Add ability to fetch the commit ID of the last commit that actually touched a file

CHANGELOG

@@ -16,6 +16,7 @@ v 8.2.0 (unreleased)
   - Fix: 500 error returned if destroy request without HTTP referer (Kazuki Shimizu)
   - Remove deprecated CI events from project settings page
   - Use issue editor as cross reference comment author when issue is edited with a new mention.
+  - [API] Add ability to fetch the commit ID of the last commit that actually touched a file
 v 8.1.1
   - Fix cloning Wiki repositories via HTTP (Stan Hu)

doc/api/repository_files.md

@@ -23,7 +23,8 @@ Example response:
   "content": "IyA9PSBTY2hlbWEgSW5mb3...",
   "ref": "master",
   "blob_id": "79f7bbd25901e8334750839545a9bd021f0e4c83",
-  "commit_id": "d5a3ff139356ce33e37e73add446f16869741b50"
+  "commit_id": "d5a3ff139356ce33e37e73add446f16869741b50",
+  "last_commit_id": "570e7b2abdd848b95f2f578043fc23bd6f6fd24d"
 }
 ```

lib/api/files.rb

@@ -43,7 +43,8 @@ module API
       #   "content": "IyA9PSBTY2hlbWEgSW5mb3...",
       #   "ref": "master",
       #   "blob_id": "79f7bbd25901e8334750839545a9bd021f0e4c83",
-      #   "commit_id": "d5a3ff139356ce33e37e73add446f16869741b50"
+      #   "commit_id": "d5a3ff139356ce33e37e73add446f16869741b50",
+      #   "last_commit_id": "570e7b2abdd848b95f2f578043fc23bd6f6fd24d",
       # }
       #
       get ":id/repository/files" do
@@ -71,6 +72,7 @@ module API
             ref: ref,
             blob_id: blob.id,
             commit_id: commit.id,
+            last_commit_id: user_project.repository.last_commit_for_path(commit.sha, file_path).id
           }
         else
           not_found! 'File'

spec/requests/api/files_spec.rb

@@ -19,6 +19,7 @@ describe API::API, api: true  do
       expect(response.status).to eq(200)
       expect(json_response['file_path']).to eq(file_path)
       expect(json_response['file_name']).to eq('popen.rb')
+      expect(json_response['last_commit_id']).to eq('570e7b2abdd848b95f2f578043fc23bd6f6fd24d')
       expect(Base64.decode64(json_response['content']).lines.first).to eq("require 'fileutils'\n")
     end