Pass unconverted data when iconv doesn't like it

When using Iconv to convert unicode data and iconv doesn't like
the source data (because it thinks that it's not actual UTF-8),
instead of stopping the operation, just use the unconverted data.
This will generally do the right thing on the filesystem, since
that is the source of the non-UTF-8 path data anyhow.

This adds some tests for creating and looking up branches with
messy Unicode names.  Also, this takes the helper function that
was previously internal to `git_repository_init` and makes it
into `git_path_does_fs_decompose_unicode` which is a useful in
tests to understand what the expected results should be.

src/path.c

@@ -799,8 +799,11 @@ int git_path_iconv(git_path_iconv_t *ic, char **in, size_t *inlen)
 		if (rv != (size_t)-1)
 			break;
 
+		/* if we cannot convert the data (probably because iconv thinks
+		 * it is not valid UTF-8 source data), then use original data
+		 */
 		if (errno != E2BIG)
-			goto fail;
+			return 0;
 
 		/* make space for 2x the remaining data to be converted
 		 * (with per retry overhead to avoid infinite loops)
@@ -823,6 +826,64 @@ fail:
 	return -1;
 }
 
+static const char *nfc_file = "\xC3\x85\x73\x74\x72\xC3\xB6\x6D.XXXXXX";
+static const char *nfd_file = "\x41\xCC\x8A\x73\x74\x72\x6F\xCC\x88\x6D.XXXXXX";
+
+/* Check if the platform is decomposing unicode data for us.  We will
+ * emulate core Git and prefer to use precomposed unicode data internally
+ * on these platforms, composing the decomposed unicode on the fly.
+ *
+ * This mainly happens on the Mac where HDFS stores filenames as
+ * decomposed unicode.  Even on VFAT and SAMBA file systems, the Mac will
+ * return decomposed unicode from readdir() even when the actual
+ * filesystem is storing precomposed unicode.
+ */
+bool git_path_does_fs_decompose_unicode(const char *root)
+{
+	git_buf path = GIT_BUF_INIT;
+	int fd;
+	bool found_decomposed = false;
+	char tmp[6];
+
+	/* Create a file using a precomposed path and then try to find it
+	 * using the decomposed name.  If the lookup fails, then we will mark
+	 * that we should precompose unicode for this repository.
+	 */
+	if (git_buf_joinpath(&path, root, nfc_file) < 0 ||
+		(fd = p_mkstemp(path.ptr)) < 0)
+		goto done;
+	p_close(fd);
+
+	/* record trailing digits generated by mkstemp */
+	memcpy(tmp, path.ptr + path.size - sizeof(tmp), sizeof(tmp));
+
+	/* try to look up as NFD path */
+	if (git_buf_joinpath(&path, root, nfd_file) < 0)
+		goto done;
+	memcpy(path.ptr + path.size - sizeof(tmp), tmp, sizeof(tmp));
+
+	found_decomposed = git_path_exists(path.ptr);
+
+	/* remove temporary file (using original precomposed path) */
+	if (git_buf_joinpath(&path, root, nfc_file) < 0)
+		goto done;
+	memcpy(path.ptr + path.size - sizeof(tmp), tmp, sizeof(tmp));
+
+	(void)p_unlink(path.ptr);
+
+done:
+	git_buf_free(&path);
+	return found_decomposed;
+}
+
+#else
+
+bool git_path_does_fs_decompose_unicode(const char *root)
+{
+	GIT_UNUSED(root);
+	return false;
+}
+
 #endif
 
 #if defined(__sun) || defined(__GNU__)

src/path.h

@@ -436,4 +436,6 @@ extern int git_path_iconv(git_path_iconv_t *ic, char **in, size_t *inlen);
 
 #endif /* GIT_USE_ICONV */
 
+extern bool git_path_does_fs_decompose_unicode(const char *root);
+
 #endif

src/repository.c

@@ -880,60 +880,6 @@ static bool are_symlinks_supported(const char *wd_path)
 	return symlinks_supported;
 }
 
-#ifdef GIT_USE_ICONV
-
-static const char *nfc_file = "\xC3\x85\x73\x74\x72\xC3\xB6\x6D.XXXXXX";
-static const char *nfd_file = "\x41\xCC\x8A\x73\x74\x72\x6F\xCC\x88\x6D.XXXXXX";
-
-/* Check if the platform is decomposing unicode data for us.  We will
- * emulate core Git and prefer to use precomposed unicode data internally
- * on these platforms, composing the decomposed unicode on the fly.
- *
- * This mainly happens on the Mac where HDFS stores filenames as
- * decomposed unicode.  Even on VFAT and SAMBA file systems, the Mac will
- * return decomposed unicode from readdir() even when the actual
- * filesystem is storing precomposed unicode.
- */
-static bool does_fs_decompose_unicode_paths(const char *wd_path)
-{
-	git_buf path = GIT_BUF_INIT;
-	int fd;
-	bool found_decomposed = false;
-	char tmp[6];
-
-	/* Create a file using a precomposed path and then try to find it
-	 * using the decomposed name.  If the lookup fails, then we will mark
-	 * that we should precompose unicode for this repository.
-	 */
-	if (git_buf_joinpath(&path, wd_path, nfc_file) < 0 ||
-		(fd = p_mkstemp(path.ptr)) < 0)
-		goto done;
-	p_close(fd);
-
-	/* record trailing digits generated by mkstemp */
-	memcpy(tmp, path.ptr + path.size - sizeof(tmp), sizeof(tmp));
-
-	/* try to look up as NFD path */
-	if (git_buf_joinpath(&path, wd_path, nfd_file) < 0)
-		goto done;
-	memcpy(path.ptr + path.size - sizeof(tmp), tmp, sizeof(tmp));
-
-	found_decomposed = git_path_exists(path.ptr);
-
-	/* remove temporary file (using original precomposed path) */
-	if (git_buf_joinpath(&path, wd_path, nfc_file) < 0)
-		goto done;
-	memcpy(path.ptr + path.size - sizeof(tmp), tmp, sizeof(tmp));
-
-	(void)p_unlink(path.ptr);
-
-done:
-	git_buf_free(&path);
-	return found_decomposed;
-}
-
-#endif
-
 static int create_empty_file(const char *path, mode_t mode)
 {
 	int fd;
@@ -1024,8 +970,9 @@ static int repo_init_fs_configs(
 #ifdef GIT_USE_ICONV
 	if ((error = git_config_set_bool(
 			cfg, "core.precomposeunicode",
-			does_fs_decompose_unicode_paths(work_dir))) < 0)
+			git_path_does_fs_decompose_unicode(work_dir))) < 0)
 		return error;
+	/* on non-iconv platforms, don't even set core.precomposeunicode */
 #endif
 
 	return 0;

tests/refs/branches/create.c

 #include "clar_libgit2.h"
 #include "refs.h"
+#include "path.h"
 
 static git_repository *repo;
 static git_commit *target;
@@ -137,3 +138,58 @@ void test_refs_branches_create__default_reflog_message(void)
 	git_reflog_free(log);
 	git_signature_free(sig);
 }
+
+static void assert_branch_matches_name(
+	const char *expected, const char *lookup_as)
+{
+	git_reference *ref;
+	git_buf b = GIT_BUF_INIT;
+
+	cl_git_pass(git_branch_lookup(&ref, repo, lookup_as, GIT_BRANCH_LOCAL));
+
+	cl_git_pass(git_buf_sets(&b, "refs/heads/"));
+	cl_git_pass(git_buf_puts(&b, expected));
+	cl_assert_equal_s(b.ptr, git_reference_name(ref));
+
+	cl_git_pass(
+		git_oid_cmp(git_reference_target(ref), git_commit_id(target)));
+
+	git_reference_free(ref);
+	git_buf_free(&b);
+}
+
+void test_refs_branches_create__can_create_branch_with_unicode(void)
+{
+	const char *nfc = "\xC3\x85\x73\x74\x72\xC3\xB6\x6D";
+	const char *nfd = "\x41\xCC\x8A\x73\x74\x72\x6F\xCC\x88\x6D";
+	const char *emoji = "\xF0\x9F\x8D\xB7";
+	const char *names[] = { nfc, nfd, emoji };
+	const char *alt[] = { nfd, nfc, NULL };
+	const char *expected[] = { nfc, nfd, emoji };
+	unsigned int i;
+
+	retrieve_known_commit(&target, repo);
+
+	if (cl_repo_get_bool(repo, "core.precomposeunicode"))
+		expected[1] = nfc;
+#ifdef __APPLE__
+	/* test decomp. because not all Mac filesystems decompose unicode */
+	else if (git_path_does_fs_decompose_unicode(git_repository_path(repo)))
+		expected[0] = nfd;
+#endif
+
+	for (i = 0; i < ARRAY_SIZE(names); ++i) {
+		cl_git_pass(git_branch_create(
+			&branch, repo, names[i], target, 0, NULL, NULL));
+		cl_git_pass(git_oid_cmp(
+			git_reference_target(branch), git_commit_id(target)));
+
+		assert_branch_matches_name(expected[i], names[i]);
+		if (alt[i])
+			assert_branch_matches_name(expected[i], alt[i]);
+
+		cl_git_pass(git_branch_delete(branch));
+		git_reference_free(branch);
+		branch = NULL;
+	}
+}