[GSoC] microproject idea: improve corrupt patch location reporting in git am

Hi,

My name is Jialong Wang, and I plan to apply to Git for GSoC 2026.

I have been reading the Git contribution documentation, including Documentation/CodingGuidelines, Documentation/SubmittingPatches, and Documentation/MyFirstContribution.txt. I have also built Git from source locally and started looking for a small microproject.

I found an older open issue that still seems reproducible on my setup:

when git am encounters a corrupt patch, it reports "corrupt patch at line <n>", but that line number does not correspond to the original mail/mbox as the user sees it.

Related discussion I found:
  - bug report from 2019-10-02:
    https://public-inbox.org/git/20191002184546.GA22174@generichostname/
  - follow-up patch from 2019-10-04:
    https://public-inbox.org/git/ec38908d05f0d40190173158ef3f0753fa9f1184.1570226253.git.liu.denton@gmail.com/
  - GitGitGadget issue #374:
    https://github.com/gitgitgadget/git/issues/374

I also saw review feedback mentioning additional test coverage for cases such as stdin input and running from a subdirectory.

I reproduced the issue locally with Git 2.51.0 on 2026-03-15, and I am considering working on a small patch in this area.

Before I start, I wanted to ask whether this still looks like an appropriate microproject for a GSoC applicant, and whether improving the error location/reporting plus adding the missing tests would be a good direction.

Thanks, Jialong