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#444 in Procedural macros

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MIT license

13KB
131 lines

procout

  • What: It prints the output of a procedural macro to a file.
  • Wherefore: To ease debugging by clarifying the source of errors with explicit line numbers instead of the unavoidably opaque errors often produced when debugging procedural macros in Rust.
  • Whereby: Add a function call to your proc macro and use the command-line feature.

This depends on the procedural macro compiling to code. If it's not at the stage where it compiles, it has to get there before this will produce useful output.

Whereby

Given a procedural macro's constructed as so,

use proc_macro::{TokenStream};
use proc_macro2::{Span};
use quote::{quote};
use syn::{Ident};

#[proc_macro]
pub fn ast(input: TokenStream) -> TokenStream {
  let module_ident = Ident::new("this_module", Span::mixed_site());
  let code_block: proc_macro2::TokenStream = quote!{
     pub mod #module_ident {
       /* ... some truly fantastic code, well done ... */
     }
  };
  // Convert and return the code
  TokenStream::from(code_block)
}

Just insert a call to procout before the conversion and return step.

use proc_macro::{TokenStream};
use proc_macro2::{Span};
use procout::{procout}; // Look!
use quote::{quote};
use syn::{Ident};

#[proc_macro]
pub fn ast(input: TokenStream) -> TokenStream {
  let module_ident = Ident::new("this_module", Span::mixed_site());
  let code_block: proc_macro2::TokenStream = quote!{
     pub mod #module_ident {
       /* ... some truly fantastic code, well done ... */
     }
  };

  // Look!
  procout(&code_block, Some(module_ident), Some("a/valid/path/string"));

  // Convert and return the code
  TokenStream::from(code_block)
}

By calling cargo test --features procout, the code will print to the a/valid/path/string specified as a file corresponding to module_ident. By default, the path string is the local tests directory, so after the first run using the procout feature, it's possible to run something like cargo test --test module_ident and get better errors from the compiler.

Now with these splendid new capabilities:

  • A unit test module will be generated with a no-op test that just imports the module named in module_ident.
  • module_ident should be the name of a generated module.
  • If no path is specified, the default path will be the current working directory's tests subfolder,
  • If no module_ident is specified, the default will be a generic timestamp.

Warning:

This will overwrite whatever's at the specified path, so be careful when prototyping.

Features

  • procout Outputs the macro to a file. Calling procout with this feature disabled is an intentional no-op.
  • formatted Calls rustfmt on the created file. This is enabled by default and is recommended.
  • notification Prints a notification to stdout on success. This is enabled by default.

License: MIT

Dependencies

~1.2–1.7MB
~33K SLoC