Implement cross-project Markdown references

Enable linking to commits, merge requests, and issues in other projects
by prepending a namespaced project path to the reference.

4 files changed, 166 insertions, 31 deletions

diff --git a/CHANGELOG b/CHANGELOG
index 14d2572f742..857a5bc9234 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -17,6 +17,7 @@ v 7.4.0
   - Font Awesome 4.2 integration (Sullivan Senechal)
   - Add Pushover service integration (Sullivan Senechal)
   - Add select field type for services options (Sullivan Senechal)
+  - Add cross-project references to the Markdown parser (Vinnie Okada)
 
 v 7.3.2
   - Fix creating new file via web editor
diff --git a/doc/markdown/markdown.md b/doc/markdown/markdown.md
index 5627fd0659f..5c095ed1487 100644
--- a/doc/markdown/markdown.md
+++ b/doc/markdown/markdown.md
@@ -177,6 +177,12 @@ GFM will recognize the following:
 - 1234567 : for commits
 - \[file\](path/to/file) : for file references
 
+GFM also recognizes references to commits, issues, and merge requests in other projects:
+
+- namespace/project#123 : for issues
+- namespace/project!123 : for merge requests
+- namespace/project@1234567 : for commits
+
 # Standard Markdown
 
 ## Headers
diff --git a/lib/gitlab/markdown.rb b/lib/gitlab/markdown.rb
index d346acf0d32..8380193deb3 100644
--- a/lib/gitlab/markdown.rb
+++ b/lib/gitlab/markdown.rb
@@ -108,15 +108,18 @@ module Gitlab
       text
     end
 
+    NAME_STR = '[a-zA-Z][a-zA-Z0-9_\-\.]*'
+    PROJ_STR = "(?<project>#{NAME_STR}/#{NAME_STR})"
+
     REFERENCE_PATTERN = %r{
       (?<prefix>\W)?                         # Prefix
       (                                      # Reference
-         @(?<user>[a-zA-Z][a-zA-Z0-9_\-\.]*) # User name
+         @(?<user>#{NAME_STR})               # User name
         |(?<issue>([A-Z\-]+-)\d+)            # JIRA Issue ID
-        |\#(?<issue>([a-zA-Z\-]+-)?\d+)      # Issue ID
-        |!(?<merge_request>\d+)              # MR ID
+        |#{PROJ_STR}?\#(?<issue>([a-zA-Z\-]+-)?\d+) # Issue ID
+        |#{PROJ_STR}?!(?<merge_request>\d+)  # MR ID
         |\$(?<snippet>\d+)                   # Snippet ID
-        |(?<commit>[\h]{6,40})               # Commit ID
+        |(#{PROJ_STR}@)?(?<commit>[\h]{6,40}) # Commit ID
         |(?<skip>gfm-extraction-[\h]{6,40})  # Skip gfm extractions. Otherwise will be parsed as commit
       )
       (?<suffix>\W)?                         # Suffix
@@ -127,38 +130,57 @@ module Gitlab
     def parse_references(text, project = @project)
       # parse reference links
       text.gsub!(REFERENCE_PATTERN) do |match|
-        prefix     = $~[:prefix]
-        suffix     = $~[:suffix]
         type       = TYPES.select{|t| !$~[t].nil?}.first
 
-        if type
-          identifier = $~[type]
-
-          # Avoid HTML entities
-          if prefix && suffix && prefix[0] == '&' && suffix[-1] == ';'
-            match
-          elsif ref_link = reference_link(type, identifier, project)
-            "#{prefix}#{ref_link}#{suffix}"
-          else
-            match
-          end
-        else
-          match
+        actual_project = project
+        project_prefix = nil
+        project_path = $LAST_MATCH_INFO[:project]
+        if project_path
+          actual_project = ::Project.find_with_namespace(project_path)
+          project_prefix = project_path
         end
+
+        parse_result($LAST_MATCH_INFO, type,
+                     actual_project, project_prefix) || match
+      end
+    end
+
+    # Called from #parse_references.  Attempts to build a gitlab reference
+    # link.  Returns nil if either +type+ or +project+ are nil, if the match
+    # string is an HTML entity, or if the reference is invalid.
+    def parse_result(match_info, type, project, project_prefix)
+      prefix = match_info[:prefix]
+      suffix = match_info[:suffix]
+
+      return nil if html_entity?(prefix, suffix) || project.nil? || type.nil?
+
+      identifier = match_info[type]
+      ref_link = reference_link(type, identifier, project, project_prefix)
+
+      if ref_link
+        "#{prefix}#{ref_link}#{suffix}"
+      else
+        nil
       end
     end
 
+    # Return true if the +prefix+ and +suffix+ indicate that the matched string
+    # is an HTML entity like &amp;
+    def html_entity?(prefix, suffix)
+      prefix && suffix && prefix[0] == '&' && suffix[-1] == ';'
+    end
+
     # Private: Dispatches to a dedicated processing method based on reference
     #
     # reference  - Object reference ("@1234", "!567", etc.)
     # identifier - Object identifier (Issue ID, SHA hash, etc.)
     #
     # Returns string rendered by the processing method
-    def reference_link(type, identifier, project = @project)
-      send("reference_#{type}", identifier, project)
+    def reference_link(type, identifier, project = @project, prefix_text = nil)
+      send("reference_#{type}", identifier, project, prefix_text)
     end
 
-    def reference_user(identifier, project = @project)
+    def reference_user(identifier, project = @project, _ = nil)
       options = html_options.merge(
           class: "gfm gfm-team_member #{html_options[:class]}"
         )
@@ -170,17 +192,17 @@ module Gitlab
       end
     end
 
-    def reference_issue(identifier, project = @project)
+    def reference_issue(identifier, project = @project, prefix_text = nil)
       if project.used_default_issues_tracker? || !external_issues_tracker_enabled?
         if project.issue_exists? identifier
           url = url_for_issue(identifier, project)
-          title = title_for_issue(identifier)
+          title = title_for_issue(identifier, project)
           options = html_options.merge(
             title: "Issue: #{title}",
             class: "gfm gfm-issue #{html_options[:class]}"
           )
 
-          link_to("##{identifier}", url, options)
+          link_to("#{prefix_text}##{identifier}", url, options)
         end
       else
         config = Gitlab.config
@@ -191,18 +213,19 @@ module Gitlab
       end
     end
 
-    def reference_merge_request(identifier, project = @project)
+    def reference_merge_request(identifier, project = @project,
+                                prefix_text = nil)
       if merge_request = project.merge_requests.find_by(iid: identifier)
         options = html_options.merge(
           title: "Merge Request: #{merge_request.title}",
           class: "gfm gfm-merge_request #{html_options[:class]}"
         )
         url = project_merge_request_url(project, merge_request)
-        link_to("!#{identifier}", url, options)
+        link_to("#{prefix_text}!#{identifier}", url, options)
       end
     end
 
-    def reference_snippet(identifier, project = @project)
+    def reference_snippet(identifier, project = @project, _ = nil)
       if snippet = project.snippets.find_by(id: identifier)
         options = html_options.merge(
           title: "Snippet: #{snippet.title}",
@@ -213,17 +236,22 @@ module Gitlab
       end
     end
 
-    def reference_commit(identifier, project = @project)
+    def reference_commit(identifier, project = @project, prefix_text = nil)
       if project.valid_repo? && commit = project.repository.commit(identifier)
         options = html_options.merge(
           title: commit.link_title,
           class: "gfm gfm-commit #{html_options[:class]}"
         )
-        link_to(identifier, project_commit_url(project, commit), options)
+        link_to(
+          "#{prefix_text}#{identifier}",
+          project_commit_url(project, commit),
+          options
+        )
       end
     end
 
-    def reference_external_issue(identifier, issue_tracker, project = @project)
+    def reference_external_issue(identifier, issue_tracker, project = @project,
+                                 _ = nil)
       url = url_for_issue(identifier, project)
       title = issue_tracker['title']
 
diff --git a/spec/helpers/gitlab_markdown_helper_spec.rb b/spec/helpers/gitlab_markdown_helper_spec.rb
index 6c865b1e079..da246ff1e0d 100644
--- a/spec/helpers/gitlab_markdown_helper_spec.rb
+++ b/spec/helpers/gitlab_markdown_helper_spec.rb
@@ -181,6 +181,74 @@ describe GitlabMarkdownHelper do
       end
     end
 
+    # Shared examples for referencing an object in a different project
+    #
+    # Expects the following attributes to be available in the example group:
+    #
+    # - object    - The object itself
+    # - reference - The object reference string (e.g., #1234, $1234, !1234)
+    # - other_project - The project that owns the target object
+    #
+    # Currently limited to Snippets, Issues and MergeRequests
+    shared_examples 'cross-project referenced object' do
+      let(:project_path) { @other_project.path_with_namespace }
+      let(:full_reference) { "#{project_path}#{reference}" }
+      let(:actual)   { "Reference to #{full_reference}" }
+      let(:expected) do
+        if object.is_a?(Commit)
+          project_commit_path(@other_project, object)
+        else
+          polymorphic_path([@other_project, object])
+        end
+      end
+
+      it 'should link using a valid id' do
+        gfm(actual).should match(expected)
+      end
+
+      it 'should link with adjacent text' do
+        # Wrap the reference in parenthesis
+        gfm(actual.gsub(full_reference, "(#{full_reference})")).should(
+          match(expected)
+        )
+
+        # Append some text to the end of the reference
+        gfm(actual.gsub(full_reference, "#{full_reference}, right?")).should(
+          match(expected)
+        )
+      end
+
+      it 'should keep whitespace intact' do
+        actual   = "Referenced #{full_reference} already."
+        expected = /Referenced <a.+>[^\s]+<\/a> already/
+        gfm(actual).should match(expected)
+      end
+
+      it 'should not link with an invalid id' do
+        # Modify the reference string so it's still parsed, but is invalid
+        if object.is_a?(Commit)
+          reference.gsub!(/^(.).+$/, '\1' + '12345abcd')
+        else
+          reference.gsub!(/^(.)(\d+)$/, '\1' + ('\2' * 2))
+        end
+        gfm(actual).should == actual
+      end
+
+      it 'should include a title attribute' do
+        if object.is_a?(Commit)
+          title = object.link_title
+        else
+          title = "#{object.class.to_s.titlecase}: #{object.title}"
+        end
+        gfm(actual).should match(/title="#{title}"/)
+      end
+
+      it 'should include standard gfm classes' do
+        css = object.class.to_s.underscore
+        gfm(actual).should match(/class="\s?gfm gfm-#{css}\s?"/)
+      end
+    end
+
     describe "referencing an issue" do
       let(:object)    { issue }
       let(:reference) { "##{issue.iid}" }
@@ -188,6 +256,38 @@ describe GitlabMarkdownHelper do
       include_examples 'referenced object'
     end
 
+    context 'cross-repo references' do
+      before(:all) do
+        @other_project = create(:project, :public)
+        @commit2 = @other_project.repository.commit
+        @issue2 = create(:issue, project: @other_project)
+        @merge_request2 = create(:merge_request,
+                                 source_project: @other_project,
+                                 target_project: @other_project)
+      end
+
+      describe 'referencing an issue in another project' do
+        let(:object)    { @issue2 }
+        let(:reference) { "##{@issue2.iid}" }
+
+        include_examples 'cross-project referenced object'
+      end
+
+      describe 'referencing an merge request in another project' do
+        let(:object)    { @merge_request2 }
+        let(:reference) { "!#{@merge_request2.iid}" }
+
+        include_examples 'cross-project referenced object'
+      end
+
+      describe 'referencing a commit in another project' do
+        let(:object)    { @commit2 }
+        let(:reference) { "@#{@commit2.id}" }
+
+        include_examples 'cross-project referenced object'
+      end
+    end
+
     describe "referencing a Jira issue" do
       let(:actual)   { "Reference to JIRA-#{issue.iid}" }
       let(:expected) { "http://jira.example/browse/JIRA-#{issue.iid}" }