ref-filter: modify the 'lstrip=<N>' option to work with negative '<N>'

Currently the 'lstrip=<N>' option only takes a positive value '<N>'
and strips '<N>' slash-separated path components from the left. Modify
the 'lstrip' option to also take a negative number '<N>' which would
strip from the left as necessary and _leave_ behind only 'N'
slash-separated path components from the right-most end.

For e.g. %(refname:lstrip=-1) would make 'foo/goo/abc' into 'abc'.

Add documentation and tests for the same.

Signed-off-by: Karthik Nayak <Karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 36 insertions, 13 deletions

diff --git a/Documentation/git-for-each-ref.txt b/Documentation/git-for-each-ref.txt
index 04ffc35524..8e4d16d7a3 100644
--- a/Documentation/git-for-each-ref.txt
+++ b/Documentation/git-for-each-ref.txt
@@ -97,8 +97,14 @@ refname::
 	The option core.warnAmbiguousRefs is used to select the strict
 	abbreviation mode. If `lstrip=<N>` is appended, strips `<N>`
 	slash-separated path components from the front of the refname
-	(e.g., `%(refname:lstrip=2)` turns `refs/tags/foo` into `foo`.
-	`<N>` must be a positive integer.
+	(e.g. `%(refname:lstrip=2)` turns `refs/tags/foo` into `foo`.
+	If `<N>` is a negative number, strip as many path components as
+	necessary from the left to leave `-<N>` path components
+	(e.g. `%(refname:lstrip=-2)` turns
+	`refs/tags/foo` into `tags/foo`). When the ref does not have
+	enough components, the result becomes an empty string if
+	stripping with positive <N>, or it becomes the full refname if
+	stripping with negative <N>.  Neither is an error.
 
 objecttype::
 	The type of the object (`blob`, `tree`, `commit`, `tag`).
diff --git a/ref-filter.c b/ref-filter.c
index 4fd6ef186c..2840ca18e3 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -34,7 +34,7 @@ struct if_then_else {
 
 struct refname_atom {
 	enum { R_NORMAL, R_SHORT, R_LSTRIP } option;
-	unsigned int lstrip;
+	int lstrip;
 };
 
 /*
@@ -93,8 +93,8 @@ static void refname_atom_parser_internal(struct refname_atom *atom,
 		atom->option = R_SHORT;
 	else if (skip_prefix(arg, "lstrip=", &arg)) {
 		atom->option = R_LSTRIP;
-		if (strtoul_ui(arg, 10, &atom->lstrip) || atom->lstrip <= 0)
-			die(_("positive value expected refname:lstrip=%s"), arg);
+		if (strtol_i(arg, 10, &atom->lstrip))
+			die(_("Integer value expected refname:lstrip=%s"), arg);
 	} else
 		die(_("unrecognized %%(%s) argument: %s"), name, arg);
 }
@@ -1091,12 +1091,28 @@ static inline char *copy_advance(char *dst, const char *src)
 	return dst;
 }
 
-static const char *lstrip_ref_components(const char *refname, unsigned int len)
+static const char *lstrip_ref_components(const char *refname, int len)
 {
 	long remaining = len;
 	const char *start = refname;
 
-	while (remaining) {
+	if (len < 0) {
+		int i;
+		const char *p = refname;
+
+		/* Find total no of '/' separated path-components */
+		for (i = 0; p[i]; p[i] == '/' ? i++ : *p++)
+			;
+		/*
+		 * The number of components we need to strip is now
+		 * the total minus the components to be left (Plus one
+		 * because we count the number of '/', but the number
+		 * of components is one more than the no of '/').
+		 */
+		remaining = i + len + 1;
+	}
+
+	while (remaining > 0) {
 		switch (*start++) {
 		case '\0':
 			return "";
@@ -1105,6 +1121,7 @@ static const char *lstrip_ref_components(const char *refname, unsigned int len)
 			break;
 		}
 	}
+
 	return start;
 }
 
diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index d3d1a97db9..203cfaa156 100755
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -53,12 +53,16 @@ test_atom head refname refs/heads/master
 test_atom head refname:short master
 test_atom head refname:lstrip=1 heads/master
 test_atom head refname:lstrip=2 master
+test_atom head refname:lstrip=-1 master
+test_atom head refname:lstrip=-2 heads/master
 test_atom head upstream refs/remotes/origin/master
 test_atom head upstream:short origin/master
 test_atom head upstream:lstrip=2 origin/master
+test_atom head upstream:lstrip=-2 origin/master
 test_atom head push refs/remotes/myfork/master
 test_atom head push:short myfork/master
 test_atom head push:lstrip=1 remotes/myfork/master
+test_atom head push:lstrip=-1 master
 test_atom head objecttype commit
 test_atom head objectsize 171
 test_atom head objectname $(git rev-parse refs/heads/master)
@@ -141,12 +145,6 @@ test_expect_success 'Check invalid atoms names are errors' '
 	test_must_fail git for-each-ref --format="%(INVALID)" refs/heads
 '
 
-test_expect_success 'arguments to :lstrip must be positive integers' '
-	test_must_fail git for-each-ref --format="%(refname:lstrip=0)" &&
-	test_must_fail git for-each-ref --format="%(refname:lstrip=-1)" &&
-	test_must_fail git for-each-ref --format="%(refname:lstrip=foo)"
-'
-
 test_expect_success 'Check format specifiers are ignored in naming date atoms' '
 	git for-each-ref --format="%(authordate)" refs/heads &&
 	git for-each-ref --format="%(authordate:default) %(authordate)" refs/heads &&
@@ -624,10 +622,12 @@ test_expect_success 'Verify usage of %(symref:short) atom' '
 
 cat >expected <<EOF
 master
+heads/master
 EOF
 
 test_expect_success 'Verify usage of %(symref:lstrip) atom' '
 	git for-each-ref --format="%(symref:lstrip=2)" refs/heads/sym > actual &&
+	git for-each-ref --format="%(symref:lstrip=-2)" refs/heads/sym >> actual &&
 	test_cmp expected actual
 '