git diff prints long usage help if not run in git repo

Mohamed Akram· Aug 22, 2022, 18:22 UTC · lore

When running `git diff` in a directory that’s not a git repo, it prints a warning that this is the case, followed by a very long help text that, on your average terminal, causes it to scroll so much that the warning isn’t even visible. It should only print the warning and nothing else like other git commands. This was tested with git version 2.37.2 on macOS.

Junio C Hamano· Aug 22, 2022, 19:43 UTC · re: Mohamed Akram · lore

Re: git diff prints long usage help if not run in git repo

Mohamed Akram <mohd.akram@outlook.com> writes:

Show 6 quoted lines

> When running `git diff` in a directory that’s not a git repo, it
> prints a warning that this is the case, followed by a very long
> help text that, on your average terminal, causes it to scroll so
> much that the warning isn’t even visible. It should only print
> the warning and nothing else like other git commands. This was
> tested with git version 2.37.2 on macOS.

Thanks for a clearly written feature request. I think it is not unreasonable to stop after telling the user to use the --no-index option.

But on the other hand, not using "--no-index" is not what causes such a "git diff" outside any repository fail. If the user said

     $ cd / && git diff

it is clear that the user does not know they need to say what they want to compare against what. The reason why the command fails is not because the user did not say

     $ cd / && git diff --no-index

but because the user did not say

     $ cd / && git diff --no-index etc/passwd etc/group

So, I dunno.

Perhaps somebody can try the following patch and tell us if it is an improvement. I know it is for the specific case "cd / && git diff" but it really depends on the reason why (1) the command was run outside any repository and why (2) the command was run without any arguments. A shallow answer to both of them are "by mistake", but what I am trying to get at is that understanding the reason why such a mistake was made is probably the key to evaluate if the behaviour updated by the attached patch is a good idea.

Thanks.

 diff-no-index.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git c/diff-no-index.c w/diff-no-index.c
index 9a8b09346b..c8f2cdce05 100644
--- c/diff-no-index.c
+++ w/diff-no-index.c
@@ -259,9 +259,10 @@ int diff_no_index(struct rev_info *revs,
 			     diff_no_index_usage, 0);
 	if (argc != 2) {
 		if (implicit_no_index)
-			warning(_("Not a git repository. Use --no-index to "
-				  "compare two paths outside a working tree"));
-		usage_with_options(diff_no_index_usage, options);
+			die(_("Not a git repository. Use --no-index to "
+			      "compare two paths outside a working tree"));
+		else
+			usage_with_options(diff_no_index_usage, options);
 	}
 	FREE_AND_NULL(options);
 	for (i = 0; i < 2; i++) {

Mohamed Akram· Aug 23, 2022, 20:03 UTC · re: Junio C Hamano · lore

Re: git diff prints long usage help if not run in git repo

I haven’t tried it but that patch seems to make sense to me, although I found another related issue so it might need tweaking. When running `git diff` in a repo owned by another user, the warning message says that this is not a git repository, instead of the warning shown by other git commands about "dubious ownership". To reproduce:

sudo mkdir repo cd repo sudo git init git diff