JSON: Add opt-in comments and trailing comma flags

[otar]

Configuration files often use a narrow JSON extension with JS-style comments, trailing commas, or both. PHP currently requires a separate parser or a string-aware preprocessing pass. This PR adds native parser support. Strict JSON remains the default.

Public API

Constant	Value	Accepted by	Effect
JSON_ALLOW_COMMENTS	1 << 23	json_decode(), json_validate()	Allows // and non-nesting /* ... */ comments at JSON whitespace boundaries.
JSON_ALLOW_TRAILING_COMMAS	1 << 24	json_decode(), json_validate()	Allows one final comma in a nonempty array or object.

The flags are independent. Neither flag applies to json_encode() or is enabled by default.

Semantics

• Line comments end at LF, CRLF, lone CR, or EOF. Block comments do not nest and end at the first */.
• Comments are allowed before and after the root value and between tokens. They are not allowed inside a token. Comment-like text in a JSON string is unchanged.
• U+2028/U+2029 and valid controls, including embedded NUL, are comment content. Malformed UTF-8 follows the existing decode flags. Validation still accepts JSON_INVALID_UTF8_IGNORE, but not JSON_INVALID_UTF8_SUBSTITUTE.
• Unterminated block comments produce JSON_ERROR_SYNTAX at the opening slash.
• A trailing comma is allowed only after the last element or member of a nonempty container. Empty or missing-element forms such as [,], {,}, and [1,,] remain invalid.
• The implementation retains existing behavior for depth, duplicate keys, bigints, associative objects, exceptions, error codes, and original-input line and column numbers.

[otar]

Sorry @bukka and @kocsismate, I accidentally tagged you on this PR. Please ignore this draft...

[NickSdot]

Suggested change

	} catch (JsonException $e) {
	echo get_class($e), ': ', $e->getCode(), ': ', $e->getMessage(), "\n";
	} catch (Throwable $e) {
	echo $e::class, ': ', $e->getCode(), ': ', $e->getMessage(), "\n";

[NickSdot]

Suggested change

	} catch (JsonException $e) {
	echo $e->getCode(), ': ', $e->getMessage(), "\n";
	}
	?>
	--EXPECT--
	NULL
	5
	array(1) {
	[0]=>
	string(2) "ab"
	}
	0
	array(1) {
	[0]=>
	string(5) "a�b"
	}
	0
	NULL
	5
	int(1)
	0
	bool(false)
	5
	bool(true)
	0
	5: Malformed UTF-8 characters, possibly incorrectly encoded near location 1:9
	} catch (Throwable $e) {
	echo $e::class, ': ', $e->getCode(), ': ', $e->getMessage(), "\n";
	}
	?>
	--EXPECT--
	NULL
	5
	array(1) {
	[0]=>
	string(2) "ab"
	}
	0
	array(1) {
	[0]=>
	string(5) "a�b"
	}
	0
	NULL
	5
	int(1)
	0
	bool(false)
	5
	bool(true)
	0
	JsonException: 5: Malformed UTF-8 characters, possibly incorrectly encoded near location 1:9

[NickSdot]

Suggested change

	} catch (JsonException $e) {
	echo $e->getCode(), ': ', $e->getMessage(), "\n";
	}
	?>
	--EXPECT--
	[1]
	[1]
	[1]
	{"a":1}
	[[1],{"a":2}]
	error 4: Syntax error near location 1:2
	error 4: Syntax error near location 1:2
	error 4: Syntax error near location 1:4
	error 4: Syntax error near location 1:4
	error 4: Syntax error near location 1:8
	error 4: Syntax error near location 1:4
	error 4: Syntax error near location 1:4
	error 4: Syntax error near location 1:4
	[1]
	{"a":1}
	error 2: State mismatch (invalid or malformed JSON) near location 1:4
	error 2: State mismatch (invalid or malformed JSON) near location 1:8
	bool(true)
	bool(true)
	bool(false)
	bool(true)
	bool(false)
	bool(false)
	4: Syntax error near location 1:4
	} catch (Throwable $e) {
	echo $e::class, ': ', $e->getCode(), ': ', $e->getMessage(), "\n";
	}
	?>
	--EXPECT--
	[1]
	[1]
	[1]
	{"a":1}
	[[1],{"a":2}]
	error 4: Syntax error near location 1:2
	error 4: Syntax error near location 1:2
	error 4: Syntax error near location 1:4
	error 4: Syntax error near location 1:4
	error 4: Syntax error near location 1:8
	error 4: Syntax error near location 1:4
	error 4: Syntax error near location 1:4
	error 4: Syntax error near location 1:4
	[1]
	{"a":1}
	error 2: State mismatch (invalid or malformed JSON) near location 1:4
	error 2: State mismatch (invalid or malformed JSON) near location 1:8
	bool(true)
	bool(true)
	bool(false)
	bool(true)
	bool(false)
	bool(false)
	JsonException: 4: Syntax error near location 1:4

[NickSdot]

Maybe you want to assert the message here too. Same format as above.

[otar]

@NickSdot thanks for the feedback. I really appreciate it and will take it into consideration.