Merge branch 'jc/rw-prefix'

* jc/rw-prefix:
  read-tree: reorganize bind_merge code.
  write-tree: --prefix=<path>
  read-tree: --prefix=<path>/ option.

7 files changed, 141 insertions, 13 deletions

diff --git a/Documentation/git-read-tree.txt b/Documentation/git-read-tree.txt
index d894f537b..11bd9c0ad 100644
--- a/Documentation/git-read-tree.txt
+++ b/Documentation/git-read-tree.txt
@@ -8,7 +8,7 @@ git-read-tree - Reads tree information into the index
 
 SYNOPSIS
 --------
-'git-read-tree' (<tree-ish> | [[-m [--aggressive]| --reset] [-u | -i]] <tree-ish1> [<tree-ish2> [<tree-ish3>]])
+'git-read-tree' (<tree-ish> | [[-m [--aggressive] | --reset | --prefix=<prefix>] [-u | -i]] <tree-ish1> [<tree-ish2> [<tree-ish3>]])
 
 
 DESCRIPTION
@@ -63,6 +63,15 @@ OPTIONS
 * when both sides adds a path identically.  The resolution
   is to add that path.
 
+--prefix=<prefix>/::
+	Keep the current index contents, and read the contents
+	of named tree-ish under directory at `<prefix>`.  The
+	original index file cannot have anything at the path
+	`<prefix>` itself, and have nothing in `<prefix>/`
+	directory.  Note that the `<prefix>/` value must end
+	with a slash.
+
+
 <tree-ish#>::
 	The id of the tree object(s) to be read/merged.
 
diff --git a/Documentation/git-write-tree.txt b/Documentation/git-write-tree.txt
index 77e12cb94..c85fa89c3 100644
--- a/Documentation/git-write-tree.txt
+++ b/Documentation/git-write-tree.txt
@@ -8,7 +8,7 @@ git-write-tree - Creates a tree object from the current index
 
 SYNOPSIS
 --------
-'git-write-tree' [--missing-ok]
+'git-write-tree' [--missing-ok] [--prefix=<prefix>/]
 
 DESCRIPTION
 -----------
@@ -30,6 +30,12 @@ OPTIONS
 	directory exist in the object database.  This option disables this
 	check.
 
+--prefix=<prefix>/::
+	Writes a tree object that represents a subdirectory
+	`<prefix>`.  This can be used to write the tree object
+	for a subproject that is in the named subdirectory.
+
+
 Author
 ------
 Written by Linus Torvalds <torvalds@osdl.org>
diff --git a/builtin-read-tree.c b/builtin-read-tree.c
index bb50fbd27..04506da89 100644
--- a/builtin-read-tree.c
+++ b/builtin-read-tree.c
@@ -24,6 +24,7 @@ static int trivial_merges_only = 0;
 static int aggressive = 0;
 static int verbose_update = 0;
 static volatile int progress_update = 0;
+static const char *prefix = NULL;
 
 static int head_idx = -1;
 static int merge_size = 0;
@@ -412,7 +413,8 @@ static int unpack_trees(merge_fn_t fn)
 			posns[i] = create_tree_entry_list((struct tree *) posn->item);
 			posn = posn->next;
 		}
-		if (unpack_trees_rec(posns, len, "", fn, &indpos))
+		if (unpack_trees_rec(posns, len, prefix ? prefix : "",
+				     fn, &indpos))
 			return -1;
 	}
 
@@ -762,6 +764,28 @@ static int twoway_merge(struct cache_entry **src)
 }
 
 /*
+ * Bind merge.
+ *
+ * Keep the index entries at stage0, collapse stage1 but make sure
+ * stage0 does not have anything there.
+ */
+static int bind_merge(struct cache_entry **src)
+{
+	struct cache_entry *old = src[0];
+	struct cache_entry *a = src[1];
+
+	if (merge_size != 1)
+		return error("Cannot do a bind merge of %d trees\n",
+			     merge_size);
+	if (a && old)
+		die("Entry '%s' overlaps.  Cannot bind.", a->name);
+	if (!a)
+		return keep_entry(old);
+	else
+		return merged_entry(a, NULL);
+}
+
+/*
  * One-way merge.
  *
  * The rule is:
@@ -851,7 +875,7 @@ static void prime_cache_tree(void)
 
 }
 
-static const char read_tree_usage[] = "git-read-tree (<sha> | -m [--aggressive] [-u | -i] <sha1> [<sha2> [<sha3>]])";
+static const char read_tree_usage[] = "git-read-tree (<sha> | [[-m [--aggressive] | --reset | --prefix=<prefix>] [-u | -i]] <sha1> [<sha2> [<sha3>]])";
 
 static struct lock_file lock_file;
 
@@ -896,12 +920,27 @@ int cmd_read_tree(int argc, const char **argv, char **envp)
 			continue;
 		}
 
+		/* "--prefix=<subdirectory>/" means keep the current index
+		 *  entries and put the entries from the tree under the
+		 * given subdirectory.
+		 */
+		if (!strncmp(arg, "--prefix=", 9)) {
+			if (stage || merge || prefix)
+				usage(read_tree_usage);
+			prefix = arg + 9;
+			merge = 1;
+			stage = 1;
+			if (read_cache_unmerged())
+				die("you need to resolve your current index first");
+			continue;
+		}
+
 		/* This differs from "-m" in that we'll silently ignore
 		 * unmerged entries and overwrite working tree files that
 		 * correspond to them.
 		 */
 		if (!strcmp(arg, "--reset")) {
-			if (stage || merge)
+			if (stage || merge || prefix)
 				usage(read_tree_usage);
 			reset = 1;
 			merge = 1;
@@ -922,7 +961,7 @@ int cmd_read_tree(int argc, const char **argv, char **envp)
 
 		/* "-m" stands for "merge", meaning we start in stage 1 */
 		if (!strcmp(arg, "-m")) {
-			if (stage || merge)
+			if (stage || merge || prefix)
 				usage(read_tree_usage);
 			if (read_cache_unmerged())
 				die("you need to resolve your current index first");
@@ -944,12 +983,31 @@ int cmd_read_tree(int argc, const char **argv, char **envp)
 	if ((update||index_only) && !merge)
 		usage(read_tree_usage);
 
+	if (prefix) {
+		int pfxlen = strlen(prefix);
+		int pos;
+		if (prefix[pfxlen-1] != '/')
+			die("prefix must end with /");
+		if (stage != 2)
+			die("binding merge takes only one tree");
+		pos = cache_name_pos(prefix, pfxlen);
+		if (0 <= pos)
+			die("corrupt index file");
+		pos = -pos-1;
+		if (pos < active_nr &&
+		    !strncmp(active_cache[pos]->name, prefix, pfxlen))
+			die("subdirectory '%s' already exists.", prefix);
+		pos = cache_name_pos(prefix, pfxlen-1);
+		if (0 <= pos)
+			die("file '%.*s' already exists.", pfxlen-1, prefix);
+	}
+
 	if (merge) {
 		if (stage < 2)
 			die("just how do you expect me to merge %d trees?", stage-1);
 		switch (stage - 1) {
 		case 1:
-			fn = oneway_merge;
+			fn = prefix ? bind_merge : oneway_merge;
 			break;
 		case 2:
 			fn = twoway_merge;
@@ -975,7 +1033,7 @@ int cmd_read_tree(int argc, const char **argv, char **envp)
 	 * valid cache-tree because the index must match exactly
 	 * what came from the tree.
 	 */
-	if (trees && trees->item && (!merge || (stage == 2))) {
+	if (trees && trees->item && !prefix && (!merge || (stage == 2))) {
 		cache_tree_free(&active_cache_tree);
 		prime_cache_tree();
 	}
diff --git a/cache-tree.c b/cache-tree.c
index a880c97b3..d9f7e1e3d 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -529,3 +529,29 @@ struct cache_tree *cache_tree_read(const char *buffer, unsigned long size)
 		return NULL; /* not the whole tree */
 	return read_one(&buffer, &size);
 }
+
+struct cache_tree *cache_tree_find(struct cache_tree *it, const char *path)
+{
+	while (*path) {
+		const char *slash;
+		struct cache_tree_sub *sub;
+
+		slash = strchr(path, '/');
+		if (!slash)
+			slash = path + strlen(path);
+		/* between path and slash is the name of the
+		 * subtree to look for.
+		 */
+		sub = find_subtree(it, path, slash - path, 0);
+		if (!sub)
+			return NULL;
+		it = sub->cache_tree;
+		if (slash)
+			while (*slash && *slash == '/')
+				slash++;
+		if (!slash || !*slash)
+			return it; /* prefix ended with slashes */
+		path = slash;
+	}
+	return it;
+}
diff --git a/cache-tree.h b/cache-tree.h
index 72c64801f..119407e3a 100644
--- a/cache-tree.h
+++ b/cache-tree.h
@@ -28,4 +28,6 @@ struct cache_tree *cache_tree_read(const char *buffer, unsigned long size);
 int cache_tree_fully_valid(struct cache_tree *);
 int cache_tree_update(struct cache_tree *, struct cache_entry **, int, int, int);
 
+struct cache_tree *cache_tree_find(struct cache_tree *, const char *);
+
 #endif
diff --git a/t/t0000-basic.sh b/t/t0000-basic.sh
index cf33989b5..2c9bbb59b 100755
--- a/t/t0000-basic.sh
+++ b/t/t0000-basic.sh
@@ -195,6 +195,20 @@ test_expect_success \
     'git-ls-tree -r output for a known tree.' \
     'diff current expected'
 
+test_expect_success \
+    'writing partial tree out with git-write-tree --prefix.' \
+    'ptree=$(git-write-tree --prefix=path3)'
+test_expect_success \
+    'validate object ID for a known tree.' \
+    'test "$ptree" = 21ae8269cacbe57ae09138dcc3a2887f904d02b3'
+
+test_expect_success \
+    'writing partial tree out with git-write-tree --prefix.' \
+    'ptree=$(git-write-tree --prefix=path3/subp3)'
+test_expect_success \
+    'validate object ID for a known tree.' \
+    'test "$ptree" = 3c5e5399f3a333eddecce7a9b9465b63f65f51e2'
+
 ################################################################
 rm .git/index
 test_expect_success \
diff --git a/write-tree.c b/write-tree.c
index d6a605893..bd07da618 100644
--- a/write-tree.c
+++ b/write-tree.c
@@ -8,8 +8,10 @@
 #include "cache-tree.h"
 
 static int missing_ok = 0;
+static char *prefix = NULL;
 
-static const char write_tree_usage[] = "git-write-tree [--missing-ok]";
+static const char write_tree_usage[] =
+"git-write-tree [--missing-ok] [--prefix=<prefix>/]";
 
 static struct lock_file lock_file;
 
@@ -21,13 +23,18 @@ int main(int argc, char **argv)
 
 	newfd = hold_lock_file_for_update(&lock_file, get_index_file());
 	entries = read_cache();
-	if (argc == 2) {
-		if (!strcmp(argv[1], "--missing-ok"))
+
+	while (1 < argc) {
+		char *arg = argv[1];
+		if (!strcmp(arg, "--missing-ok"))
 			missing_ok = 1;
+		else if (!strncmp(arg, "--prefix=", 9))
+			prefix = arg + 9;
 		else
 			die(write_tree_usage);
+		argc--; argv++;
 	}
-	
+
 	if (argc > 2)
 		die("too many options");
 
@@ -54,6 +61,12 @@ int main(int argc, char **argv)
 		 * performance penalty and not a big deal.
 		 */
 	}
-	printf("%s\n", sha1_to_hex(active_cache_tree->sha1));
+	if (prefix) {
+		struct cache_tree *subtree =
+			cache_tree_find(active_cache_tree, prefix);
+		printf("%s\n", sha1_to_hex(subtree->sha1));
+	}
+	else
+		printf("%s\n", sha1_to_hex(active_cache_tree->sha1));
 	return 0;
 }