feat: added new rule table-column-count

README.md

@@ -85,6 +85,7 @@ export default defineConfig([
 | [`no-missing-atx-heading-space`](./docs/rules/no-missing-atx-heading-space.md) | Disallow headings without a space after the hash characters | yes |
 | [`no-missing-label-refs`](./docs/rules/no-missing-label-refs.md) | Disallow missing label references | yes |
 | [`require-alt-text`](./docs/rules/require-alt-text.md) | Require alternative text for images | yes |
+| [`table-column-count`](./docs/rules/table-column-count.md) | Disallow data rows in a GitHub Flavored Markdown table from having more cells than the header row | yes |
 <!-- Rule Table End -->
 
 **Note:** This plugin does not provide formatting rules. We recommend using a source code formatter such as [Prettier](https://prettier.io) for that purpose.

docs/rules/table-column-count.md

@@ -0,0 +1,65 @@
+# table-column-count
+
+Disallow data rows in a GitHub Flavored Markdown table from having more cells than the header row.
+
+## Background
+
+In GitHub Flavored Markdown [tables](https://github.github.com/gfm/#tables-extension-), rows should maintain a consistent number of cells. While variations are sometimes tolerated, data rows having *more* cells than the header can lead to lost data or rendering issues. This rule focuses on preventing data rows from exceeding the header's column count.
+
+## Rule Details
+
+> [!IMPORTANT] <!-- eslint-disable-line -- This should be fixed in https://github.com/eslint/markdown/issues/294 -->
+>
+> This rule relies on the `table` AST node, typically available when using a GFM-compatible parser (e.g., `language: "markdown/gfm"`).
+
+This rule is triggered if a data row in a GFM table contains more cells than the header row. It does not flag rows with fewer cells than the header.
+
+Examples of **incorrect** code for this rule (i.e., will be flagged):
+
+```markdown
+<!-- eslint markdown/table-column-count: "error" -->
+
+| Head1 | Head2 |
+| ----- | ----- |
+| R1C1  | R1C2  | R2C3  | <!-- This data row has 3 cells, header has 2 -->
+
+| A |
+| - |
+| 1 | 2 | <!-- This data row has 2 cells, header has 1 -->
+```
+
+Examples of **correct** code for this rule (i.e., will NOT be flagged):
+
+```markdown
+<!-- eslint markdown/table-column-count: "error" -->
+
+<!-- Standard correct table -->
+| Header | Header |
+| ------ | ------ |
+| Cell   | Cell   |
+| Cell   | Cell   |
+
+<!-- Data row with fewer cells than header (VALID for this rule) -->
+| Header | Header | Header |
+| ------ | ------ | ------ |
+| Cell   | Cell   |        |
+
+<!-- Table with some empty cells (VALID for this rule) -->
+| Col A | Col B | Col C |
+| ----- | ----- | ----- |
+| 1     |       | 3     |
+| 4     | 5     |       |
+
+<!-- Single column table -->
+| Single Header |
+| ------------- |
+| Single Cell   |
+```
+
+## When Not To Use It
+
+If you are intentionally creating Markdown tables where data rows are expected to contain more cells than the header, and you have a specific (perhaps non-standard) processing or rendering pipeline that handles this scenario correctly, you might choose to disable this rule. However, for typical GFM rendering and data consistency, adhering to this rule is recommended.
+
+## Prior Art
+
+* [table-column-count](https://github.com/DavidAnson/markdownlint/blob/main/doc/Rules.md#md056---table-column-count)

src/rules/table-column-count.js

@@ -0,0 +1,68 @@
+/**
+ * @fileoverview Rule to ensure GitHub Flavored Markdown tables have a consistent number of cells in each row.
+ * @author Sweta Tanwar (@SwetaTanwar)
+ */
+
+//-----------------------------------------------------------------------------
+// Type Definitions
+//-----------------------------------------------------------------------------
+
+/**
+ * @typedef {import("../types.ts").MarkdownRuleDefinition<{ RuleOptions: []; }>} TableColumnCountRuleDefinition
+ */
+
+//-----------------------------------------------------------------------------
+// Rule Definition
+//-----------------------------------------------------------------------------
+
+/** @type {TableColumnCountRuleDefinition} */
+export default {
+	meta: {
+		type: "problem",
+
+		docs: {
+			recommended: true,
+			description:
+				"Disallow data rows in a GitHub Flavored Markdown table from having more cells than the header row",
+			url: "https://github.com/eslint/markdown/blob/main/docs/rules/table-column-count.md",
+		},
+
+		fixable: null,
+		schema: [],
+
+		messages: {
+			inconsistentColumnCount:
+				"Data row {{dataRowIndex}} (1-indexed) has {{actualCells}} cells, but header has {{expectedCells}} cells (should not exceed header count).",
+		},
+	},
+
+	create(context) {
+		return {
+			table(node) {
+				if (!node.children || node.children.length < 1) {
+					return;
+				}
+
+				const headerRow = node.children[0];
+				const expectedCells = headerRow.children.length;
+
+				for (let i = 1; i < node.children.length; i++) {
+					const currentRow = node.children[i];
+					const actualCells = currentRow.children.length;
+
+					if (actualCells > expectedCells) {
+						context.report({
+							node: currentRow,
+							messageId: "inconsistentColumnCount",
+							data: {
+								dataRowIndex: String(i),
+								actualCells: String(actualCells),
+								expectedCells: String(expectedCells),
+							},
+						});
+					}
+				}
+			},
+		};
+	},
+};

tests/rules/table-column-count.test.js

@@ -0,0 +1,142 @@
+/**
+ * @fileoverview Tests for table-column-count rule.
+ * @author Sweta Tanwar (@SwetaTanwar)
+ */
+
+//------------------------------------------------------------------------------
+// Imports
+//------------------------------------------------------------------------------
+
+import rule from "../../src/rules/table-column-count.js";
+import markdown from "../../src/index.js";
+import { RuleTester } from "eslint";
+import dedent from "dedent";
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+const ruleTester = new RuleTester({
+	plugins: {
+		markdown,
+	},
+	language: "markdown/gfm",
+});
+
+ruleTester.run("table-column-count", rule, {
+	valid: [
+		dedent`
+            | Header | Header |
+            | ------ | ------ |
+            | Cell   | Cell   |
+            | Cell   | Cell   |
+        `,
+		dedent`
+            | Header | Header | Header |
+            | ------ | ------ | ------ |
+            | Cell   | Cell   |
+            | Cell   |        |
+        `,
+		dedent`
+            | A | B |
+            |---|---|
+            |   |   |
+            | C |   |
+        `,
+		`Just some text. | not a table |`,
+		dedent`
+            | Header | Header |
+            | ------ | ------ | ----- |
+            | Cell   | Cell   |
+        `,
+		dedent`
+            | Header | Header |
+            | ------ | ------ |
+        `,
+		dedent`
+            Some text before.
+
+            | H1 | H2 |
+            |----|----|
+            | D1 | D2 |
+
+            Some text after.
+        `,
+		dedent`
+            | Valid | Table |
+            | ----- | ----- |
+            | Row   | Here  |
+        `,
+	],
+
+	invalid: [
+		{
+			code: dedent`
+                | Head1 | Head2 |
+                | ----- | ----- |
+                | R1C1  | R1C2  | R2C3  |
+            `,
+			errors: [
+				{
+					messageId: "inconsistentColumnCount",
+					data: {
+						dataRowIndex: "1",
+						actualCells: "3",
+						expectedCells: "2",
+					},
+					line: 3,
+					column: 1,
+					endLine: 3,
+					endColumn: 26,
+				},
+			],
+		},
+		{
+			code: dedent`
+                | A |
+                | - |
+                | 1 | 2 |
+            `,
+			errors: [
+				{
+					messageId: "inconsistentColumnCount",
+					data: {
+						dataRowIndex: "1",
+						actualCells: "2",
+						expectedCells: "1",
+					},
+					line: 3,
+					column: 1,
+					endLine: 3,
+					endColumn: 10,
+				},
+			],
+		},
+		{
+			code: dedent`
+                Some introductory text.
+
+                | Header1 | Header2 |
+                | ------- | ------- |
+                | Data1   | Data2   | Data3 |
+                | D4      | D5      |
+
+                Some concluding text.
+            `,
+			errors: [
+				{
+					messageId: "inconsistentColumnCount",
+					data: {
+						dataRowIndex: "1",
+						actualCells: "3",
+						expectedCells: "2",
+					},
+					line: 5,
+					column: 1,
+					endLine: 5,
+					endColumn: 30,
+				},
+			],
+		},
+	],
+});