[PATCH 1/5] diff-merges: implement [no-]hide option and log.diffMergesHide config

[Sergey Organov <sorganov@gmail.com>]

The set of diff-merges options happened to be incomplete, and failed
to implement exact semantics of -m option that hides output of diffs
for merge commits unless -p option is active as well.

The new "hide" option fixes this issue, so that now

  --diff-merges=on --diff-merges=hide

combo is the exact synonym for -m.

The log.diffMerges configuration also accepts "hide" and "no-hide"
values, and governs the default value for the hide bit. The
configuration behaves as if "--diff-merges=[no-]hide" is inserted
first in the command-line.

New log.diffMergesHide boolean configuration is implemented as well,
for the case when log.diffMerges is already in use for specifying the
format.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
---
 Documentation/config/log.txt                  |  6 +++
 Documentation/diff-options.txt                | 13 +++--
 builtin/log.c                                 |  2 +
 diff-merges.c                                 | 40 ++++++++++++--
 diff-merges.h                                 |  2 +
 t/t4013-diff-various.sh                       | 54 ++++++++++++++++++-
 ...ges=first-parent_--diff-merges=hide_master | 34 ++++++++++++
 t/t9902-completion.sh                         |  3 ++
 8 files changed, 147 insertions(+), 7 deletions(-)
 create mode 100644 t/t4013/diff.log_--diff-merges=first-parent_--diff-merges=hide_master

diff --git a/Documentation/config/log.txt b/Documentation/config/log.txt
index cbe34d759221..9c6be643bcf6 100644
--- a/Documentation/config/log.txt
+++ b/Documentation/config/log.txt
@@ -33,6 +33,12 @@ log.diffMerges::
 	Set diff format to be used when `--diff-merges=on` is
 	specified, see `--diff-merges` in linkgit:git-log[1] for
 	details. Defaults to `separate`.
++
+When used with 'hide' or 'no-hide', sets the default hiding of
+diffs for merge commits when `-p` option is not used.
+
+log.diffMergesHide::
+	`true` implies `--diff-merges=hide` option.
 
 log.follow::
 	If `true`, `git log` will act as if the `--follow` option was used when
diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 3674ac48e92c..351d51215717 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -34,7 +34,7 @@ endif::git-diff[]
 endif::git-format-patch[]
 
 ifdef::git-log[]
---diff-merges=(off|none|on|first-parent|1|separate|m|combined|c|dense-combined|cc|remerge|r)::
+--diff-merges=(off|none|on|first-parent|1|separate|m|combined|c|dense-combined|cc|remerge|r|[no-]hide)::
 --no-diff-merges::
 	Specify diff format to be used for merge commits. Default is
 	{diff-merges-default} unless `--first-parent` is in use, in which case
@@ -49,10 +49,11 @@ ifdef::git-log[]
 --diff-merges=m:::
 -m:::
 	This option makes diff output for merge commits to be shown in
-	the default format. `-m` will produce the output only if `-p`
-	is given as well. The default format could be changed using
+	the default format. The default format could be changed using
 	`log.diffMerges` configuration parameter, which default value
 	is `separate`.
++
+	`-m` is a shortcut for '--diff-merges=on --diff-merges=hide'
 +
 --diff-merges=first-parent:::
 --diff-merges=1:::
@@ -72,6 +73,12 @@ ifdef::git-log[]
 	with conflict markers and such.  A diff is then shown between
 	that temporary tree and the actual merge commit.
 +
+--diff-merges=hide:::
+--diff-merges=no-hide:::
+	Hide (do not hide) the diff for merge commits unless `-p` options is given
+	as well. The default `no-hide` could be changed using `log.diffMerges`
+	configuration parameter.
++
 The output emitted when this option is used is subject to change, and
 so is its interaction with other options (unless explicitly
 documented).
diff --git a/builtin/log.c b/builtin/log.c
index 56e2d95e869d..e031021e53b2 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -581,6 +581,8 @@ static int git_log_config(const char *var, const char *value, void *cb)
 	}
 	if (!strcmp(var, "log.diffmerges"))
 		return diff_merges_config(value);
+	if (!strcmp(var, "log.diffmergeshide"))
+		return diff_merges_hide_config(git_config_bool(var, value));
 	if (!strcmp(var, "log.showroot")) {
 		default_show_root = git_config_bool(var, value);
 		return 0;
diff --git a/diff-merges.c b/diff-merges.c
index 85cbefa5afd7..55fe5b70c102 100644
--- a/diff-merges.c
+++ b/diff-merges.c
@@ -7,6 +7,7 @@ static void set_separate(struct rev_info *revs);
 
 static diff_merges_setup_func_t set_to_default = set_separate;
 static int suppress_m_parsing;
+static int hide = 0;
 
 static void suppress(struct rev_info *revs)
 {
@@ -20,10 +21,15 @@ static void suppress(struct rev_info *revs)
 	revs->remerge_diff = 0;
 }
 
+static void set_need_diff(struct rev_info *revs)
+{
+	revs->merges_need_diff = !hide;
+}
+
 static void common_setup(struct rev_info *revs)
 {
 	suppress(revs);
-	revs->merges_need_diff = 1;
+	set_need_diff(revs);
 }
 
 static void set_none(struct rev_info *revs)
@@ -31,6 +37,18 @@ static void set_none(struct rev_info *revs)
 	suppress(revs);
 }
 
+static void set_hide(struct rev_info *revs)
+{
+	hide = 1;
+	set_need_diff(revs);
+}
+
+static void set_no_hide(struct rev_info *revs)
+{
+	hide = 0;
+	set_need_diff(revs);
+}
+
 static void set_separate(struct rev_info *revs)
 {
 	common_setup(revs);
@@ -69,6 +87,10 @@ static diff_merges_setup_func_t func_by_opt(const char *optarg)
 {
 	if (!strcmp(optarg, "off") || !strcmp(optarg, "none"))
 		return set_none;
+	if (!strcmp(optarg, "hide"))
+		return set_hide;
+	if (!strcmp(optarg, "no-hide"))
+		return set_no_hide;
 	if (!strcmp(optarg, "1") || !strcmp(optarg, "first-parent"))
 		return set_first_parent;
 	if (!strcmp(optarg, "separate"))
@@ -105,7 +127,19 @@ int diff_merges_config(const char *value)
 	if (!func)
 		return -1;
 
-	set_to_default = func;
+	if (func == set_hide)
+		hide = 1;
+	else if (func == set_no_hide)
+		hide = 0;
+	else
+		set_to_default = func;
+
+	return 0;
+}
+
+int diff_merges_hide_config(int on)
+{
+	hide = on;
 	return 0;
 }
 
@@ -122,7 +156,7 @@ int diff_merges_parse_opts(struct rev_info *revs, const char **argv)
 
 	if (!suppress_m_parsing && !strcmp(arg, "-m")) {
 		set_to_default(revs);
-		revs->merges_need_diff = 0;
+		set_hide(revs);
 	} else if (!strcmp(arg, "-c")) {
 		set_combined(revs);
 		revs->merges_imply_patch = 1;
diff --git a/diff-merges.h b/diff-merges.h
index 19639689bb05..e86e5381693b 100644
--- a/diff-merges.h
+++ b/diff-merges.h
@@ -11,6 +11,8 @@ struct rev_info;
 
 int diff_merges_config(const char *value);
 
+int diff_merges_hide_config(int hide);
+
 void diff_merges_suppress_m_parsing(void);
 
 int diff_merges_parse_opts(struct rev_info *revs, const char **argv);
diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
index dfcf3a0aaae3..4fc8ba2fc59c 100755
--- a/t/t4013-diff-various.sh
+++ b/t/t4013-diff-various.sh
@@ -334,6 +334,7 @@ log --first-parent --diff-merges=off -p master
 log -p --first-parent master
 log -p --diff-merges=first-parent master
 log --diff-merges=first-parent master
+log --diff-merges=first-parent --diff-merges=hide master
 log -m -p --first-parent master
 log -m -p master
 log --cc -m -p master
@@ -460,7 +461,18 @@ EOF
 test_expect_success 'log -m matches pure log' '
 	git log master >result &&
 	process_diffs result >expected &&
-	git log -m >result &&
+	git log -m master >result &&
+	process_diffs result >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'log --diff-merges=on matches -m only with --diff-merges=hide' '
+	git log -m master >result &&
+	process_diffs result >expected &&
+	git log --diff-merges=on master >result &&
+	process_diffs result >actual &&
+	! test_cmp expected actual &&
+	git log --diff-merges=on --diff-merges=hide master >result &&
 	process_diffs result >actual &&
 	test_cmp expected actual
 '
@@ -496,6 +508,46 @@ test_expect_success 'git config log.diffMerges first-parent vs -m' '
 	test_cmp expected actual
 '
 
+test_expect_success 'git config log.diffMerges hide: has effect' '
+	git log --diff-merges=on master >result &&
+	process_diffs result >no-hide &&
+	test_config log.diffMerges hide &&
+	git log --diff-merges=on master >result &&
+	process_diffs result >hide &&
+	! test_cmp no-hide hide
+'
+
+test_expect_success 'git config log.diffMerges no-hide: is the default' '
+	git log --diff-merges=on master >result &&
+	process_diffs result >default &&
+	test_config log.diffMerges no-hide &&
+	git log --diff-merges=on master >result &&
+	process_diffs result >no-hide &&
+	test_cmp default no-hide
+'
+
+# As "-m" is synonym for "--diff-merges=hide --diff-merges=on", the
+# "log.diffMerges=hide" configuration should have no effect on "-m"
+test_expect_success 'git config log.diffMerges hide: has no effect on -m' '
+	git log -m master >result &&
+	process_diffs result >expected &&
+	test_config log.diffMerges hide &&
+	git log -m master >result &&
+	process_diffs result >actual &&
+	test_cmp expected actual
+'
+
+# As "--cc" implies "-p", the "log.diffMerges=hide" configuration
+# should have no effect on "--cc"
+test_expect_success 'git config log.diffMerges hide: has no effect on --cc' '
+	git log --cc master >result &&
+	process_diffs result >expected &&
+	test_config log.diffMerges hide &&
+	git log --cc master >result &&
+	process_diffs result >actual &&
+	test_cmp expected actual
+'
+
 # -m in "git diff-index" means "match missing", that differs
 # from its meaning in "git diff". Let's check it in diff-index.
 # The line in the output for removed file should disappear when
diff --git a/t/t4013/diff.log_--diff-merges=first-parent_--diff-merges=hide_master b/t/t4013/diff.log_--diff-merges=first-parent_--diff-merges=hide_master
new file mode 100644
index 000000000000..596caec64298
--- /dev/null
+++ b/t/t4013/diff.log_--diff-merges=first-parent_--diff-merges=hide_master
@@ -0,0 +1,34 @@
+$ git log --diff-merges=first-parent --diff-merges=hide master
+commit 59d314ad6f356dd08601a4cd5e530381da3e3c64
+Merge: 9a6d494 c7a2ab9
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:04:00 2006 +0000
+
+    Merge branch 'side'
+
+commit c7a2ab9e8eac7b117442a607d5a9b3950ae34d5a
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:03:00 2006 +0000
+
+    Side
+
+commit 9a6d4949b6b76956d9d5e26f2791ec2ceff5fdc0
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:02:00 2006 +0000
+
+    Third
+
+commit 1bde4ae5f36c8d9abe3a0fce0c6aab3c4a12fe44
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:01:00 2006 +0000
+
+    Second
+    
+    This is the second commit.
+
+commit 444ac553ac7612cc88969031b02b3767fb8a353a
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:00:00 2006 +0000
+
+    Initial
+$
diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
index 43de868b8005..fc6b0722216a 100755
--- a/t/t9902-completion.sh
+++ b/t/t9902-completion.sh
@@ -2497,6 +2497,7 @@ test_expect_success 'git config - variable name' '
 	log.date Z
 	log.decorate Z
 	log.diffMerges Z
+	log.diffMergesHide Z
 	EOF
 '
 
@@ -2525,6 +2526,7 @@ test_expect_success 'git -c - variable name' '
 	log.date=Z
 	log.decorate=Z
 	log.diffMerges=Z
+	log.diffMergesHide=Z
 	EOF
 '
 
@@ -2547,6 +2549,7 @@ test_expect_success 'git clone --config= - variable name' '
 	log.date=Z
 	log.decorate=Z
 	log.diffMerges=Z
+	log.diffMergesHide=Z
 	EOF
 '
 
-- 
2.37.3.526.g5f84746cb16b