diff: don't error out on an invalid regex

When parsing user-provided regex patterns for functions, we must not
fail to provide a diff just because a pattern is not well
formed. Ignore it instead.

src/diff_driver.c

@@ -97,8 +97,7 @@ static int diff_driver_add_patterns(
 	for (scan = regex_str; scan; scan = end) {
 		/* get pattern to fill in */
 		if ((pat = git_array_alloc(drv->fn_patterns)) == NULL) {
-			error = -1;
-			break;
+			return -1;
 		}
 
 		pat->flags = regex_flags;
@@ -117,10 +116,9 @@ static int diff_driver_add_patterns(
 			break;
 
 		if ((error = regcomp(&pat->re, buf.ptr, regex_flags)) != 0) {
-			/* if regex fails to compile, warn? fail? */
-			error = giterr_set_regex(&pat->re, error);
-			regfree(&pat->re);
-			break;
+			/*
+			 * TODO: issue a warning
+			 */
 		}
 	}
 
@@ -128,7 +126,8 @@ static int diff_driver_add_patterns(
 		(void)git_array_pop(drv->fn_patterns); /* release last item */
 	git_buf_free(&buf);
 
-	return error;
+	/* We want to ignore bad patterns, so return success regardless */
+	return 0;
 }
 
 static int diff_driver_xfuncname(const git_config_entry *entry, void *payload)

tests/diff/drivers.c

@@ -250,3 +250,29 @@ void test_diff_drivers__builtins(void)
 	git_buf_free(&expected);
 	git_vector_free(&files);
 }
+
+void test_diff_drivers__invalid_pattern(void)
+{
+	git_config *cfg;
+	git_index *idx;
+	git_diff *diff;
+	git_patch *patch;
+	git_diff_options opts = GIT_DIFF_OPTIONS_INIT;
+
+	g_repo = cl_git_sandbox_init("userdiff");
+	cl_git_mkfile("userdiff/.gitattributes", "*.storyboard diff=storyboard\n");
+
+	cl_git_pass(git_repository_config__weakptr(&cfg, g_repo));
+	cl_git_pass(git_config_set_string(cfg, "diff.storyboard.xfuncname", "<!--(.*?)-->"));
+
+	cl_git_mkfile("userdiff/dummy.storyboard", "");
+	cl_git_pass(git_repository_index__weakptr(&idx, g_repo));
+	cl_git_pass(git_index_add_bypath(idx, "dummy.storyboard"));
+	cl_git_mkfile("userdiff/dummy.storyboard", "some content\n");
+
+	cl_git_pass(git_diff_index_to_workdir(&diff, g_repo, NULL, &opts));
+	cl_git_pass(git_patch_from_diff(&patch, diff, 0));
+
+	git_patch_free(patch);
+	git_diff_free(diff);
+}