get_sha1: support $commit^{/regex} syntax

This works like ":/regex" syntax that finds a recently created commit
starting from all refs, but limits the discovery to those reachable from
the named commit.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/revisions.txt

@@ -106,6 +106,12 @@ the `$GIT_DIR/refs` directory or from the `$GIT_DIR/packed-refs` file.
   and dereference the tag recursively until a non-tag object is
   found.
 
+* A suffix '{caret}' to a revision parameter followed by a brace
+  pair that contains a text led by a slash (e.g. `HEAD^{/fix nasty bug}`):
+  this is the same as `:/fix nasty bug` syntax below except that
+  it returns the youngest matching commit which is reachable from
+  the ref before '{caret}'.
+
 * A colon, followed by a slash, followed by a text (e.g. `:/fix nasty bug`): this names
   a commit whose commit message matches the specified regular expression.
   This name returns the youngest matching commit which is

sha1_name.c

@@ -7,6 +7,8 @@
 #include "refs.h"
 #include "remote.h"
 
+static int get_sha1_oneline(const char *, unsigned char *, struct commit_list *);
+
 static int find_short_object_filename(int len, const char *name, unsigned char *sha1)
 {
 	struct alternate_object_database *alt;
@@ -562,6 +564,8 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 		expected_type = OBJ_BLOB;
 	else if (sp[0] == '}')
 		expected_type = OBJ_NONE;
+	else if (sp[0] == '/')
+		expected_type = OBJ_COMMIT;
 	else
 		return -1;
 
@@ -576,19 +580,30 @@ static int peel_onion(const char *name, int len, unsigned char *sha1)
 		if (!o || (!o->parsed && !parse_object(o->sha1)))
 			return -1;
 		hashcpy(sha1, o->sha1);
+		return 0;
 	}
-	else {
+
 	/*
 	 * At this point, the syntax look correct, so
 	 * if we do not get the needed object, we should
 	 * barf.
 	 */
 	o = peel_to_type(name, len, o, expected_type);
-		if (o) {
-			hashcpy(sha1, o->sha1);
-			return 0;
-		}
+	if (!o)
 		return -1;
+
+	hashcpy(sha1, o->sha1);
+	if (sp[0] == '/') {
+		/* "$commit^{/foo}" */
+		char *prefix;
+		int ret;
+		struct commit_list *list = NULL;
+
+		prefix = xstrndup(sp + 1, name + len - 1 - (sp + 1));
+		commit_list_insert((struct commit *)o, &list);
+		ret = get_sha1_oneline(prefix, sha1, list);
+		free(prefix);
+		return ret;
 	}
 	return 0;
 }

t/t1511-rev-parse-caret.sh

@@ -0,0 +1,73 @@
+#!/bin/sh
+
+test_description='tests for ref^{stuff}'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	echo blob >a-blob &&
+	git tag -a -m blob blob-tag `git hash-object -w a-blob`
+	mkdir a-tree &&
+	echo moreblobs >a-tree/another-blob &&
+	git add . &&
+	TREE_SHA1=`git write-tree` &&
+	git tag -a -m tree tree-tag "$TREE_SHA1" &&
+	git commit -m Initial &&
+	git tag -a -m commit commit-tag &&
+	git branch ref &&
+	git checkout master &&
+	echo modified >>a-blob &&
+	git add -u &&
+	git commit -m Modified
+'
+
+test_expect_success 'ref^{non-existent}' '
+	test_must_fail git rev-parse ref^{non-existent}
+'
+
+test_expect_success 'ref^{}' '
+	git rev-parse ref >expected &&
+	git rev-parse ref^{} >actual &&
+	test_cmp expected actual &&
+	git rev-parse commit-tag^{} >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'ref^{commit}' '
+	git rev-parse ref >expected &&
+	git rev-parse ref^{commit} >actual &&
+	test_cmp expected actual &&
+	git rev-parse commit-tag^{commit} >actual &&
+	test_cmp expected actual &&
+	test_must_fail git rev-parse tree-tag^{commit} &&
+	test_must_fail git rev-parse blob-tag^{commit}
+'
+
+test_expect_success 'ref^{tree}' '
+	echo $TREE_SHA1 >expected &&
+	git rev-parse ref^{tree} >actual &&
+	test_cmp expected actual &&
+	git rev-parse commit-tag^{tree} >actual &&
+	test_cmp expected actual &&
+	git rev-parse tree-tag^{tree} >actual &&
+	test_cmp expected actual &&
+	test_must_fail git rev-parse blob-tag^{tree}
+'
+
+test_expect_success 'ref^{/.}' '
+	git rev-parse master >expected &&
+	git rev-parse master^{/.} >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'ref^{/non-existent}' '
+	test_must_fail git rev-parse master^{/non-existent}
+'
+
+test_expect_success 'ref^{/Initial}' '
+	git rev-parse ref >expected &&
+	git rev-parse master^{/Initial} >actual &&
+	test_cmp expected actual
+'
+
+test_done