From ffda02e12e505e459859dcc6b4ce1273b246a483 Mon Sep 17 00:00:00 2001
From: James <james@eli.cx>
Date: Thu, 19 Jun 2025 08:52:44 +0100
Subject: [PATCH] fix: delete comment if new comment is empty

---
 src/comment.ts | 16 +++++++++++++++-
 src/run.ts     | 18 +++++++++++-------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/src/comment.ts b/src/comment.ts
index f69efab9..8edd41d6 100644
--- a/src/comment.ts
+++ b/src/comment.ts
@@ -9,6 +9,8 @@ type Comment = {
 
 export type UpdateIfExistsType = 'create' | 'replace' | 'append' | 'recreate'
 
+export const createCommentKey = (key: string): string => `<!-- diff-action/${key} -->`
+
 export const addComment = async (github: GitHubContext, comment: Comment): Promise<void> => {
   if (!github.issueNumber) {
     core.info(`Ignored non pull request event: ${github.eventName}`)
@@ -31,7 +33,7 @@ export const addComment = async (github: GitHubContext, comment: Comment): Promi
     return
   }
 
-  const commentKey = `<!-- diff-action/${comment.updateIfExistsKey} -->`
+  const commentKey = createCommentKey(comment.updateIfExistsKey)
   core.info(`Finding key ${commentKey} from comments in #${github.issueNumber}`)
   const existingComment = await findComment(github, commentKey)
   if (!existingComment) {
@@ -107,3 +109,15 @@ const findComment = async (github: GitHubContext, key: string): Promise<Existing
     }
   }
 }
+
+export const deleteCommentIfExists = async (github: GitHubContext, updateIfExistsKey: string): Promise<void> => {
+  const comment = await findComment(github, createCommentKey(updateIfExistsKey))
+
+  if (comment) {
+    await github.octokit.rest.issues.deleteComment({
+      owner: github.owner,
+      repo: github.repo,
+      comment_id: comment.id,
+    })
+  }
+}
diff --git a/src/run.ts b/src/run.ts
index e1ff1faf..d4fe304e 100644
--- a/src/run.ts
+++ b/src/run.ts
@@ -2,7 +2,7 @@ import * as core from '@actions/core'
 import { GitHubContext } from './github.js'
 import { computeDiff, showColorDiff } from './diff.js'
 import { addLabels, removeLabels } from './label.js'
-import { UpdateIfExistsType, addComment } from './comment.js'
+import { UpdateIfExistsType, addComment, deleteCommentIfExists } from './comment.js'
 import { formatComment } from './format.js'
 
 type Inputs = {
@@ -33,12 +33,16 @@ export const run = async (github: GitHubContext, inputs: Inputs): Promise<Output
     workflowRunURL: github.workflowRunURL,
   })
 
-  if (inputs.comment && commentBody.length > 0) {
-    await addComment(github, {
-      body: `${inputs.commentHeader}\n\n${commentBody}\n\n${inputs.commentFooter}`,
-      updateIfExists: inputs.updateIfExists,
-      updateIfExistsKey: inputs.updateIfExistsKey,
-    })
+  if (inputs.comment) {
+    if (commentBody.length === 0) {
+      await deleteCommentIfExists(github, inputs.updateIfExistsKey)
+    } else {
+      await addComment(github, {
+        body: `${inputs.commentHeader}\n\n${commentBody}\n\n${inputs.commentFooter}`,
+        updateIfExists: inputs.updateIfExists,
+        updateIfExistsKey: inputs.updateIfExistsKey,
+      })
+    }
   }
 
   if (diffs.length > 0) {