From d843e319f88f85323ec9865529170181d04b7361 Mon Sep 17 00:00:00 2001
From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Fri, 28 Jan 2022 12:02:48 +0000
Subject: [PATCH 1/3] docs(diff): lose incorrect claim about `diff-files
 --diff-filter=A`

Originally, before we had `--intent-to-add`, there was no way that `git
diff-files` could see added files: if a file did not exist in the index,
`git diff-files` would not show it because it looks only at worktree
files when there is an index entry at the same path.

We used this example in the documentation of the diff options to explain
that not every `--diff-filter=<option>` has an effect in all scenarios.

Even when we added `--intent-to-add`, the comment was still correct,
because initially we showed such files as modified instead of added.

However, when that bug was fixed in feea6946a5b (diff-files: treat
"i-t-a" files as "not-in-index", 2020-06-20), the comment in the
documentation became incorrect.

Let's just remove it.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Documentation/diff-options.txt | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index c89d530d3d..2549df0d21 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -616,11 +616,8 @@ ifndef::git-format-patch[]
 Also, these upper-case letters can be downcased to exclude.  E.g.
 `--diff-filter=ad` excludes added and deleted paths.
 +
-Note that not all diffs can feature all types. For instance, diffs
-from the index to the working tree can never have Added entries
-(because the set of paths included in the diff is limited by what is in
-the index).  Similarly, copied and renamed entries cannot appear if
-detection for those types is disabled.
+Note that not all diffs can feature all types. For instance, copied and
+renamed entries cannot appear if detection for those types is disabled.
 
 -S<string>::
 	Look for differences that change the number of occurrences of

From 4d4d4eaa7b7f7ceda0648273ad33b71fc68e36c1 Mon Sep 17 00:00:00 2001
From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Fri, 28 Jan 2022 12:02:49 +0000
Subject: [PATCH 2/3] diff.c: move the diff filter bits definitions up a bit

This prepares for a more careful handling of the `--diff-filter`
options over the next few commits.

This commit is best viewed with `--color-moved`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 diff.c | 74 +++++++++++++++++++++++++++++-----------------------------
 1 file changed, 37 insertions(+), 37 deletions(-)

diff --git a/diff.c b/diff.c
index c862771a58..5081052c43 100644
--- a/diff.c
+++ b/diff.c
@@ -4570,6 +4570,43 @@ void repo_diff_setup(struct repository *r, struct diff_options *options)
 	prep_parse_options(options);
 }
 
+static const char diff_status_letters[] = {
+	DIFF_STATUS_ADDED,
+	DIFF_STATUS_COPIED,
+	DIFF_STATUS_DELETED,
+	DIFF_STATUS_MODIFIED,
+	DIFF_STATUS_RENAMED,
+	DIFF_STATUS_TYPE_CHANGED,
+	DIFF_STATUS_UNKNOWN,
+	DIFF_STATUS_UNMERGED,
+	DIFF_STATUS_FILTER_AON,
+	DIFF_STATUS_FILTER_BROKEN,
+	'\0',
+};
+
+static unsigned int filter_bit['Z' + 1];
+
+static void prepare_filter_bits(void)
+{
+	int i;
+
+	if (!filter_bit[DIFF_STATUS_ADDED]) {
+		for (i = 0; diff_status_letters[i]; i++)
+			filter_bit[(int) diff_status_letters[i]] = (1 << i);
+	}
+}
+
+static unsigned filter_bit_tst(char status, const struct diff_options *opt)
+{
+	return opt->filter & filter_bit[(int) status];
+}
+
+unsigned diff_filter_bit(char status)
+{
+	prepare_filter_bits();
+	return filter_bit[(int) status];
+}
+
 void diff_setup_done(struct diff_options *options)
 {
 	unsigned check_mask = DIFF_FORMAT_NAME |
@@ -4774,43 +4811,6 @@ static int parse_dirstat_opt(struct diff_options *options, const char *params)
 	return 1;
 }
 
-static const char diff_status_letters[] = {
-	DIFF_STATUS_ADDED,
-	DIFF_STATUS_COPIED,
-	DIFF_STATUS_DELETED,
-	DIFF_STATUS_MODIFIED,
-	DIFF_STATUS_RENAMED,
-	DIFF_STATUS_TYPE_CHANGED,
-	DIFF_STATUS_UNKNOWN,
-	DIFF_STATUS_UNMERGED,
-	DIFF_STATUS_FILTER_AON,
-	DIFF_STATUS_FILTER_BROKEN,
-	'\0',
-};
-
-static unsigned int filter_bit['Z' + 1];
-
-static void prepare_filter_bits(void)
-{
-	int i;
-
-	if (!filter_bit[DIFF_STATUS_ADDED]) {
-		for (i = 0; diff_status_letters[i]; i++)
-			filter_bit[(int) diff_status_letters[i]] = (1 << i);
-	}
-}
-
-static unsigned filter_bit_tst(char status, const struct diff_options *opt)
-{
-	return opt->filter & filter_bit[(int) status];
-}
-
-unsigned diff_filter_bit(char status)
-{
-	prepare_filter_bits();
-	return filter_bit[(int) status];
-}
-
 static int diff_opt_diff_filter(const struct option *option,
 				const char *optarg, int unset)
 {

From 75408ca94980c125b3a800003c3e6b7cdcb27d44 Mon Sep 17 00:00:00 2001
From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Fri, 28 Jan 2022 12:02:50 +0000
Subject: [PATCH 3/3] diff-filter: be more careful when looking for negative
 bits

The `--diff-filter=<bits>` option allows to filter the diff by certain
criteria, for example `R` to only show renamed files. It also supports
negating a filter via a down-cased letter, i.e. `r` to show _everything
but_ renamed files.

However, the code is a bit overzealous when trying to figure out whether
`git diff` should start with all diff-filters turned on because the user
provided a lower-case letter: if the `--diff-filter` argument starts
with an upper-case letter, we must not start with all bits turned on.

Even worse, it is possible to specify the diff filters in multiple,
separate options, e.g. `--diff-filter=AM [...] --diff-filter=m`.

Let's accumulate the include/exclude filters independently, and only
special-case the "only exclude filters were specified" case after
parsing the options altogether.

Note: The code replaced by this commit took pains to avoid setting any
unused bits of `options->filter`. That was unnecessary, though, as all
accesses happen via the `filter_bit_tst()` function using specific bits,
and setting the unused bits has no effect. Therefore, we can simplify
the code by using `~0` (or in this instance, `~<unwanted-bit>`).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 diff.c         | 23 +++++++----------------
 diff.h         |  2 +-
 t/t4202-log.sh | 13 +++++++++++++
 3 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/diff.c b/diff.c
index 5081052c43..4ab4299b81 100644
--- a/diff.c
+++ b/diff.c
@@ -4720,6 +4720,12 @@ void diff_setup_done(struct diff_options *options)
 	if (!options->use_color || external_diff())
 		options->color_moved = 0;
 
+	if (options->filter_not) {
+		if (!options->filter)
+			options->filter = ~filter_bit[DIFF_STATUS_FILTER_AON];
+		options->filter &= ~options->filter_not;
+	}
+
 	FREE_AND_NULL(options->parseopts);
 }
 
@@ -4820,21 +4826,6 @@ static int diff_opt_diff_filter(const struct option *option,
 	BUG_ON_OPT_NEG(unset);
 	prepare_filter_bits();
 
-	/*
-	 * If there is a negation e.g. 'd' in the input, and we haven't
-	 * initialized the filter field with another --diff-filter, start
-	 * from full set of bits, except for AON.
-	 */
-	if (!opt->filter) {
-		for (i = 0; (optch = optarg[i]) != '\0'; i++) {
-			if (optch < 'a' || 'z' < optch)
-				continue;
-			opt->filter = (1 << (ARRAY_SIZE(diff_status_letters) - 1)) - 1;
-			opt->filter &= ~filter_bit[DIFF_STATUS_FILTER_AON];
-			break;
-		}
-	}
-
 	for (i = 0; (optch = optarg[i]) != '\0'; i++) {
 		unsigned int bit;
 		int negate;
@@ -4851,7 +4842,7 @@ static int diff_opt_diff_filter(const struct option *option,
 			return error(_("unknown change class '%c' in --diff-filter=%s"),
 				     optarg[i], optarg);
 		if (negate)
-			opt->filter &= ~bit;
+			opt->filter_not |= bit;
 		else
 			opt->filter |= bit;
 	}
diff --git a/diff.h b/diff.h
index 8ba85c5e60..a70e7c478c 100644
--- a/diff.h
+++ b/diff.h
@@ -283,7 +283,7 @@ struct diff_options {
 	struct diff_flags flags;
 
 	/* diff-filter bits */
-	unsigned int filter;
+	unsigned int filter, filter_not;
 
 	int use_color;
 
diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index 5049559861..b25182379f 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -142,6 +142,19 @@ test_expect_success 'diff-filter=R' '
 
 '
 
+test_expect_success 'multiple --diff-filter bits' '
+
+	git log -M --pretty="format:%s" --diff-filter=R HEAD >expect &&
+	git log -M --pretty="format:%s" --diff-filter=Ra HEAD >actual &&
+	test_cmp expect actual &&
+	git log -M --pretty="format:%s" --diff-filter=aR HEAD >actual &&
+	test_cmp expect actual &&
+	git log -M --pretty="format:%s" \
+		--diff-filter=a --diff-filter=R HEAD >actual &&
+	test_cmp expect actual
+
+'
+
 test_expect_success 'diff-filter=C' '
 
 	git log -C -C --pretty="format:%s" --diff-filter=C HEAD >actual &&