[ryanmitchell]

Parsing YAML is one of the biggest costs of building the Stache. symfony/yaml parses nested blocks recursively: for each nested block it collects that block's lines and parses them again with a new parser. Every line is scanned once per level of nesting, which makes deeply nested content like Bard slow, and memory-hungry.

This PR adds Statamic\Yaml\FastParser, which Yaml::parse() now uses. It walks the lines once, descending into each nested block as it meets it.

• Keys and values: plain keys and the most common values are read directly. Any other key or value goes to symfony's own Inline parser, so it's interpreted exactly as symfony would interpret it.
• Literal blocks: | and |- blocks are read directly. Anything awkward is handed to symfony as a small document of its own.
• Fallback: anything outside the subset it understands, including all invalid YAML, makes it give up. The whole document is then parsed by symfony/yaml as before, so errors, messages and line numbers are always symfony's.
• Only reading changes. Dumping is unchanged.

Built together with @DanielDarrenJones.

Speed

	symfony/yaml	Fast parser	Faster
Cold Stache build, 2,000 Bard entries (whole paths() build)	2,226ms	607ms	3.7x
Parse only, 3,284 files from a real site (9.5MB)	1,557ms	186ms	8.4x
Parse only, 300 Bard-heavy entries (4KB, 192 lines each)	258ms	23.5ms	11x

Peak memory while parsing

	symfony/yaml	Fast parser	Change
Real site, average per file	38.4KB	29.4KB	−23%
Real site, largest file	861KB	408KB	−53%
Bard-heavy entry (4KB)	82.8KB	48.8KB	−41%
One 2MB document	28.0MB	18.3MB	−35%

The parsed result is identical, so memory held after parsing is unchanged; these are the temporary peaks during the parse. On the real site, 99.4% of files took the fast path, and the rest fell back to symfony/yaml at its normal speed.

Correctness

No differences from symfony/yaml 8.1.5 were found in any of these, including invalid YAML, where both must throw the same error:

Test set	Inputs	Result
symfony/yaml's own ParserTest, routed through the fast parser	376 tests	All pass
Official yaml-test-suite (data-2022-01-17)	402 documents	0 differences
Content from two real sites	3,284 + 5,096 files	0 differences
Differential fuzzing: random and mutated documents, including invalid YAML	~10M documents	0 differences
Statamic's test suite	11,591 tests	All pass

Cases the fuzzing found are deliberately left to symfony. These include an unindented list after a blank line, malformed flow collections like [1{2], deep nesting (symfony applies its own limit), and a symfony/yaml 8.1 quirk where a nested | block followed by one last line of front matter loses its final newline.

The new FastParserTest compares every result with symfony's rather than with hard-coded values. It covers hand-picked edge cases, a check that Statamic-dumped content stays on the fast path, and seeded fuzz tests that compare against whichever symfony/yaml version is installed.

Notes

• The parser caches parsed keys for the life of the process, capped at 2,000 entries so long-running processes (Octane, queue workers) don't grow without limit.
• Benchmarks were run on macOS with PHP 8.4.25 and symfony/yaml 8.1.5, taking the fastest of 5 runs.

🤖 Generated with Claude Code