[Fix] no-unused-modules: 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/prefix-child.js

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

tests/files/no-unused-modules/prefix-parent-bom.js

@@ -0,0 +1 @@
+import {foo} from './prefix-child.js';

tests/files/no-unused-modules/prefix-parent-bomhashbang.js

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

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

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

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

@@ -0,0 +1,2 @@
+#!/usr/bin/env node
+import {foo} from './prefix-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 +1302,70 @@ describe('support ES2022 Arbitrary module namespace identifier names', () => {
     ),
   });
 });
+
+describe('parser ignores prefixes like BOM and hashbang', () => {
+  // bom, hashbang
+  ruleTester.run('no-unused-modules', rule, {
+    valid: [
+      test({
+        options: unusedExportsOptions,
+        code: 'export const foo = 1;\n',
+        filename: testFilePath('./no-unused-modules/prefix-child.js'),
+      }),
+      test({
+        options: unusedExportsOptions,
+        code: `\uFEFF#!/usr/bin/env node\nimport {foo} from './prefix-child.js';\n`,
+        filename: testFilePath('./no-unused-modules/prefix-parent-bom.js'),
+      }),
+    ],
+    invalid: [],
+  });
+  // no bom, hashbang
+  ruleTester.run('no-unused-modules', rule, {
+    valid: [
+      test({
+        options: unusedExportsOptions,
+        code: 'export const foo = 1;\n',
+        filename: testFilePath('./no-unused-modules/prefix-child.js'),
+      }),
+      test({
+        options: unusedExportsOptions,
+        code: `#!/usr/bin/env node\nimport {foo} from './prefix-child.js';\n`,
+        filename: testFilePath('./no-unused-modules/prefix-parent-hashbang.js'),
+      }),
+    ],
+    invalid: [],
+  });
+  // bom, no hashbang
+  ruleTester.run('no-unused-modules', rule, {
+    valid: [
+      test({
+        options: unusedExportsOptions,
+        code: 'export const foo = 1;\n',
+        filename: testFilePath('./no-unused-modules/prefix-child.js'),
+      }),
+      test({
+        options: unusedExportsOptions,
+        code: `\uFEFF#!/usr/bin/env node\nimport {foo} from './prefix-child.js';\n`,
+        filename: testFilePath('./no-unused-modules/prefix-parent-bomhashbang.js'),
+      }),
+    ],
+    invalid: [],
+  });
+  // no bom, no hashbang
+  ruleTester.run('no-unused-modules', rule, {
+    valid: [
+      test({
+        options: unusedExportsOptions,
+        code: 'export const foo = 1;\n',
+        filename: testFilePath('./no-unused-modules/prefix-child.js'),
+      }),
+      test({
+        options: unusedExportsOptions,
+        code: `import {foo} from './prefix-child.js';\n`,
+        filename: testFilePath('./no-unused-modules/prefix-parent.js'),
+      }),
+    ],
+    invalid: [],
+  });
+});