blob: 3943c6b4eadec215a320381d2ab3ad32e5090cc6 [file] [log] [blame]
extern crate proc_macro;
extern crate syn;
#[macro_use] extern crate synstructure;
#[macro_use] extern crate quote;
decl_derive!([Fail, attributes(fail, cause)] => fail_derive);
fn fail_derive(s: synstructure::Structure) -> quote::Tokens {
let cause_body = s.each_variant(|v| {
if let Some(cause) = v.bindings().iter().find(is_cause) {
quote!(return Some(#cause))
} else {
quote!(return None)
}
});
let bt_body = s.each_variant(|v| {
if let Some(bi) = v.bindings().iter().find(is_backtrace) {
quote!(return Some(#bi))
} else {
quote!(return None)
}
});
#[cfg(feature = "std")]
let fail = s.bound_impl("::failure::Fail", quote! {
#[allow(unreachable_code)]
fn cause(&self) -> ::std::option::Option<&::failure::Fail> {
match *self { #cause_body }
None
}
#[allow(unreachable_code)]
fn backtrace(&self) -> ::std::option::Option<&::failure::Backtrace> {
match *self { #bt_body }
None
}
});
#[cfg(not(feature = "std"))]
let fail = s.bound_impl("::failure::Fail", quote! {
#[allow(unreachable_code)]
fn cause(&self) -> ::core::option::Option<&::failure::Fail> {
match *self { #cause_body }
None
}
#[allow(unreachable_code)]
fn backtrace(&self) -> ::core::option::Option<&::failure::Backtrace> {
match *self { #bt_body }
None
}
});
#[cfg(feature = "std")]
let display = display_body(&s).map(|display_body| {
s.bound_impl("::std::fmt::Display", quote! {
#[allow(unreachable_code)]
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
match *self { #display_body }
write!(f, "An error has occurred.")
}
})
});
#[cfg(not(feature = "std"))]
let display = display_body(&s).map(|display_body| {
s.bound_impl("::core::fmt::Display", quote! {
#[allow(unreachable_code)]
fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
match *self { #display_body }
write!(f, "An error has occurred.")
}
})
});
quote! {
#fail
#display
}
}
fn display_body(s: &synstructure::Structure) -> Option<quote::Tokens> {
let mut msgs = s.variants().iter().map(|v| find_error_msg(&v.ast().attrs));
if msgs.all(|msg| msg.is_none()) { return None; }
Some(s.each_variant(|v| {
let msg = find_error_msg(&v.ast().attrs).expect("All variants must have display attribute.");
if msg.is_empty() {
panic!("Expected at least one argument to fail attribute");
}
let s = match msg[0] {
syn::NestedMetaItem::MetaItem(syn::MetaItem::NameValue(ref i, ref lit)) if i == "display" => {
lit.clone()
}
_ => panic!("Fail attribute must begin `display = \"\"` to control the Display message."),
};
let args = msg[1..].iter().map(|arg| match *arg {
syn::NestedMetaItem::Literal(syn::Lit::Int(i, _)) => {
let bi = &v.bindings()[i as usize];
quote!(#bi)
}
syn::NestedMetaItem::MetaItem(syn::MetaItem::Word(ref id)) => {
if id.as_ref().starts_with("_") {
if let Ok(idx) = id.as_ref()[1..].parse::<usize>() {
let bi = &v.bindings()[idx];
return quote!(#bi)
}
}
for bi in v.bindings() {
if bi.ast().ident.as_ref() == Some(id) {
return quote!(#bi);
}
}
panic!("Couldn't find a field with this name!");
}
_ => panic!("Invalid argument to fail attribute!"),
});
quote! {
return write!(f, #s #(, #args)*)
}
}))
}
fn find_error_msg(attrs: &[syn::Attribute]) -> Option<&[syn::NestedMetaItem]> {
let mut error_msg = None;
for attr in attrs {
if attr.name() == "fail" {
if error_msg.is_some() {
panic!("Cannot have two display attributes")
} else {
if let syn::MetaItem::List(_, ref list) = attr.value {
error_msg = Some(&list[..]);
} else {
panic!("fail attribute must take a list in parantheses")
}
}
}
}
error_msg
}
fn is_backtrace(bi: &&synstructure::BindingInfo) -> bool {
match bi.ast().ty {
syn::Ty::Path(None, syn::Path { segments: ref path, .. }) => {
path.last().map_or(false, |s| s.ident == "Backtrace" && s.parameters.is_empty())
}
_ => false
}
}
fn is_cause(bi: &&synstructure::BindingInfo) -> bool {
bi.ast().attrs.iter().any(|attr| attr.name() == "cause")
}