gc: do not explode objects which will be immediately pruned

diff --git a/builtin/read-tree.c b/builtin/read-tree.c
index 9ad1e66916545dd2aeeb110661e56edfa5921019..df6c4c8819e7903f34cd6dc6bb0078a6cddac310 100644 (file)
--- a/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@ -16,6 +16,7 @@
 #include "resolve-undo.h"
 
 static int nr_trees;
+static int read_empty;
 static struct tree *trees[MAX_UNPACK_TREES];
 
 static int list_tree(unsigned char *sha1)
@@ -32,7 +33,7 @@ static int list_tree(unsigned char *sha1)
 }
 
 static const char * const read_tree_usage[] = {
-       "git read-tree [[-m [--trivial] [--aggressive] | --reset | --prefix=<prefix>] [-u [--exclude-per-directory=<gitignore>] | -i]] [--no-sparse-checkout] [--index-output=<file>] <tree-ish1> [<tree-ish2> [<tree-ish3>]]",
+       "git read-tree [[-m [--trivial] [--aggressive] | --reset | --prefix=<prefix>] [-u [--exclude-per-directory=<gitignore>] | -i]] [--no-sparse-checkout] [--index-output=<file>] (--empty | <tree-ish1> [<tree-ish2> [<tree-ish3>]])",
        NULL
 };
 
@@ -103,10 +104,12 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
        struct unpack_trees_options opts;
        int prefix_set = 0;
        const struct option read_tree_options[] = {
-               { OPTION_CALLBACK, 0, "index-output", NULL, "FILE",
-                 "write resulting index to <FILE>",
+               { OPTION_CALLBACK, 0, "index-output", NULL, "file",
+                 "write resulting index to <file>",
                  PARSE_OPT_NONEG, index_output_cb },
-               OPT__VERBOSE(&opts.verbose_update),
+               OPT_SET_INT(0, "empty", &read_empty,
+                           "only empty the index", 1),
+               OPT__VERBOSE(&opts.verbose_update, "be verbose"),
                OPT_GROUP("Merging"),
                OPT_SET_INT('m', NULL, &opts.merge,
                            "perform a merge in addition to a read", 1),
@@ -127,6 +130,7 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
                  PARSE_OPT_NONEG, exclude_per_directory_cb },
                OPT_SET_INT('i', NULL, &opts.index_only,
                            "don't check the working tree after merging", 1),
+               OPT__DRY_RUN(&opts.dry_run, "don't update the index or the work tree"),
                OPT_SET_INT(0, "no-sparse-checkout", &opts.skip_sparse_checkout,
                            "skip applying sparse checkout filter", 1),
                OPT_SET_INT(0, "debug-unpack", &opts.debug_unpack,
@@ -166,6 +170,11 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
                        die("failed to unpack tree object %s", arg);
                stage++;
        }
+       if (nr_trees == 0 && !read_empty)
+               warning("read-tree: emptying the index with no arguments is deprecated; use --empty");
+       else if (nr_trees > 0 && read_empty)
+               die("passing trees as arguments contradicts --empty");
+
        if (1 < opts.index_only + opts.update)
                die("-u and -i at the same time makes no sense");
        if ((opts.update||opts.index_only) && !opts.merge)
@@ -211,7 +220,7 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
        if (unpack_trees(nr_trees, t, &opts))
                return 128;
 
-       if (opts.debug_unpack)
+       if (opts.debug_unpack || opts.dry_run)
                return 0; /* do not write the index out */
 
        /*