forgit log cannot diff merge commits

[carlfriedrich]

Check list

• I have read through the README
• I have the latest version of forgit
• I have searched through the existing issues

Environment info

• OS
  • Linux
  • Mac OS X
  • Windows
  • Others:
• Shell
  • bash
  • zsh
  • fish

Problem / Steps to reproduce

Merge commits cannot be diffed from within forgit log.

Steps to reproduce:

git init
touch 1.txt
git add 1.txt
git commit -m "Add file 1"
git checkout -b branch
touch 2.txt
git add 2.txt
git commit -m "Add file 2"
git checkout main
git merge --no-ff branch -m "Merge branch"

Afterwards call git forgit log and try to view the merge commit by pressing enter. It does not work (immediately returns).

The reason is that our current implementation using the ^! operator on the commit does not work for merge commits. According to this stack overflow answer there are only three ways to correctly show the diff for a merge commit:

git show -m c05f017
git show --first-parent c05f017
git diff c05f017^ c05f017

A quick fix would be to change our implementation to the third option. The cleaner solution IMO, though, would be to implement a forgit show command. I am planning to do the latter.