fix: enforce fn-head nested parens at parse time#118
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mkaput wants to merge 4 commits intoelixir-tools:mainfrom
Open
fix: enforce fn-head nested parens at parse time#118mkaput wants to merge 4 commits intoelixir-tools:mainfrom
mkaput wants to merge 4 commits intoelixir-tools:mainfrom
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I dove way to deep into the rabbithole with these tests. They popped for me through proptests, I used LLMs to find all these variations, and I fixed them by having an LLM port Elixir's parser logic. 1. **`stab_expr` fn-clause head shapes** Ported concept: separate and normalize bare heads vs parenthesized heads before building `->` clauses. Source: [`elixir_parser.yrl` `stab_expr` rules](https://github.com/elixir-lang/elixir/blob/v1.18.2/lib/elixir/src/elixir_parser.yrl#L340-L353) 2. **`when` vs `<-` / `\\` precedence behavior in fn heads** Ported concept: preserve operator precedence model, and lower guard parsing precedence only for specific simple fn-head forms. Source: [precedence table](https://github.com/elixir-lang/elixir/blob/v1.18.2/lib/elixir/src/elixir_parser.yrl#L59-L63) 3. **`unwrap_when`-style reassociation** Ported concept: reassociate trailing `when` in head args so non-`when` operators bind to the last head arg/guard the same way compiler parser does. Source: [`unwrap_when/1`](https://github.com/elixir-lang/elixir/blob/v1.18.2/lib/elixir/src/elixir_parser.yrl#L1135-L1141) 4. **Nested-parens rejection semantics (`unexpected parentheses`)** Ported concept: reject nested parenthesized fn-head arg forms during fn-head construction, but keep Spitfire recovery by recording errors and continuing AST construction.
Recent fn-head parsing changes introduced infix reassociation branches that assume comma/when operands always carry list arguments. In the absinthe matrix CI run, a malformed intermediate AST used , which passed the guard and crashed in . This change hardens the parser by requiring list operands before reassociation in , and by making fn-head nested-parens validation a no-op for non-list argument payloads. This preserves existing behavior for valid AST shapes while preventing parser crashes on recoverable malformed intermediates encountered during large real-world repo parsing.
Add a focused parser parity regression for the snippet that triggered the CI crash: comma = ascii_char([?,]) This comes from absinthe-graphql/absinthe lexer code and protects against regressions where an identifier named `comma` can produce malformed intermediate lhs state during infix parsing.
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I dove way to deep into the rabbithole with these tests. They popped for me through proptests, I used LLMs to find all these variations, and I fixed them by having an LLM port Elixir's parser logic.
stab_exprfn-clause head shapesPorted concept: separate and normalize bare heads vs parenthesized heads before building
->clauses.Source:
elixir_parser.yrlstab_exprruleswhenvs<-/\\precedence behavior in fn headsPorted concept: preserve operator precedence model, and lower guard parsing precedence only for specific simple fn-head forms.
Source: precedence table
unwrap_when-style reassociationPorted concept: reassociate trailing
whenin head args so non-whenoperators bind to the last head arg/guard the same way compiler parser does.Source:
unwrap_when/1Nested-parens rejection semantics (
unexpected parentheses)Ported concept: reject nested parenthesized fn-head arg forms during fn-head construction, but keep Spitfire recovery by recording errors and continuing AST construction.