RFR: 1854: Add "clean" label for merge PRs that have no merge resolution [v4]

[Zhao Song]

On Wed, 12 Apr 2023 23:37:03 GMT, Zhao Song <zsong at openjdk.org> wrote:

>> In this patch, PR bot would add clean label to Merge-style PRs if one of the following conditions is met.
>> 
>> 1. There isn't a merge commit at HEAD. 
>> To verify this condition, we can simply check the number of parents that the HEAD commit has. If the HEAD commit has one parent, it is not a merge commit. However, if it has two parents, then it is considered a merge commit.
>> 
>> 2. The merge commit at HEAD is empty(has no merge resolutions)
>> To verify this condition, we should be able to tell the difference between an empty merge commit and a non-empty merge commit.
>> 
>> Using `git show <Hash>` would help us differentiate between this two types of commits.
>> 
>> (1) git show output for empty merge commit
>> 
>> commit 9752b806edafbdc210db00f3099404cd8bd11edf
>> Merge: 982b5ad5d8b 99f8d05da93
>> Author: Zhao Song <zhao.song at oracle.com>
>> Date:   Tue Apr 11 14:26:18 2023 -0700
>> 
>>     Merge branch 'feature'
>> 
>> 
>> 
>> (2) git show output for non-empty merge commit
>> 
>> commit 242a0c07cf3204c662a2f1d55a2ca3e494f955fd (HEAD -> master)
>> Merge: af35791d093 0ebf3bd5fe1
>> Author: Zhao Song <zhao.song at oracle.com>
>> Date:   Tue Apr 11 14:38:05 2023 -0700
>> 
>>     Merge branch 'feature2'
>> 
>> diff --cc test.java
>> index 7c736ab8f08,09647d12eda..a3c5725e39d
>> --- a/test.java
>> +++ b/test.java
>> @@@ -3,4 -3,4 +3,5 @@@
>>   aaaaa
>>   +++++
>>   11111
>>  +33333
>> + 22222
>> 
>> 
>> 
>> We could find that the difference between the two is whether the commit message body is empty or not.
>> 
>> Since we only care about commit message body, we can use the `git show --pretty=format:%b <Hash>` command to extract solely the commit message body.
>
> Zhao Song has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix problems

Thanks for the review!

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PR Comment: https://git.openjdk.org/skara/pull/1500#issuecomment-1507232864