[PATCH] get_sha1: support relative path ":path" syntax

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Currently :path and ref:path can be used to refer to a specific object
in index or ref respectively. "path" component is absolute path. This
patch allows "path" to be written as "./path" or "../path", which is
relative to user's original cwd.

This does not work in commands for which startup_info is NULL
(i.e. non-builtin ones, it seems none of them needs this anyway).

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Updated the message when startup_info == NULL

 Documentation/revisions.txt    |    4 ++
 sha1_name.c                    |   37 ++++++++++++++++++++++--
 t/t1506-rev-parse-diagnosis.sh |   62 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 100 insertions(+), 3 deletions(-)

diff --git a/Documentation/revisions.txt b/Documentation/revisions.txt
index 3d4b79c..8b519d7 100644
--- a/Documentation/revisions.txt
+++ b/Documentation/revisions.txt
@@ -121,6 +121,10 @@ the `$GIT_DIR/refs` directory or from the `$GIT_DIR/packed-refs` file.
   ':path' (with an empty part before the colon, e.g. `:README`)
   is a special case of the syntax described next: content
   recorded in the index at the given path.
+  A path starting with './' or '../' is relative to current working directory.
+  The given path will be converted to be relative to working tree's root directory.
+  This is most useful to address a blob or tree from a commit or tree that has
+  the same tree structure with the working tree.
 
 * A colon, optionally followed by a stage number (0 to 3) and a
   colon, followed by a path (e.g. `:0:README`); this names a blob object in the
diff --git a/sha1_name.c b/sha1_name.c
index 484081d..f918faf 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -1046,6 +1046,23 @@ int get_sha1_with_mode_1(const char *name, unsigned char *sha1, unsigned *mode,
 	return ret;
 }
 
+static char *resolve_relative_path(const char *rel)
+{
+	if (prefixcmp(rel, "./") && prefixcmp(rel, "../"))
+		return NULL;
+
+	if (!startup_info)
+		die("BUG: startup_info struct is not initialized.");
+
+	if (!is_inside_work_tree())
+		die("relative path syntax can't be used outside working tree.");
+
+	/* die() inside prefix_path() if resolved path is outside worktree */
+	return prefix_path(startup_info->prefix,
+			   startup_info->prefix ? strlen(startup_info->prefix) : 0,
+			   rel);
+}
+
 int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 			    struct object_context *oc,
 			    int gently, const char *prefix)
@@ -1060,25 +1077,31 @@ int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 	if (!ret)
 		return ret;
 	/* sha1:path --> object name of path in ent sha1
-	 * :path -> object name of path in index
+	 * :path -> object name of absolute path in index
+	 * :./path -> object name of path relative to cwd in index
 	 * :[0-3]:path -> object name of path in index at stage
 	 * :/foo -> recent commit matching foo
 	 */
 	if (name[0] == ':') {
 		int stage = 0;
 		struct cache_entry *ce;
+		char *new_path = NULL;
 		int pos;
 		if (namelen > 2 && name[1] == '/')
 			return get_sha1_oneline(name + 2, sha1);
 		if (namelen < 3 ||
 		    name[2] != ':' ||
-		    name[1] < '0' || '3' < name[1])
+		    name[1] < '0' || '3' < name[1]) {
 			cp = name + 1;
+			new_path = resolve_relative_path(cp);
+			if (new_path)
+				cp = new_path;
+		}
 		else {
 			stage = name[1] - '0';
 			cp = name + 3;
 		}
-		namelen = namelen - (cp - name);
+		namelen = strlen(cp);
 
 		strncpy(oc->path, cp,
 			sizeof(oc->path));
@@ -1096,12 +1119,14 @@ int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 				break;
 			if (ce_stage(ce) == stage) {
 				hashcpy(sha1, ce->sha1);
+				free(new_path);
 				return 0;
 			}
 			pos++;
 		}
 		if (!gently)
 			diagnose_invalid_index_path(stage, prefix, cp);
+		free(new_path);
 		return -1;
 	}
 	for (cp = name, bracket_depth = 0; *cp; cp++) {
@@ -1122,6 +1147,11 @@ int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 		}
 		if (!get_sha1_1(name, cp-name, tree_sha1)) {
 			const char *filename = cp+1;
+			char *new_filename = NULL;
+
+			new_filename = resolve_relative_path(filename);
+			if (new_filename)
+				filename = new_filename;
 			ret = get_tree_entry(tree_sha1, filename, sha1, &oc->mode);
 			if (!gently) {
 				diagnose_invalid_sha1_path(prefix, filename,
@@ -1133,6 +1163,7 @@ int get_sha1_with_context_1(const char *name, unsigned char *sha1,
 				sizeof(oc->path));
 			oc->path[sizeof(oc->path)-1] = '\0';
 
+			free(new_filename);
 			return ret;
 		} else {
 			if (!gently)
diff --git a/t/t1506-rev-parse-diagnosis.sh b/t/t1506-rev-parse-diagnosis.sh
index 0eeeb0e..f7a4076 100755
--- a/t/t1506-rev-parse-diagnosis.sh
+++ b/t/t1506-rev-parse-diagnosis.sh
@@ -31,6 +31,43 @@ test_expect_success 'correct file objects' '
 	 test $HASH_file = $(git rev-parse :0:file.txt) )
 '
 
+test_expect_success 'correct relative file objects (0)' '
+	git rev-parse :file.txt >expected &&
+	git rev-parse :./file.txt >result &&
+	test_cmp expected result
+'
+
+test_expect_success 'correct relative file objects (1)' '
+	git rev-parse HEAD:file.txt >expected &&
+	git rev-parse HEAD:./file.txt >result &&
+	test_cmp expected result
+'
+
+test_expect_success 'correct relative file objects (2)' '
+	(
+		cd subdir &&
+		git rev-parse HEAD:../file.txt >result &&
+		test_cmp ../expected result
+	)
+'
+
+test_expect_success 'correct relative file objects (3)' '
+	(
+		cd subdir &&
+		git rev-parse HEAD:../subdir/../file.txt >result &&
+		test_cmp ../expected result
+	)
+'
+
+test_expect_success 'correct relative file objects (4)' '
+	git rev-parse HEAD:subdir/file.txt >expected &&
+	(
+		cd subdir &&
+		git rev-parse HEAD:./file.txt >result &&
+		test_cmp ../expected result
+	)
+'
+
 test_expect_success 'incorrect revision id' '
 	test_must_fail git rev-parse foobar:file.txt 2>error &&
 	grep "Invalid object name '"'"'foobar'"'"'." error &&
@@ -75,4 +112,29 @@ test_expect_success 'invalid @{n} reference' '
 	grep "fatal: Log for [^ ]* only has [0-9][0-9]* entries." error
 '
 
+test_expect_success 'relative path not found' '
+	(
+		cd subdir &&
+		test_must_fail git rev-parse HEAD:./nonexistent.txt 2>error &&
+		grep subdir/nonexistent.txt error
+	)
+'
+
+test_expect_success 'relative path outside worktree' '
+	test_must_fail git rev-parse HEAD:../file.txt >output 2>error &&
+	test -z "$(cat output)" &&
+	grep "outside repository" error
+'
+
+test_expect_success 'relative path when cwd is outside worktree' '
+	test_must_fail git --git-dir=.git --work-tree=subdir rev-parse HEAD:./file.txt >output 2>error &&
+	test -z "$(cat output)" &&
+	grep "relative path syntax can.t be used outside working tree." error
+'
+
+test_expect_success 'relative path when startup_info is NULL' '
+	test_must_fail test-match-trees HEAD:./file.txt HEAD:./file.txt 2>error &&
+	grep "Relative path syntax is not supported in this command" error
+'
+
 test_done
-- 
1.7.3.2.316.gda8b3