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jaybosamiya avatar jaybosamiya commented on September 25, 2024

Unfortunately it doesn't seem like there is an easy way to get a partial parse tree out of Pest.

However, if we just keep repeatedly (almost blindly) adding one of the "expected" at the point it expects it, then we can force it to give a complete tree, and this helps identify the issue and fix it.

For example, taking the above example and completing it to something the parser (before the fix) would finish parsing, we get:

fn get(&'a self) -> (o: &':a !V) {
    0
}

which parses to

- fn
  - fn_str: "fn"
  - name > identifier: "get"
  - param_list > param
    - pat_no_top_alt > pat_inner > ref_pat > pat > pat_inner > literal_pat > literal > char: "'a self) -> (o: &'"
    - colon_str: ":"
    - type > macro_type > macro_call
      - path > path_segment > name_ref > identifier: "a"
      - bang_str: "!"
      - token_tree > token > identifier: "V"
  - fn_qualifier: ""
  - fn_terminator > fn_block_expr > expr > expr_inner > literal > int_number: "0"

Clearly that char there is just bogus, so I looked at the char definition and fixed it in 4490ebe

After the fix, the original code, when sent through the parser succeeds with the correct parse tree:

- fn
  - fn_str: "fn"
  - name > identifier: "get"
  - param_list > param > type > ref_type
    - lifetime > lifetime_ident: "'a"
    - type > path_type > path > path_segment > name_ref > self_str: "self"
  - ret_type
    - rarrow_str: "->"
    - lparen_str: "("
    - name > identifier: "o"
    - colon_str: ":"
    - type > ref_type
      - lifetime > lifetime_ident: "'a"
      - type > path_type > path > path_segment > name_ref > identifier: "V"
    - rparen_str: ")"
  - fn_qualifier: ""
  - fn_terminator > fn_block_expr > expr > expr_inner > literal > int_number: "0"

from verusfmt.

parno avatar parno commented on September 25, 2024

Ah, nice find. Thanks for tracking it down and for the explanation.

from verusfmt.

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