feat(eslint-plugin-mark): create no-consecutive-blank-line rule

eslint.config.mjs

@@ -40,6 +40,7 @@ export default defineConfig([
             'Fix',
             'Limitations',
             'When Not To Use It',
+            'Further Reading',
             'Prior Art',
           ],
         },

packages/eslint-plugin-mark/src/core/ast/index.js

@@ -1,4 +1,5 @@
 import getElementsByTagName from './html.js';
+import isBlankLine from './is-blank-line.js';
 import SkipRanges from './skip-ranges.js';
 
-export { getElementsByTagName, SkipRanges };
+export { getElementsByTagName, isBlankLine, SkipRanges };

packages/eslint-plugin-mark/src/core/ast/is-blank-line.js

@@ -0,0 +1,29 @@
+/**
+ * @fileoverview Check if a line is blank.
+ * @see https://spec.commonmark.org/0.31.2/#blank-line
+ */
+
+// --------------------------------------------------------------------------------
+// Helper
+// --------------------------------------------------------------------------------
+
+const whitespaceChars = new Set([' ', '\t']);
+
+// --------------------------------------------------------------------------------
+// Export
+// --------------------------------------------------------------------------------
+
+/**
+ * Check if a line is blank.
+ * @param {string} str Line string.
+ * @returns {boolean} `true` if the line is blank. `false` otherwise.
+ */
+export default function isBlankLine(str) {
+  for (let i = 0; i < str.length; i++) {
+    if (!whitespaceChars.has(str[i])) {
+      return false;
+    }
+  }
+
+  return true;
+}

packages/eslint-plugin-mark/src/core/ast/is-blank-line.test.js

@@ -0,0 +1 @@
+// TODO

packages/eslint-plugin-mark/src/rules/index.js

@@ -12,6 +12,7 @@ import consistentThematicBreakStyle from './consistent-thematic-break-style.js';
 import enCapitalization from './en-capitalization.js';
 import headingId from './heading-id.js';
 import noBoldParagraph from './no-bold-paragraph.js';
+import noConsecutiveBlankLine from './no-consecutive-blank-line.js';
 import noControlCharacter from './no-control-character.js';
 import noCurlyQuote from './no-curly-quote.js';
 import noDoubleSpace from './no-double-space.js';
@@ -35,6 +36,7 @@ export default {
   'en-capitalization': enCapitalization,
   'heading-id': headingId,
   'no-bold-paragraph': noBoldParagraph,
+  'no-consecutive-blank-line': noConsecutiveBlankLine,
   'no-control-character': noControlCharacter,
   'no-curly-quote': noCurlyQuote,
   'no-double-space': noDoubleSpace,

packages/eslint-plugin-mark/src/rules/no-consecutive-blank-line.js

@@ -0,0 +1,126 @@
+/**
+ * @fileoverview Rule to disallow consecutive blank lines.
+ * @author 루밀LuMir(lumirlumir)
+ */
+
+// --------------------------------------------------------------------------------
+// Import
+// --------------------------------------------------------------------------------
+
+import { isBlankLine } from '../core/ast/index.js';
+import { URL_RULE_DOCS } from '../core/constants.js';
+
+// --------------------------------------------------------------------------------
+// Typedef
+// --------------------------------------------------------------------------------
+
+/**
+ * @import { RuleModule } from '../core/types.js';
+ * @typedef {[{ max: number, skipCode: boolean }]} RuleOptions
+ * @typedef {'noConsecutiveBlankLine'} MessageIds
+ */
+
+// --------------------------------------------------------------------------------
+// Rule Definition
+// --------------------------------------------------------------------------------
+
+/** @type {RuleModule<RuleOptions, MessageIds>} */
+export default {
+  meta: {
+    type: 'layout',
+
+    docs: {
+      description: 'Disallow consecutive blank lines',
+      url: URL_RULE_DOCS('no-consecutive-blank-line'),
+      recommended: false,
+      stylistic: true,
+    },
+
+    fixable: 'whitespace',
+
+    schema: [
+      {
+        type: 'object',
+        properties: {
+          max: {
+            type: 'integer',
+            minimum: 0, // TODO: Think about proper minimum value
+          },
+          skipCode: {
+            type: 'boolean',
+          },
+        },
+        additionalProperties: false,
+      },
+    ],
+
+    defaultOptions: [
+      {
+        max: 1,
+        skipCode: true,
+      },
+    ],
+
+    messages: {
+      noConsecutiveBlankLine: 'Consecutive blank lines are not allowed.',
+    },
+
+    language: 'markdown',
+
+    dialects: ['commonmark', 'gfm'],
+  },
+
+  create(context) {
+    const {
+      sourceCode: { lines },
+    } = context;
+    const [{ max /* skipCode */ }] = context.options;
+
+    return {
+      'root:exit'() {
+        /** @type {number | null} */
+        let startIdx = null;
+
+        for (let currentIdx = 0; currentIdx < lines.length; currentIdx++) {
+          if (isBlankLine(lines[currentIdx])) {
+            if (startIdx === null) {
+              startIdx = currentIdx;
+            }
+          } else if (startIdx !== null) {
+            if (currentIdx - startIdx > max) {
+              context.report({
+                loc: {
+                  start: { line: startIdx + max + 1, column: 1 },
+                  end: {
+                    line: currentIdx + 1,
+                    column: 1,
+                  },
+                },
+                messageId: 'noConsecutiveBlankLine',
+              });
+            }
+
+            startIdx = null;
+          }
+        }
+
+        /*
+         * Handle the case where the file ends with blank lines.
+         * Now, `currentIdx` is equal to `lines.length`.
+         */
+        if (startIdx !== null && lines.length - startIdx > max) {
+          context.report({
+            loc: {
+              start: { line: startIdx + max + 1, column: 1 },
+              end: {
+                line: lines.length + 1,
+                column: 1,
+              },
+            },
+            messageId: 'noConsecutiveBlankLine',
+          });
+        }
+      },
+    };
+  },
+};

packages/eslint-plugin-mark/src/rules/no-consecutive-blank-line.test.js

@@ -0,0 +1,30 @@
+/**
+ * @fileoverview Test for `no-consecutive-blank-line.js`.
+ * @author 루밀LuMir(lumirlumir)
+ */
+
+// --------------------------------------------------------------------------------
+// Import
+// --------------------------------------------------------------------------------
+
+import { getFileName, ruleTester } from '../core/tests/index.js';
+import rule from './no-consecutive-blank-line.js';
+
+// --------------------------------------------------------------------------------
+// Test
+// --------------------------------------------------------------------------------
+
+ruleTester(getFileName(import.meta.url), rule, {
+  valid: [
+    {
+      name: 'Empty',
+      code: '',
+    },
+    {
+      name: 'Empty string',
+      code: '  ',
+    },
+  ],
+
+  invalid: [],
+});

website/docs/rules/no-consecutive-blank-line.md

@@ -0,0 +1,141 @@
+<!-- markdownlint-disable-next-line no-inline-html first-line-h1 -->
+<header v-html="$frontmatter.rule"></header>
+
+## Rule Details
+
+This rule enforces a single, consistent style for emphasis (italic text) in Markdown files. Consistent formatting makes it easier to understand a document, and mixing different emphasis styles can reduce readability.
+
+An emphasis is defined as text wrapped in either `*` (asterisks) or `_` (underscores). While Markdown allows any of these styles, this rule ensures that only one is used throughout the document.
+
+## Examples
+
+### :x: Incorrect {#incorrect}
+
+Examples of **incorrect** code for this rule:
+
+#### Default
+
+```md eslint-check
+<!-- eslint mark/consistent-emphasis-style: "error" -->
+
+*foo*
+_bar_
+*baz*
+**_foo_**
+__*bar*__
+_**foo**_
+*__bar__*
+___foo___
+***bar***
+```
+
+```md eslint-check
+<!-- eslint mark/consistent-emphasis-style: "error" -->
+
+_foo_
+*bar*
+_baz_
+__*foo*__
+**_bar_**
+*__foo__*
+_**bar**_
+***foo***
+___bar___
+```
+
+#### With `{ style: '*' }` Option
+
+```md eslint-check
+<!-- eslint mark/consistent-emphasis-style: ["error", { style: '*' }] -->
+
+_foo_
+**_bar_**
+_**baz**_
+___qux___
+```
+
+#### With `{ style: '_' }` Option
+
+```md eslint-check
+<!-- eslint mark/consistent-emphasis-style: ["error", { style: '_' }] -->
+
+*foo*
+__*bar*__
+*__baz__*
+***qux***
+```
+
+### :white_check_mark: Correct {#correct}
+
+Examples of **correct** code for this rule:
+
+#### Default
+
+```md eslint-check
+<!-- eslint mark/consistent-emphasis-style: "error" -->
+
+*foo*
+__*bar*__
+*__baz__*
+***qux***
+```
+
+```md eslint-check
+<!-- eslint mark/consistent-emphasis-style: "error" -->
+
+_foo_
+**_bar_**
+_**baz**_
+___qux___
+```
+
+#### With `{ style: '*' }` Option
+
+```md eslint-check
+<!-- eslint mark/consistent-emphasis-style: ["error", { style: '*' }] -->
+
+*foo*
+__*bar*__
+*__baz__*
+***qux***
+```
+
+#### With `{ style: '_' }` Option
+
+```md eslint-check
+<!-- eslint mark/consistent-emphasis-style: ["error", { style: '_' }] -->
+
+_foo_
+**_bar_**
+_**baz**_
+___qux___
+```
+
+## Options
+
+```js
+'mark/consistent-emphasis-style': ['error', {
+  style: 'consistent',
+}]
+```
+
+### `style`
+
+> Type: `'consistent' | '*' | '_'` / Default: `'consistent'`
+
+When `style` is set to `'consistent'`, the rule enforces that all emphasis in the document use the same style as the first one encountered.
+
+You can also specify a particular style by setting style to `'*'` or `'_'`, which will enforce that all emphasis use the specified style.
+
+## Fix
+
+This rule fixes the emphasis by replacing them with the configured style.
+
+## Further Reading
+
+- [CommonMark Spec: Blank Line](https://spec.commonmark.org/0.31.2/#blank-line)
+
+## Prior Art
+
+- [`MD012` - Multiple consecutive blank lines](https://github.com/DavidAnson/markdownlint/blob/main/doc/md012.md#md012---multiple-consecutive-blank-lines)
+- [`remark-lint-no-consecutive-blank-lines`](https://github.com/remarkjs/remark-lint/tree/main/packages/remark-lint-no-consecutive-blank-lines#remark-lint-no-consecutive-blank-lines)