reflog: allow adding entries with newlines in their message

Currently, the reflog disallows any entries that have a message with
newlines, as that would effectively break the reflog format, which may
contain a single line per entry, only. Upstream git behaves a bit
differently, though, especially when considering stashes: instead of
rejecting any reflog entry with newlines, git will simply replace
newlines with spaces. E.g. executing 'git stash push -m "foo\nbar"' will
create a reflog entry with "foo bar" as entry message.

This commit adjusts our own logic to stop rejecting commit messages with
newlines. Previously, this logic was part of `git_reflog_append`, only.
There is a second place though where we add reflog entries, which is the
serialization code in the filesystem refdb. As it didn't contain any
sanity checks whatsoever, the refdb would have been perfectly happy to
write malformatted reflog entries to the disk. This is being fixed with
the same logic as for the reflog itself.

src/refdb_fs.c

@@ -1856,8 +1856,15 @@ static int serialize_reflog_entry(
 	git_buf_rtrim(buf);
 
 	if (msg) {
+		size_t i;
+
 		git_buf_putc(buf, '\t');
 		git_buf_puts(buf, msg);
+
+		for (i = 0; i < buf->size - 2; i++)
+			if (buf->ptr[i] == '\n')
+				buf->ptr[i] = ' ';
+		git_buf_rtrim(buf);
 	}
 
 	git_buf_putc(buf, '\n');

src/reflog.c

@@ -74,9 +74,8 @@ int git_reflog_write(git_reflog *reflog)
 
 int git_reflog_append(git_reflog *reflog, const git_oid *new_oid, const git_signature *committer, const char *msg)
 {
-	git_reflog_entry *entry;
 	const git_reflog_entry *previous;
-	const char *newline;
+	git_reflog_entry *entry;
 
 	assert(reflog && new_oid && committer);
 
@@ -87,19 +86,18 @@ int git_reflog_append(git_reflog *reflog, const git_oid *new_oid, const git_sign
 		goto cleanup;
 
 	if (msg != NULL) {
-		if ((entry->msg = git__strdup(msg)) == NULL)
-			goto cleanup;
+		size_t i, msglen = strlen(msg);
 
-		newline = strchr(msg, '\n');
-
-		if (newline) {
-			if (newline[1] != '\0') {
-				git_error_set(GIT_ERROR_INVALID, "reflog message cannot contain newline");
-				goto cleanup;
-			}
+		if ((entry->msg = git__strndup(msg, msglen)) == NULL)
+			goto cleanup;
 
-			entry->msg[newline - msg] = '\0';
-		}
+		/*
+		 * Replace all newlines with spaces, except for
+		 * the final trailing newline.
+		 */
+		for (i = 0; i < msglen; i++)
+			if (entry->msg[i] == '\n')
+				entry->msg[i] = ' ';
 	}
 
 	previous = git_reflog_entry_byindex(reflog, 0);

tests/refs/reflog/messages.c

@@ -281,6 +281,27 @@ void test_refs_reflog_messages__creating_a_direct_reference(void)
 	git_reference_free(reference);
 }
 
+void test_refs_reflog_messages__newline_gets_replaced(void)
+{
+	const git_reflog_entry *entry;
+	git_signature *signature;
+	git_reflog *reflog;
+	git_oid oid;
+
+	cl_git_pass(git_signature_now(&signature, "me", "foo@example.com"));
+	cl_git_pass(git_oid_fromstr(&oid, "a65fedf39aefe402d3bb6e24df4d4f5fe4547750"));
+
+	cl_git_pass(git_reflog_read(&reflog, g_repo, "HEAD"));
+	cl_assert_equal_sz(7, git_reflog_entrycount(reflog));
+	cl_git_pass(git_reflog_append(reflog, &oid, signature, "inner\nnewline"));
+	cl_assert_equal_sz(8, git_reflog_entrycount(reflog));
+
+	cl_assert(entry = git_reflog_entry_byindex(reflog, 0));
+	cl_assert_equal_s(git_reflog_entry_message(entry), "inner newline");
+
+	git_signature_free(signature);
+	git_reflog_free(reflog);
+}
 
 void test_refs_reflog_messages__renaming_ref(void)
 {

tests/refs/reflog/reflog.c

@@ -87,15 +87,13 @@ void test_refs_reflog_reflog__append_then_read(void)
 	cl_git_pass(git_signature_now(&committer, "foo", "foo@bar"));
 
 	cl_git_pass(git_reflog_read(&reflog, g_repo, new_ref));
-
-	cl_git_fail(git_reflog_append(reflog, &oid, committer, "no inner\nnewline"));
 	cl_git_pass(git_reflog_append(reflog, &oid, committer, NULL));
 	cl_git_pass(git_reflog_append(reflog, &oid, committer, commit_msg "\n"));
 	cl_git_pass(git_reflog_write(reflog));
-	git_reflog_free(reflog);
 
 	assert_appends(committer, &oid);
 
+	git_reflog_free(reflog);
 	git_signature_free(committer);
 }
 

tests/stash/save.c

@@ -283,6 +283,26 @@ void test_stash_save__stashing_updates_the_reflog(void)
 	assert_object_oid("refs/stash@{1}", NULL, GIT_OBJECT_COMMIT);
 }
 
+void test_stash_save__multiline_message(void)
+{
+	const char *msg = "This\n\nis a multiline message\n";
+	const git_reflog_entry *entry;
+	git_reflog *reflog;
+
+	assert_object_oid("refs/stash@{0}", NULL, GIT_OBJECT_COMMIT);
+
+	cl_git_pass(git_stash_save(&stash_tip_oid, repo, signature, msg, GIT_STASH_DEFAULT));
+
+	cl_git_pass(git_reflog_read(&reflog, repo, "refs/stash"));
+	cl_assert(entry = git_reflog_entry_byindex(reflog, 0));
+	cl_assert_equal_s(git_reflog_entry_message(entry), "On master: This  is a multiline message");
+
+	assert_object_oid("refs/stash@{0}", git_oid_tostr_s(&stash_tip_oid), GIT_OBJECT_COMMIT);
+	assert_commit_message_contains("refs/stash@{0}", msg);
+
+	git_reflog_free(reflog);
+}
+
 void test_stash_save__cannot_stash_when_there_are_no_local_change(void)
 {
 	git_index *index;