Subject: Re: git rev-list fails to verify ssh-signed commits (but git log works)

From: Jeff King <[email-masked]>
Date: Wed, 8 Feb 2023 11:43:57 -0500

On Wed, Feb 08, 2023 at 04:56:53PM +0100, Max Gautier wrote:

> I was trying to implement a pre-push hook to verify my commits are
> properly signed before pushing them, and stumbled upon the following
> output (which looks like a bug to me):
> 
> $ git rev-list @{u}..HEAD --format='%G? %H'
> commit 9497d347b048dbea7f527624f815f7926594c4bc
> error: gpg.ssh.allowedSignersFile needs to be configured and exist for ssh signature verification
>
> [...]
>
> While git log works and is able to retrieve the signatures

Yeah, I think this is a bug. The issue is that not every command loads
the config callback for every config option. This is how we
traditionally implemented the split between porcelain and plumbing
(e.g., user-facing "git diff" will parse and respect "color.diff", but
the scriptable "git diff-files" would not).

In this case, the gpg config has been pushed to its own handler, and a
few specific commands (like git-log) call it. I don't know if there is a
good reason to avoid loading the config in plumbing, or if it was simply
cargo-culted.

I didn't test, but I suspect the patch below would fix your problem:

diff --git a/config.c b/config.c
index 00090a32fc..7ac9f1f5bc 100644
--- a/config.c
+++ b/config.c
@@ -1881,6 +1881,14 @@ int git_default_config(const char *var, const char *value, void *cb)
 	if (starts_with(var, "core."))
 		return git_default_core_config(var, value, cb);
 
+	/*
+	 * yikes, this needs to come early in the function because it
+	 * also handles user.signingkey, which would otherwise get
+	 * shunted to git_ident_config() below
+	 */
+	if (git_gpg_config(var, value, cb) < 0)
+		return -1;
+
 	if (starts_with(var, "user.") ||
 	    starts_with(var, "author.") ||
 	    starts_with(var, "committer."))

but it would need a bit more work:

  1. Somebody would need to dig into the reasons, if any, for not
     calling git_gpg_config() everywhere. It might be fine, but there
     may be a good reason which we're now violating. Digging in the
     history and looking at the code might yield some hints.

  2. The individual calls to git_gpg_config() in other programs should
     go away.

  3. It's possible some refactoring may let us avoid the "yikes" comment
     above (e.g., should user.signingkey just go into the normal ident
     config handler?).

-Peff