baml_fmt: basically a formatter#3111
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📝 WalkthroughWalkthroughAdds a new baml_fmt formatter crate (AST, printer, trivia classifier, Salsa entry), integrates formatter tests and tools, updates parser to handle pending '>'/ '>>' in type arguments, and adds SyntaxKind::is_keyword. Changes
Sequence Diagram(s)sequenceDiagram
participant Source as Source
participant Lexer as Lexer
participant Parser as Parser/CST
participant Trivia as TriviaClassifier
participant AST as AST Builder
participant Printer as Formatter
Source->>Lexer: lex -> tokens
Lexer->>Parser: token stream
Parser->>Parser: build CST (handle pending '>' / '>>')
Parser->>Trivia: provide CST root
Trivia->>AST: provide EmittableTrivia for tokens
Parser->>AST: provide SOURCE_FILE CST
AST->>Printer: Strong AST + FormatOptions + TriviaInfo
Printer->>Printer: Printable.print with Shape decisions
Printer->>Source: formatted output
Estimated Code Review Effort🎯 5 (Critical) | ⏱️ ~120 minutes Possibly related PRs
🚥 Pre-merge checks | ✅ 2 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (2 passed)
✏️ Tip: You can configure your own custom pre-merge checks in the settings. ✨ Finishing Touches🧪 Generate unit tests (beta)
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Actionable comments posted: 11
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baml_language/crates/baml_compiler_parser/src/parser.rs (1)
606-616:⚠️ Potential issue | 🟡 MinorUpdate stale comment in pending
>handling.The comment says nothing is emitted, but the code now emits a
GREATERtoken.✏️ Suggested doc fix
- // First check if we have a pending '>' from a previous '>>' split. - // Don't emit anything - the '>>' token is already in the tree. + // First check if we have a pending '>' from a previous '>>' split. + // Emit that pending token now to keep the CST balanced.
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2kai2kai2
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baml_language/crates/baml_compiler_parser/src/parser.rs (1)
605-640:⚠️ Potential issue | 🟡 MinorFix the stale comment about pending
>emission.
The code now emits aGREATERtoken whenpending_greaters > 0, but the comment still says “Don’t emit anything,” which is misleading.📝 Proposed comment tweak
- // First check if we have a pending '>' from a previous '>>' split. - // Don't emit anything - the '>>' token is already in the tree. + // First check if we have a pending '>' from a previous '>>' split. + // Emit a virtual '>' token for the pending split.
aaronvg
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Feb 17, 2026
| pub struct ClientField { | ||
| pub keyword: t::Client, | ||
| // not currently allowed | ||
| // pub colon: Option<t::Colon>, |
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what do you mean -- are colons not allowed inside of clients? It should be possible.
| pub struct ConfigItem { | ||
| pub key: ConfigItemKey, | ||
| // /// Colons are currently invalid, it seems | ||
| // pub colon: Option<t::Colon>, |
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oh yeah this should definitely also be possible. Like either whitespace or colon
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baml_language/crates/baml_compiler_parser/src/parser.rs (1)
3074-3084:⚠️ Potential issue | 🟠 MajorEmit a parse error for trailing commas in generic args.
Lines 3079-3083 currently treat
, >/, >>as a silent break, which can allow invalid trailing commas to pass parsing and later fail during formatting. Consider emitting an unexpected-token error when the comma is trailing.🛠️ Suggested change
while p.eat(TokenKind::Comma) { - if p.at(TokenKind::Greater) || p.at(TokenKind::GreaterGreater) { - break; // Trailing comma - } + if p.at(TokenKind::Greater) || p.at(TokenKind::GreaterGreater) { + p.error_unexpected_token("type argument after comma".to_string()); + break; // Trailing comma + } p.parse_type(); }Based on learnings: In BAML, when formatting generic type parameter lists (angle-bracket syntax), do not use a trailing comma after the last type parameter.
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Core formatter (crates/baml_fmt/, ~7,900 lines):
lib.rs— Public API:format(source, options) -> Result<String, FormatterError>. Refuses to format files with parse errors.trivia_classifier.rs— Single forward pass over the CST that tags each comment and blank line as leading, trailing, or before-EOF. Keeps the printer free of lookahead.ast/— Strong AST layer withFromCSTtrait. Converts the lossless Rowan CST into typed structs that are easy for the printer to consume, similar tosynfor rust.printer.rs— Output engine withPrintable/PrintMultiLinetraits andShape-based width tracking. Uses the "try single-line, fallback to multi-line" strategy throughout.Key formatting behaviors:
a.b.c().d) flatten and break at field access pointsParser fixes (prerequisite changes):
>>token splitting when expecting>(e.g. forMap<string, Map<string, int>>)Test infrastructure (crates/baml_tests/):
format(format(x)) == format(x)for all valid filesSummary by CodeRabbit
New Features
Refactors
Tests
Bug Fixes