Remove an unused disable directive together with its line

eslint core replaces an unused directive comment with a single space,
so --fix left a blank line wherever the comment sat on a line of its
own. A processor now widens that fix: the whole line when the comment
is alone on it, otherwise the comment and the space beside it. Fixes
with a rule id, and the removal of one rule name out of several, are
unchanged.

packages/dev/config/eslint.directives.js

@@ -0,0 +1,78 @@
+// Copyright 2017-2026 @pezkuwi/dev authors & contributors
+// SPDX-License-Identifier: Apache-2.0
+
+/** @type {Map<string, string>} */
+const sources = new Map();
+
+/**
+ * Widens the fix eslint core gives an unused disable directive.
+ *
+ * Core removes only the comment and puts a single space in its place
+ * (lib/linter/apply-disable-directives.js), so --fix turns
+ *
+ *   const a = 1;
+ *   // eslint-disable-next-line no-console
+ *   const b = 2;
+ *
+ * into a whitespace-only line between the two statements, which the layout
+ * rules then leave behind as a blank line. Measured on the consumers after the
+ * eslint 10 move: 23 such lines in api alone, each removed by hand.
+ *
+ * Only a fix that removes a whole directive comment is changed: alone on its
+ * line, the line goes; after code, the space before it goes; before code, the
+ * space after it goes. Removing one rule name out of several is left as core
+ * makes it, as is every message with a rule id.
+ *
+ * @param {import('eslint').Linter.LintMessage} message
+ * @param {string} text the source the message was produced from
+ * @returns {import('eslint').Linter.LintMessage}
+ */
+function widenDirectiveFix (message, text) {
+  if (message.ruleId !== null || message.fix?.text.trim() !== '') {
+    return message;
+  }
+
+  let [start, end] = message.fix.range;
+
+  if (!/^\/[/*]/.test(text.slice(start, end))) {
+    return message;
+  }
+
+  const lineStart = text.lastIndexOf('\n', start - 1) + 1;
+  const newline = text.indexOf('\n', end);
+  const lineEnd = newline === -1 ? text.length : newline;
+  const aloneBefore = text.slice(lineStart, start).trim() === '';
+  const aloneAfter = text.slice(end, lineEnd).trim() === '';
+
+  if (aloneBefore && aloneAfter) {
+    return { ...message, fix: { range: [lineStart, newline === -1 ? text.length : newline + 1], text: '' } };
+  } else if (aloneBefore) {
+    while (end < lineEnd && /[ \t]/.test(text[end] ?? '')) {
+      end++;
+    }
+  } else {
+    while (start > lineStart && /[ \t]/.test(text[start - 1] ?? '')) {
+      start--;
+    }
+  }
+
+  return { ...message, fix: { range: [start, end], text: '' } };
+}
+
+/** @type {import('eslint').Linter.Processor} */
+export const directiveLines = {
+  meta: { name: '@pezkuwi/dev/directive-lines' },
+  postprocess (lists, filename) {
+    const text = sources.get(filename) ?? '';
+
+    sources.delete(filename);
+
+    return lists.flat().map((m) => widenDirectiveFix(m, text));
+  },
+  preprocess (text, filename) {
+    sources.set(filename, text);
+
+    return [text];
+  },
+  supportsAutofix: true
+};

packages/dev/config/eslint.js

@@ -22,6 +22,7 @@ import simpleImportSortPlugin from 'eslint-plugin-simple-import-sort';
 import sortDestructureKeysPlugin from 'eslint-plugin-sort-destructure-keys';
 import globals from 'globals';
 
+import { directiveLines } from './eslint.directives.js';
 import { overrideAll, overrideJs, overrideJsx, overrideSpec } from './eslint.rules.js';
 import { standardRules } from './eslint.standard.js';
 import { withoutContextualAssertions } from './eslint.typeAssertion.js';
@@ -127,6 +128,8 @@ export default [
   },
   {
     files: extsToGlobs(EXT_ALL),
+    // see eslint.directives.js
+    processor: directiveLines,
     rules: {
       ...eslintJs.configs.recommended.rules,
       ...standardRules,

packages/dev/src/directives.spec.ts

@@ -0,0 +1,95 @@
+// Copyright 2017-2026 @pezkuwi/dev authors & contributors
+// SPDX-License-Identifier: Apache-2.0
+
+/// <reference types="@pezkuwi/dev-test/globals.d.ts" />
+
+import type { Linter } from 'eslint';
+
+import { ESLint } from 'eslint';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+
+// Loaded by path: the config directory is plain JavaScript outside this
+// package's TypeScript root.
+const PROCESSOR = path.join(process.cwd(), 'packages/dev/config/eslint.directives.js');
+
+const SOURCE = `const a = 1;
+// eslint-disable-next-line no-console
+const b = 2;
+
+function f () {
+  // eslint-disable-next-line no-console
+  return a + b;
+}
+
+f(); // eslint-disable-line no-console
+/* eslint-disable-next-line no-console */ export const c = 3;
+// eslint-disable-next-line no-alert, no-console
+console.log(c);
+`;
+
+const FIXED = `const a = 1;
+const b = 2;
+
+function f () {
+  return a + b;
+}
+
+f();
+export const c = 3;
+// eslint-disable-next-line no-console
+console.log(c);
+`;
+
+async function fix (processor?: Linter.Processor): Promise<string> {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'directives-'));
+
+  try {
+    fs.writeFileSync(path.join(dir, 'sample.js'), SOURCE);
+
+    const eslint = new ESLint({
+      cwd: dir,
+      fix: true,
+      overrideConfig: [{
+        files: ['**/*.js'],
+        linterOptions: { reportUnusedDisableDirectives: 'error' },
+        ...(processor ? { processor } : {}),
+        rules: { 'no-alert': 'error', 'no-console': 'error' }
+      }],
+      overrideConfigFile: true
+    });
+    const [result] = await eslint.lintFiles(['sample.js']);
+
+    return result.output ?? SOURCE;
+  } finally {
+    fs.rmSync(dir, { force: true, recursive: true });
+  }
+}
+
+describe('directiveLines', (): void => {
+  it('removes an unused directive with its line or the space around it', async (): Promise<void> => {
+    const { directiveLines } = await import(PROCESSOR) as { directiveLines: Linter.Processor };
+
+    expect(await fix(directiveLines)).toEqual(FIXED);
+  });
+
+  it('is needed: core leaves a space where each comment was', async (): Promise<void> => {
+    expect((await fix()).split('\n')).toEqual([
+      'const a = 1;',
+      ' ',
+      'const b = 2;',
+      '',
+      'function f () {',
+      '   ',
+      '  return a + b;',
+      '}',
+      '',
+      'f();  ',
+      '  export const c = 3;',
+      '// eslint-disable-next-line no-console',
+      'console.log(c);',
+      ''
+    ]);
+  });
+});