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parser: Implement recovery for potential unknown macro variables $ IDENT #69229

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petrochenkov opened this issue Feb 17, 2020 · 0 comments
Open
12 tasks

parser: Implement recovery for potential unknown macro variables $ IDENT #69229

petrochenkov opened this issue Feb 17, 2020 · 0 comments
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@petrochenkov
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A-diagnostics Area: Messages for errors, warnings, and lints A-parser Area: The parsing of Rust source code to an AST C-enhancement Category: An issue proposing an enhancement or a PR with one. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@petrochenkov
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#69211 simplified parsing and fixed treatment of $ tokens coming from proc macros, but slightly regressed diagnostics.

If a declarative macro body contains something that looks like an unknown macro variable $ var, then it's preserved and outputted like two-token sequence punctuation $ and identifier var.

We previously tried to detect such sequences in Parser::bump, but the detection wasn't correct and wasn't done in the best way for recovery.

Instead, we need to support parsing the $ IDENT sequences in context dependent fashion, as an error expression in expression position, as an error type in type position etc.

Currently supported positions for macro variables (roughly in the order of importance):

  • expr
  • ty
  • pat
  • item
  • ident
  • lifetime
  • vis
  • path
  • block
  • literal
  • meta
  • stmt

It's quite possible that implementing this recovery for ident can successfully make implementing it for expr, ty, pat, path and meta unnecessary.
@petrochenkov petrochenkov mentioned this issue Feb 17, 2020
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@Centril Centril added A-parser Area: The parsing of Rust source code to an AST T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. A-diagnostics Area: Messages for errors, warnings, and lints C-enhancement Category: An issue proposing an enhancement or a PR with one. labels Feb 17, 2020
@petrochenkov petrochenkov self-assigned this Mar 14, 2020
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A-diagnostics Area: Messages for errors, warnings, and lints A-parser Area: The parsing of Rust source code to an AST C-enhancement Category: An issue proposing an enhancement or a PR with one. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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