feat: add hint about what exactly will be cleared

options/locale/locale_en-US.ini

@@ -1619,6 +1619,7 @@ pulls.merge_instruction_hint = `You can also view <a class="show-instruction">co
 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.
 
 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

@@ -352,6 +352,7 @@
 									'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}},

web_src/js/components/PullRequestMergeForm.vue

@@ -25,9 +25,14 @@
           </div>
           <div class="field">
             <textarea name="merge_message_field" rows="5" :placeholder="mergeForm.mergeMessageFieldPlaceHolder" v-model="mergeMessageFieldValue"/>
-            <button v-if="mergeMessageFieldValue !== mergeForm.defaultMergeMessage" @click.prevent="clearMergeMessage" class="ui tertiary button">
-              {{ mergeForm.textClearMergeMessage }}
-            </button>
+            <template v-if="mergeMessageFieldValue !== mergeForm.defaultMergeMessage">
+              <button @click.prevent="clearMergeMessage" class="ui tertiary button">
+                {{ mergeForm.textClearMergeMessage }}
+              </button>
+              <div class="ui label">
+                {{ mergeForm.textClearMergeMessageHint }}
+              </div>
+            </template>
           </div>
         </template>