2 unstable releases

Uses old Rust 2015

0.2.0 Dec 4, 2018
0.1.0 May 31, 2018

#2306 in Parser implementations

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Used in polonius


250 lines

Polonius Parser

The polonius parser is a small, hand-written parser used to parse polonius test cases that are not obtained from rustc:

// program description
placeholders { 'a, 'b, 'c }

// block description
block B0 {
    // 0:

    // 1:

    loan_invalidated_at(L1) / use('a, 'b);

    // CFG
    goto B1, B2;

block B1 {
    use('a), outlives('a: 'b), loan_issued_at('b, L1);


The polonius_parser crate provides a single function parse_input, which takes a program description as its input string. Input will either be successfully parsed into an ir::Input, or a ParseError will be returned. The ir structs are a small, public data model.


polonius_parser is implemented as a Lexer, which is an Iterator that extracts Tokens from the source text, and a Parser, which operates on these Tokens. The parser is a simple recursive descent parser with 1 token of look-ahead (using Peekable). We use the T! macro across the implementation to quickly and legibly reference token kinds.

Adding Facts

To extend the parser with a new fact loan_bazzles_var_at, perform the following changes:

  • Add a new variant KwLoanBazzlesVarAt to TokenKind for the loan_bazzles_var_at keyword (token.rs).
  • Add a shorthand for the keyword to the T! macro and add the new keyword kind to the Display impl for TokenKind.
  • Repeat the above for any additional tokens introduced as new syntax, e.g., if the relation is represented as L1 $ V1, add $.
  • In Lexer::valid_token (lexer.rs), add a case
    kw if kw.starts_with("loan_bazzles_var_at".as_bytes()) => {
        ("loan_bazzles_var_at".len() as u32, T![loan_bazzles_var_at])
  • For additional token kinds, add cases as appropriate. In our example, add
    [b'$', ..] => (1, T![$]),
  • Add a variant to the Fact enum in the ir datamodel to represent the new fact. For us, that's
    LoanBazzlesVarAt { loan: String, variable: String },
  • Add a case for the new fact to Parser::parse_fact (parser.rs)
    T![loan_bazzles_var_at] => { /* New parsing logic here */ }
    which returns Ok(Fact::LoanBazzlesVarAt { .. }) if successful. For our example:
      T![loan_bazzles_var_at] => { 
          let loan = self.parse_parameter(T![loan])?;
          let variable = self.parse_parameter(T![variable])?;
          Ok(Fact::LoanBazzlesVarAt { loan, variable })

Custom Relations

Of course, it's also possible to add custom relations by following the same steps to add tokens to the lexer, writing their own parsing method, and add them to parse_input. A corresponding ir representation should be added to the data model in this case.


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