feat: add button to quickly clear merge message (#21548)

This PR adds a button to allow quickly clearing the merge message of a
PR. The button will remove everything but the git trailers.

I found myself often pruning the commit message before merging,
especially for PRs generated by renovate - renovate puts a very long and
detailed comment with the full changelog in each PR it opens. This
clutters the commit message. However, I want to explicitly preserve the
git commit trailers. Doing this manually works, but having a button is a
lot easier.

Screenshot:

![image](https://user-images.githubusercontent.com/13721712/197337525-d456d0f8-1f7c-43a9-815d-ca93b1e7a90a.png)

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>

options/locale/locale_en-US.ini

@@ -1630,6 +1630,8 @@ pulls.reopened_at = `reopened this pull request <a id="%[1]s" href="#%[1]s">%[2]
 pulls.merge_instruction_hint = `You can also view <a class="show-instruction">command line instructions</a>.`
 pulls.merge_instruction_step1_desc = From your project repository, check out a new branch and test the changes.
 pulls.merge_instruction_step2_desc = Merge the changes and update on Gitea.
+pulls.clear_merge_message = Clear merge message
+pulls.clear_merge_message_hint = Clearing the merge message will only remove the commit message content and keep generated git trailers such as "Co-Authored-By …".
 
 pulls.auto_merge_button_when_succeed = (When checks succeed)
 pulls.auto_merge_when_succeed = Auto merge when all checks succeed

templates/repo/issue/view_content/pull.tmpl

@@ -351,6 +351,8 @@
 									'textAutoMergeButtonWhenSucceed': {{$.locale.Tr "repo.pulls.auto_merge_button_when_succeed"}},
 									'textAutoMergeWhenSucceed': {{$.locale.Tr "repo.pulls.auto_merge_when_succeed"}},
 									'textAutoMergeCancelSchedule': {{$.locale.Tr "repo.pulls.auto_merge_cancel_schedule"}},
+									'textClearMergeMessage': {{$.locale.Tr "repo.pulls.clear_merge_message"}},
+									'textClearMergeMessageHint': {{$.locale.Tr "repo.pulls.clear_merge_message_hint"}},
 
 									'canMergeNow': {{$canMergeNow}},
 									'allOverridableChecksOk': {{not $notAllOverridableChecksOk}},
@@ -360,6 +362,7 @@
 									'defaultMergeStyle': {{.MergeStyle}},
 									'defaultDeleteBranchAfterMerge': {{$prUnit.PullRequestsConfig.DefaultDeleteBranchAfterMerge}},
 									'mergeMessageFieldPlaceHolder': {{$.locale.Tr "repo.editor.commit_message_desc"}},
+									'defaultMergeMessage': defaultMergeMessage,
 
 									'hasPendingPullRequestMerge': {{.HasPendingPullRequestMerge}},
 									'hasPendingPullRequestMergeTip': {{$hasPendingPullRequestMergeTip}},

web_src/js/components/PullRequestMergeForm.vue

@@ -25,6 +25,14 @@
           </div>
           <div class="field">
             <textarea name="merge_message_field" rows="5" :placeholder="mergeForm.mergeMessageFieldPlaceHolder" v-model="mergeMessageFieldValue"/>
+            <template v-if="mergeMessageFieldValue !== mergeForm.defaultMergeMessage">
+              <button @click.prevent="clearMergeMessage" class="ui tertiary button">
+                {{ mergeForm.textClearMergeMessage }}
+              </button>
+              <div class="ui label"><!-- TODO: Convert to tooltip once we can use tooltips in Vue templates -->
+                {{ mergeForm.textClearMergeMessageHint }}
+              </div>
+            </template>
           </div>
         </template>
 
@@ -174,6 +182,9 @@ export default {
       this.mergeStyle = name;
       this.autoMergeWhenSucceed = autoMerge;
     },
+    clearMergeMessage() {
+      this.mergeMessageFieldValue = this.mergeForm.defaultMergeMessage;
+    },
   },
 };
 </script>