[PATCH] Fix git-rev-parse's parent handling

git-rev-parse HEAD^1 would fail, because of an off-by-one bug (but HEAD^
would yield the expected result). Also, when the parent does not exist, do
not silently return an incorrect SHA1. Of course, this no longer applies
to git-rev-parse alone, but every user of get_sha1().

While at it, add a test.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

sha1_name.c

@@ -202,15 +202,18 @@ static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 		parent = name[len-1] - '0';
 		len -= 2;
 	}
-	else if (len > 1 && name[len-1] == '^')
+	else if (len > 1 && name[len-1] == '^') {
 		parent = 1;
-	else
+		len--;
+	} else
 		parent = -1;
 
 	if (0 <= parent) {
-		ret = get_parent(name, len-1, sha1, parent);
+		ret = get_parent(name, len, sha1, parent);
 		if (!ret)
 			return 0;
+		else if(parent>0)
+			return ret;
 	}
 	ret = get_sha1_basic(name, len, sha1);
 	if (!ret)

t/t6101-rev-parse-parents.sh

@@ -0,0 +1,33 @@
+#!/bin/sh
+#
+# Copyright (c) 2005 Johannes Schindelin
+#
+
+test_description='Test git-rev-parse with different parent options'
+
+. ./test-lib.sh
+. ../t6000lib.sh # t6xxx specific functions
+
+date >path0
+git-update-cache --add path0
+save_tag tree git-write-tree
+hide_error save_tag start unique_commit "start" tree
+save_tag second unique_commit "second" tree -p start
+hide_error save_tag start2 unique_commit "start2" tree
+save_tag two_parents unique_commit "next" tree -p second -p start2
+save_tag final unique_commit "final" tree -p two_parents
+
+test_expect_success 'start is valid' 'git-rev-parse start | grep "^[0-9a-f]\{40\}$"'
+test_expect_success 'start^0' "test $(cat .git/refs/tags/start) = $(git-rev-parse start^0)"
+test_expect_success 'start^1 not valid' "test $(git-rev-parse start^1) = start^1"
+test_expect_success 'second^1 = second^' "test $(git-rev-parse second^1) = $(git-rev-parse second^)"
+test_expect_success 'final^1^1^1' "test $(git-rev-parse start) = $(git-rev-parse final^1^1^1)"
+test_expect_success 'final^1^1^1 = final^^^' "test $(git-rev-parse final^1^1^1) = $(git-rev-parse final^^^)"
+test_expect_success 'final^1^2' "test $(git-rev-parse start2) = $(git-rev-parse final^1^2)"
+test_expect_success 'final^1^2 != final^1^1' "test $(git-rev-parse final^1^2) != $(git-rev-parse final^1^1)"
+test_expect_success 'final^1^3 not valid' "test $(git-rev-parse final^1^3) = final^1^3"
+test_expect_failure '--verify start2^1' 'git-rev-parse --verify start2^1'
+test_expect_success '--verify start2^0' 'git-rev-parse --verify start2^0'
+
+test_done
+