
+        StringPrototypeSlice(path, pkgPath.length)}", imported from ${
+        basePath}.\n Automatic extension resolution of the "main" field is ` +
+      'deprecated for ES modules.',
+      'DeprecationWarning',
+      'DEP0151',
+    );
+  }
 }
 
 const realpathCache = new SafeMap();

test/es-module/test-esm-extension-lookup-deprecation.mjs

@@ -0,0 +1,121 @@
+import { spawnPromisified } from '../common/index.mjs';
+import * as tmpdir from '../common/tmpdir.js';
+
+import assert from 'node:assert';
+import { mkdir, writeFile } from 'node:fs/promises';
+import * as path from 'node:path';
+import { execPath } from 'node:process';
+import { describe, it, before } from 'node:test';
+
+describe('ESM in main field', { concurrency: true }, () => {
+  before(() => tmpdir.refresh());
+
+  it('should handle fully-specified relative path without any warning', async () => {
+    const cwd = path.join(tmpdir.path, Math.random().toString());
+    const pkgPath = path.join(cwd, './node_modules/pkg/');
+    await mkdir(pkgPath, { recursive: true });
+    writeFile(path.join(pkgPath, './index.js'), 'console.log("Hello World!")');
+    writeFile(path.join(pkgPath, './package.json'), JSON.stringify({
+      main: './index.js',
+      type: 'module',
+    }));
+    const { code, stdout, stderr } = await spawnPromisified(execPath, [
+      '--input-type=module',
+      '--eval', 'import "pkg"',
+    ], { cwd });
+
+    assert.strictEqual(stderr, '');
+    assert.match(stdout, /^Hello World!\r?\n$/);
+    assert.strictEqual(code, 0);
+  });
+  it('should handle fully-specified absolute path without any warning', async () => {
+    const cwd = path.join(tmpdir.path, Math.random().toString());
+    const pkgPath = path.join(cwd, './node_modules/pkg/');
+    await mkdir(pkgPath, { recursive: true });
+    writeFile(path.join(pkgPath, './index.js'), 'console.log("Hello World!")');
+    writeFile(path.join(pkgPath, './package.json'), JSON.stringify({
+      main: path.join(pkgPath, './index.js'),
+      type: 'module',
+    }));
+    const { code, stdout, stderr } = await spawnPromisified(execPath, [
+      '--input-type=module',
+      '--eval', 'import "pkg"',
+    ], { cwd });
+
+    assert.strictEqual(stderr, '');
+    assert.match(stdout, /^Hello World!\r?\n$/);
+    assert.strictEqual(code, 0);
+  });
+
+  it('should emit warning when "main" and "exports" are missing', async () => {
+    const cwd = path.join(tmpdir.path, Math.random().toString());
+    const pkgPath = path.join(cwd, './node_modules/pkg/');
+    await mkdir(pkgPath, { recursive: true });
+    writeFile(path.join(pkgPath, './index.js'), 'console.log("Hello World!")');
+    writeFile(path.join(pkgPath, './package.json'), JSON.stringify({
+      type: 'module',
+    }));
+    const { code, stdout, stderr } = await spawnPromisified(execPath, [
+      '--input-type=module',
+      '--eval', 'import "pkg"',
+    ], { cwd });
+
+    assert.match(stderr, /\[DEP0151\]/);
+    assert.match(stdout, /^Hello World!\r?\n$/);
+    assert.strictEqual(code, 0);
+  });
+  it('should emit warning when "main" is falsy', async () => {
+    const cwd = path.join(tmpdir.path, Math.random().toString());
+    const pkgPath = path.join(cwd, './node_modules/pkg/');
+    await mkdir(pkgPath, { recursive: true });
+    writeFile(path.join(pkgPath, './index.js'), 'console.log("Hello World!")');
+    writeFile(path.join(pkgPath, './package.json'), JSON.stringify({
+      type: 'module',
+      main: '',
+    }));
+    const { code, stdout, stderr } = await spawnPromisified(execPath, [
+      '--input-type=module',
+      '--eval', 'import "pkg"',
+    ], { cwd });
+
+    assert.match(stderr, /\[DEP0151\]/);
+    assert.match(stdout, /^Hello World!\r?\n$/);
+    assert.strictEqual(code, 0);
+  });
+  it('should emit warning when "main" is a relative path without extension', async () => {
+    const cwd = path.join(tmpdir.path, Math.random().toString());
+    const pkgPath = path.join(cwd, './node_modules/pkg/');
+    await mkdir(pkgPath, { recursive: true });
+    writeFile(path.join(pkgPath, './index.js'), 'console.log("Hello World!")');
+    writeFile(path.join(pkgPath, './package.json'), JSON.stringify({
+      main: 'index',
+      type: 'module',
+    }));
+    const { code, stdout, stderr } = await spawnPromisified(execPath, [
+      '--input-type=module',
+      '--eval', 'import "pkg"',
+    ], { cwd });
+
+    assert.match(stderr, /\[DEP0151\]/);
+    assert.match(stdout, /^Hello World!\r?\n$/);
+    assert.strictEqual(code, 0);
+  });
+  it('should emit warning when "main" is an absolute path without extension', async () => {
+    const cwd = path.join(tmpdir.path, Math.random().toString());
+    const pkgPath = path.join(cwd, './node_modules/pkg/');
+    await mkdir(pkgPath, { recursive: true });
+    writeFile(path.join(pkgPath, './index.js'), 'console.log("Hello World!")');
+    writeFile(path.join(pkgPath, './package.json'), JSON.stringify({
+      main: pkgPath + 'index',
+      type: 'module',
+    }));
+    const { code, stdout, stderr } = await spawnPromisified(execPath, [
+      '--input-type=module',
+      '--eval', 'import "pkg"',
+    ], { cwd });
+
+    assert.match(stderr, /\[DEP0151\]/);
+    assert.match(stdout, /^Hello World!\r?\n$/);
+    assert.strictEqual(code, 0);
+  });
+});