Linter: Implement erb-space-indentation rule

Author: markokajzer

javascript/packages/linter/docs/rules/README.md

@@ -34,6 +34,7 @@ This page contains documentation for all Herb Linter rules.
 - [`erb-require-trailing-newline`](./erb-require-trailing-newline.md) - Enforces that all HTML+ERB template files end with exactly one trailing newline character.
 - [`erb-require-whitespace-inside-tags`](./erb-require-whitespace-inside-tags.md) - Requires whitespace around ERB tags
 - [`erb-right-trim`](./erb-right-trim.md) - Enforce consistent right-trimming syntax.
+- [`erb-space-indentation`](./erb-space-indentation.md) - Indent with spaces instead of tabs.
 - [`erb-strict-locals-comment-syntax`](./erb-strict-locals-comment-syntax.md) - Enforce strict locals comment syntax.
 - [`herb-disable-comment-malformed`](./herb-disable-comment-malformed.md) - Detect malformed `herb:disable` comments.
 - [`herb-disable-comment-missing-rules`](./herb-disable-comment-missing-rules.md) - Require rule names in `herb:disable` comments.

javascript/packages/linter/docs/rules/erb-space-indentation.md

@@ -0,0 +1,29 @@
+# Linter Rule: Space Indentation
+
+**Rule:** `erb-space-indentation`
+
+## Description
+
+Detects indentation with tabs. Consistent use of spaces for indentation improves readability and avoids alignment issues across editors and tools.
+
+## Examples
+
+### ✅ Good
+
+```erb
+<div>
+  <p>Hello</p>
+</div>
+```
+
+### ❌ Bad
+
+```erb
+<div>
+	<p>Hello</p>
+</div>
+```
+
+## References
+
+- [Shopify/erb_lint - `SpaceIndentation`](https://github.com/Shopify/erb_lint/blob/main/lib/erb_lint/linters/space_indentation.rb)

javascript/packages/linter/src/rules.ts

@@ -32,6 +32,7 @@ import { ERBPreferImageTagHelperRule } from "./rules/erb-prefer-image-tag-helper
 import { ERBRequireTrailingNewlineRule } from "./rules/erb-require-trailing-newline.js"
 import { ERBRequireWhitespaceRule } from "./rules/erb-require-whitespace-inside-tags.js"
 import { ERBRightTrimRule } from "./rules/erb-right-trim.js"
+import { ERBSpaceIndentationRule } from "./rules/erb-space-indentation.js"
 import { ERBStrictLocalsCommentSyntaxRule } from "./rules/erb-strict-locals-comment-syntax.js"
 import { ERBStrictLocalsRequiredRule } from "./rules/erb-strict-locals-required.js"
 
@@ -117,6 +118,7 @@ export const rules: RuleClass[] = [
   ERBNoUnsafeScriptInterpolationRule,
   ERBPreferImageTagHelperRule,
   ERBRequireTrailingNewlineRule,
+  ERBSpaceIndentationRule,
   ERBRequireWhitespaceRule,
   ERBRightTrimRule,
   ERBStrictLocalsCommentSyntaxRule,

javascript/packages/linter/src/rules/erb-space-indentation.ts

@@ -0,0 +1,50 @@
+import { Location } from "@herb-tools/core"
+
+import { BaseSourceRuleVisitor, positionFromOffset } from "./rule-utils.js"
+import { SourceRule } from "../types.js"
+import type { UnboundLintOffense, LintContext, FullRuleConfig } from "../types.js"
+
+const START_BLANKS = /^[^\S\n]*\t[^\S\n]*/
+
+class ERBSpaceIndentationVisitor extends BaseSourceRuleVisitor {
+  protected visitSource(source: string): void {
+    const lines = source.split("\n")
+    let offset = 0
+
+    lines.forEach((line) => {
+      const match = line.match(START_BLANKS)
+
+      if (match) {
+        const start = positionFromOffset(source, offset)
+        const end = positionFromOffset(source, offset + match[0].length)
+        const location = new Location(start, end)
+
+        this.addOffense(
+          "Indent with spaces instead of tabs.",
+          location,
+        )
+      }
+
+      offset += line.length + 1
+    })
+  }
+}
+
+export class ERBSpaceIndentationRule extends SourceRule {
+  static ruleName = "erb-space-indentation"
+
+  get defaultConfig(): FullRuleConfig {
+    return {
+      enabled: true,
+      severity: "error"
+    }
+  }
+
+  check(source: string, context?: Partial<LintContext>): UnboundLintOffense[] {
+    const visitor = new ERBSpaceIndentationVisitor(this.ruleName, context)
+
+    visitor.visit(source)
+
+    return visitor.offenses
+  }
+}

javascript/packages/linter/src/rules/index.ts

@@ -33,6 +33,7 @@ export * from "./erb-prefer-image-tag-helper.js"
 export * from "./erb-require-trailing-newline.js"
 export * from "./erb-require-whitespace-inside-tags.js"
 export * from "./erb-right-trim.js"
+export * from "./erb-space-indentation.js"
 export * from "./erb-strict-locals-comment-syntax.js"
 export * from "./erb-strict-locals-required.js"
 

javascript/packages/linter/test/__snapshots__/cli.test.ts.snap

@@ -0,0 +1,46 @@
+import { describe, test } from "vitest"
+
+import { ERBSpaceIndentationRule } from "../../src/rules/erb-space-indentation.js"
+import { createLinterTest } from "../helpers/linter-test-helper.js"
+
+const { expectNoOffenses, expectError, assertOffenses } = createLinterTest(ERBSpaceIndentationRule)
+
+describe("ERBSpaceIndentationRule", () => {
+  test("no indentation present", () => {
+    expectNoOffenses("this is a line")
+  })
+
+  test("space indentation present", () => {
+    expectNoOffenses("   this is a line\n   another line\n")
+  })
+
+  test("tab indentation", () => {
+    expectError("Indent with spaces instead of tabs.", [1])
+    expectError("Indent with spaces instead of tabs.", [2])
+    assertOffenses("\t\tthis is a line\n\t\tanother line\n")
+  })
+
+  test("tab and spaces indentation", () => {
+    expectError("Indent with spaces instead of tabs.", [1])
+    expectError("Indent with spaces instead of tabs.", [2])
+    assertOffenses("  \t    this is a line\n  \t  another line\n")
+  })
+
+  test("mixed content with tabs", () => {
+    expectError("Indent with spaces instead of tabs.", [2])
+    assertOffenses("<div>\n\t<p>hello</p>\n</div>\n")
+  })
+
+  test("tabs only at start of line", () => {
+    expectNoOffenses("hello\tworld\n")
+  })
+
+  test("empty lines are fine", () => {
+    expectNoOffenses("\n\n\n")
+  })
+
+  test("ERB content with tab indentation", () => {
+    expectError("Indent with spaces instead of tabs.", [2])
+    assertOffenses("<div>\n\t<%= hello %>\n</div>\n")
+  })
+})