[RFC PATCH] prefix_path: show gitdir when arg is outside repo

From: Emily Shaffer <emilyshaffer@google.com>

When developing a script, it can be painful to understand why Git thinks something is outside the current repo, if the current repo isn't what the user thinks it is. Since this can be tricky to diagnose, especially in cases like submodules or nested worktrees, let's give the user a hint about which repository is offended about that path.

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
---
This one comes from a user feature request. This user is running some
Git client commands on a build machine somewhere and finding it hard to
reason about the cause of the "outside repo" error.

I see two arguments:

For:
 - A user checking their own `pwd` might still not come to the same
   conclusion Git does about the current repo, if their filesystem is in
   some weird state
 - This warning is intended for human eyes (die(), stderr) so it's reasonable
   to give some info to make the human's life easier

Against:
 - It's chatty, especially given the absolute directory. This may be a
   pretty common mistake ('git add' with thumbfingers?) so it could be
   chatty, frequently - not great.
   (Sidebar: Just including the relative directory is really not very
   useful - since you're still left thinking, "relative to where?")

I also dug around a little to see whether I could consolidate the pathspec.c logic, which is nearly identical to setup.c, into another helper in setup.c (a la prefix_path_1()). But since the die() message is somewhat different, and init_pathspec_item() is the _only_ place which uses prefix_path_gently() in this way, it wasn't feasible. (The other caller of prefix_path_gently() is immediately below prefix_path(), and doesn't die at all, print errors, or capture out-params from prefix_path_gently().)

 - Emily

 pathspec.c | 3 ++-
 setup.c    | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)