Merge branch '18019-fix-wiki-linking' into 'master'

Fix wiki linking behavior for markdown wiki pages

Related to #18019 

- As per the documentation in !4372 

## TODO
- [ ] !4432 Have wiki linking behave as per the documentation
    - [x] Move `WikiLinkFilter` specs to the pipeline level
    - [x] Verify current behavior on wiki `show` page
    - [x] Fix current behavior on wiki `show` page
    - [x] Verify current behaviour on wiki preview
    - [x] Fix current behaviour on wiki preview
        - [x] Rewrite all links and get preview links working
        - [x] Make sure all links are on-par with the wiki `show` page
        - [x] TDD `WikiLinkFilter` and get it working
        - [x] Hook `WikiLinkFilter` up
    - [x] Fix tests 
        - [x] Fix `markdown_spec`
        - [x] Fix `wiki` spinach feature
        - [x] Wait for [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/4f50dd2/builds) to pass
        - [x] Make sure all wiki-related pages are working as expected (history, all pages, etc.)
    - [x] Test in different ruby versions
    - [x] GitLab instances hosted on a relative URL
    - [x] Non-markdown rendering formats?
        - [x] RDoc
        - [x] ASCIIDoc
        - [x] Create issues to fix things for RDoc and ASCIIDoc
    - [x] Gauge performance impact
    - [x] Refactor
    - [x] Re-organize commits
    - [x] Make sure [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/f860e9a8dcabe7d5f160c32fc549807c98baa4a1/builds) passes
    - [x] Respond to @rymai's comments
        - [x] `class WikiLinkFilter < HTML::Pipeline::Filter`
        - [x] blank line after guard clause
        - [x] keyword arguments for `wiki` and `slug`
        - [x] invert the condition
        - [x] inline `user` in spec
        - [x] Make sure spec names are not out of date
        - [x] Comment for each rewrite rule
    - [x] Add CHANGELOG entry
    - [x] Reorganize commits
    - [x] Make sure [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/19b91e749a6320d12fb299d33f1f6440777e0e26/builds) passes
    - [ ] Wait for merge

See merge request !4432

2 files changed, 46 insertions, 26 deletions

diff --git a/lib/banzai/filter/wiki_link_filter.rb b/lib/banzai/filter/wiki_link_filter.rb
index 7dc771afd71..37a2779d453 100644
--- a/lib/banzai/filter/wiki_link_filter.rb
+++ b/lib/banzai/filter/wiki_link_filter.rb
@@ -2,7 +2,8 @@ require 'uri'
 
 module Banzai
   module Filter
-    # HTML filter that "fixes" relative links to files in a repository.
+    # HTML filter that "fixes" links to pages/files in a wiki.
+    # Rewrite rules are documented in the `WikiPipeline` spec.
     #
     # Context options:
     #   :project_wiki
@@ -25,36 +26,15 @@ module Banzai
       end
 
       def process_link_attr(html_attr)
-        return if html_attr.blank? || file_reference?(html_attr) || hierarchical_link?(html_attr)
+        return if html_attr.blank?
 
-        uri = URI(html_attr.value)
-        if uri.relative? && uri.path.present?
-          html_attr.value = rebuild_wiki_uri(uri).to_s
-        end
+        html_attr.value = apply_rewrite_rules(html_attr.value)
       rescue URI::Error
         # noop
       end
 
-      def rebuild_wiki_uri(uri)
-        uri.path = ::File.join(project_wiki_base_path, uri.path)
-        uri
-      end
-
-      def project_wiki
-        context[:project_wiki]
-      end
-
-      def file_reference?(html_attr)
-        !File.extname(html_attr.value).blank?
-      end
-
-      # Of the form `./link`, `../link`, or similar
-      def hierarchical_link?(html_attr)
-        html_attr.value[0] == '.'
-      end
-
-      def project_wiki_base_path
-        project_wiki && project_wiki.wiki_base_path
+      def apply_rewrite_rules(link_string)
+        Rewriter.new(link_string, wiki: context[:project_wiki], slug: context[:page_slug]).apply_rules
       end
     end
   end
diff --git a/lib/banzai/filter/wiki_link_filter/rewriter.rb b/lib/banzai/filter/wiki_link_filter/rewriter.rb
new file mode 100644
index 00000000000..2e2c8da311e
--- /dev/null
+++ b/lib/banzai/filter/wiki_link_filter/rewriter.rb
@@ -0,0 +1,40 @@
+module Banzai
+  module Filter
+    class WikiLinkFilter < HTML::Pipeline::Filter
+      class Rewriter
+        def initialize(link_string, wiki:, slug:)
+          @uri = Addressable::URI.parse(link_string)
+          @wiki_base_path = wiki && wiki.wiki_base_path
+          @slug = slug
+        end
+
+        def apply_rules
+          apply_file_link_rules!
+          apply_hierarchical_link_rules!
+          apply_relative_link_rules!
+          @uri.to_s
+        end
+
+        private
+
+        # Of the form 'file.md'
+        def apply_file_link_rules!
+          @uri = Addressable::URI.join(@slug, @uri) if @uri.extname.present?
+        end
+
+        # Of the form `./link`, `../link`, or similar
+        def apply_hierarchical_link_rules!
+          @uri = Addressable::URI.join(@slug, @uri) if @uri.to_s[0] == '.'
+        end
+
+        # Any link _not_ of the form `http://example.com/`
+        def apply_relative_link_rules!
+          if @uri.relative? && @uri.path.present?
+            link = ::File.join(@wiki_base_path, @uri.path)
+            @uri = Addressable::URI.parse(link)
+          end
+        end
+      end
+    end
+  end
+end