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[PATCH 1/3] submodule.c: add has_submodules to check if we have any submodules




When submodules are involved, it often slows down the process, as most
submodule related handling is either done via a child process or by
iterating over the index finding all gitlinks.

For most commands that may interact with submodules, we need have a
quick check if we do have any submodules at all, such that we can
be fast in the case when no submodules are in use.  For this quick
check introduce a function that checks with different heuristics if
we do have submodules around, checking if
* anything related to submodules is configured,
* absorbed git dirs for submodules are present,
* the '.gitmodules' file exists
* gitlinks are recorded in the index.

Each heuristic has advantages and disadvantages.
For example in a later patch, when we first use this function in
git-clone, we'll just check for the existence of the '.gitmodules'
file, because at the time of running the clone command there will
be no absorbed git dirs or submodule configuration around.

Checking for any configuration related to submodules would be useful
in a later stage (after cloning) to see if the submodules are actually
in use.

Checking for absorbed git directories is good to see if the user has
actually cloned submodules already (i.e. not just initialized them by
configuring them).

The heuristic for checking the configuration requires this patch
to have have a global state, whether the submodule config has already
been read, and if there were any submodule related keys. Make
'submodule_config' private to the submodule code, and introduce
'load_submodule_config' that will take care of this global state.

Signed-off-by: Stefan Beller <sbeller@xxxxxxxxxx>
---
 builtin/checkout.c          |  2 +-
 builtin/fetch.c             |  2 +-
 builtin/read-tree.c         |  2 +-
 builtin/reset.c             |  2 +-
 builtin/submodule--helper.c |  6 ++--
 submodule.c                 | 78 +++++++++++++++++++++++++++++++++++----------
 submodule.h                 |  8 ++++-
 unpack-trees.c              |  2 +-
 8 files changed, 77 insertions(+), 25 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index bfa5419f33..2787b343b1 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1215,7 +1215,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	}
 
 	if (recurse_submodules != RECURSE_SUBMODULES_OFF) {
-		git_config(submodule_config, NULL);
+		load_submodule_config();
 		if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT)
 			set_config_update_recurse_submodules(recurse_submodules);
 	}
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 4ef7a08afc..510ef1c9de 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -1344,7 +1344,7 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 			set_config_fetch_recurse_submodules(arg);
 		}
 		gitmodules_config();
-		git_config(submodule_config, NULL);
+		load_submodule_config();
 	}
 
 	if (all) {
diff --git a/builtin/read-tree.c b/builtin/read-tree.c
index 23e212ee8c..fe2ec60a51 100644
--- a/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@ -177,7 +177,7 @@ int cmd_read_tree(int argc, const char **argv, const char *unused_prefix)
 
 	if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT) {
 		gitmodules_config();
-		git_config(submodule_config, NULL);
+		load_submodule_config();
 		set_config_update_recurse_submodules(RECURSE_SUBMODULES_ON);
 	}
 
diff --git a/builtin/reset.c b/builtin/reset.c
index 5ce27fcaed..f3aca487d9 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -321,7 +321,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 
 	if (recurse_submodules != RECURSE_SUBMODULES_DEFAULT) {
 		gitmodules_config();
-		git_config(submodule_config, NULL);
+		load_submodule_config();
 		set_config_update_recurse_submodules(RECURSE_SUBMODULES_ON);
 	}
 
diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 85aafe46a4..770a95ca14 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -1015,7 +1015,7 @@ static int update_clone(int argc, const char **argv, const char *prefix)
 
 	/* Overlay the parsed .gitmodules file with .git/config */
 	gitmodules_config();
-	git_config(submodule_config, NULL);
+	load_submodule_config();
 
 	if (max_jobs < 0)
 		max_jobs = parallel_submodules();
@@ -1058,7 +1058,7 @@ static const char *remote_submodule_branch(const char *path)
 {
 	const struct submodule *sub;
 	gitmodules_config();
-	git_config(submodule_config, NULL);
+	load_submodule_config();
 
 	sub = submodule_from_path(null_sha1, path);
 	if (!sub)
@@ -1130,7 +1130,7 @@ static int absorb_git_dirs(int argc, const char **argv, const char *prefix)
 			     git_submodule_helper_usage, 0);
 
 	gitmodules_config();
-	git_config(submodule_config, NULL);
+	load_submodule_config();
 
 	if (module_list_compute(argc, argv, prefix, &pathspec, &list) < 0)
 		return 1;
diff --git a/submodule.c b/submodule.c
index 20ed5b5681..14ea405048 100644
--- a/submodule.c
+++ b/submodule.c
@@ -24,6 +24,12 @@ static int initialized_fetch_ref_tips;
 static struct sha1_array ref_tips_before_fetch;
 static struct sha1_array ref_tips_after_fetch;
 
+static enum {
+	SUBMODULE_CONFIG_NOT_READ = 0,
+	SUBMODULE_CONFIG_NO_CONFIG,
+	SUBMODULE_CONFIG_EXISTS,
+} submodule_config_reading;
+
 /*
  * The following flag is set if the .gitmodules file is unmerged. We then
  * disable recursion for all submodules where .git/config doesn't have a
@@ -83,6 +89,62 @@ int update_path_in_gitmodules(const char *oldpath, const char *newpath)
 	return 0;
 }
 
+static int submodule_config(const char *var, const char *value, void *cb)
+{
+	if (!strcmp(var, "submodule.fetchjobs")) {
+		submodule_config_reading = SUBMODULE_CONFIG_EXISTS;
+		parallel_jobs = git_config_int(var, value);
+		if (parallel_jobs < 0)
+			die(_("negative values not allowed for submodule.fetchJobs"));
+		return 0;
+	} else if (starts_with(var, "submodule.")) {
+		submodule_config_reading = SUBMODULE_CONFIG_EXISTS;
+		return parse_submodule_config_option(var, value);
+	} else if (!strcmp(var, "fetch.recursesubmodules")) {
+		submodule_config_reading = SUBMODULE_CONFIG_EXISTS;
+		config_fetch_recurse_submodules = parse_fetch_recurse_submodules_arg(var, value);
+		return 0;
+	}
+	return 0;
+}
+
+void load_submodule_config(void)
+{
+	submodule_config_reading = SUBMODULE_CONFIG_NO_CONFIG;
+	git_config(submodule_config, NULL);
+}
+
+int has_submodules(unsigned what_to_check)
+{
+	if (what_to_check & SUBMODULE_CHECK_ANY_CONFIG) {
+		if (submodule_config_reading == SUBMODULE_CONFIG_NOT_READ)
+			load_submodule_config();
+		if (submodule_config_reading == SUBMODULE_CONFIG_EXISTS)
+			return 1;
+	}
+
+	if ((what_to_check & SUBMODULE_CHECK_ABSORBED_GIT_DIRS) &&
+	    file_exists(git_path("modules")))
+		return 1;
+
+	if ((what_to_check & SUBMODULE_CHECK_GITMODULES_IN_WT) &&
+	    (!is_bare_repository() && file_exists(".gitmodules")))
+		return 1;
+
+	if (what_to_check & SUBMODULE_CHECK_GITLINKS_IN_TREE) {
+		int i;
+
+		if (read_cache() < 0)
+			die(_("index file corrupt"));
+
+		for (i = 0; i < active_nr; i++)
+			if (S_ISGITLINK(active_cache[i]->ce_mode))
+				return 1;
+	}
+
+	return 0;
+}
+
 /*
  * Try to remove the "submodule.<name>" section from .gitmodules where the given
  * path is configured. Return 0 only if a .gitmodules file was found, a section
@@ -152,22 +214,6 @@ void set_diffopt_flags_from_submodule_config(struct diff_options *diffopt,
 	}
 }
 
-int submodule_config(const char *var, const char *value, void *cb)
-{
-	if (!strcmp(var, "submodule.fetchjobs")) {
-		parallel_jobs = git_config_int(var, value);
-		if (parallel_jobs < 0)
-			die(_("negative values not allowed for submodule.fetchJobs"));
-		return 0;
-	} else if (starts_with(var, "submodule."))
-		return parse_submodule_config_option(var, value);
-	else if (!strcmp(var, "fetch.recursesubmodules")) {
-		config_fetch_recurse_submodules = parse_fetch_recurse_submodules_arg(var, value);
-		return 0;
-	}
-	return 0;
-}
-
 void gitmodules_config(void)
 {
 	const char *work_tree = get_git_work_tree();
diff --git a/submodule.h b/submodule.h
index 8a8bc49dc9..5ec72fbb16 100644
--- a/submodule.h
+++ b/submodule.h
@@ -1,6 +1,12 @@
 #ifndef SUBMODULE_H
 #define SUBMODULE_H
 
+#define SUBMODULE_CHECK_ANY_CONFIG		(1<<0)
+#define SUBMODULE_CHECK_ABSORBED_GIT_DIRS	(1<<1)
+#define SUBMODULE_CHECK_GITMODULES_IN_WT	(1<<2)
+#define SUBMODULE_CHECK_GITLINKS_IN_TREE 	(1<<3)
+int has_submodules(unsigned what_to_check);
+
 struct diff_options;
 struct argv_array;
 struct sha1_array;
@@ -37,7 +43,7 @@ extern int remove_path_from_gitmodules(const char *path);
 extern void stage_updated_gitmodules(void);
 extern void set_diffopt_flags_from_submodule_config(struct diff_options *,
 		const char *path);
-extern int submodule_config(const char *var, const char *value, void *cb);
+extern void load_submodule_config(void);
 extern void gitmodules_config(void);
 extern void gitmodules_config_sha1(const unsigned char *commit_sha1);
 extern int is_submodule_initialized(const char *path);
diff --git a/unpack-trees.c b/unpack-trees.c
index 4b3f9518e5..fe42d03a74 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -292,7 +292,7 @@ static void reload_gitmodules_file(struct index_state *index,
 				submodule_free();
 				checkout_entry(ce, state, NULL);
 				gitmodules_config();
-				git_config(submodule_config, NULL);
+				load_submodule_config();
 			} else
 				break;
 		}
-- 
2.13.0.18.g7d86cc8ba0