1 files changed, 100 insertions, 0 deletions
diff --git a/haml_lint/linter/documentation_links.rb b/haml_lint/linter/documentation_links.rb
new file mode 100644
index 00000000000..f8e0eec5cdc
--- /dev/null
+++ b/haml_lint/linter/documentation_links.rb
@@ -0,0 +1,100 @@
+# frozen_string_literal: true
+
+require_relative '../../lib/gitlab/utils/markdown'
+
+module HamlLint
+  class Linter
+    # This class is responsible for detection of help_page_path helpers
+    # with incorrect links or anchors
+    class DocumentationLinks < Linter
+      include ::HamlLint::LinterRegistry
+      include ::Gitlab::Utils::Markdown
+
+      DOCS_DIRECTORY = File.join(File.expand_path('../..', __dir__), 'doc')
+
+      HELP_PATH_LINK_PATTERN = <<~PATTERN
+      `(send nil? :help_page_path $...)
+      PATTERN
+
+      MARKDOWN_HEADER = %r{\A\#{1,6}\s+(?<header>.+)\Z}.freeze
+
+      def visit_script(node)
+        check(node)
+      end
+
+      def visit_silent_script(node)
+        check(node)
+      end
+
+      def visit_tag(node)
+        check(node)
+      end
+
+      private
+
+      def check(node)
+        match = extract_link_and_anchor(node)
+
+        return if match.empty?
+
+        path_to_file = detect_path_to_file(match[:link])
+
+        unless File.file?(path_to_file)
+          record_lint(node, "help_page_path points to the unknown location: #{path_to_file}")
+          return
+        end
+
+        unless correct_anchor?(path_to_file, match[:anchor])
+          record_lint(node, "anchor (#{match[:anchor]}) is missing in: #{path_to_file}")
+        end
+      end
+
+      def extract_link_and_anchor(node)
+        ast_tree = fetch_ast_tree(node)
+
+        return {} unless ast_tree
+
+        link_match, attributes_match = ::RuboCop::NodePattern.new(HELP_PATH_LINK_PATTERN).match(ast_tree)
+
+        { link: fetch_link(link_match), anchor: fetch_anchor(attributes_match) }.compact
+      end
+
+      def fetch_ast_tree(node)
+        # Sometimes links are provided via data attributes in html tag
+        return node.parsed_attributes.syntax_tree if node.type == :tag
+
+        node.parsed_script.syntax_tree
+      end
+
+      def detect_path_to_file(link)
+        path = File.join(DOCS_DIRECTORY, link)
+        path += '.md' unless path.end_with?('.md')
+        path
+      end
+
+      def fetch_link(link_match)
+        return unless link_match && link_match.str_type?
+
+        link_match.value
+      end
+
+      def fetch_anchor(attributes_match)
+        return unless attributes_match
+
+        attributes_match.each_pair do |pkey, pvalue|
+          break pvalue.value if pkey.value == :anchor
+        end
+      end
+
+      def correct_anchor?(path_to_file, anchor)
+        return true unless anchor
+
+        File.open(path_to_file).any? do |line|
+          result = line.match(MARKDOWN_HEADER)
+
+          string_to_anchor(result[:header]) == anchor if result
+        end
+      end
+    end
+  end
+end