submodule update: learn `--[no-]recommend-shallow` option

Sometimes the history of a submodule is not considered important by
the projects upstream. To make it easier for downstream users, allow
a boolean field 'submodule.<name>.shallow' in .gitmodules, which can
be used to recommend whether upstream considers the history important.

This field is honored in the initial clone by default, it can be
ignored by giving the `--no-recommend-shallow` option.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-submodule.txt

@@ -15,8 +15,9 @@ SYNOPSIS
 'git submodule' [--quiet] init [--] [<path>...]
 'git submodule' [--quiet] deinit [-f|--force] (--all|[--] <path>...)
 'git submodule' [--quiet] update [--init] [--remote] [-N|--no-fetch]
-	      [-f|--force] [--rebase|--merge] [--reference <repository>]
+	      [--[no-]recommend-shallow] [-f|--force] [--rebase|--merge]
-	      [--depth <depth>] [--recursive] [--jobs <n>] [--] [<path>...]
+	      [--reference <repository>] [--depth <depth>] [--recursive]
+	      [--jobs <n>] [--] [<path>...]
 'git submodule' [--quiet] summary [--cached|--files] [(-n|--summary-limit) <n>]
 	      [commit] [--] [<path>...]
 'git submodule' [--quiet] foreach [--recursive] <command>
@@ -384,6 +385,12 @@ for linkgit:git-clone[1]'s `--reference` and `--shared` options carefully.
 	clone with a history truncated to the specified number of revisions.
 	See linkgit:git-clone[1]
 
+--[no-]recommend-shallow::
+	This option is only valid for the update command.
+	The initial clone of a submodule will use the recommended
+	`submodule.<name>.shallow` as provided by the .gitmodules file
+	by default. To ignore the suggestions use `--no-recommend-shallow`.
+
 -j <n>::
 --jobs <n>::
 	This option is only valid for the update command.

builtin/submodule--helper.c

@@ -581,6 +581,7 @@ struct submodule_update_clone {
 
 	/* configuration parameters which are passed on to the children */
 	int quiet;
+	int recommend_shallow;
 	const char *reference;
 	const char *depth;
 	const char *recursive_prefix;
@@ -593,7 +594,7 @@ struct submodule_update_clone {
 	unsigned quickstop : 1;
 };
 #define SUBMODULE_UPDATE_CLONE_INIT {0, MODULE_LIST_INIT, 0, \
-	SUBMODULE_UPDATE_STRATEGY_INIT, 0, NULL, NULL, NULL, NULL, \
+	SUBMODULE_UPDATE_STRATEGY_INIT, 0, -1, NULL, NULL, NULL, NULL, \
 	STRING_LIST_INIT_DUP, 0}
 
 
@@ -698,6 +699,8 @@ static int prepare_to_clone_next_submodule(const struct cache_entry *ce,
 		argv_array_push(&child->args, "--quiet");
 	if (suc->prefix)
 		argv_array_pushl(&child->args, "--prefix", suc->prefix, NULL);
+	if (suc->recommend_shallow && sub->recommend_shallow == 1)
+		argv_array_push(&child->args, "--depth=1");
 	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);
@@ -780,6 +783,8 @@ static int update_clone(int argc, const char **argv, const char *prefix)
 			      "specified number of revisions")),
 		OPT_INTEGER('j', "jobs", &max_jobs,
 			    N_("parallel jobs")),
+		OPT_BOOL(0, "recommend-shallow", &suc.recommend_shallow,
+			    N_("whether the initial clone should follow the shallow recommendation")),
 		OPT__QUIET(&suc.quiet, N_("don't print cloning progress")),
 		OPT_END()
 	};

git-submodule.sh

@@ -9,7 +9,7 @@ USAGE="[--quiet] add [-b <branch>] [-f|--force] [--name <name>] [--reference <re
    or: $dashless [--quiet] status [--cached] [--recursive] [--] [<path>...]
    or: $dashless [--quiet] init [--] [<path>...]
    or: $dashless [--quiet] deinit [-f|--force] (--all| [--] <path>...)
-   or: $dashless [--quiet] update [--init] [--remote] [-N|--no-fetch] [-f|--force] [--checkout|--merge|--rebase] [--reference <repository>] [--recursive] [--] [<path>...]
+   or: $dashless [--quiet] update [--init] [--remote] [-N|--no-fetch] [-f|--force] [--checkout|--merge|--rebase] [--[no-]recommend-shallow] [--reference <repository>] [--recursive] [--] [<path>...]
    or: $dashless [--quiet] summary [--cached|--files] [--summary-limit <n>] [commit] [--] [<path>...]
    or: $dashless [--quiet] foreach [--recursive] <command>
    or: $dashless [--quiet] sync [--recursive] [--] [<path>...]"
@@ -559,6 +559,12 @@ cmd_update()
 		--checkout)
 			update="checkout"
 			;;
+		--recommend-shallow)
+			recommend_shallow="--recommend-shallow"
+			;;
+		--no-recommend-shallow)
+			recommend_shallow="--no-recommend-shallow"
+			;;
 		--depth)
 			case "$2" in '') usage ;; esac
 			depth="--depth=$2"
@@ -601,6 +607,7 @@ cmd_update()
 		${update:+--update "$update"} \
 		${reference:+--reference "$reference"} \
 		${depth:+--depth "$depth"} \
+		${recommend_shallow:+"$recommend_shallow"} \
 		${jobs:+$jobs} \
 		"$@" || echo "#unmatched"
 	} | {

t/t5614-clone-submodules.sh

@@ -82,4 +82,56 @@ test_expect_success 'non shallow clone with shallow submodule' '
 	)
 '
 
+test_expect_success 'clone follows shallow recommendation' '
+	test_when_finished "rm -rf super_clone" &&
+	git config -f .gitmodules submodule.sub.shallow true &&
+	git add .gitmodules &&
+	git commit -m "recommed shallow for sub" &&
+	git clone --recurse-submodules --no-local "file://$pwd/." super_clone &&
+	(
+		cd super_clone &&
+		git log --oneline >lines &&
+		test_line_count = 4 lines
+	) &&
+	(
+		cd super_clone/sub &&
+		git log --oneline >lines &&
+		test_line_count = 1 lines
+	)
+'
+
+test_expect_success 'get unshallow recommended shallow submodule' '
+	test_when_finished "rm -rf super_clone" &&
+	git clone --no-local "file://$pwd/." super_clone &&
+	(
+		cd super_clone &&
+		git submodule update --init --no-recommend-shallow &&
+		git log --oneline >lines &&
+		test_line_count = 4 lines
+	) &&
+	(
+		cd super_clone/sub &&
+		git log --oneline >lines &&
+		test_line_count = 3 lines
+	)
+'
+
+test_expect_success 'clone follows non shallow recommendation' '
+	test_when_finished "rm -rf super_clone" &&
+	git config -f .gitmodules submodule.sub.shallow false &&
+	git add .gitmodules &&
+	git commit -m "recommed non shallow for sub" &&
+	git clone --recurse-submodules --no-local "file://$pwd/." super_clone &&
+	(
+		cd super_clone &&
+		git log --oneline >lines &&
+		test_line_count = 5 lines
+	) &&
+	(
+		cd super_clone/sub &&
+		git log --oneline >lines &&
+		test_line_count = 3 lines
+	)
+'
+
 test_done