[Fix] Ignore hashbang and BOM while parsing

ESLint does this outside their espree parser, so we need to do it as
well. Just like ESLint, the code will convert hashbang to comments and
strip off the BOM completely before handing the content to the parser.

Author: silverwind

tests/files/no-unused-modules/hashbang-child.js

@@ -0,0 +1 @@
+export const foo = 1;

tests/files/no-unused-modules/hashbang-parent.js

@@ -0,0 +1,2 @@
+#!/usr/bin/env node
+import {foo} from './hashbang-child.js';

tests/src/rules/no-unused-modules.js

@@ -307,7 +307,7 @@ describe('dynamic imports', () => {
       `,
         filename: testFilePath('./unused-modules-reexport-crash/src/index.tsx'),
         parser: parsers.TS_NEW,
-        options: [{        
+        options: [{
           unusedExports: true,
           ignoreExports: ['**/magic/**'],
         }],
@@ -1302,3 +1302,21 @@ describe('support ES2022 Arbitrary module namespace identifier names', () => {
     ),
   });
 });
+
+describe('parser ignores hashbang and BOM', () => {
+  ruleTester.run('no-unused-modules', rule, {
+    valid: [
+      test({
+        options: unusedExportsOptions,
+        code: 'export const foo = 1;\n',
+        filename: testFilePath('./no-unused-modules/hashbang-child.js'),
+      }),
+      test({
+        options: unusedExportsOptions,
+        code: `\uFEFF#!/usr/bin/env node\nimport {foo} from './hashbang-child.js';\n`,
+        filename: testFilePath('./no-unused-modules/hashbang-parent.js'),
+      }),
+    ],
+    invalid: [],
+  });
+});

utils/CHANGELOG.md

@@ -5,6 +5,9 @@ This change log adheres to standards from [Keep a CHANGELOG](https://keepachange
 
 ## Unreleased
 
+### Fixed
+- [Fix] Ignore hashbang and BOM while parsing ([#2431], thanks [@silverwind])
+
 ## v2.7.3 - 2022-01-26
 
 ### Fixed
@@ -115,6 +118,7 @@ Yanked due to critical issue with cache key resulting from #839.
 ### Fixed
 - `unambiguous.test()` regex is now properly in multiline mode
 
+[#2431]: https://github.com/import-js/eslint-plugin-import/pull/2431
 [#2350]: https://github.com/import-js/eslint-plugin-import/issues/2350
 [#2343]: https://github.com/import-js/eslint-plugin-import/pull/2343
 [#2261]: https://github.com/import-js/eslint-plugin-import/pull/2261

utils/parse.js

@@ -42,6 +42,14 @@ function makeParseReturn(ast, visitorKeys) {
   return ast;
 }
 
+function stripUnicodeBOM(text) {
+  return text.charCodeAt(0) === 0xFEFF ? text.slice(1) : text;
+}
+
+function transformHashbang(text) {
+  return text.replace(/^#!([^\r\n]+)/u, (_, captured) => `//${captured}`);
+}
+
 exports.default = function parse(path, content, context) {
 
   if (context == null) throw new Error('need context to parse properly');
@@ -78,6 +86,10 @@ exports.default = function parse(path, content, context) {
   // require the parser relative to the main module (i.e., ESLint)
   const parser = moduleRequire(parserPath);
 
+  // replicate bom strip and hashbang transform of ESLint
+  // https://github.com/eslint/eslint/blob/b93af98b3c417225a027cabc964c38e779adb945/lib/linter/linter.js#L779
+  content = transformHashbang(stripUnicodeBOM(String(content)));
+
   if (typeof parser.parseForESLint === 'function') {
     let ast;
     try {