[PATCHv2 0/6] git clone: Marry --recursive and --reference

[PATCHv2 0/6] git clone: Marry --recursive and --reference

[Stefan Beller]

v2:
 * fixed the p1,2 cleanups
 * added documentation to patches 5,6
 * improved commit message in v4
 
 Thanks,
 Stefan
 
v1:
 
 Currently when cloning a superproject with --recursive and --reference
 only the superproject learns about its alternates. The submodules are
 cloned independently, which may incur lots of network costs.
 
 Assume that the reference repository has the submodules at the same
 paths as the to-be-cloned submodule and try to setup alternates from
 there.
 
 Some submodules in the referenced superproject may not be there, 
 (they are just not initialized/cloned/checked out), which yields
 an error for now. In future work we may want to soften the alternate
 check and not die in the clone when one of the given alternates doesn't
 exist.
 
 patch 1,2 are modernizing style of t7408, 
 patches 3,4 are not strictly necessary, but I think it is a good thing
 to not leave the submodule related C code in a crippled state (i.e.
 allowing only one reference). The shell code would also need this update,
 but it looked ugly to me, so I postpone it until more of the submodule code
 is written in C. 
 
 Thanks,
 Stefan 

Stefan Beller (6):
  t7408: modernize style
  t7408: merge short tests, factor out testing method
  submodule--helper module-clone: allow multiple references
  submodule--helper update-clone: allow multiple references
  submodule update: add super-reference flag
  clone: reference flag is used for submodules as well

 builtin/clone.c                |  22 ++++--
 builtin/submodule--helper.c    |  45 ++++++++----
 git-submodule.sh               |  12 +++-
 t/t7408-submodule-reference.sh | 153 +++++++++++++++++++++++------------------
 4 files changed, 147 insertions(+), 85 deletions(-)

-- 
2.9.2.572.g9d9644e.dirty

[PATCHv2 1/6] t7408: modernize style

[Stefan Beller]

No functional change intended. This commit only changes formatting
to the style we recently use, e.g. starting the body of a test with a
single quote on the same line as the header, and then having the test
indented in the following lines.

Whenever we change directories, we do that in subshells.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/t7408-submodule-reference.sh | 140 +++++++++++++++++++++--------------------
 1 file changed, 71 insertions(+), 69 deletions(-)

diff --git a/t/t7408-submodule-reference.sh b/t/t7408-submodule-reference.sh
index eaea19b..beee0bb 100755
--- a/t/t7408-submodule-reference.sh
+++ b/t/t7408-submodule-reference.sh
@@ -8,74 +8,76 @@ test_description='test clone --reference'
 
 base_dir=$(pwd)
 
-U=$base_dir/UPLOAD_LOG
-
-test_expect_success 'preparing first repository' \
-'test_create_repo A && cd A &&
-echo first > file1 &&
-git add file1 &&
-git commit -m A-initial'
-
-cd "$base_dir"
-
-test_expect_success 'preparing second repository' \
-'git clone A B && cd B &&
-echo second > file2 &&
-git add file2 &&
-git commit -m B-addition &&
-git repack -a -d &&
-git prune'
-
-cd "$base_dir"
-
-test_expect_success 'preparing superproject' \
-'test_create_repo super && cd super &&
-echo file > file &&
-git add file &&
-git commit -m B-super-initial'
-
-cd "$base_dir"
-
-test_expect_success 'submodule add --reference' \
-'cd super && git submodule add --reference ../B "file://$base_dir/A" sub &&
-git commit -m B-super-added'
-
-cd "$base_dir"
-
-test_expect_success 'after add: existence of info/alternates' \
-'test_line_count = 1 super/.git/modules/sub/objects/info/alternates'
-
-cd "$base_dir"
-
-test_expect_success 'that reference gets used with add' \
-'cd super/sub &&
-echo "0 objects, 0 kilobytes" > expected &&
-git count-objects > current &&
-diff expected current'
-
-cd "$base_dir"
-
-test_expect_success 'cloning superproject' \
-'git clone super super-clone'
-
-cd "$base_dir"
-
-test_expect_success 'update with reference' \
-'cd super-clone && git submodule update --init --reference ../B'
-
-cd "$base_dir"
-
-test_expect_success 'after update: existence of info/alternates' \
-'test_line_count = 1 super-clone/.git/modules/sub/objects/info/alternates'
-
-cd "$base_dir"
-
-test_expect_success 'that reference gets used with update' \
-'cd super-clone/sub &&
-echo "0 objects, 0 kilobytes" > expected &&
-git count-objects > current &&
-diff expected current'
-
-cd "$base_dir"
+test_expect_success 'preparing first repository' '
+	test_create_repo A &&
+	(
+		cd A &&
+		echo first >file1 &&
+		git add file1 &&
+		git commit -m A-initial
+	)
+'
+
+test_expect_success 'preparing second repository' '
+	git clone A B &&
+	(
+		cd B &&
+		echo second >file2 &&
+		git add file2 &&
+		git commit -m B-addition &&
+		git repack -a -d &&
+		git prune
+	)
+'
+
+test_expect_success 'preparing superproject' '
+	test_create_repo super &&
+	(
+		cd super &&
+		echo file >file &&
+		git add file &&
+		git commit -m B-super-initial
+	)
+'
+
+test_expect_success 'submodule add --reference' '
+	(
+		cd super &&
+		git submodule add --reference ../B "file://$base_dir/A" sub &&
+		git commit -m B-super-added
+	)
+'
+
+test_expect_success 'after add: existence of info/alternates' '
+	test_line_count = 1 super/.git/modules/sub/objects/info/alternates
+'
+
+test_expect_success 'that reference gets used with add' '
+	(
+		cd super/sub &&
+		echo "0 objects, 0 kilobytes" > expected &&
+		git count-objects > current &&
+		diff expected current
+	)
+'
+
+test_expect_success 'cloning superproject' '
+	git clone super super-clone
+'
+
+test_expect_success 'update with reference' '
+	cd super-clone && git submodule update --init --reference ../B
+'
+
+test_expect_success 'after update: existence of info/alternates' '
+	test_line_count = 1 super-clone/.git/modules/sub/objects/info/alternates
+'
+
+test_expect_success 'that reference gets used with update' '
+	cd super-clone/sub &&
+	echo "0 objects, 0 kilobytes" > expected &&
+	git count-objects > current &&
+	diff expected current
+'
 
 test_done
-- 
2.9.2.572.g9d9644e.dirty

[PATCHv2 2/6] t7408: merge short tests, factor out testing method

[Stefan Beller]

Tests consisting of one line each can be consolidated to have fewer tests
to run as well as fewer lines of code.

When having just a few git commands, do not create a new shell but
use the -C flag in Git to execute in the correct directory.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 t/t7408-submodule-reference.sh | 49 +++++++++++++++---------------------------
 1 file changed, 17 insertions(+), 32 deletions(-)

diff --git a/t/t7408-submodule-reference.sh b/t/t7408-submodule-reference.sh
index beee0bb..1d9326e 100755
--- a/t/t7408-submodule-reference.sh
+++ b/t/t7408-submodule-reference.sh
@@ -8,6 +8,15 @@ test_description='test clone --reference'
 
 base_dir=$(pwd)
 
+test_alternate_usage() {
+	alternates_file="$1" &&
+	working_dir="$2" &&
+	test_line_count = 1 "$alternates_file" &&
+	echo "0 objects, 0 kilobytes" >expect &&
+	git -C "$working_dir" count-objects >actual &&
+	test_cmp expect actual
+}
+
 test_expect_success 'preparing first repository' '
 	test_create_repo A &&
 	(
@@ -40,44 +49,20 @@ test_expect_success 'preparing superproject' '
 	)
 '
 
-test_expect_success 'submodule add --reference' '
+test_expect_success 'submodule add --reference uses alternates' '
 	(
 		cd super &&
 		git submodule add --reference ../B "file://$base_dir/A" sub &&
 		git commit -m B-super-added
-	)
-'
-
-test_expect_success 'after add: existence of info/alternates' '
-	test_line_count = 1 super/.git/modules/sub/objects/info/alternates
-'
-
-test_expect_success 'that reference gets used with add' '
-	(
-		cd super/sub &&
-		echo "0 objects, 0 kilobytes" > expected &&
-		git count-objects > current &&
-		diff expected current
-	)
-'
-
-test_expect_success 'cloning superproject' '
-	git clone super super-clone
-'
-
-test_expect_success 'update with reference' '
-	cd super-clone && git submodule update --init --reference ../B
-'
-
-test_expect_success 'after update: existence of info/alternates' '
-	test_line_count = 1 super-clone/.git/modules/sub/objects/info/alternates
+	) &&
+	test_alternate_usage super/.git/modules/sub/objects/info/alternates super/sub
 '
 
-test_expect_success 'that reference gets used with update' '
-	cd super-clone/sub &&
-	echo "0 objects, 0 kilobytes" > expected &&
-	git count-objects > current &&
-	diff expected current
+test_expect_success 'updating superproject keeps alternates' '
+	test_when_finished "rm -rf super-clone" &&
+	git clone super super-clone &&
+	git -C super-clone submodule update --init --reference ../B &&
+	test_alternate_usage super-clone/.git/modules/sub/objects/info/alternates super-clone/sub
 '
 
 test_done
-- 
2.9.2.572.g9d9644e.dirty

Re: [PATCHv2 2/6] t7408: merge short tests, factor out testing method

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> +test_alternate_usage() {

According to Documentation/CodingGuidelines, this should be:

    test_alternate_usage () {

Somehow the helper name sounds as if it is testing if an alternate
is used correctly (i.e. the machinery may attempt to use alternate
but not in a correct way), not testing if an alternate is correctly
used (i.e. the machinery incorrectly forgets to use an alternate at
all), but maybe it is just me.

> +test_expect_success 'updating superproject keeps alternates' '
> +	test_when_finished "rm -rf super-clone" &&

This one is new; we do not remove A, B or super.  According to the
previous round of review, this is a deliberate design, that needs to
be spelled out by having a comment block before this test so that
other people who add more tests can understand why they need to
clean when they follow suit.  Perhaps something like:

    ###############################################################
    # The tests up to this point, and repositories created by them
    # (A, B, super and super/sub), are about setting up the stage
    # forsubsequent tests and meant to be kept throughout the
    # remainder of the test.
    # Tests from here on, if they create their own test repository,
    # are expected to clean after themselves.

    test_expect_success 'updating superproject keeps alternates' '
            test_when_finished "rm -rf super-clone" &&

[PATCHv2 3/6] submodule--helper module-clone: allow multiple references

[Stefan Beller]

Allow users to pass in multiple references, just as clone accepts multiple
references as well.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/submodule--helper.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 6f6d67a..f2b19ea 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -442,7 +442,7 @@ static int module_name(int argc, const char **argv, const char *prefix)
 }
 
 static int clone_submodule(const char *path, const char *gitdir, const char *url,
-			   const char *depth, const char *reference, int quiet)
+			   const char *depth, struct string_list *reference, int quiet)
 {
 	struct child_process cp;
 	child_process_init(&cp);
@@ -453,8 +453,11 @@ static int clone_submodule(const char *path, const char *gitdir, const char *url
 		argv_array_push(&cp.args, "--quiet");
 	if (depth && *depth)
 		argv_array_pushl(&cp.args, "--depth", depth, NULL);
-	if (reference && *reference)
-		argv_array_pushl(&cp.args, "--reference", reference, NULL);
+	if (reference->nr) {
+		struct string_list_item *item;
+		for_each_string_list_item(item, reference)
+			argv_array_pushl(&cp.args, "--reference", item->string, NULL);
+	}
 	if (gitdir && *gitdir)
 		argv_array_pushl(&cp.args, "--separate-git-dir", gitdir, NULL);
 
@@ -470,13 +473,13 @@ static int clone_submodule(const char *path, const char *gitdir, const char *url
 
 static int module_clone(int argc, const char **argv, const char *prefix)
 {
-	const char *name = NULL, *url = NULL;
-	const char *reference = NULL, *depth = NULL;
+	const char *name = NULL, *url = NULL, *depth = NULL;
 	int quiet = 0;
 	FILE *submodule_dot_git;
 	char *p, *path = NULL, *sm_gitdir;
 	struct strbuf rel_path = STRBUF_INIT;
 	struct strbuf sb = STRBUF_INIT;
+	struct string_list reference = STRING_LIST_INIT_NODUP;
 
 	struct option module_clone_options[] = {
 		OPT_STRING(0, "prefix", &prefix,
@@ -491,8 +494,8 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "url", &url,
 			   N_("string"),
 			   N_("url where to clone the submodule from")),
-		OPT_STRING(0, "reference", &reference,
-			   N_("string"),
+		OPT_STRING_LIST(0, "reference", &reference,
+			   N_("repo"),
 			   N_("reference repository")),
 		OPT_STRING(0, "depth", &depth,
 			   N_("string"),
@@ -528,7 +531,7 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 	if (!file_exists(sm_gitdir)) {
 		if (safe_create_leading_directories_const(sm_gitdir) < 0)
 			die(_("could not create directory '%s'"), sm_gitdir);
-		if (clone_submodule(path, sm_gitdir, url, depth, reference, quiet))
+		if (clone_submodule(path, sm_gitdir, url, depth, &reference, quiet))
 			die(_("clone of '%s' into submodule path '%s' failed"),
 			    url, path);
 	} else {
-- 
2.9.2.572.g9d9644e.dirty

[PATCHv2 4/6] submodule--helper update-clone: allow multiple references

[Stefan Beller]

Allow the user to pass in multiple references to update_clone.
Currently this is only internal API, but once the shell script is
replaced by a C version, this is needed.

This fixes an API bug between the shell script and the helper.
Currently the helper accepts "--reference" "--reference=foo"
as a OPT_STRING whose value happens to be "--reference=foo", and
then uses

        if (suc->reference)
                argv_array_push(&child->args, suc->reference)

where suc->reference _is_ "--reference=foo" when invoking the
underlying "git clone", it cancels out.

with this change we omit one of the "--reference" arguments when passing
references from the shell script to the helper.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/submodule--helper.c | 14 +++++++++-----
 git-submodule.sh            |  2 +-
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index f2b19ea..b7710a7 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -583,7 +583,7 @@ struct submodule_update_clone {
 	/* configuration parameters which are passed on to the children */
 	int quiet;
 	int recommend_shallow;
-	const char *reference;
+	struct string_list references;
 	const char *depth;
 	const char *recursive_prefix;
 	const char *prefix;
@@ -599,7 +599,8 @@ struct submodule_update_clone {
 	int failed_clones_nr, failed_clones_alloc;
 };
 #define SUBMODULE_UPDATE_CLONE_INIT {0, MODULE_LIST_INIT, 0, \
-	SUBMODULE_UPDATE_STRATEGY_INIT, 0, -1, NULL, NULL, NULL, NULL, \
+	SUBMODULE_UPDATE_STRATEGY_INIT, 0, -1, STRING_LIST_INIT_DUP, \
+	NULL, NULL, NULL, \
 	STRING_LIST_INIT_DUP, 0, NULL, 0, 0}
 
 
@@ -709,8 +710,11 @@ static int prepare_to_clone_next_submodule(const struct cache_entry *ce,
 	argv_array_pushl(&child->args, "--path", sub->path, NULL);
 	argv_array_pushl(&child->args, "--name", sub->name, NULL);
 	argv_array_pushl(&child->args, "--url", url, NULL);
-	if (suc->reference)
-		argv_array_push(&child->args, suc->reference);
+	if (suc->references.nr) {
+		struct string_list_item *item;
+		for_each_string_list_item(item, &suc->references)
+			argv_array_pushl(&child->args, "--reference", item->string, NULL);
+	}
 	if (suc->depth)
 		argv_array_push(&child->args, suc->depth);
 
@@ -829,7 +833,7 @@ static int update_clone(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "update", &update,
 			   N_("string"),
 			   N_("rebase, merge, checkout or none")),
-		OPT_STRING(0, "reference", &suc.reference, N_("repo"),
+		OPT_STRING_LIST(0, "reference", &suc.references, N_("repo"),
 			   N_("reference repository")),
 		OPT_STRING(0, "depth", &suc.depth, "<depth>",
 			   N_("Create a shallow clone truncated to the "
diff --git a/git-submodule.sh b/git-submodule.sh
index c90dc33..3b412f5 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -575,7 +575,7 @@ cmd_update()
 		${wt_prefix:+--prefix "$wt_prefix"} \
 		${prefix:+--recursive-prefix "$prefix"} \
 		${update:+--update "$update"} \
-		${reference:+--reference "$reference"} \
+		${reference:+"$reference"} \
 		${depth:+--depth "$depth"} \
 		${recommend_shallow:+"$recommend_shallow"} \
 		${jobs:+$jobs} \
-- 
2.9.2.572.g9d9644e.dirty

Re: [PATCHv2 4/6] submodule--helper update-clone: allow multiple references

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> Allow the user to pass in multiple references to update_clone.
> Currently this is only internal API, but once the shell script is
> replaced by a C version, this is needed.
>
> This fixes an API bug between the shell script and the helper.
> Currently the helper accepts "--reference" "--reference=foo"
> as a OPT_STRING whose value happens to be "--reference=foo", and
> then uses
>
>         if (suc->reference)
>                 argv_array_push(&child->args, suc->reference)
>
> where suc->reference _is_ "--reference=foo" when invoking the
> underlying "git clone", it cancels out.
>
> with this change we omit one of the "--reference" arguments when passing

s/with this change/With this change/;

After the "We won't look at what is queued on 'pu'", I am debating
myself if I should amend this locally.

[PATCHv2 5/6] submodule update: add super-reference flag

[Stefan Beller]

When we have a another clone of a superproject, we may want to
mirror the submodules using alternates. Introduce an option
`--super-reference` that let's a user point to another superproject,
which is assumed to have the same structure as the one they are
running the "submodule update" command from and has all submodules
checked out to borrow the submodule objects from within the other
superprojects git directory.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 Documentation/git-submodule.txt |  8 +++++++-
 builtin/submodule--helper.c     | 14 +++++++++++++-
 git-submodule.sh                | 10 ++++++++++
 3 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/Documentation/git-submodule.txt b/Documentation/git-submodule.txt
index bf3bb37..6f2f873 100644
--- a/Documentation/git-submodule.txt
+++ b/Documentation/git-submodule.txt
@@ -16,7 +16,7 @@ SYNOPSIS
 'git submodule' [--quiet] deinit [-f|--force] (--all|[--] <path>...)
 'git submodule' [--quiet] update [--init] [--remote] [-N|--no-fetch]
 	      [--[no-]recommend-shallow] [-f|--force] [--rebase|--merge]
-	      [--reference <repository>] [--depth <depth>] [--recursive]
+	      [--[super-]reference <repository>] [--depth <depth>] [--recursive]
 	      [--jobs <n>] [--] [<path>...]
 'git submodule' [--quiet] summary [--cached|--files] [(-n|--summary-limit) <n>]
 	      [commit] [--] [<path>...]
@@ -370,6 +370,12 @@ the submodule itself.
 	This option is only valid for add and update commands.  These
 	commands sometimes need to clone a remote repository. In this case,
 	this option will be passed to the linkgit:git-clone[1] command.
+
+--super-reference <superproject repository>::
+	This option is only valid for the update command. When update needs
+	to clone a repository, a reference will be passed to the clone command
+	that points at the submodule path inside the reference superproject.
+
 +
 *NOTE*: Do *not* use this option unless you have read the note
 for linkgit:git-clone[1]'s `--reference` and `--shared` options carefully.
diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index b7710a7..ea6b27c 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -584,6 +584,7 @@ struct submodule_update_clone {
 	int quiet;
 	int recommend_shallow;
 	struct string_list references;
+	struct string_list super_references;
 	const char *depth;
 	const char *recursive_prefix;
 	const char *prefix;
@@ -600,7 +601,7 @@ struct submodule_update_clone {
 };
 #define SUBMODULE_UPDATE_CLONE_INIT {0, MODULE_LIST_INIT, 0, \
 	SUBMODULE_UPDATE_STRATEGY_INIT, 0, -1, STRING_LIST_INIT_DUP, \
-	NULL, NULL, NULL, \
+	STRING_LIST_INIT_DUP, NULL, NULL, NULL, \
 	STRING_LIST_INIT_DUP, 0, NULL, 0, 0}
 
 
@@ -715,6 +716,15 @@ static int prepare_to_clone_next_submodule(const struct cache_entry *ce,
 		for_each_string_list_item(item, &suc->references)
 			argv_array_pushl(&child->args, "--reference", item->string, NULL);
 	}
+	if (suc->super_references.nr) {
+		struct string_list_item *item;
+		for_each_string_list_item(item, &suc->super_references) {
+			strbuf_reset(&sb);
+			argv_array_pushf(&child->args, "--reference=%s/%s",
+					 relative_path(item->string, suc->prefix, &sb),
+					 sub->path);
+		}
+	}
 	if (suc->depth)
 		argv_array_push(&child->args, suc->depth);
 
@@ -835,6 +845,8 @@ static int update_clone(int argc, const char **argv, const char *prefix)
 			   N_("rebase, merge, checkout or none")),
 		OPT_STRING_LIST(0, "reference", &suc.references, N_("repo"),
 			   N_("reference repository")),
+		OPT_STRING_LIST(0, "super-reference", &suc.super_references, N_("repo"),
+			   N_("superproject of a reference repository")),
 		OPT_STRING(0, "depth", &suc.depth, "<depth>",
 			   N_("Create a shallow clone truncated to the "
 			      "specified number of revisions")),
diff --git a/git-submodule.sh b/git-submodule.sh
index 3b412f5..17f4ace 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -34,6 +34,7 @@ command=
 branch=
 force=
 reference=
+superreference=
 cached=
 recursive=
 init=
@@ -520,6 +521,14 @@ cmd_update()
 		--reference=*)
 			reference="$1"
 			;;
+		--super-reference)
+			case "$2" in '') usage ;; esac
+			superreference="--super-reference=$2"
+			shift
+			;;
+		--super-reference=*)
+			superreference="$1"
+			;;
 		-m|--merge)
 			update="merge"
 			;;
@@ -576,6 +585,7 @@ cmd_update()
 		${prefix:+--recursive-prefix "$prefix"} \
 		${update:+--update "$update"} \
 		${reference:+"$reference"} \
+		${superreference:+"$superreference"} \
 		${depth:+--depth "$depth"} \
 		${recommend_shallow:+"$recommend_shallow"} \
 		${jobs:+$jobs} \
-- 
2.9.2.572.g9d9644e.dirty

Re: [PATCHv2 5/6] submodule update: add super-reference flag

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

> When we have a another clone of a superproject, we may want to
> mirror the submodules using alternates. Introduce an option
> `--super-reference` that let's a user point to another superproject,
> which is assumed to have the same structure as the one they are
> running the "submodule update" command from and has all submodules
> checked out to borrow the submodule objects from within the other
> superprojects git directory.

That's much better than the previous round.

I however have trouble with the "checked out", though.  Isn't it
that it merely has to be "init"ed?  For that matter, as long as
super.git has $GIT_DIR/modules/ populated fully, it does not matter
it has checkout, and more interestingly and importantly, the
superproject mirror can even be a bare repository!

> +--super-reference <superproject repository>::
> +	This option is only valid for the update command. When update needs
> +	to clone a repository, a reference will be passed to the clone command
> +	that points at the submodule path inside the reference superproject.

"points at the submodule path inside" sounds as if we would look at

    /var/cache/super/libs/xyzzy

in the scenario in <xmqqoa57vvzl.fsf@gitster.mtv.corp.google.com>, 
when you give us "--super-reference=/var/cache/super".  Can we
clarify to avoid such a misread?

> +superreference=

Please don't name a multiple_word field "multipleword".

>  cached=
>  recursive=
>  init=
> @@ -520,6 +521,14 @@ cmd_update()
>  		--reference=*)
>  			reference="$1"
>  			;;
> +		--super-reference)
> +			case "$2" in '') usage ;; esac
> +			superreference="--super-reference=$2"
> +			shift
> +			;;
> +		--super-reference=*)
> +			superreference="$1"
> +			;;
>  		-m|--merge)
>  			update="merge"
>  			;;
> @@ -576,6 +585,7 @@ cmd_update()
>  		${prefix:+--recursive-prefix "$prefix"} \
>  		${update:+--update "$update"} \
>  		${reference:+"$reference"} \
> +		${superreference:+"$superreference"} \
>  		${depth:+--depth "$depth"} \
>  		${recommend_shallow:+"$recommend_shallow"} \
>  		${jobs:+$jobs} \

[PATCHv2 6/6] clone: reference flag is used for submodules as well

[Stefan Beller]

When giving a --reference while also giving --recurse, the alternates
for the submodules are assumed to be in the superproject as well.

In case they are not, we error out when cloning the submodule.
However we error out completely, we did not record the alternates yet,
so a following update command succeeds as usual (with no alternates).

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 Documentation/git-clone.txt    |  5 +++++
 builtin/clone.c                | 22 ++++++++++++++++++----
 t/t7408-submodule-reference.sh | 31 ++++++++++++++++++++++++++++++-
 3 files changed, 53 insertions(+), 5 deletions(-)

diff --git a/Documentation/git-clone.txt b/Documentation/git-clone.txt
index ec41d3d..2c6dea6 100644
--- a/Documentation/git-clone.txt
+++ b/Documentation/git-clone.txt
@@ -100,6 +100,11 @@ objects from the source repository into a pack in the cloned repository.
 +
 *NOTE*: see the NOTE for the `--shared` option, and also the
 `--dissociate` option.
++
+When `--reference` is given together with `--recursive`,
+the reference repository is assumed to contain the submodules
+as well and the submodules are setup as alternates of the
+submodules in the given reference project.
 
 --dissociate::
 	Borrow the objects from reference repositories specified
diff --git a/builtin/clone.c b/builtin/clone.c
index f044a8c..e8272b5 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -51,6 +51,7 @@ static int option_progress = -1;
 static enum transport_family family;
 static struct string_list option_config = STRING_LIST_INIT_NODUP;
 static struct string_list option_reference = STRING_LIST_INIT_NODUP;
+static struct string_list super_references = STRING_LIST_INIT_DUP;
 static int option_dissociate;
 static int max_jobs = -1;
 
@@ -280,10 +281,11 @@ static void strip_trailing_slashes(char *dir)
 	*end = '\0';
 }
 
-static int add_one_reference(struct string_list_item *item, void *cb_data)
+static int add_one_reference(struct string_list_item *item, void *cb_dir)
 {
 	char *ref_git;
 	const char *repo;
+	const char *dir = cb_dir;
 	struct strbuf alternate = STRBUF_INIT;
 
 	/* Beware: read_gitfile(), real_path() and mkpath() return static buffer */
@@ -316,6 +318,13 @@ static int add_one_reference(struct string_list_item *item, void *cb_data)
 	if (!access(mkpath("%s/info/grafts", ref_git), F_OK))
 		die(_("reference repository '%s' is grafted"), item->string);
 
+	if (option_recursive) {
+		struct strbuf sb = STRBUF_INIT;
+		char *rel = xstrdup(relative_path(item->string, dir, &sb));
+		string_list_append(&super_references, rel);
+		strbuf_reset(&sb);
+	}
+
 	strbuf_addf(&alternate, "%s/objects", ref_git);
 	add_to_alternates_file(alternate.buf);
 	strbuf_release(&alternate);
@@ -323,9 +332,9 @@ static int add_one_reference(struct string_list_item *item, void *cb_data)
 	return 0;
 }
 
-static void setup_reference(void)
+static void setup_reference(char *dir)
 {
-	for_each_string_list(&option_reference, add_one_reference, NULL);
+	for_each_string_list(&option_reference, add_one_reference, dir);
 }
 
 static void copy_alternates(struct strbuf *src, struct strbuf *dst,
@@ -736,6 +745,7 @@ static int checkout(void)
 
 	if (!err && option_recursive) {
 		struct argv_array args = ARGV_ARRAY_INIT;
+		static struct string_list_item *item;
 		argv_array_pushl(&args, "submodule", "update", "--init", "--recursive", NULL);
 
 		if (option_shallow_submodules == 1)
@@ -744,6 +754,10 @@ static int checkout(void)
 		if (max_jobs != -1)
 			argv_array_pushf(&args, "--jobs=%d", max_jobs);
 
+		if (super_references.nr)
+			for_each_string_list_item(item, &super_references)
+				argv_array_pushf(&args, "--super-reference=%s", item->string);
+
 		err = run_command_v_opt(args.argv, RUN_GIT_CMD);
 		argv_array_clear(&args);
 	}
@@ -978,7 +992,7 @@ int cmd_clone(int argc, const char **argv, const char *prefix)
 	strbuf_reset(&key);
 
 	if (option_reference.nr)
-		setup_reference();
+		setup_reference(dir);
 
 	fetch_pattern = value.buf;
 	refspec = parse_fetch_refspec(1, &fetch_pattern);
diff --git a/t/t7408-submodule-reference.sh b/t/t7408-submodule-reference.sh
index 1d9326e..588d53e 100755
--- a/t/t7408-submodule-reference.sh
+++ b/t/t7408-submodule-reference.sh
@@ -53,7 +53,8 @@ test_expect_success 'submodule add --reference uses alternates' '
 	(
 		cd super &&
 		git submodule add --reference ../B "file://$base_dir/A" sub &&
-		git commit -m B-super-added
+		git commit -m B-super-added &&
+		git repack -ad
 	) &&
 	test_alternate_usage super/.git/modules/sub/objects/info/alternates super/sub
 '
@@ -65,4 +66,32 @@ test_expect_success 'updating superproject keeps alternates' '
 	test_alternate_usage super-clone/.git/modules/sub/objects/info/alternates super-clone/sub
 '
 
+test_expect_success 'submodules use alternates when cloning a superproject' '
+	test_when_finished "rm -rf super-clone" &&
+	git clone --reference super --recursive super super-clone &&
+	(
+		cd super-clone &&
+		# test superproject has alternates setup correctly
+		test_alternate_usage .git/objects/info/alternates . &&
+		# test submodule has correct setup
+		test_alternate_usage .git/modules/sub/objects/info/alternates sub
+	)
+'
+
+test_expect_success 'cloning superproject, missing submodule alternates' '
+	test_when_finished "rm -rf super-clone" &&
+	git clone super super2 &&
+	test_must_fail git clone --recursive --reference super2 super2 super-clone &&
+	(
+		cd super-clone &&
+		# test superproject has alternates setup correctly
+		test_alternate_usage .git/objects/info/alternates . &&
+		# update of the submodule succeeds
+		git submodule update --init &&
+		# and we have no alternates:
+		test_must_fail test_alternate_usage .git/modules/sub/objects/info/alternates sub &&
+		test_path_is_file sub/file1
+	)
+'
+
 test_done
-- 
2.9.2.572.g9d9644e.dirty

Re: [PATCHv2 0/6] git clone: Marry --recursive and --reference

[Junio C Hamano]

Stefan Beller <sbeller@google.com> writes:

>  Some submodules in the referenced superproject may not be there, 
>  (they are just not initialized/cloned/checked out), which yields
>  an error for now.

Perhaps you can teach "git clone --reference" an new option
(--reference-if-able) to do this?  Then 

    When `--reference` is given together with `--recursive`,
    the reference repository is assumed to contain the submodules
    as well and the submodules are setup as alternates of the
    submodules in the given reference project.
 
in which "assumed" is a horrible wording (leave the reader
wondering: "so what happens to my data when the assumption does not
hold") can become a lot more reasonable

    When using --reference with --recursive, the --reference is used
    to specify a repository that has a copy of the superproject.  If
    that copy has submodules cloned for itself in its $GIT_DIR/modules,
    they are used as --reference when cloning submodules in the
    resulting clone.

and readers expectation would match with the reality.  Their
submodules would be cloned in a regular fashion if the central
mirror does not have it, and would take advantage of it if there is
already a clone.

Come to think of it, do we even need --super-reference?  "git clone
--reference --recursive" is a two step process, in that first the
superproject is cloned while creating objects/info/alternates, and
then submodules are cloned (via "update --init").  Can we make the
procedure to clone a submodule always look at the reference of the
superproject (i.e. objects/info/alternates) and try to borrow from
the place in it that corresponds to the submodule?  That way, not
just "git clone --reference --recursive" would take advantage of the
existing mirrors of submodules, a user who does this:

    $ git clone --reference $URL super
    $ cd super
    $ git submodule update --init ...

would be able to take advantage of the "what the mirror the
superproject uses already has" when cloning the submodules, no?

Re: [PATCHv2 0/6] git clone: Marry --recursive and --reference

[Stefan Beller]

On Sat, Aug 6, 2016 at 10:29 AM, Junio C Hamano <gitster@pobox.com> wrote:
> Stefan Beller <sbeller@google.com> writes:
>
>>  Some submodules in the referenced superproject may not be there,
>>  (they are just not initialized/cloned/checked out), which yields
>>  an error for now.
>
> Perhaps you can teach "git clone --reference" an new option
> (--reference-if-able) to do this?  Then
>
>     When `--reference` is given together with `--recursive`,
>     the reference repository is assumed to contain the submodules
>     as well and the submodules are setup as alternates of the
>     submodules in the given reference project.
>
> in which "assumed" is a horrible wording (leave the reader
> wondering: "so what happens to my data when the assumption does not
> hold") can become a lot more reasonable
>
>     When using --reference with --recursive, the --reference is used
>     to specify a repository that has a copy of the superproject.  If
>     that copy has submodules cloned for itself in its $GIT_DIR/modules,
>     they are used as --reference when cloning submodules in the
>     resulting clone.
>
> and readers expectation would match with the reality.  Their
> submodules would be cloned in a regular fashion if the central
> mirror does not have it, and would take advantage of it if there is
> already a clone.

That makes sense.

>
> Come to think of it, do we even need --super-reference?  "git clone
> --reference --recursive" is a two step process, in that first the
> superproject is cloned while creating objects/info/alternates, and
> then submodules are cloned (via "update --init").  Can we make the
> procedure to clone a submodule always look at the reference of the
> superproject (i.e. objects/info/alternates) and try to borrow from
> the place in it that corresponds to the submodule?  That way, not
> just "git clone --reference --recursive" would take advantage of the
> existing mirrors of submodules, a user who does this:
>
>     $ git clone --reference $URL super
>     $ cd super
>     $ git submodule update --init ...
>
> would be able to take advantage of the "what the mirror the
> superproject uses already has" when cloning the submodules, no?

That would work, too.

I'll implement that.

Thanks,
Stefan