[PATCH] Make "git diff" work inside relative subdirectories

We always show the diff as an absolute path, but pathnames to diff are
taken relative to the current working directory (and if no pathnames are
given, the default ends up being all of the current working directory).

Note that "../xyz" also works, so you can do

	cd linux/drivers/char
	git diff ../block

and it will generate a diff of the linux/drivers/block changes.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

8 files changed, 147 insertions, 19 deletions

diff --git a/Makefile b/Makefile
index 16ab0c7f02..db7596504a 100644
--- a/Makefile
+++ b/Makefile
@@ -97,7 +97,7 @@ LIB_H=cache.h object.h blob.h tree.h commit.h tag.h delta.h epoch.h csum-file.h
 LIB_OBJS=read-cache.o sha1_file.o usage.o object.o commit.o tree.o blob.o \
 	 tag.o date.o index.o diff-delta.o patch-delta.o entry.o path.o \
 	 refs.o csum-file.o pack-check.o pkt-line.o connect.o ident.o \
-	 sha1_name.o
+	 sha1_name.o setup.o
 
 LIB_H += rev-cache.h
 LIB_OBJS += rev-cache.o
diff --git a/cache.h b/cache.h
index f14a4ce91a..6365381c17 100644
--- a/cache.h
+++ b/cache.h
@@ -140,6 +140,9 @@ extern char *get_graft_file(void);
 
 #define ALTERNATE_DB_ENVIRONMENT "GIT_ALTERNATE_OBJECT_DIRECTORIES"
 
+extern const char **get_pathspec(const char *prefix, char **pathspec);
+extern const char *setup_git_directory(void);
+
 #define alloc_nr(x) (((x)+16)*3/2)
 
 /* Initialize and use the cache information */
diff --git a/diff-cache.c b/diff-cache.c
index 47a4e09ecc..400a4cb2ad 100644
--- a/diff-cache.c
+++ b/diff-cache.c
@@ -168,10 +168,11 @@ static const char diff_cache_usage[] =
 "[<common diff options>] <tree-ish> [<path>...]"
 COMMON_DIFF_OPTIONS_HELP;
 
-int main(int argc, const char **argv)
+int main(int argc, char **argv)
 {
 	const char *tree_name = NULL;
 	unsigned char sha1[20];
+	const char *prefix = setup_git_directory();
 	const char **pathspec = NULL;
 	void *tree;
 	unsigned long size;
@@ -179,15 +180,12 @@ int main(int argc, const char **argv)
 	int allow_options = 1;
 	int i;
 
-	read_cache();
 	for (i = 1; i < argc; i++) {
 		const char *arg = argv[i];
 
 		if (!allow_options || *arg != '-') {
-			if (tree_name) {
-				pathspec = argv + i;
+			if (tree_name)
 				break;
-			}
 			tree_name = arg;
 			continue;
 		}
@@ -265,12 +263,16 @@ int main(int argc, const char **argv)
 		usage(diff_cache_usage);
 	}
 
+	pathspec = get_pathspec(prefix, argv + i);
+
 	if (find_copies_harder && detect_rename != DIFF_DETECT_COPY)
 		usage(diff_cache_usage);
 
 	if (!tree_name || get_sha1(tree_name, sha1))
 		usage(diff_cache_usage);
 
+	read_cache();
+
 	/* The rest is for paths restriction. */
 	diff_setup(diff_setup_opt);
 
diff --git a/diff-files.c b/diff-files.c
index 2e6416e386..89eb29b3e2 100644
--- a/diff-files.c
+++ b/diff-files.c
@@ -41,12 +41,12 @@ static void show_modified(int oldmode, int mode,
 	diff_change(oldmode, mode, old_sha1, sha1, path, NULL);
 }
 
-int main(int argc, const char **argv)
+int main(int argc, char **argv)
 {
 	static const unsigned char null_sha1[20] = { 0, };
 	const char **pathspec;
-	int entries = read_cache();
-	int i;
+	const char *prefix = setup_git_directory();
+	int entries, i;
 
 	while (1 < argc && argv[1][0] == '-') {
 		if (!strcmp(argv[1], "-p") || !strcmp(argv[1], "-u"))
@@ -95,8 +95,9 @@ int main(int argc, const char **argv)
 		argv++; argc--;
 	}
 
-	/* Do we have a pathspec? */
-	pathspec = (argc > 1) ? argv + 1 : NULL;
+	/* Find the directory, and set up the pathspec */
+	pathspec = get_pathspec(prefix, argv + 1);
+	entries = read_cache();
 
 	if (find_copies_harder && detect_rename != DIFF_DETECT_COPY)
 		usage(diff_files_usage);
diff --git a/diff-tree.c b/diff-tree.c
index 0dd3cdacb2..fc87902a3d 100644
--- a/diff-tree.c
+++ b/diff-tree.c
@@ -395,16 +395,25 @@ static int diff_tree_stdin(char *line)
 	return diff_tree_commit(commit, line);
 }
 
+static int count_paths(const char **paths)
+{
+	int i = 0;
+	while (*paths++)
+		i++;
+	return i;
+}
+
 static const char diff_tree_usage[] =
 "git-diff-tree [--stdin] [-m] [-s] [-v] [--pretty] [-t] "
 "[<common diff options>] <tree-ish> <tree-ish>"
 COMMON_DIFF_OPTIONS_HELP;
 
-int main(int argc, const char **argv)
+int main(int argc, char **argv)
 {
 	int nr_sha1;
 	char line[1000];
 	unsigned char sha1[2][20];
+	const char *prefix = setup_git_directory();
 
 	nr_sha1 = 0;
 	for (;;) {
@@ -523,11 +532,11 @@ int main(int argc, const char **argv)
 	if (find_copies_harder && detect_rename != DIFF_DETECT_COPY)
 		usage(diff_tree_usage);
 
-	if (argc > 0) {
+	paths = get_pathspec(prefix, argv);
+	if (paths) {
 		int i;
 
-		paths = argv;
-		nr_paths = argc;
+		nr_paths = count_paths(paths);
 		pathlens = xmalloc(nr_paths * sizeof(int));
 		for (i=0; i<nr_paths; i++)
 			pathlens[i] = strlen(paths[i]);
diff --git a/git-diff-script b/git-diff-script
index 03ed555e77..926f594be4 100755
--- a/git-diff-script
+++ b/git-diff-script
@@ -1,7 +1,5 @@
 #!/bin/sh
-. git-sh-setup-script || die "Not a git archive"
-
-rev=($(git-rev-parse --revs-only "$@"))
+rev=($(git-rev-parse --revs-only "$@")) || exit
 flags=($(git-rev-parse --no-revs --flags "$@"))
 files=($(git-rev-parse --no-revs --no-flags "$@"))
 case "${#rev[*]}" in
diff --git a/rev-parse.c b/rev-parse.c
index 1c6ae76f9a..39cf63540e 100644
--- a/rev-parse.c
+++ b/rev-parse.c
@@ -134,7 +134,8 @@ int main(int argc, char **argv)
 {
 	int i, as_is = 0;
 	unsigned char sha1[20];
-
+	const char *prefix = setup_git_directory();
+	
 	for (i = 1; i < argc; i++) {
 		char *arg = argv[i];
 		char *dotdot;
@@ -189,6 +190,10 @@ int main(int argc, char **argv)
 				for_each_ref(show_reference);
 				continue;
 			}
+			if (!strcmp(arg, "--show-prefix")) {
+				puts(prefix);
+				continue;
+			}
 			show_arg(arg);
 			continue;
 		}
diff --git a/setup.c b/setup.c
new file mode 100644
index 0000000000..453bddbb17
--- /dev/null
+++ b/setup.c
@@ -0,0 +1,110 @@
+#include "cache.h"
+
+const char **get_pathspec(const char *prefix, char **pathspec)
+{
+	char *entry = *pathspec;
+	char **p;
+	int prefixlen;
+
+	if (!prefix) {
+		char **p;
+		if (!entry)
+			return NULL;
+		p = pathspec;
+		do {
+			if (*entry != '.')
+				continue;
+			/* fixup ? */
+		} while ((entry = *++p) != NULL);
+		return (const char **) pathspec;
+	}
+
+	if (!entry) {
+		static const char *spec[2];
+		spec[0] = prefix;
+		spec[1] = NULL;
+		return spec;
+	}
+
+	/* Otherwise we have to re-write the entries.. */
+	prefixlen = strlen(prefix);
+	p = pathspec;
+	do {
+		int speclen, len = prefixlen;
+		char *n;
+
+		for (;;) {
+			if (!strcmp(entry, ".")) {
+				entry++;
+				break;
+			}
+			if (!strncmp(entry, "./", 2)) {
+				entry += 2;
+				continue;
+			}
+			if (!strncmp(entry, "../", 3)) {
+				do {
+					if (!len)
+						die("'%s' is outside repository", *p);
+					len--;
+				} while (len && prefix[len-1] != '/');
+				entry += 3;
+				continue;
+			}
+			break;
+		}
+		speclen = strlen(entry);
+		n = xmalloc(speclen + len + 1);
+		
+		memcpy(n, prefix, len);
+		memcpy(n + len, entry, speclen+1);
+		*p = n;
+	} while ((entry = *++p) != NULL);
+	return (const char **) pathspec;
+}
+
+const char *setup_git_directory(void)
+{
+	static char cwd[PATH_MAX+1];
+	int len, offset;
+
+	/*
+	 * If GIT_DIR is set explicitly, we're not going
+	 * to do any discovery
+	 */
+	if (gitenv(GIT_DIR_ENVIRONMENT))
+		return NULL;
+
+	if (!getcwd(cwd, sizeof(cwd)) || cwd[0] != '/')
+		die("Unable to read current working directory");
+
+	offset = len = strlen(cwd);
+	for (;;) {
+		/*
+		 * We always want to see a .git/HEAD and a .git/refs/
+		 * subdirectory
+		 */
+		if (!access(".git/HEAD", R_OK) && !access(".git/refs/", X_OK)) {
+			/*
+			 * Then we need either a GIT_OBJECT_DIRECTORY define
+			 * or a .git/objects/ directory
+			 */
+			if (gitenv(DB_ENVIRONMENT) || !access(".git/objects/", X_OK))
+				break;
+		}
+		chdir("..");
+		do {
+			if (!offset)
+				die("Not a git repository");
+		} while (cwd[--offset] != '/');
+	}
+
+	if (offset == len)
+		return NULL;
+
+	/* Make "offset" point to past the '/', and add a '/' at the end */
+	offset++;
+	cwd[len++] = '/';
+	cwd[len] = 0;
+	return cwd + offset;
+}