[PATCH] diff: teach --stat to ignore uninteresting modifications

From: Matthew Rogers via GitGitGadget <gitgitgadget@gmail.com>
Date: Aug 1, 2020, 23:33 UTC
Message-ID: <pull.689.git.1596324796918.gitgitgadget@gmail.com>

From: Matthew Rogers <mattr94@gmail.com>

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 <mattr94@gmail.com>
---
    diff: teach --stat to ignore uninteresting modifications
    
    This patch is based on the discussion these email threads:
    
    https://lore.kernel.org/git/1484704915.2096.16.camel@mattmccutchen.net/
    https://lore.kernel.org/git/CAOjrSZtQPQ8Xxuz+7SGykR8Q-gFDEZANSE5yQASqKjpbUAq_5Q@mail.gmail.com/
    
    With the code mostly taken from this specific message:
    https://lore.kernel.org/git/20170118111705.6bqzkklluikda3r5@sigill.intra.peff.net/
    
    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(-)

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 &&

base-commit: e8ab941b671da6890181aea5b5755d1d9eea24ec

-- 
gitgitgadget