[RFC/PATCH 04/11] ref-filter: add 'ifexists' atom

[Karthik Nayak <karthik.188@gmail.com>]

The 'ifexists' atom allows us to print a required format if the
preceeding atom has a value. If the preceeding atom has no value then
the format given is not printed. e.g. to print "[<refname>]" we can
now use the format "%(ifexists:[%s])%(refname)".

Add documentation and test for the same.

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
---
 Documentation/git-for-each-ref.txt |  8 ++++++++
 ref-filter.c                       | 37 ++++++++++++++++++++++++++++++++++---
 ref-filter.h                       |  5 +++--
 t/t6302-for-each-ref-filter.sh     | 21 +++++++++++++++++++++
 4 files changed, 66 insertions(+), 5 deletions(-)

diff --git a/Documentation/git-for-each-ref.txt b/Documentation/git-for-each-ref.txt
index 9dc02aa..4424020 100644
--- a/Documentation/git-for-each-ref.txt
+++ b/Documentation/git-for-each-ref.txt
@@ -138,6 +138,14 @@ colornext::
 	`<:colorname>`.  Not compatible with `padright` and resets any
 	previous `color`, if set.
 
+ifexists::
+	Print required string only if the next atom specified in the
+	'--format' option exists.
+	e.g. --format="%(ifexists:[%s])%(symref)" prints the symref
+	like "[<symref>]" only if the ref has a symref.  This was
+	incorporated to simulate the output of 'git branch -vv', where
+	we need to display the upstream branch in square brackets.
+
 In addition to the above, for commit and tag objects, the header
 field names (`tree`, `parent`, `object`, `type`, and `tag`) can
 be used to specify the value in the header field.
diff --git a/ref-filter.c b/ref-filter.c
index 3f40144..ff5a16b 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -58,6 +58,7 @@ static struct {
 	{ "color" },
 	{ "padright" },
 	{ "colornext" },
+	{ "ifexists" },
 };
 
 /*
@@ -722,6 +723,13 @@ static void populate_value(struct ref_array_item *ref)
 			v->modifier_atom = 1;
 			v->color_next = 1;
 			continue;
+		} else if (starts_with(name, "ifexists:")) {
+			skip_prefix(name, "ifexists:", &v->s);
+			if (!*v->s)
+				die(_("no string given with 'ifexists:'"));
+			v->modifier_atom = 1;
+			v->ifexists = 1;
+			continue;
 		} else
 			continue;
 
@@ -1315,11 +1323,32 @@ static void apply_formatting_state(struct ref_formatting_state *state,
 {
 	if (state->color_next && state->pad_to_right)
 		die(_("cannot use `colornext` and `padright` together"));
-	if (state->color_next) {
+	if (state->pad_to_right && state->ifexists)
+		die(_("cannot use 'align' and 'ifexists' together"));
+	if (state->color_next && !state->ifexists) {
 		strbuf_addf(value, "%s%s%s", state->color_next, v->s, GIT_COLOR_RESET);
 		return;
-	}
-	else if (state->pad_to_right) {
+	} else if (state->ifexists) {
+		const char *sp = state->ifexists;
+
+		while (*sp) {
+			if (*sp != '%') {
+				strbuf_addch(value, *sp++);
+				continue;
+			} else if (sp[1] == '%') {
+				strbuf_addch(value, *sp++);
+				continue;
+			} else if (sp[1] == 's') {
+				if (state->color_next)
+					strbuf_addf(value, "%s%s%s", state->color_next, v->s, GIT_COLOR_RESET);
+				else
+					strbuf_addstr(value, v->s);
+				sp += 2;
+			}
+		}
+
+		return;
+	} else if (state->pad_to_right) {
 		if (!is_utf8(v->s))
 			strbuf_addf(value, "%-*s", state->pad_to_right, v->s);
 		else {
@@ -1413,6 +1442,8 @@ static void store_formatting_state(struct ref_formatting_state *state,
 		state->color_next = atomv->s;
 	if (atomv->pad_to_right)
 		state->pad_to_right = atomv->ul;
+	if (atomv->ifexists)
+		state->ifexists = atomv->s;
 }
 
 static void reset_formatting_state(struct ref_formatting_state *state)
diff --git a/ref-filter.h b/ref-filter.h
index a021b04..7d1871d 100644
--- a/ref-filter.h
+++ b/ref-filter.h
@@ -28,13 +28,14 @@ struct atom_value {
 	unsigned long ul; /* used for sorting when not FIELD_STR */
 	unsigned int modifier_atom : 1, /*  atoms which act as modifiers for the next atom */
 		pad_to_right : 1,
-		color_next : 1;
+		color_next : 1,
+		ifexists : 1;
 };
 
 struct ref_formatting_state {
 	int quote_style;
 	unsigned int pad_to_right;
-	const char *color_next;
+	const char *color_next, *ifexists;
 };
 
 struct ref_sorting {
diff --git a/t/t6302-for-each-ref-filter.sh b/t/t6302-for-each-ref-filter.sh
index 6aad069..29ed97b 100755
--- a/t/t6302-for-each-ref-filter.sh
+++ b/t/t6302-for-each-ref-filter.sh
@@ -149,4 +149,25 @@ test_expect_success 'check `colornext` format option' '
 	test_cmp expect actual
 '
 
+test_expect_success 'check `ifexists` format option' '
+	cat >expect <<-\EOF &&
+	[foo1.10]
+	[foo1.3]
+	[foo1.6]
+	EOF
+	git for-each-ref --format="%(ifexists:[%s])%(refname:short)" | grep "foo" >actual &&
+	test_cmp expect actual
+'
+
+cat >expect <<EOF &&
+[$(get_color green)foo1.10$(get_color reset)]||foo1.10
+[$(get_color green)foo1.3$(get_color reset)]||foo1.3
+[$(get_color green)foo1.6$(get_color reset)]||foo1.6
+EOF
+
+test_expect_success 'check `ifexists` with `colornext` format option' '
+	git for-each-ref --format="%(ifexists:[%s])%(colornext:green)%(refname:short)||%(refname:short)" | grep "foo" >actual &&
+	test_cmp expect actual
+'
+
 test_done
-- 
2.4.6