Merge pull request #279 from issyl0/lint-erb-comment-syntax

lib/erb_lint/linters: Add a new CommentSyntax linter

README.md

@@ -94,6 +94,7 @@ linters:
 | ------------------------------------------------ |:--------:|-------------|
 | [AllowedScriptType](#AllowedScriptType)          | Yes      | prevents the addition of `<script>` tags that have `type` attributes that are not in a white-list of allowed values |
 | ClosingErbTagIndent                              | Yes      |             |
+| [CommentSyntax](#CommentSyntax)                  | Yes      | detects bad ERB comment syntax |
 | ExtraNewline                                     | Yes      |             |
 | [FinalNewline](#FinalNewline)                    | Yes      | warns about missing newline at the end of a ERB template |
 | [NoJavascriptTagHelper](#NoJavascriptTagHelper)  | Yes      | prevents the usage of Rails' `javascript_tag` |
@@ -487,6 +488,27 @@ Linter-Specific Option    | Description
 `allow_blank`             | True or false, depending on whether or not the `type` attribute may be omitted entirely from a `<script>` tag. Defaults to `true`.
 `disallow_inline_scripts` | Do not allow inline `<script>` tags anywhere in ERB templates. Defaults to `false`.
 
+## CommentSyntax
+
+This linter enforces the use of the correct ERB comment syntax, since Ruby comments (`<% # comment %>` with a space) are not technically valid ERB comments.
+
+```erb
+Bad ❌
+<% # This is a Ruby comment %>
+Good ✅
+<%# This is an ERB comment %>
+
+Bad ❌
+<% # This is a Ruby comment; it can fail to parse. %>
+Good ✅
+<%# This is an ERB comment; it is parsed correctly. %>
+
+Good ✅
+<%
+  # This is a multi-line ERB comment.
+%>
+```
+
 ## Custom Linters
 
 `erb-lint` allows you to create custom linters specific to your project. It will load linters from the `.erb-linters` directory in the root of your

lib/erb_lint/linters/comment_syntax.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+module ERBLint
+  module Linters
+    # Detects comment syntax that isn't valid ERB.
+    class CommentSyntax < Linter
+      include LinterRegistry
+
+      def initialize(file_loader, config)
+        super
+      end
+
+      def run(processed_source)
+        file_content = processed_source.file_content
+        return if file_content.empty?
+
+        processed_source.ast.descendants(:erb).each do |erb_node|
+          indicator_node, _, code_node, _ = *erb_node
+          next if code_node.nil?
+
+          indicator_node_str = indicator_node&.deconstruct&.last
+          next if indicator_node_str == "#"
+
+          code_node_str = code_node.deconstruct.last
+          next unless code_node_str.start_with?(" #")
+
+          range = find_range(erb_node, code_node_str)
+          source_range = processed_source.to_source_range(range)
+
+          correct_erb_tag = indicator_node_str == "=" ? "<%#=" : "<%#"
+
+          add_offense(
+            source_range,
+            <<~EOF.chomp
+              Bad ERB comment syntax. Should be #{correct_erb_tag} without a space between.
+              Leaving a space between ERB tags and the Ruby comment character can cause parser errors.
+            EOF
+          )
+        end
+      end
+
+      def find_range(node, str)
+        match = node.loc.source.match(Regexp.new(Regexp.quote(str.strip)))
+        return unless match
+
+        range_begin = match.begin(0) + node.loc.begin_pos
+        range_end   = match.end(0) + node.loc.begin_pos
+        (range_begin...range_end)
+      end
+    end
+  end
+end

lib/erb_lint/runner_config.rb

@@ -63,6 +63,7 @@ def default(default_enabled: nil)
             SpaceInHtmlTag: { enabled: default_enabled },
             TrailingWhitespace: { enabled: default_enabled },
             RequireInputAutocomplete: { enabled: default_enabled },
+            CommentSyntax: { enabled: default_enabled },
           },
         )
       end

spec/erb_lint/linters/comment_syntax_spec.rb

@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+describe ERBLint::Linters::CommentSyntax do
+  let(:linter_config) { described_class.config_schema.new }
+
+  let(:file_loader) { ERBLint::FileLoader.new(".") }
+  let(:linter) { described_class.new(file_loader, linter_config) }
+  let(:processed_source) { ERBLint::ProcessedSource.new("file.rb", file) }
+
+  subject { linter.offenses }
+  before { linter.run(processed_source) }
+
+  context "when the ERB comment syntax is correct" do
+    let(:file) { <<~FILE }
+      <%# good comment %>
+    FILE
+
+    it "does not report any offenses" do
+      expect(subject.size).to(eq(0))
+    end
+  end
+
+  context "when the ERB multi-line comment syntax is correct" do
+    let(:file) { <<~FILE }
+      <%
+        # good comment
+      %>
+    FILE
+
+    it "does not report any offenses" do
+      expect(subject.size).to(eq(0))
+    end
+  end
+
+  context "when the ERB comment syntax is incorrect" do
+    let(:file) { <<~FILE }
+      <% # bad comment %>
+    FILE
+
+    it "reports one offense" do
+      expect(subject.size).to(eq(1))
+    end
+
+    it "reports the suggested fix" do
+      expect(subject.first.message).to(include("Bad ERB comment syntax. Should be <%# without a space between."))
+    end
+  end
+
+  context "when the ERB comment syntax is incorrect multiple times in one file" do
+    let(:file) { <<~FILE }
+      <% # first bad comment %>
+      <%= # second bad comment %>
+    FILE
+
+    it "reports two offenses" do
+      expect(subject.size).to(eq(2))
+    end
+
+    it "reports the suggested fixes" do
+      expect(subject.first.message).to(include("Bad ERB comment syntax. Should be <%# without a space between."))
+      expect(subject.last.message).to(include("Bad ERB comment syntax. Should be <%#= without a space between."))
+    end
+  end
+end