Linter: Implement erb-no-extra-whitespace-inside-tags linter rule

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

@@ -8,6 +8,7 @@ This page contains documentation for all Herb Linter rules.
 - [`erb-no-case-node-children`](./erb-no-case-node-children.md) - Don't use `children` for `case/when` and `case/in` nodes
 - [`erb-no-empty-tags`](./erb-no-empty-tags.md) - Disallow empty ERB tags
 - [`erb-no-extra-newline`](./erb-no-extra-newline.md) - Disallow extra newlines.
+- [`erb-no-extra-whitespace-inside-tags`](./erb-no-extra-whitespace-inside-tags.md) - Disallow multiple consecutive spaces inside ERB tags
 - [`erb-no-output-control-flow`](./erb-no-output-control-flow.md) - Prevents outputting control flow blocks
 - [`erb-no-silent-tag-in-attribute-name`](./erb-no-silent-tag-in-attribute-name.md) - Disallow ERB silent tags in HTML attribute names
 - [`erb-prefer-image-tag-helper`](./erb-prefer-image-tag-helper.md) - Prefer `image_tag` helper over `<img>` with ERB expressions

javascript/packages/linter/docs/rules/erb-no-extra-whitespace-inside-tags.md

@@ -0,0 +1,39 @@
+# Linter Rule: Avoid extra whitespace inside ERB tags
+
+**Rule:** `erb-no-extra-whitespace-inside-tags`
+
+## Description
+
+This rule disallows **multiple consecutive spaces** immediately inside ERB tags (`<%`, `<%=`) or before the closing delimiter (`%>`). It ensures that ERB code is consistently and cleanly formatted, with exactly one space after the opening tag and one space before the closing tag (when appropriate).
+
+## Rationale
+
+Excess whitespace inside ERB tags can lead to inconsistent formatting and untidy templates. By enforcing a consistent amount of whitespace inside ERB tags, this rule improves code readability, aligns with the formatter and style guide expectations, and avoids unnecessary visual noise.
+
+## Examples
+
+### ✅ Good
+
+```erb
+<%= output %>
+
+<% if condition %>
+  True
+<% end %>
+```
+
+### 🚫 Bad
+
+```erb
+<%=  output %>
+
+<%= output  %>
+
+<%  if condition  %>
+  True
+<% end %>
+```
+
+## References
+
+\-

javascript/packages/linter/src/rules.ts

@@ -4,6 +4,7 @@ import { ERBCommentSyntax } from "./rules/erb-comment-syntax.js";
 import { ERBNoCaseNodeChildrenRule } from "./rules/erb-no-case-node-children.js"
 import { ERBNoEmptyTagsRule } from "./rules/erb-no-empty-tags.js"
 import { ERBNoExtraNewLineRule } from "./rules/erb-no-extra-newline.js"
+import { ERBNoExtraWhitespaceRule } from "./rules/erb-no-extra-whitespace-inside-tags.js"
 import { ERBNoOutputControlFlowRule } from "./rules/erb-no-output-control-flow.js"
 import { ERBNoSilentTagInAttributeNameRule } from "./rules/erb-no-silent-tag-in-attribute-name.js"
 import { ERBPreferImageTagHelperRule } from "./rules/erb-prefer-image-tag-helper.js"
@@ -59,6 +60,7 @@ export const rules: RuleClass[] = [
   ERBNoCaseNodeChildrenRule,
   ERBNoEmptyTagsRule,
   ERBNoExtraNewLineRule,
+  ERBNoExtraWhitespaceRule,
   ERBNoOutputControlFlowRule,
   ERBNoSilentTagInAttributeNameRule,
   ERBPreferImageTagHelperRule,

javascript/packages/linter/src/rules/erb-no-extra-whitespace-inside-tags.ts

@@ -0,0 +1,147 @@
+import { ParserRule, BaseAutofixContext, Mutable } from "../types.js"
+import { BaseRuleVisitor } from "./rule-utils.js"
+
+import type { ParseResult, Token, ERBNode } from "@herb-tools/core"
+import { Location } from "@herb-tools/core"
+import type { UnboundLintOffense, LintOffense, LintContext, FullRuleConfig } from "../types.js"
+
+interface ERBNoExtraWhitespaceAutofixContext extends BaseAutofixContext {
+  node: Mutable<ERBNode>
+  openTag: Token
+  closeTag: Token
+  content: string
+  fixType: "after-open" | "before-close" | "after-comment-equals"
+}
+
+class ERBNoExtraWhitespaceInsideTagsVisitor extends BaseRuleVisitor<ERBNoExtraWhitespaceAutofixContext> {
+
+  visitERBNode(node: ERBNode): void {
+    const openTag = node.tag_opening
+    const closeTag = node.tag_closing
+    const { value } = node.content ?? {}
+
+    if (!openTag || !closeTag || !value) return
+
+    if (this.hasExtraLeadingWhitespace(value)) {
+      this.reportWhitespace(node, openTag, closeTag, value, "start", 0, `Remove extra whitespace after \`${openTag.value}\`.`, "after-open")
+    }
+
+    if (openTag.value === "<%#" && value.startsWith("=") && value.length > 1) {
+      const afterEquals = value.substring(1)
+
+      if (afterEquals.match(/^\s{2,}/) && !afterEquals.startsWith("  \n") && !afterEquals.startsWith("\n")) {
+        this.reportWhitespace(node, openTag, closeTag, value, "start", 1, `Remove extra whitespace after \`<%#=\`.`, "after-comment-equals")
+      }
+    }
+
+    if (this.hasExtraTrailingWhitespace(value)) {
+      this.reportWhitespace(node, openTag, closeTag, value, "end", 0, `Remove extra whitespace before \`${closeTag.value}\`.`, "before-close")
+    }
+  }
+
+  private hasExtraLeadingWhitespace(content: string): boolean {
+    return content.startsWith("  ") && !content.startsWith("  \n")
+  }
+
+  private hasExtraTrailingWhitespace(content: string): boolean {
+    return !content.includes("\n") && /\s{2,}$/.test(content)
+  }
+
+  private getWhitespaceLocation(node: ERBNode, content: string, position: "start" | "end", offset: number = 0): Location {
+    const contentLocation = node.content!.location
+
+    if (position === "start") {
+      const match = content.substring(offset).match(/^\s+/)
+      const length = match ? match[0].length : 0
+      const startColumn = contentLocation.start.column + offset
+
+      return Location.from(
+        contentLocation.start.line,
+        startColumn,
+        contentLocation.start.line,
+        startColumn + length
+      )
+    } else {
+      const match = content.match(/\s+$/)
+      const length = match ? match[0].length : 0
+
+      return Location.from(
+        contentLocation.end.line,
+        contentLocation.end.column - length,
+        contentLocation.end.line,
+        contentLocation.end.column
+      )
+    }
+  }
+
+  private reportWhitespace(
+    node: ERBNode,
+    openTag: Token,
+    closeTag: Token,
+    content: string,
+    position: "start" | "end",
+    offset: number,
+    message: string,
+    fixType: "after-open" | "before-close" | "after-comment-equals"
+  ): void {
+    const location = this.getWhitespaceLocation(node, content, position, offset)
+    this.addOffense(message, location, {
+      node,
+      openTag,
+      closeTag,
+      content,
+      fixType
+    })
+  }
+}
+
+export class ERBNoExtraWhitespaceRule extends ParserRule<ERBNoExtraWhitespaceAutofixContext> {
+  static autocorrectable = true
+  name = "erb-no-extra-whitespace-inside-tags"
+
+  get defaultConfig(): FullRuleConfig {
+    return {
+      enabled: true,
+      severity: "error"
+    }
+  }
+
+  check(result: ParseResult, context?: Partial<LintContext>): UnboundLintOffense<ERBNoExtraWhitespaceAutofixContext>[] {
+    const visitor = new ERBNoExtraWhitespaceInsideTagsVisitor(this.name, context)
+
+    visitor.visit(result.value)
+
+    return visitor.offenses
+  }
+
+  autofix(offense: LintOffense<ERBNoExtraWhitespaceAutofixContext>, result: ParseResult, _context?: Partial<LintContext>): ParseResult | null {
+    if (!offense.autofixContext) return null
+
+    const { node, fixType } = offense.autofixContext
+    if (!node.content) return null
+
+    const content = node.content.value
+
+    switch (fixType) {
+      case "before-close":
+        node.content.value = content.replace(/\s{2,}$/, " ")
+        break
+
+      case "after-open":
+        node.content.value = content.replace(/^\s{2,}/, " ")
+        break
+
+      case "after-comment-equals":
+        if (content.startsWith("=")) {
+          const afterEquals = content.substring(1)
+          node.content.value = "= " + afterEquals.replace(/^\s{2,}/, "")
+        }
+
+        break
+      default:
+        return null
+    }
+
+    return result
+  }
+}

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

@@ -5,10 +5,12 @@ export * from "./erb-comment-syntax.js"
 export * from "./erb-no-case-node-children.js"
 export * from "./erb-no-empty-tags.js"
 export * from "./erb-no-extra-newline.js"
+export * from "./erb-no-extra-whitespace-inside-tags.js"
 export * from "./erb-no-output-control-flow.js"
 export * from "./erb-no-silent-tag-in-attribute-name.js"
 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 "./herb-disable-comment-valid-rule-name.js"