Magit shows magit-diff with HEAD^ instead of HEAD when invoked from console

Question

When I start a commit from console (zsh on mac os Terminal) using git commit -a, then Emacs opens two windows as emacsclient in my existing Emacs App Window. One is the correct COMMIT_EDITMSG. The other is a magit-diff window. However, magit uses HEAD^ instead of HEAD as revision. The title says "Changes from HEAD^ to working tree" and that is what is shown.

In contrast, when I run magit-commit from within Emacs, the correct magit-diff window is opened, showing HEAD agains my working tree.

Any idea why this is and how I can fix it?

Emacs from brew: GNU Emacs 25.2.1 (x86_64-apple-darwin13.4.0, NS appkit-1265.21 Version 10.9.5 (Build 13F1911)) of 2017-04-21
Magit 20180410.1528, Git 2.17.0, Emacs 25.2.1, darwin

Answer 1

Both diffs can be useful and you can toggle between them by pressing C-c C-d.

Initially the diff is shown using the function magit-commit-diff, which decides which of these diffs to show based on the value of last-command, or if that isn't one of the commands it knows how to handle it falls back to this:

(if (magit-anything-staged-p)
    (magit-diff-staged nil args)
  (magit-diff-while-amending args))

Since you didn't invoke the commit using a Magit command, magit-commit-diff does not know which diff would be most appropriate and falls back to the above heuristic.

Answer 2

Just to be clear, using C-c C-d after using git commit -a will toggle to Staged Changes (which may be empty) and the HEAD^ vs. working tree diff. It doesn't toggle to HEAD vs. working tree for me.