warnings-macro 0.2.0

A macro for defining warnings
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89

use proc_macro::TokenStream;
use quote::{format_ident, quote};
use syn::spanned::Spanned;
use syn::{parse_macro_input, FnArg, GenericParam, ItemFn};

/// Turns a function into a warning that is only called if the lint is enabled.
#[proc_macro_attribute]
pub fn warning(_: TokenStream, input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(input as ItemFn);
    let fn_name = &input.sig.ident;

    let argument_types = input
        .sig
        .inputs
        .iter()
        .filter_map(|arg| match arg {
            FnArg::Receiver(_) => None,
            FnArg::Typed(arg) => Some(&arg.ty),
        })
        .collect::<Vec<_>>();
    let argument_idents = input
        .sig
        .inputs
        .iter()
        .enumerate()
        .filter_map(|(index, arg)| match arg {
            FnArg::Receiver(_) => None,
            FnArg::Typed(arg) => Some(syn::Ident::new(&format!("arg{}", index), arg.pat.span())),
        })
        .collect::<Vec<_>>();

    let private_mod = format_ident!("__{}", fn_name);

    let vis = &input.vis;

    let (impl_generics, ty_generics, where_clause) = input.sig.generics.split_for_impl();
    let generics = &input.sig.generics.params;
    let phantom_data = (!input.sig.generics.params.is_empty()).then(|| {
        let ty_generics_tuple = input.sig.generics.params.iter().map(|param| match param {
            GenericParam::Type(ty) => {
                let ty = &ty.ident;
                quote!(#ty)
            }
            GenericParam::Lifetime(lifetime) => quote!(&#lifetime ()),
            GenericParam::Const(_) => quote!(()),
        });
        quote!(PhantomData(std::marker::PhantomData<(#(#ty_generics_tuple),*)>))
    });

    let attrs = &input.attrs;

    // Hand the resulting function body back to the compiler.
    TokenStream::from(quote! {
        #[allow(non_camel_case_types)]
        #(#attrs)*
        #vis struct #fn_name {}

        mod #private_mod {
            use super::*;

            pub(crate) enum __Callable<#generics> #where_clause {
                #[allow(non_camel_case_types)]
                #fn_name,
                #phantom_data
            }

            impl #impl_generics  __Callable #ty_generics #where_clause {
                fn __run_if_enabled(#(#argument_idents: #argument_types),*) {
                    <#fn_name as ::warnings::Warning>::ID.if_enabled(|| {
                        #input
                        #fn_name(#(#argument_idents),*);
                    });
                }
            }

            impl #impl_generics std::ops::Deref for __Callable #ty_generics #where_clause {
                type Target = fn(#(#argument_types),*);
                fn deref(&self) -> &Self::Target {
                    &(Self::__run_if_enabled as fn(#(#argument_types),*))
                }
            }
        }
        #vis use #private_mod::__Callable::*;

        impl ::warnings::Warning for #fn_name {
            const ID: ::warnings::WarningId = ::warnings::WarningId::of::<#fn_name>();
        }
    })
}