clone: --dissociate option to mark that reference is only temporary

While use of the --reference option to borrow objects from an
existing local repository of the same project is an effective way to
reduce traffic when cloning a project over the network, it makes the
resulting "borrowing" repository dependent on the "borrowed"
repository.  After running

	git clone --reference=P $URL Q

the resulting repository Q will be broken if the borrowed repository
P disappears.

The way to allow the borrowed repository to be removed is to repack
the borrowing repository (i.e. run "git repack -a -d" in Q); while
power users may know it very well, it is not easily discoverable.

Teach a new "--dissociate" option to "git clone" to run this
repacking for the user.

Helped-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git-clone.txt b/Documentation/git-clone.txt
index 0363d00..f1f2a3f 100644 (file)
--- a/Documentation/git-clone.txt
+++ b/Documentation/git-clone.txt
@@ -12,7 +12,7 @@ SYNOPSIS
 'git clone' [--template=<template_directory>]
          [-l] [-s] [--no-hardlinks] [-q] [-n] [--bare] [--mirror]
          [-o <name>] [-b <name>] [-u <upload-pack>] [--reference <repository>]
-         [--separate-git-dir <git dir>]
+         [--dissociate] [--separate-git-dir <git dir>]
          [--depth <depth>] [--[no-]single-branch]
          [--recursive | --recurse-submodules] [--] <repository>
          [<directory>]
@@ -98,7 +98,14 @@ objects from the source repository into a pack in the cloned repository.
        require fewer objects to be copied from the repository
        being cloned, reducing network and local storage costs.
 +
-*NOTE*: see the NOTE for the `--shared` option.
+*NOTE*: see the NOTE for the `--shared` option, and also the
+`--dissociate` option.
+
+--dissociate::
+       Borrow the objects from reference repositories specified
+       with the `--reference` options only to reduce network
+       transfer and stop borrowing from them after a clone is made
+       by making necessary local copies of borrowed objects.
 
 --quiet::
 -q::

diff --git a/builtin/clone.c b/builtin/clone.c
index bbd169c..e1ad4df 100644 (file)
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -48,6 +48,7 @@ static int option_verbosity;
 static int option_progress = -1;
 static struct string_list option_config;
 static struct string_list option_reference;
+static int option_dissociate;
 
 static int opt_parse_reference(const struct option *opt, const char *arg, int unset)
 {
@@ -93,6 +94,8 @@ static struct option builtin_clone_options[] = {
                    N_("create a shallow clone of that depth")),
        OPT_BOOL(0, "single-branch", &option_single_branch,
                    N_("clone only one branch, HEAD or --branch")),
+       OPT_BOOL(0, "dissociate", &option_dissociate,
+                N_("use --reference only while cloning")),
        OPT_STRING(0, "separate-git-dir", &real_git_dir, N_("gitdir"),
                   N_("separate git dir from working tree")),
        OPT_STRING_LIST('c', "config", &option_config, N_("key=value"),
@@ -736,6 +739,16 @@ static void write_refspec_config(const char* src_ref_prefix,
        strbuf_release(&value);
 }
 
+static void dissociate_from_references(void)
+{
+       static const char* argv[] = { "repack", "-a", "-d", NULL };
+
+       if (run_command_v_opt(argv, RUN_GIT_CMD|RUN_COMMAND_NO_STDIN))
+               die(_("cannot repack to clean up"));
+       if (unlink(git_path("objects/info/alternates")) && errno != ENOENT)
+               die_errno(_("cannot unlink temporary alternates file"));
+}
+
 int cmd_clone(int argc, const char **argv, const char *prefix)
 {
        int is_bundle = 0, is_local;
@@ -883,6 +896,10 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 
        if (option_reference.nr)
                setup_reference();
+       else if (option_dissociate) {
+               warning(_("--dissociate given, but there is no --reference"));
+               option_dissociate = 0;
+       }
 
        fetch_pattern = value.buf;
        refspec = parse_fetch_refspec(1, &fetch_pattern);
@@ -996,6 +1013,9 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
        transport_unlock_pack(transport);
        transport_disconnect(transport);
 
+       if (option_dissociate)
+               dissociate_from_references();
+
        junk_mode = JUNK_LEAVE_REPO;
        err = checkout();
 

diff --git a/t/t5700-clone-reference.sh b/t/t5700-clone-reference.sh
index 6537911..3e783fc 100755 (executable)
--- a/t/t5700-clone-reference.sh
+++ b/t/t5700-clone-reference.sh
@@ -198,4 +198,21 @@ test_expect_success 'clone using repo pointed at by gitfile as reference' '
        test_cmp expected "$base_dir/O/.git/objects/info/alternates"
 '
 
+test_expect_success 'clone and dissociate from reference' '
+       git init P &&
+       (
+               cd P && test_commit one
+       ) &&
+       git clone P Q &&
+       (
+               cd Q && test_commit two
+       ) &&
+       git clone --no-local --reference=P Q R &&
+       git clone --no-local --reference=P --dissociate Q S &&
+       # removing the reference P would corrupt R but not S
+       rm -fr P &&
+       test_must_fail git -C R fsck &&
+       git -C S fsck
+'
+
 test_done