Subject: [PATCH v6 10/10] submodule: hash the submodule name for the gitdir path

From: Adrian Ratiu <[email-masked]>
Date: Sat, 13 Dec 2025 10:08:16 +0200

If none of the previous plain-text / encoding / derivation steps work
and case 2.4 is reached, then try a hash of the submodule name to see
if that can be a valid gitdir before giving up and throwing an error.

This is a "last resort" type of measure to avoid conflicts since it
loses the human readability of the gitdir path. This logic will be
reached in rare cases, as can be seen in the test we added.

Signed-off-by: Adrian Ratiu <[email-masked]>
---
 builtin/submodule--helper.c                | 19 +++++++
 t/t7425-submodule-gitdir-path-extension.sh | 59 ++++++++++++++++++++++
 2 files changed, 78 insertions(+)

diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 5851d49b28..3cbacadbe8 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -465,6 +465,10 @@ static int validate_and_set_submodule_gitdir(struct strbuf *gitdir_path,
 static void create_default_gitdir_config(const char *submodule_name)
 {
 	struct strbuf gitdir_path = STRBUF_INIT;
+	struct git_hash_ctx ctx;
+	char hex_name_hash[GIT_MAX_HEXSZ + 1], header[128];
+	unsigned char raw_name_hash[GIT_MAX_RAWSZ];
+	int header_len;
 
 	/* The config is set only when extensions.submodulePathConfig is enabled */
 	if (!the_repository->repository_format_submodule_path_cfg &&
@@ -511,6 +515,21 @@ static void create_default_gitdir_config(const char *submodule_name)
 			return;
 	}
 
+	/* Case 2.4: If all the above failed, try a hash of the name as a last resort */
+	header_len = snprintf(header, sizeof(header), "blob %zu", strlen(submodule_name));
+	the_hash_algo->init_fn(&ctx);
+	the_hash_algo->update_fn(&ctx, header, header_len);
+	the_hash_algo->update_fn(&ctx, "\0", 1);
+	the_hash_algo->update_fn(&ctx, submodule_name, strlen(submodule_name));
+	the_hash_algo->final_fn(raw_name_hash, &ctx);
+	hash_to_hex_algop_r(hex_name_hash, raw_name_hash, the_hash_algo);
+	strbuf_reset(&gitdir_path);
+	repo_git_path_append(the_repository, &gitdir_path, "modules/%s", hex_name_hash);
+	if (!validate_and_set_submodule_gitdir(&gitdir_path, submodule_name)) {
+		strbuf_release(&gitdir_path);
+		return;
+	}
+
 	/* Case 3: nothing worked, error out */
 	die(_("failed to set a valid default config for 'submodule.%s.gitdir'. "
 	      "Please ensure it is set, for example by running something like: "
diff --git a/t/t7425-submodule-gitdir-path-extension.sh b/t/t7425-submodule-gitdir-path-extension.sh
index a3c6c0c6b9..1599d28587 100755
--- a/t/t7425-submodule-gitdir-path-extension.sh
+++ b/t/t7425-submodule-gitdir-path-extension.sh
@@ -307,4 +307,63 @@ test_expect_success CASE_INSENSITIVE_FS 'verify case-folding conflicts are corre
 	verify_submodule_gitdir_path cloned-folding "fooBar" "modules/fooBar0"
 '
 
+test_expect_success CASE_INSENSITIVE_FS 'verify hashing conflict resolution as a last resort' '
+	git clone -c extensions.submodulePathConfig=true main cloned-hash &&
+	(
+		cd cloned-hash &&
+
+		# conflict: add all submodule conflicting variants until we reach the
+		# final hashing conflict resolution for submodule "foo"
+		git submodule add ../new-sub "foo" &&
+		git submodule add ../new-sub "foo0" &&
+		git submodule add ../new-sub "foo1" &&
+		git submodule add ../new-sub "foo2" &&
+		git submodule add ../new-sub "foo3" &&
+		git submodule add ../new-sub "foo4" &&
+		git submodule add ../new-sub "foo5" &&
+		git submodule add ../new-sub "foo6" &&
+		git submodule add ../new-sub "foo7" &&
+		git submodule add ../new-sub "foo8" &&
+		git submodule add ../new-sub "foo9" &&
+		git submodule add ../new-sub "%46oo" &&
+		git submodule add ../new-sub "%46oo0" &&
+		git submodule add ../new-sub "%46oo1" &&
+		git submodule add ../new-sub "%46oo2" &&
+		git submodule add ../new-sub "%46oo3" &&
+		git submodule add ../new-sub "%46oo4" &&
+		git submodule add ../new-sub "%46oo5" &&
+		git submodule add ../new-sub "%46oo6" &&
+		git submodule add ../new-sub "%46oo7" &&
+		git submodule add ../new-sub "%46oo8" &&
+		git submodule add ../new-sub "%46oo9" &&
+		test_commit add-foo-variants &&
+		git submodule add ../new-sub "Foo" &&
+		test_commit add-uppercase-foo
+	) &&
+	verify_submodule_gitdir_path cloned-hash "foo" "modules/foo" &&
+	verify_submodule_gitdir_path cloned-hash "foo0" "modules/foo0" &&
+	verify_submodule_gitdir_path cloned-hash "foo1" "modules/foo1" &&
+	verify_submodule_gitdir_path cloned-hash "foo2" "modules/foo2" &&
+	verify_submodule_gitdir_path cloned-hash "foo3" "modules/foo3" &&
+	verify_submodule_gitdir_path cloned-hash "foo4" "modules/foo4" &&
+	verify_submodule_gitdir_path cloned-hash "foo5" "modules/foo5" &&
+	verify_submodule_gitdir_path cloned-hash "foo6" "modules/foo6" &&
+	verify_submodule_gitdir_path cloned-hash "foo7" "modules/foo7" &&
+	verify_submodule_gitdir_path cloned-hash "foo8" "modules/foo8" &&
+	verify_submodule_gitdir_path cloned-hash "foo9" "modules/foo9" &&
+	verify_submodule_gitdir_path cloned-hash "%46oo" "modules/%46oo" &&
+	verify_submodule_gitdir_path cloned-hash "%46oo0" "modules/%46oo0" &&
+	verify_submodule_gitdir_path cloned-hash "%46oo1" "modules/%46oo1" &&
+	verify_submodule_gitdir_path cloned-hash "%46oo2" "modules/%46oo2" &&
+	verify_submodule_gitdir_path cloned-hash "%46oo3" "modules/%46oo3" &&
+	verify_submodule_gitdir_path cloned-hash "%46oo4" "modules/%46oo4" &&
+	verify_submodule_gitdir_path cloned-hash "%46oo5" "modules/%46oo5" &&
+	verify_submodule_gitdir_path cloned-hash "%46oo6" "modules/%46oo6" &&
+	verify_submodule_gitdir_path cloned-hash "%46oo7" "modules/%46oo7" &&
+	verify_submodule_gitdir_path cloned-hash "%46oo8" "modules/%46oo8" &&
+	verify_submodule_gitdir_path cloned-hash "%46oo9" "modules/%46oo9" &&
+	hash=$(printf "Foo" | git hash-object --stdin) &&
+	verify_submodule_gitdir_path cloned-hash "Foo" "modules/${hash}"
+'
+
 test_done
-- 
2.51.2