ref-filter: add an 'rstrip=<N>' option to atoms which deal with refnames

Complimenting the existing 'lstrip=<N>' option, add an 'rstrip=<N>'
option which strips `<N>` slash-separated path components from the end
of the refname (e.g., `%(refname:rstrip=2)` turns `refs/tags/foo` into
`refs`).

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

Documentation/git-for-each-ref.txt

@@ -95,13 +95,15 @@ refname::
 	The name of the ref (the part after $GIT_DIR/).
 	For a non-ambiguous short name of the ref append `:short`.
 	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`.
+	abbreviation mode. If `lstrip=<N>` (`rstrip=<N>`) is appended, strips `<N>`
+	slash-separated path components from the front (back) of the refname
+	(e.g. `%(refname:lstrip=2)` turns `refs/tags/foo` into `foo` and
+	`%(refname:rstrip=2)` turns `refs/tags/foo` into `refs`).
 	If `<N>` is a negative number, strip as many path components as
-	necessary from the left to leave `-<N>` path components
+	necessary from the specified end to leave `-<N>` path components
 	(e.g. `%(refname:lstrip=-2)` turns
-	`refs/tags/foo` into `tags/foo`). When the ref does not have
+	`refs/tags/foo` into `tags/foo` and `%(refname:rstrip=-1)`
+	turns `refs/tags/foo` into `refs`). 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.
@@ -121,22 +123,23 @@ objectname::
 
 upstream::
 	The name of a local ref which can be considered ``upstream''
-	from the displayed ref. Respects `:short` and `:lstrip` in the
-	same way as `refname` above.  Additionally respects `:track`
-	to show "[ahead N, behind M]" and `:trackshort` to show the
-	terse version: ">" (ahead), "<" (behind), "<>" (ahead and
-	behind), or "=" (in sync). `:track` also prints "[gone]"
-	whenever unknown upstream ref is encountered. Append
-	`:track,nobracket` to show tracking information without
-	brackets (i.e "ahead N, behind M").  Has no effect if the ref
-	does not have tracking information associated with it.  All
-	the options apart from `nobracket` are mutually exclusive, but
-	if used together the last option is selected.
+	from the displayed ref. Respects `:short`, `:lstrip` and
+	`:rstrip` in the same way as `refname` above.  Additionally
+	respects `:track` to show "[ahead N, behind M]" and
+	`:trackshort` to show the terse version: ">" (ahead), "<"
+	(behind), "<>" (ahead and behind), or "=" (in sync). `:track`
+	also prints "[gone]" whenever unknown upstream ref is
+	encountered. Append `:track,nobracket` to show tracking
+	information without brackets (i.e "ahead N, behind M").  Has
+	no effect if the ref does not have tracking information
+	associated with it.  All the options apart from `nobracket`
+	are mutually exclusive, but if used together the last option
+	is selected.
 
 push::
 	The name of a local ref which represents the `@{push}`
 	location for the displayed ref. Respects `:short`, `:lstrip`,
-	`:track`, and `:trackshort` options as `upstream`
+	`:rstrip`, `:track`, and `:trackshort` options as `upstream`
 	does. Produces an empty string if no `@{push}` ref is
 	configured.
 
@@ -178,8 +181,9 @@ if::
 
 symref::
 	The ref which the given symbolic ref refers to. If not a
-	symbolic ref, nothing is printed. Respects the `:short` and
-	`:lstrip` options in the same way as `refname` above.
+	symbolic ref, nothing is printed. Respects the `:short`,
+	`:lstrip` and `:rstrip` options in the same way as `refname`
+	above.
 
 In addition to the above, for commit and tag objects, the header
 field names (`tree`, `parent`, `object`, `type`, and `tag`) can

ref-filter.c

@@ -33,8 +33,8 @@ struct if_then_else {
 };
 
 struct refname_atom {
-	enum { R_NORMAL, R_SHORT, R_LSTRIP } option;
-	int lstrip;
+	enum { R_NORMAL, R_SHORT, R_LSTRIP, R_RSTRIP } option;
+	int lstrip, rstrip;
 };
 
 /*
@@ -95,6 +95,10 @@ static void refname_atom_parser_internal(struct refname_atom *atom,
 		atom->option = R_LSTRIP;
 		if (strtol_i(arg, 10, &atom->lstrip))
 			die(_("Integer value expected refname:lstrip=%s"), arg);
+	} else if (skip_prefix(arg, "rstrip=", &arg)) {
+		atom->option = R_RSTRIP;
+		if (strtol_i(arg, 10, &atom->rstrip))
+			die(_("Integer value expected refname:rstrip=%s"), arg);
 	} else
 		die(_("unrecognized %%(%s) argument: %s"), name, arg);
 }
@@ -1125,12 +1129,45 @@ static const char *lstrip_ref_components(const char *refname, int len)
 	return start;
 }
 
+static const char *rstrip_ref_components(const char *refname, int len)
+{
+	long remaining = len;
+	char *start = xstrdup(refname);
+
+	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) {
+		char *p = strrchr(start, '/');
+		if (p == NULL)
+			return "";
+		else
+			p[0] = '\0';
+	}
+	return start;
+}
+
 static const char *show_ref(struct refname_atom *atom, const char *refname)
 {
 	if (atom->option == R_SHORT)
 		return shorten_unambiguous_ref(refname, warn_ambiguous_refs);
 	else if (atom->option == R_LSTRIP)
 		return lstrip_ref_components(refname, atom->lstrip);
+	else if (atom->option == R_RSTRIP)
+		return rstrip_ref_components(refname, atom->rstrip);
 	else
 		return refname;
 }

t/t6300-for-each-ref.sh

@@ -55,14 +55,22 @@ 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 refname:rstrip=1 refs/heads
+test_atom head refname:rstrip=2 refs
+test_atom head refname:rstrip=-1 refs
+test_atom head refname:rstrip=-2 refs/heads
 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 upstream:rstrip=2 refs/remotes
+test_atom head upstream:rstrip=-2 refs/remotes
 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 push:rstrip=1 refs/remotes/myfork
+test_atom head push:rstrip=-1 refs
 test_atom head objecttype commit
 test_atom head objectsize 171
 test_atom head objectname $(git rev-parse refs/heads/master)
@@ -631,4 +639,15 @@ test_expect_success 'Verify usage of %(symref:lstrip) atom' '
 	test_cmp expected actual
 '
 
+cat >expected <<EOF
+refs
+refs/heads
+EOF
+
+test_expect_success 'Verify usage of %(symref:rstrip) atom' '
+	git for-each-ref --format="%(symref:rstrip=2)" refs/heads/sym > actual &&
+	git for-each-ref --format="%(symref:rstrip=-2)" refs/heads/sym >> actual &&
+	test_cmp expected actual
+'
+
 test_done