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[PATCH v6 08/10] submodule: add a helper to check if it is safe to write to .gitmodules

From
Antonio Ospite <ao2@ao2.it>
Date
Oct 5, 2018, 13:05 UTC
Message-ID
<20181005130601.15879-9-ao2@ao2.it>
In-Reply-To
<20181005130601.15879-1-ao2@ao2.it>

Introduce a helper function named is_writing_gitmodules_ok() to verify that the .gitmodules file is safe to write.

The function name follows the scheme of is_staging_gitmodules_ok().

The two symbolic constants GITMODULES_INDEX and GITMODULES_HEAD are used to get help from the C preprocessor in preventing typos, especially for future users.

This is in preparation for a future change which teaches git how to read .gitmodules from the index or from the current branch if the file is not available in the working tree.

The rationale behind the check is that writing to .gitmodules requires the file to be present in the working tree, unless a brand new .gitmodules is being created (in which case the .gitmodules file would not exist at all: neither in the working tree nor in the index or in the current branch).

Expose the functionality also via a "submodule-helper config --check-writeable" command, as git scripts may want to perform the check before modifying submodules configuration.

Signed-off-by: Antonio Ospite <ao2@ao2.it>
---
 builtin/submodule--helper.c | 24 +++++++++++++++++++++++-
 cache.h                     |  2 ++
 submodule.c                 | 18 ++++++++++++++++++
 submodule.h                 |  1 +
 t/t7411-submodule-config.sh | 31 +++++++++++++++++++++++++++++++
 5 files changed, 75 insertions(+), 1 deletion(-)
diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index e1bdca8f0b..28f3ccca6d 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -2127,6 +2127,28 @@ static int check_name(int argc, const char **argv, const char *prefix)
 
 static int module_config(int argc, const char **argv, const char *prefix)
 {
+	enum {
+		CHECK_WRITEABLE = 1
+	} command = 0;
+
+	struct option module_config_options[] = {
+		OPT_CMDMODE(0, "check-writeable", &command,
+			    N_("check if it is safe to write to the .gitmodules file"),
+			    CHECK_WRITEABLE),
+		OPT_END()
+	};
+	const char *const git_submodule_helper_usage[] = {
+		N_("git submodule--helper config name [value]"),
+		N_("git submodule--helper config --check-writeable"),
+		NULL
+	};
+
+	argc = parse_options(argc, argv, prefix, module_config_options,
+			     git_submodule_helper_usage, PARSE_OPT_KEEP_ARGV0);
+
+	if (argc == 1 && command == CHECK_WRITEABLE)
+		return is_writing_gitmodules_ok() ? 0 : -1;
+
 	/* Equivalent to ACTION_GET in builtin/config.c */
 	if (argc == 2)
 		return print_config_from_gitmodules(the_repository, argv[1]);
@@ -2135,7 +2157,7 @@ static int module_config(int argc, const char **argv, const char *prefix)
 	if (argc == 3)
 		return config_set_in_gitmodules_file_gently(argv[1], argv[2]);
 
-	die("submodule--helper config takes 1 or 2 arguments: name [value]");
+	usage_with_options(git_submodule_helper_usage, module_config_options);
 }
 
 #define SUPPORT_SUPER_PREFIX (1<<0)
diff --git a/cache.h b/cache.h
index d508f3d4f8..2d495fc800 100644
--- a/cache.h
+++ b/cache.h
@@ -486,6 +486,8 @@ static inline enum object_type object_type(unsigned int mode)
 #define INFOATTRIBUTES_FILE "info/attributes"
 #define ATTRIBUTE_MACRO_PREFIX "[attr]"
 #define GITMODULES_FILE ".gitmodules"
+#define GITMODULES_INDEX ":.gitmodules"
+#define GITMODULES_HEAD "HEAD:.gitmodules"
 #define GIT_NOTES_REF_ENVIRONMENT "GIT_NOTES_REF"
 #define GIT_NOTES_DEFAULT_REF "refs/notes/commits"
 #define GIT_NOTES_DISPLAY_REF_ENVIRONMENT "GIT_NOTES_DISPLAY_REF"
diff --git a/submodule.c b/submodule.c
index 3b23e76e55..bd2506c5ba 100644
--- a/submodule.c
+++ b/submodule.c
@@ -51,6 +51,24 @@ int is_gitmodules_unmerged(const struct index_state *istate)
 	return 0;
 }
 
+/*
+ * Check if the .gitmodules file is safe to write.
+ *
+ * Writing to the .gitmodules file requires that the file exists in the
+ * working tree or, if it doesn't, that a brand new .gitmodules file is going
+ * to be created (i.e. it's neither in the index nor in the current branch).
+ *
+ * It is not safe to write to .gitmodules if it's not in the working tree but
+ * it is in the index or in the current branch, because writing new values
+ * (and staging them) would blindly overwrite ALL the old content.
+ */
+int is_writing_gitmodules_ok(void)
+{
+	struct object_id oid;
+	return file_exists(GITMODULES_FILE) ||
+		(get_oid(GITMODULES_INDEX, &oid) < 0 && get_oid(GITMODULES_HEAD, &oid) < 0);
+}
+
 /*
  * Check if the .gitmodules file has unstaged modifications.  This must be
  * checked before allowing modifications to the .gitmodules file with the
diff --git a/submodule.h b/submodule.h
index e452919aa4..7a22f71cb9 100644
--- a/submodule.h
+++ b/submodule.h
@@ -40,6 +40,7 @@ struct submodule_update_strategy {
 #define SUBMODULE_UPDATE_STRATEGY_INIT {SM_UPDATE_UNSPECIFIED, NULL}
 
 int is_gitmodules_unmerged(const struct index_state *istate);
+int is_writing_gitmodules_ok(void);
 int is_staging_gitmodules_ok(struct index_state *istate);
 int update_path_in_gitmodules(const char *oldpath, const char *newpath);
 int remove_path_from_gitmodules(const char *path);
diff --git a/t/t7411-submodule-config.sh b/t/t7411-submodule-config.sh
index 791245f18d..45953f9300 100755
--- a/t/t7411-submodule-config.sh
+++ b/t/t7411-submodule-config.sh
@@ -161,4 +161,35 @@ test_expect_success 'overwriting unstaged submodules config with "submodule--hel
 	)
 '
 
+test_expect_success 'writeable .gitmodules when it is in the working tree' '
+	git -C super submodule--helper config --check-writeable
+'
+
+test_expect_success 'writeable .gitmodules when it is nowhere in the repository' '
+	ORIG=$(git -C super rev-parse HEAD) &&
+	test_when_finished "git -C super reset --hard $ORIG" &&
+	(cd super &&
+		git rm .gitmodules &&
+		git commit -m "remove .gitmodules from the current branch" &&
+		git submodule--helper config --check-writeable
+	)
+'
+
+test_expect_success 'non-writeable .gitmodules when it is in the index but not in the working tree' '
+	test_when_finished "git -C super checkout .gitmodules" &&
+	(cd super &&
+		rm -f .gitmodules &&
+		test_must_fail git submodule--helper config --check-writeable
+	)
+'
+
+test_expect_success 'non-writeable .gitmodules when it is in the current branch but not in the index' '
+	ORIG=$(git -C super rev-parse HEAD) &&
+	test_when_finished "git -C super reset --hard $ORIG" &&
+	(cd super &&
+		git rm .gitmodules &&
+		test_must_fail git submodule--helper config --check-writeable
+	)
+'
+
 test_done

-- 
2.19.0
Previous: Antonio OspiteNext: Stefan Beller
Message 15 of 23 in “Make submodules work if .gitmodules is not checked out”
  1. 00/10 Make submodules work if .gitmodules is not checked outAntonio Ospite, Oct 5, 2018
  2. 03/10 t7411: merge tests 5 and 6Antonio Ospite, Oct 5, 2018
  3. 09/10 submodule: support reading .gitmodules when it's not in the working treeAntonio Ospite, Oct 5, 2018
  4. Stefan BellerOct 8, 2018
  5. Antonio OspiteOct 10, 2018
  6. Stefan BellerOct 10, 2018
  7. Junio C HamanoOct 9, 2018
  8. Junio C HamanoOct 9, 2018
  9. 04/10 t7411: be nicer to future tests and really clean things upAntonio Ospite, Oct 5, 2018
  10. 10/10 t/helper: add test-submodule-nested-repo-configAntonio Ospite, Oct 5, 2018
  11. 02/10 submodule: factor out a config_set_in_gitmodules_file_gently functionAntonio Ospite, Oct 5, 2018
  12. 01/10 submodule: add a print_config_from_gitmodules() helperAntonio Ospite, Oct 5, 2018
  13. 06/10 submodule: use the 'submodule--helper config' commandAntonio Ospite, Oct 5, 2018
  14. 05/10 submodule--helper: add a new 'config' subcommandAntonio Ospite, Oct 5, 2018
  15. 08/10 submodule: add a helper to check if it is safe to write to .gitmodulesAntonio Ospite, Oct 5, 2018
  16. Stefan BellerOct 5, 2018
  17. Antonio OspiteOct 6, 2018
  18. Junio C HamanoOct 6, 2018
  19. Antonio OspiteOct 8, 2018
  20. 07/10 t7506: clean up .gitmodules properly before setting up new scenarioAntonio Ospite, Oct 5, 2018
  21. Antonio OspiteOct 6, 2018
  22. Junio C HamanoOct 25, 2018
  23. Antonio OspiteOct 25, 2018

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