Set AsciiDoc docname attribute using the requested path

changelogs/unreleased/asciidoc-attr.yml

+---
+title: Support Asciidoc docname attribute
+merge_request: 22313
+author: Jouke Witteveen
+type: added

doc/user/asciidoc.md

@@ -91,6 +91,8 @@ stem:[sqrt(4) = 2]
 
 ### Attributes
 
+**User-defined attributes**
+
 ```asciidoc
 // define attributes in the document header
 :name: value
@@ -104,6 +106,15 @@ C{pp} is not required, only Ruby.
 Use a leading backslash to output a word enclosed in curly braces, like \{name}.
 ```
 
+**Environment attributes**
+
+GitLab sets the following environment attributes:
+
+| Attribute       | Description                                                                                                            |
+| :-------------- | :--------------------------------------------------------------------------------------------------------------------- |
+| `docname`       | Root name of the source document (no leading path or file extension).                                                  |
+| `outfilesuffix` | File extension corresponding to the backend output (defaults to `.adoc` to make inter-document cross references work). |
+
 ### Links
 
 ```asciidoc

lib/gitlab/asciidoc.rb

@@ -25,6 +25,19 @@ module Gitlab
         'max-include-depth' => MAX_INCLUDE_DEPTH
     }.freeze
 
+    def self.path_attrs(path)
+      return {} unless path
+
+      {
+        # Set an empty docname if the path is a directory
+        'docname' => if path[-1] == ::File::SEPARATOR
+                       ''
+                     else
+                       ::File.basename(path, '.*')
+                     end
+      }
+    end
+
     # Public: Converts the provided Asciidoc markup into HTML.
     #
     # input         - the source text in Asciidoc format
@@ -35,9 +48,10 @@ module Gitlab
         include_processor ::Gitlab::Asciidoc::IncludeProcessor.new(context)
       end
 
+      extra_attrs = path_attrs(context[:requested_path])
       asciidoc_opts = { safe: :secure,
                         backend: :gitlab_html5,
-                        attributes: DEFAULT_ADOC_ATTRS,
+                        attributes: DEFAULT_ADOC_ATTRS.merge(extra_attrs),
                         extensions: extensions }
 
       context[:pipeline] = :ascii_doc

spec/lib/gitlab/asciidoc_spec.rb

@@ -46,6 +46,27 @@ module Gitlab
         end
       end
 
+      context "with requested path" do
+        input = <<~ADOC
+          Document name: {docname}.
+        ADOC
+
+        it "ignores {docname} when not available" do
+          expect(render(input, {})).to include(input.strip)
+        end
+
+        [
+          ['/',                   '',       'root'],
+          ['README',              'README', 'just a filename'],
+          ['doc/api/',            '',       'a directory'],
+          ['doc/api/README.adoc', 'README', 'a complete path']
+        ].each do |path, basename, desc|
+          it "sets {docname} for #{desc}" do
+            expect(render(input, { requested_path: path })).to include(": #{basename}.")
+          end
+        end
+      end
+
       context "XSS" do
         items = {
           'link with extra attribute' => {