Fix performance regression for partial commits

When running "git commit paths" to create a partial commit, we
used to carefully build the temporary index so that we do not
lose the cached stat information.  The rewrite of the command in
C lost it by carelessly using read_tree().

This resurrects the earlier behaviour to keep the cached stat
information as much as possible by using one-tree merge logic.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin-commit.c b/builtin-commit.c
index 73f1e3576a019d33ee7034d46a4fe4a2d7ab3f7b..6d2ca808b55136b60e65994e8929c3a068b425d6 100644 (file)
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -21,6 +21,7 @@
 #include "utf8.h"
 #include "parse-options.h"
 #include "path-list.h"
+#include "unpack-trees.h"
 
 static const char * const builtin_commit_usage[] = {
        "git-commit [options] [--] <filepattern>...",
@@ -177,10 +178,34 @@ static void add_remove_files(struct path_list *list)
        }
 }
 
+static void create_base_index(void)
+{
+       struct tree *tree;
+       struct unpack_trees_options opts;
+       struct tree_desc t;
+
+       if (initial_commit) {
+               discard_cache();
+               return;
+       }
+
+       memset(&opts, 0, sizeof(opts));
+       opts.head_idx = 1;
+       opts.index_only = 1;
+       opts.merge = 1;
+
+       opts.fn = oneway_merge;
+       tree = parse_tree_indirect(head_sha1);
+       if (!tree)
+               die("failed to unpack HEAD tree object");
+       parse_tree(tree);
+       init_tree_desc(&t, tree->buffer, tree->size);
+       unpack_trees(1, &t, &opts);
+}
+
 static char *prepare_index(int argc, const char **argv, const char *prefix)
 {
        int fd;
-       struct tree *tree;
        struct path_list partial;
        const char **pathspec = NULL;
 
@@ -278,14 +303,8 @@ static char *prepare_index(int argc, const char **argv, const char *prefix)
 
        fd = hold_lock_file_for_update(&false_lock,
                                       git_path("next-index-%d", getpid()), 1);
-       discard_cache();
-       if (!initial_commit) {
-               tree = parse_tree_indirect(head_sha1);
-               if (!tree)
-                       die("failed to unpack HEAD tree object");
-               if (read_tree(tree, 0, NULL))
-                       die("failed to read HEAD tree object");
-       }
+
+       create_base_index();
        add_remove_files(&partial);
        refresh_cache(REFRESH_QUIET);