croc-look is a tool to make testing and debuging proc macros easier by these two features
- Printing the implementation specific generated code to the console
- Giving a real time live view of the output of the macro on rust code
croc-look allows you to narrow down your search and also provide real time view of the generated code.
croc-look requires a nightly toolchain installed, it does not need to be the default toolchain
rustup install nightly
cargo install croc-look
-t: Defines the trait you want to see the expansion off, this is gonna be the trait your derive macro is implementing or it could be any other trait you want to see the expansion off. For example
#[derive(Clone, Debug, MyTrait)]
So the value for this flag can be either
Debug or whatever trait your
MyTrait derive macro is implementing
-i: This helps you narrow down your search for a trait impl for the flag mentioned above. If you have multiple structs deriving your trait then you can do
croc-look --trait-impl Clone -iand get the impl for the struct you want.
-s: If you want to expand a particlar struct. This is useful when a macro is manupilating the struct itself, like adding fields, etc.
-p: (requies cargo expand to be installed) Use
cargo expandinternally to narrow down code to modules. eg
croc-look -p cmd -t Clone -i Context(This finds the impl Clone for Context in cmd module)
-f: For expanding a function.
-b: To expand a
cargo --bin BINARY, if not specified then
-w: This starts watching the directory/file you want to watch, this also opens up an interactive TUI which has support for live reloading changes as you do them in your proc-macro project.
cargo expand doesn't allow you to view a whole trait impl to check generics or watch particular code blocks. The motive of croc-look is to narroy arry down your search to a simple single body and reduce cluter.
You can use the
--path flag to use
cargo expand to narrow down searches module level