From 6a1b913bc5790fddf460aec4ea4700605a7079c6 Mon Sep 17 00:00:00 2001
From: Zsolt Parragi <zsolt.parragi@percona.com>
Date: Mon, 20 Jul 2026 09:13:51 +0000
Subject: [PATCH v2 2/8] Add JSON5 trailing comma support to the JSON parser

When the json5 flag is set, allow one trailing comma before a closing
] or } in the recursive-descent parser.
---
 src/common/jsonapi.c                          |  4 ++
 .../json5_trailing_commas.json5               |  7 +++
 .../json5_trailing_commas.out                 | 32 ++++++++++++++
 .../test_json_parser/t/005_test_json5.pl      | 43 +++++++++++++++----
 4 files changed, 78 insertions(+), 8 deletions(-)
 create mode 100644 src/test/modules/test_json_parser/json5_trailing_commas.json5
 create mode 100644 src/test/modules/test_json_parser/json5_trailing_commas.out

diff --git a/src/common/jsonapi.c b/src/common/jsonapi.c
index 81410d62bbf..e74e2fbfd4c 100644
--- a/src/common/jsonapi.c
+++ b/src/common/jsonapi.c
@@ -1577,6 +1577,8 @@ parse_object(JsonLexContext *lex, const JsonSemAction *sem)
 				result = json_lex(lex);
 				if (result != JSON_SUCCESS)
 					break;
+				if (unlikely(lex->json5) && lex_peek(lex) == JSON_TOKEN_OBJECT_END)
+					break;
 				result = parse_object_field(lex, sem);
 			}
 			break;
@@ -1689,6 +1691,8 @@ parse_array(JsonLexContext *lex, const JsonSemAction *sem)
 			result = json_lex(lex);
 			if (result != JSON_SUCCESS)
 				break;
+			if (unlikely(lex->json5) && lex_peek(lex) == JSON_TOKEN_ARRAY_END)
+				break;
 			result = parse_array_element(lex, sem);
 		}
 	}
diff --git a/src/test/modules/test_json_parser/json5_trailing_commas.json5 b/src/test/modules/test_json_parser/json5_trailing_commas.json5
new file mode 100644
index 00000000000..b41af4393ee
--- /dev/null
+++ b/src/test/modules/test_json_parser/json5_trailing_commas.json5
@@ -0,0 +1,7 @@
+{
+  "arr": [1, 2, 3,],
+  "nested_arr": [[1,], [2,],],
+  "obj": {"a": 1, "b": 2,},
+  "nested_obj": {"x": {"y": 1,},},
+  "last": true,
+}
diff --git a/src/test/modules/test_json_parser/json5_trailing_commas.out b/src/test/modules/test_json_parser/json5_trailing_commas.out
new file mode 100644
index 00000000000..86f88bda47f
--- /dev/null
+++ b/src/test/modules/test_json_parser/json5_trailing_commas.out
@@ -0,0 +1,32 @@
+{
+"arr": [
+1,
+2,
+3
+]
+,
+"nested_arr": [
+[
+1
+]
+,
+[
+2
+]
+
+]
+,
+"obj": {
+"a": 1,
+"b": 2
+}
+,
+"nested_obj": {
+"x": {
+"y": 1
+}
+
+}
+,
+"last": true
+}
diff --git a/src/test/modules/test_json_parser/t/005_test_json5.pl b/src/test/modules/test_json_parser/t/005_test_json5.pl
index 815d4699306..18024aedeef 100644
--- a/src/test/modules/test_json_parser/t/005_test_json5.pl
+++ b/src/test/modules/test_json_parser/t/005_test_json5.pl
@@ -55,7 +55,32 @@ my @features = (
 		name => 'comments',
 		file => 'json5_comments',
 		error => qr/Token "\/" is invalid/,
-	},);
+	},
+	{ name => 'trailing commas', file => 'json5_trailing_commas' },);
+
+# Inputs that stay invalid even in json5 mode.
+my @json5_invalid = (
+	[ 'doubled trailing comma', '[1,,]' ],
+	[ 'doubled trailing comma in object', '{"a":1,,}' ],
+	[ 'leading comma', '[,1]' ],
+	[ 'leading comma in object', '{,"a":1}' ],
+	[ 'lone comma', '[,]' ],
+	[ 'lone comma in object', '{,}' ],
+	[ 'missing comma', '[true false]' ],
+	[ 'missing comma in object', '{"a":1 "b":2}' ],);
+
+# Write $content to a temp file and return the file name.  The file is
+# written in binary mode, so that CR and LF in $content reach the parser
+# as they are.
+sub inline_file
+{
+	my ($content) = @_;
+	my ($fh, $fname) = tempfile(DIR => $dir);
+	binmode($fh);
+	print $fh $content;
+	close($fh);
+	return $fname;
+}
 
 # Run the parser executable @$exe with @args and return its output, with
 # the CRLF line ends that printf() produces on Windows normalized to LF.
@@ -116,13 +141,7 @@ foreach my $exe (@exes)
 	foreach my $c (@json5_inline_cases)
 	{
 		my ($label, $content, $expected) = @$c;
-		my ($fh, $fname) = tempfile(DIR => $dir);
-
-		# binary mode, so that CR and LF in $content reach the parser as
-		# they are
-		binmode($fh);
-		print $fh $content;
-		close($fh);
+		my $fname = inline_file($content);
 
 		if (defined $expected)
 		{
@@ -148,6 +167,14 @@ foreach my $exe (@exes)
 		check_rejected($exe, $file, "non-json5 mode: $f->{name}",
 			$f->{error});
 	}
+
+	foreach my $inv (@json5_invalid)
+	{
+		my ($label, $content) = @$inv;
+		my $fname = inline_file($content);
+
+		check_rejected($exe, $fname, "json5 mode: $label", undef, "--json5");
+	}
 }
 
 done_testing();
-- 
2.55.0