Merge branch 'relative-markdown-links' into 'master'

Add support for relative links starting with ./ or / to RelativeLinkFilter

## What does this MR do?

- Allow explicit relative links in Markdown (starting with `./`).
- Allow absolute links (relative to the branch's root directory) in Markdown (starting with `/`).

## Why was this MR needed?

Those link types were not supported before.

## What are the relevant issue numbers?

fixes #19028

See merge request !5586

CHANGELOG

@@ -4,6 +4,7 @@ v 8.11.0 (unreleased)
   - Fix the title of the toggle dropdown button. !5515 (herminiotorres)
   - Improve diff performance by eliminating redundant checks for text blobs
   - Remove magic comments (`# encoding: UTF-8`) from Ruby files. !5456 (winniehell)
+  - Add support for relative links starting with ./ or / to RelativeLinkFilter (winniehell)
   - Fix CI status icon link underline (ClemMakesApps)
   - Cache the commit author in RequestStore to avoid extra lookups in PostReceive
   - Fix of 'Commits being passed to custom hooks are already reachable when using the UI'

lib/banzai/filter/relative_link_filter.rb

@@ -87,10 +87,13 @@ module Banzai
       def build_relative_path(path, request_path)
         return request_path if path.empty?
         return path unless request_path
+        return path[1..-1] if path.start_with?('/')
 
         parts = request_path.split('/')
         parts.pop if uri_type(request_path) != :tree
 
+        path.sub!(%r{^\./}, '')
+
         while path.start_with?('../')
           parts.pop
           path.sub!('../', '')

spec/lib/banzai/filter/relative_link_filter_spec.rb

@@ -78,12 +78,24 @@ describe Banzai::Filter::RelativeLinkFilter, lib: true do
   end
 
   context 'with a valid repository' do
+    it 'rebuilds absolute URL for a file in the repo' do
+      doc = filter(link('/doc/api/README.md'))
+      expect(doc.at_css('a')['href']).
+        to eq "/#{project_path}/blob/#{ref}/doc/api/README.md"
+    end
+
     it 'rebuilds relative URL for a file in the repo' do
       doc = filter(link('doc/api/README.md'))
       expect(doc.at_css('a')['href']).
         to eq "/#{project_path}/blob/#{ref}/doc/api/README.md"
     end
 
+    it 'rebuilds relative URL for a file in the repo with leading ./' do
+      doc = filter(link('./doc/api/README.md'))
+      expect(doc.at_css('a')['href']).
+        to eq "/#{project_path}/blob/#{ref}/doc/api/README.md"
+    end
+
     it 'rebuilds relative URL for a file in the repo up one directory' do
       relative_link = link('../api/README.md')
       doc = filter(relative_link, requested_path: 'doc/update/7.14-to-8.0.md')