Expand GitHub style references in ChangeLog to URL (#1547)

Currently, ruby/ruby formats ChangeLog and expands such references to
links.
But such links in ChangeLog that is a plain text does not make sense.
I think it is suitable to be done at conversion from ChangeLog to HTML

---------

Co-authored-by: Sutou Kouhei <kou@cozmixng.org>

Author: nobu

lib/rdoc/parser/changelog.rb

@@ -274,6 +274,27 @@ def create_entries(entries)
       def initialize(base, commit, author, email, date, contents)
         case contents
         when String
+          if base&.match(%r[\A([^:/]+:/+[^/]+/)[^/]+/[^/]+/])
+            repo, host = $&, $1
+            contents = contents.dup
+            # base: https://github.com/ruby/ruby/
+            #   Fix #15791 -> Fix [#15791](https://github.com/ruby/ruby/pull/15791)
+            #   GH-15791 -> [GH-15791](https://github.com/ruby/ruby/pull/15791)
+            #   (#15791) -> ([#15791](https://github.com/ruby/ruby/pull/15791))
+            contents.gsub!(/\b(?:(?i:fix(?:e[sd])?) +)\K\#(\d+\b)|\bGH-(\d+)\b|\(\K\#(\d+)(?=\))/) do
+              "[#{$&}](#{repo}pull/#{$1 || $2 || $3})"
+            end
+            # repo#PR, repo@HASH
+            #   ruby/ruby#15791 -> [ruby/ruby#15791](https://github.com/ruby/ruby/pull/15791)
+            #   ruby/ruby@a8a989b6 -> [ruby/ruby@a8a989b6](https://github.com/ruby/ruby/commit/a8a989b6)
+            # ref in branckets is not extended
+            #   [ruby/net-imap#543][ruby/ruby#15791] -> [ruby/net-imap#543][ruby/ruby#15791]
+            contents.gsub!(%r[(?<![-\w#/@]|\]\[)([-\w]+/[-\w]+)(?:@(\h{8,40})|\#(\d+))(?![-\w#/@]|\]\[)]) do
+              path = defined?($2) ? "commit/#{$2}" : "pull/#{$3}"
+              "[#{$&}](#{host}#{$1}/#{path})"
+            end
+          end
+
           contents = RDoc::Markdown.parse(contents).parts.each do |body|
             case body
             when RDoc::Markup::Heading

test/rdoc/parser/changelog_test.rb

@@ -473,6 +473,32 @@ def test_scan_git_commit_date
     assert_equal expected, @top_level.comment.parse
   end
 
+  def test_scan_git_reference
+    ruby = "https://github.com/ruby/"
+    repo = "#{ruby}ruby/"
+    entry = log_entry("#{repo}commit/",
+                      "a8a989b6f651b878c690f5fd0a728e19a54dd2b9",
+                      "Nobuyoshi Nakada", "nobu@ruby-lang.org",
+                      "2026-01-03 13:28:58 +0900",
+                      <<~LOG)
+      Test net-imap with ruby/net-imap#593
+
+      Fix #15791
+
+      GH-15791
+
+      (#15791)
+
+      Fix up [ruby/net-imap#543].
+      LOG
+    head, *bodies = entry.contents
+    assert_include head.text, "{ruby/net-imap#593}[#{ruby}net-imap/pull/593]"
+    assert_include bodies.shift.text, "Fix {#15791}[#{repo}pull/15791]"
+    assert_include bodies.shift.text, "{GH-15791}[#{repo}pull/15791]"
+    assert_include bodies.shift.text, "({#15791}[#{repo}pull/15791])"
+    assert_include bodies.shift.text, "{ruby/net-imap#543}[#{ruby}net-imap/pull/543]"
+  end
+
   def util_parser(content = '')
     RDoc::Parser::ChangeLog.new @top_level, content, @options, @stats
   end