diff: teach --stat to ignore uninteresting modifications

Commit Message

Linus Arver via GitGitGadget Aug. 1, 2020, 11:33 p.m. UTC

From: Matthew Rogers <[e-mail]>

Sometimes when diffing, files may show as being momdified even when
there are no interesting diffs to show.  This happens naturally when
using options such as --ignore-space-change.  We don't want to prevent
the display  of all files that have 0 effective diffs since they could
be the result of a rename, permission change, or other similar operation
that may still be of interest so we special case additions and deletions
as they are always interesting.

Signed-off-by: Matthew Rogers <[e-mail]>
---
    diff: teach --stat to ignore uninteresting modifications
    
    This patch is based on the discussion these email threads:
    
    https://lore.kernel.org/git/[e-mail]/
    https://lore.kernel.org/git/[e-mail]/
    
    With the code mostly taken from this specific message:
    https://lore.kernel.org/git/[e-mail]/
    
    The summary is that when running git diff --stat in combination with
    --ignore-all-space or similar options, you'll see many lines of the
    form:
    
    some-file.txt | 0
    
    which can be misleading when you are explicitly telling git to "ignore
    all space" or something similar. To rectify this issue, this patch
    categorizes all files that are modified but have no effective changes as
    not fit to display to the user.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-689%2FROGERSM94%2Fzero-diffs-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-689/ROGERSM94/zero-diffs-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/689

 diff.c                     | 36 +++++++++++++++++++++++++++++-------
 t/t4015-diff-whitespace.sh |  8 +++++++-
 2 files changed, 36 insertions(+), 8 deletions(-)


base-commit: e8ab941b671da6890181aea5b5755d1d9eea24ec

Comments

Junio C Hamano Aug. 2, 2020, 12:31 a.m. UTC | #1

"Matthew Rogers via GitGitGadget" <[e-mail]> writes:

> +		if (DIFF_FILE_VALID(one) && DIFF_FILE_VALID(two)) {
> +			struct diffstat_file *file = 
> +				diffstat->files[diffstat->nr - 1];
> +			/*
> +			 * Omit diffstats of modified files where nothing changed. 
> +			 * Even if !same_contents, this might be the case due to
> +			 * ignoring whitespace changes, etc.
> +			 * 
> +			 * But note that we special-case additions and deletions,
> +			 * as adding an empty file, for example is still of interest.
> +			 */
> +			if (p->status == DIFF_STATUS_MODIFIED 
> +				&& !file->added
> +				&& !file->deleted) {
> +				free_diffstat_file(file);
> +				diffstat->nr--;
> +			}
> +		}
>  	}
> 
>  	diff_free_filespec_data(one);

There are some "trailing whitespace" errors detected by "git am/apply".

> diff --git a/t/t4015-diff-whitespace.sh b/t/t4015-diff-whitespace.sh
> index 88d3026894..32c1b967f9 100755
> --- a/t/t4015-diff-whitespace.sh
> +++ b/t/t4015-diff-whitespace.sh
> @@ -789,7 +789,7 @@ test_expect_success 'checkdiff allows new blank lines' '
>  	git diff --check
>  '
>  
> -test_expect_success 'whitespace-only changes not reported' '
> +test_expect_success 'whitespace-only changes not reported (diff)' '
>  	git reset --hard &&
>  	echo >x "hello world" &&
>  	git add x &&
> @@ -799,6 +799,12 @@ test_expect_success 'whitespace-only changes not reported' '
>  	test_must_be_empty actual
>  '
>  
> +test_expect_success 'whitespace-only changes not reported (diffstat)' '
> +	# reuse state from previous test
> +	git diff --stat -b >actual &&
> +	test_must_be_empty actual
> +'
> +

This is a "let's show off our shiny new toy" test, which shows that
the code change covered the case you are interested in changing.
We'd also need tests that makes sure that the effect of the code
change is not seen when it should not trigger.

For example, if we further change mode bits of file 'x' (which has a
whitespace-only changes applied in the test in the previous hunk),
e.g.

	git update-index --chmod=+x x &&
	git diff --stat -b --cached >actual

should that be counted as a file with 0-line change that is worth
reporting, or is it hidden?  I _think_ the new code will do a wrong
thing here.  That is,

 - If the change truly is only mode bits and one and two have
   "same_contents", the new code is bypassed, and we'll continue to
   show "0 lines changed, but the file is worth reporting".

 - If the change is whitespace-only change plus mode bits, i.e. one
   and two do not have "same_contents", the new code triggers and
   the stat output is suppressed for the path.

Matt Rogers Aug. 2, 2020, 1:51 a.m. UTC | #2

>
> For example, if we further change mode bits of file 'x' (which has a
> whitespace-only changes applied in the test in the previous hunk),
> e.g.
>
>         git update-index --chmod=+x x &&
>         git diff --stat -b --cached >actual
>
> should that be counted as a file with 0-line change that is worth
> reporting, or is it hidden?  I _think_ the new code will do a wrong
> thing here.  That is,
>
>  - If the change truly is only mode bits and one and two have
>    "same_contents", the new code is bypassed, and we'll continue to
>    show "0 lines changed, but the file is worth reporting".
>

This first one is the behavior I was going for, I think it's most reasonable

>  - If the change is whitespace-only change plus mode bits, i.e. one
>    and two do not have "same_contents", the new code triggers and
>    the stat output is suppressed for the path.
>

I just ran some tests on my end, and you're correct here, I'll try to come
up with a reroll that addresses this and adds this as a test condition.

Patch

diff --git a/diff.c b/diff.c
index d24aaa3047..9868f82ece 100644
--- a/diff.c
+++ b/diff.c
@@ -3153,16 +3153,19 @@  static void show_dirstat_by_line(struct diffstat_t *data, struct diff_options *o
 	gather_dirstat(options, &dir, changed, "", 0);
 }
 
+static void free_diffstat_file(struct diffstat_file *f)
+{
+	free(f->print_name);
+	free(f->name);
+	free(f->from_name);
+	free(f);
+}
+
 void free_diffstat_info(struct diffstat_t *diffstat)
 {
 	int i;
-	for (i = 0; i < diffstat->nr; i++) {
-		struct diffstat_file *f = diffstat->files[i];
-		free(f->print_name);
-		free(f->name);
-		free(f->from_name);
-		free(f);
-	}
+	for (i = 0; i < diffstat->nr; i++)
+		free_diffstat_file(diffstat->files[i]);
 	free(diffstat->files);
 }
 
@@ -3718,6 +3721,25 @@  static void builtin_diffstat(const char *name_a, const char *name_b,
 		if (xdi_diff_outf(&mf1, &mf2, discard_hunk_line,
 				  diffstat_consume, diffstat, &xpp, &xecfg))
 			die("unable to generate diffstat for %s", one->path);
+
+		if (DIFF_FILE_VALID(one) && DIFF_FILE_VALID(two)) {
+			struct diffstat_file *file = 
+				diffstat->files[diffstat->nr - 1];
+			/*
+			 * Omit diffstats of modified files where nothing changed. 
+			 * Even if !same_contents, this might be the case due to
+			 * ignoring whitespace changes, etc.
+			 * 
+			 * But note that we special-case additions and deletions,
+			 * as adding an empty file, for example is still of interest.
+			 */
+			if (p->status == DIFF_STATUS_MODIFIED 
+				&& !file->added
+				&& !file->deleted) {
+				free_diffstat_file(file);
+				diffstat->nr--;
+			}
+		}
 	}
 
 	diff_free_filespec_data(one);
diff --git a/t/t4015-diff-whitespace.sh b/t/t4015-diff-whitespace.sh
index 88d3026894..32c1b967f9 100755
--- a/t/t4015-diff-whitespace.sh
+++ b/t/t4015-diff-whitespace.sh
@@ -789,7 +789,7 @@  test_expect_success 'checkdiff allows new blank lines' '
 	git diff --check
 '
 
-test_expect_success 'whitespace-only changes not reported' '
+test_expect_success 'whitespace-only changes not reported (diff)' '
 	git reset --hard &&
 	echo >x "hello world" &&
 	git add x &&
@@ -799,6 +799,12 @@  test_expect_success 'whitespace-only changes not reported' '
 	test_must_be_empty actual
 '
 
+test_expect_success 'whitespace-only changes not reported (diffstat)' '
+	# reuse state from previous test
+	git diff --stat -b >actual &&
+	test_must_be_empty actual
+'
+
 test_expect_success 'whitespace-only changes reported across renames' '
 	git reset --hard &&
 	for i in 1 2 3 4 5 6 7 8 9; do echo "$i$i$i$i$i$i"; done >x &&