Re: [PATCH] diff: don't read index when --no-index is given

[Junio C Hamano <gitster@pobox.com>]

Thomas Gummerer <t.gummerer@gmail.com> writes:

> git diff --no-index ... currently reads the index, during setup, when
> calling gitmodules_config().  In the usual case this gives us some
> performance drawbacks, but it's especially annoying if there is a broken
> index file.
>
> Avoid calling the unnecessary gitmodules_config() when the --no-index
> option is given.  Also add a test to guard against similar breakages in the future.
>
> Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
> ---
>  builtin/diff.c           | 13 +++++++++++--
>  t/t4053-diff-no-index.sh |  6 ++++++
>  2 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/builtin/diff.c b/builtin/diff.c
> index adb93a9..47c0833 100644
> --- a/builtin/diff.c
> +++ b/builtin/diff.c
> @@ -257,7 +257,7 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
>  	int blobs = 0, paths = 0;
>  	const char *path = NULL;
>  	struct blobinfo blob[2];
> -	int nongit;
> +	int nongit, no_index = 0;
>  	int result = 0;
>  
>  	/*
> @@ -282,9 +282,18 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
>  	 *
>  	 * Other cases are errors.
>  	 */
> +	for (i = 1; i < argc; i++) {
> +		if (!strcmp(argv[i], "--"))
> +			break;
> +		if (!strcmp(argv[i], "--no-index")) {
> +			no_index = 1;
> +			break;
> +		}
> +	}

This seems to duplicate only half the logic at the beginning of
diff_no_index(), right?  E.g., running "git diff /var/tmp/[12]"
inside a working tree that is controlled by a Git repository when
/var/tmp/ is outside, we do want to behave as if the command line
were "git diff --no-index /var/tmp/[12]", but this half duplication
makes these two behave differently, no?

I think the issue you are trying to address is worth tackling, but I
wonder if a bit of preparatory refactoring is necessary to avoid the
partial duplication.

>  	prefix = setup_git_directory_gently(&nongit);
> -	gitmodules_config();
> +	if (!no_index)
> +		gitmodules_config();
>  	git_config(git_diff_ui_config, NULL);
>  
>  	init_revisions(&rev, prefix);
> diff --git a/t/t4053-diff-no-index.sh b/t/t4053-diff-no-index.sh
> index 979e983..a24ae4d 100755
> --- a/t/t4053-diff-no-index.sh
> +++ b/t/t4053-diff-no-index.sh
> @@ -29,4 +29,10 @@ test_expect_success 'git diff --no-index relative path outside repo' '
>  	)
>  '
>  
> +test_expect_success 'git diff --no-index with broken index' '
> +	cd repo &&
> +	echo broken >.git/index &&
> +	test_expect_code 0 git diff --no-index a ../non/git/a
> +'
> +
>  test_done