twigphp/Twig · error · SyntaxError

The lexer or the parser ended up in an unsupported state.

Error message

The lexer or the parser ended up in an unsupported state.

What it means

This is a defensive internal error: Parser::subparse's switch reached a default branch for a token type it cannot handle (only BLOCK_START, VAR_START and COMMENT_START are expected). It means the lexer produced a token sequence the parser was not designed to receive, i.e. an internal invariant violation rather than a user syntax problem.

Solutions

Ensure all twig/twig packages are at one consistent version (composer update / composer why-not)
Remove or fix custom Lexer/Parser subclasses or overrides
Reproduce with a minimal template and stock Twig configuration to isolate the custom code
Report to the extension maintainer if a third-party lexer/parser hook causes it

Example fix

// before
composer require twig/twig:^3.9  # while another package pins ^3.0
// after
composer update twig/twig  # resolve so a single twig/twig version is installed

Defensive patterns

Strategy: try-catch

Validate before calling

// verify consistent twig/twig version: composer show twig/twig and composer why-not twig/twig

Try / catch

try { $env->render($name); } catch (\Twig\Error\SyntaxError $e) { if (str_contains($e->getMessage(), 'unsupported state')) { /* internal inconsistency: check custom lexers/parsers and version pins */ } }

Prevention

Keep a single twig/twig version across the dependency tree
Avoid subclassing/monkey-patching Lexer or Parser
Test custom extensions against stock Twig with minimal templates

When it happens

Trigger: The lexer emitted a token type other than BLOCK_START_TYPE/VAR_START_TYPE/COMMENT_START_TYPE at a position where subparse expects markup; typically caused by a custom Lexer/TokenStream modification, a broken subclass overriding lexer/parser internals, or a Twig core version mismatch.

Common situations: Custom Twig extensions or forks that alter token types; mismatched twig/twig3 component versions after a partial dependency upgrade; monkey-patching or decorating the Lexer incorrectly.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of twigphp/Twig@a414c3a491 (2026-09-13). Data as JSON: /api/errors/33a8d97dce961b21. Report an issue: GitHub.

Appendix: source

Thrown at src/Parser.php:256

                        $node = $subparser->parse($token);
                        $documentationTarget = $this->documentationTargets[$documentationTargetIndex];
                    } finally {
                        array_pop($this->documentationTargets);
                    }
                    if (!$node) {
                        trigger_deprecation('twig/twig', '3.12', 'Returning "null" from "%s" is deprecated and forbidden by "TokenParserInterface".', $subparser::class);
                    } else {
                        $node->setNodeTag($subparser->getTag());
                        NodeDocumentation::add($node, $startToken);
                        if (null !== $documentationTarget && $node !== $documentationTarget) {
                            NodeDocumentation::move($node, $documentationTarget);
                        }
                        $rv[] = $node;
                    }
                    break;

                default:
                    throw new SyntaxError('The lexer or the parser ended up in an unsupported state.', $this->getCurrentToken()->getLine(), $this->stream->getSourceContext());
            }
        }

        if (1 === \count($rv)) {
            return $rv[0];
        }

        return new Nodes($rv, $lineno);
    }

    public function getBlockStack(): array
    {
        trigger_deprecation('twig/twig', '3.12', 'Method "%s()" is deprecated.', __METHOD__);

        return $this->blockStack;
    }

    /**

View on GitHub (pinned to a414c3a491)