ref-filter: Do not abruptly die when using the 'lstrip=<N>' option

Currently when we use the 'lstrip=<N>' option, if 'N' is greater than
the number of components available in the refname, we abruptly end
program execution by calling die().

This behavior is undesired since a single refname with few components
could end program execution. To avoid this, return an empty string
whenever the value 'N' is greater than the number of components
available, instead of calling die().

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

Author: KarthikNayak

Documentation/git-for-each-ref.txt

@@ -98,8 +98,7 @@ refname::
 	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.  If a displayed ref has fewer
-	components than `<N>`, the command aborts with an error.
+	`<N>` must be a positive integer.
 
 objecttype::
 	The type of the object (`blob`, `tree`, `commit`, `tag`).

ref-filter.c

@@ -1099,8 +1099,7 @@ static const char *lstrip_ref_components(const char *refname, unsigned int len)
 	while (remaining) {
 		switch (*start++) {
 		case '\0':
-			die(_("ref '%s' does not have %ud components to :lstrip"),
-			    refname, len);
+			return "";
 		case '/':
 			remaining--;
 			break;

t/t6300-for-each-ref.sh

@@ -147,10 +147,6 @@ test_expect_success 'arguments to :lstrip must be positive integers' '
 	test_must_fail git for-each-ref --format="%(refname:lstrip=foo)"
 '
 
-test_expect_success 'stripping refnames too far gives an error' '
-	test_must_fail git for-each-ref --format="%(refname:lstrip=3)"
-'
-
 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 &&