CODEWITHSUNDEEP
unit-testingrustmacros
Garuno
Garuno

Reputation: 2190

Is there a way to test macros in rust?

I'm trying to get started with TDD in Rust and I need to write a macro, which returns the number of variants in an enum. My implementation is similar to this one:

extern crate proc_macro;
extern crate syn;
#[macro_use]
extern crate quote;

use proc_macro::TokenStream;

#[proc_macro_derive(EnumVariantCount)]
pub fn derive_enum_variant_count(input: TokenStream) -> TokenStream {
    let syn_item: syn::DeriveInput = syn::parse(input).unwrap();
    let len = match syn_item.data {
        syn::Data::Enum(enum_item) => enum_item.variants.len(),
        _ => panic!("EnumVariantCount only works on Enums"),
    };
    let expanded = quote! {
    const LENGTH: usize = #len;
        };
    expanded.into()
}

So first I want to write a test to check if this macro only works on an enum. How would this even work? Can I somehow check if a file compiles in a unit test? Is there some documentation on testing rust macros that I overlooked?

Upvotes: 6

Views: 4240

Answers (1)

mcarton
mcarton

Reputation: 29981

The trybuild crate has been created specifically for this: it compiles a test file and then checks for expected compile-time errors.

Upvotes: 7

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