matching all functions in Rust (poor man's tracing)

[FrancescElies]

I would like to do some sort of quick and dirty tracing in a project, by that I would like to print the function's name in every function.

The following command fine for many function signatures but leaves out. pub(crate) async fn my_fn(...) {...} or pub unsafe extern "C" fn my_fn ....

(
    ast-grep -p 'fn $FUNC($$$ARGS) $$$RT { $$$BODY }'
     -r '
fn $FUNC($$$ARGS) $$$RT {
    eprintln!("called: $FUNC");
    $$$BODY
}'
    -l rs
    -U
)

I tried the pattern $$$PREFIX fn $FUNC($$$ARGS) $$$RT { $$$BODY } but in this case I get

Error: Cannot parse query as a valid pattern.
Help: The pattern either fails to parse or contains error. Please refer to pattern syntax guide.
See also: https://ast-grep.github.io/guide/pattern-syntax.html

✖ Caused by
╰▻ Multiple AST nodes are detected. Please check the pattern source `µµµPREFIX fn µFUNC(µµµARGS) µµµRT { µµµBODY }`.

Questions

• How do I solve this, ideas?
• Is there a builtin way to add the filename to the eprintln?

[HerringtonDarkholme]

you can use ast-grep playground to debug the pattern https://ast-grep.github.io/playground.html#eyJtb2RlIjoiUGF0Y2giLCJsYW5nIjoicnVzdCIsInF1ZXJ5IjoiZm4gJEZVTkMoJCQkQVJHUykgeyAkJCRCT0RZIH0iLCJyZXdyaXRlIjoiIiwic3RyaWN0bmVzcyI6InNtYXJ0Iiwic2VsZWN0b3IiOiIiLCJjb25maWciOiJydWxlOlxuICBwYXR0ZXJuOiAkRlVOQygpXG50cmFuc2Zvcm06XG4gIFNXQVBQRUQ6XG4gICAgcmVwbGFjZTpcbiAgICAgIHNvdXJjZTogJEZVTkNcbiAgICAgIHJlcGxhY2U6ICdeKGdldHxzZXQpKC4rKSQnXG4gICAgICBieTogJyQyJDEnXG5maXg6ICRTV0FQUEVEIiwic291cmNlIjoicHViKGNyYXRlKSBhc3luYyBmbiBteV9mbigpIHt9In0=

the pub modifier is inside the function declaration so it does not make the pattern match.

a better way is to use --inline-rules

ast-grep scan --inline-rules '
id: find-fn
language: rust
rule:
  kind: function_item'

Also see https://ast-grep.github.io/advanced/faq.html