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extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro2::Ident;
use quote::quote;
use std::iter::FromIterator;
use syn::{
parse::{Parse, ParseStream},
parse_macro_input,
punctuated::Punctuated,
Attribute, Token,
};
use syn_mid::{Block, ItemFn};
use self::Setting::*;
#[proc_macro_attribute]
pub fn proc_macro_error(attr: TokenStream, input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as ItemFn);
let mut settings = match syn::parse::<Settings>(attr) {
Ok(settings) => settings,
Err(err) => {
let err = err.to_compile_error();
return quote!(#input #err).into();
}
};
let is_proc_macro = is_proc_macro(&input.attrs);
if is_proc_macro {
settings.set(AssertUnwindSafe);
}
if detect_proc_macro_hack(&input.attrs) {
settings.set(ProcMacroHack);
}
if !(settings.is_set(AllowNotMacro) || is_proc_macro) {
return quote!(
#input
compile_error!("#[proc_macro_error] attribute can be used only with a proc-macro\n\n \
hint: if you are really sure that #[proc_macro_error] should be applied \
to this exact function use #[proc_macro_error(allow_not_macro)]\n");
)
.into();
}
let ItemFn {
attrs,
vis,
constness,
asyncness,
unsafety,
abi,
fn_token,
ident,
generics,
inputs,
output,
block,
..
} = input;
let body = gen_body(block, settings);
quote!(
#(#attrs)*
#vis
#constness
#asyncness
#unsafety
#abi
#fn_token
#ident
#generics
(#inputs)
#output
{ #body }
)
.into()
}
#[derive(PartialEq)]
enum Setting {
AssertUnwindSafe,
AllowNotMacro,
ProcMacroHack,
}
impl Parse for Setting {
fn parse(input: ParseStream) -> syn::Result<Self> {
let ident: Ident = input.parse()?;
match &*ident.to_string() {
"assert_unwind_safe" => Ok(AssertUnwindSafe),
"allow_not_macro" => Ok(AllowNotMacro),
"proc_macro_hack" => Ok(ProcMacroHack),
_ => Err(syn::Error::new(
ident.span(),
format!(
"unknown setting `{}`, expected one of \
`assert_unwind_safe`, `allow_not_macro`, `proc_macro_hack`",
ident
),
)),
}
}
}
struct Settings(Vec<Setting>);
impl Parse for Settings {
fn parse(input: ParseStream) -> syn::Result<Self> {
let punct = Punctuated::<Setting, Token![,]>::parse_terminated(input)?;
Ok(Settings(Vec::from_iter(punct)))
}
}
impl Settings {
fn is_set(&self, setting: Setting) -> bool {
self.0.iter().any(|s| *s == setting)
}
fn set(&mut self, setting: Setting) {
self.0.push(setting)
}
}
#[rustversion::since(1.37)]
fn gen_body(block: Block, settings: Settings) -> proc_macro2::TokenStream {
let is_proc_macro_hack = settings.is_set(ProcMacroHack);
let closure = if settings.is_set(AssertUnwindSafe) {
quote!(::std::panic::AssertUnwindSafe(|| #block ))
} else {
quote!(|| #block)
};
quote!( ::proc_macro_error::entry_point(#closure, #is_proc_macro_hack) )
}
// FIXME:
// proc_macro::TokenStream does not implement UnwindSafe until 1.37.0.
// Considering this is the closure's return type the unwind safety check would fail
// for virtually every closure possible, the check is meaningless.
#[rustversion::before(1.37)]
fn gen_body(block: Block, settings: Settings) -> proc_macro2::TokenStream {
let is_proc_macro_hack = settings.is_set(ProcMacroHack);
let closure = quote!(::std::panic::AssertUnwindSafe(|| #block ));
quote!( ::proc_macro_error::entry_point(#closure, #is_proc_macro_hack) )
}
fn detect_proc_macro_hack(attrs: &[Attribute]) -> bool {
attrs
.iter()
.any(|attr| attr.path.is_ident("proc_macro_hack"))
}
fn is_proc_macro(attrs: &[Attribute]) -> bool {
attrs.iter().any(|attr| {
attr.path.is_ident("proc_macro")
|| attr.path.is_ident("proc_macro_derive")
|| attr.path.is_ident("proc_macro_attribute")
})
}
|
