rust-lang / rust-lang/fls

RFC 3101 reserved prefixes

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Description

RFC 3101 (rust-lang/rfcs#3101) reserves lexical forms like the following:

  • ident#foo
  • ident"foo"
  • ident'f'
  • ident#123

This isn't covered in the FLS.

They're reserved in the 2021 edition and later, and the FLS currently describes the 2021 edition.

rust-lang/rust#126452 extended the RFC to reserving forms like

  • 'ident#foo

Here, "reserves" means that it's a lexing-time error if any of those forms appear.

These are covered in the Reference under lex.token.reserved-prefix. That models them as separate forms of token, using grammar productions which don't overlap with the productions for accepted tokens.

There is some discussion of this approach in rust-lang/reference#1128.

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Research direction

Start with RFC 3101 and the Reference section lex.token.reserved-prefix, then review the discussion in rust-lang/reference#1128. Compare those reserved lexical forms with the FLS's current 2021-edition lexer description. Done means the FLS specifies the reserved prefixes, including 'ident#foo, and describes their lexing-time errors without overlapping accepted-token productions.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
documentation
Issue type
Documentation
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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