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Merge pull request #55 from iqlusioninc/custom-custom-fail-derive-macro
iq-cli-derive: Add support for deriving `Fail`
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,207 @@ | ||
| //! Provides `derive(Fail)` for the `iq_cli` crate | ||
| //! | ||
| //! # `derive(Fail)` | ||
| //! | ||
| //! `derive(Fail)` generates an implementation of the trait `Fail`, | ||
| //! creating an option for each field of the decorated `enum`. | ||
| //! | ||
| //! # Notice | ||
| //! | ||
| //! The `errors` module of the `iq-cli-derive` crate is a fork of the | ||
| //! `failure_derive` crate: | ||
| //! | ||
| //! <https://github.com/rust-lang-nursery/failure> | ||
| use proc_macro2::TokenStream; | ||
| use syn; | ||
| use synstructure::{BindingInfo, Structure}; | ||
|
|
||
| #[allow(unknown_lints, needless_pass_by_value)] | ||
| pub(crate) fn fail_derive(s: Structure) -> TokenStream { | ||
| let make_dyn = if cfg!(has_dyn_trait) { | ||
| quote! { &dyn } | ||
| } else { | ||
| quote! { & } | ||
| }; | ||
|
|
||
| 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) | ||
| } | ||
| }); | ||
|
|
||
| let fail = s.unbound_impl( | ||
| quote!(::failure::Fail), | ||
| quote! { | ||
| #[allow(unreachable_code)] | ||
| fn cause(&self) -> ::failure::_core::option::Option<#make_dyn(::failure::Fail)> { | ||
| match *self { #cause_body } | ||
| None | ||
| } | ||
|
|
||
| #[allow(unreachable_code)] | ||
| fn backtrace(&self) -> ::failure::_core::option::Option<&::failure::Backtrace> { | ||
| match *self { #bt_body } | ||
| None | ||
| } | ||
| }, | ||
| ); | ||
| let display = display_body(&s).map(|display_body| { | ||
| s.unbound_impl( | ||
| quote!(::failure::_core::fmt::Display), | ||
| quote! { | ||
| #[allow(unreachable_code)] | ||
| fn fmt(&self, f: &mut ::failure::_core::fmt::Formatter) -> ::failure::_core::fmt::Result { | ||
| match *self { #display_body } | ||
| write!(f, "An error has occurred.") | ||
| } | ||
| }, | ||
| ) | ||
| }); | ||
|
|
||
| quote! { | ||
| #fail | ||
| #display | ||
| } | ||
| } | ||
|
|
||
| fn display_body(s: &Structure) -> Option<TokenStream> { | ||
| 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.nested.is_empty() { | ||
| panic!("Expected at least one argument to fail attribute"); | ||
| } | ||
|
|
||
| let format_string = match msg.nested[0] { | ||
| syn::NestedMeta::Meta(syn::Meta::NameValue(ref nv)) if nv.ident == "display" => { | ||
| nv.lit.clone() | ||
| } | ||
| _ => { | ||
| panic!("Fail attribute must begin `display = \"\"` to control the Display message.") | ||
| } | ||
| }; | ||
| let args = msg.nested.iter().skip(1).map(|arg| match *arg { | ||
| syn::NestedMeta::Literal(syn::Lit::Int(ref i)) => { | ||
| let bi = &v.bindings()[i.value() as usize]; | ||
| quote!(#bi) | ||
| } | ||
| syn::NestedMeta::Meta(syn::Meta::Word(ref id)) => { | ||
| let id_s = id.to_string(); | ||
| if id_s.starts_with('_') { | ||
| if let Ok(idx) = id_s[1..].parse::<usize>() { | ||
| let bi = match v.bindings().get(idx) { | ||
| Some(bi) => bi, | ||
| None => { | ||
| panic!( | ||
| "display attempted to access field `{}` in `{}::{}` which \ | ||
| does not exist (there are {} field{})", | ||
| idx, | ||
| s.ast().ident, | ||
| v.ast().ident, | ||
| v.bindings().len(), | ||
| if v.bindings().len() != 1 { "s" } else { "" } | ||
| ); | ||
| } | ||
| }; | ||
| return quote!(#bi); | ||
| } | ||
| } | ||
| for bi in v.bindings() { | ||
| if bi.ast().ident.as_ref() == Some(id) { | ||
| return quote!(#bi); | ||
| } | ||
| } | ||
| panic!( | ||
| "Couldn't find field `{}` in `{}::{}`", | ||
| id, | ||
| s.ast().ident, | ||
| v.ast().ident | ||
| ); | ||
| } | ||
| _ => panic!("Invalid argument to fail attribute!"), | ||
| }); | ||
|
|
||
| quote! { | ||
| return write!(f, #format_string #(, #args)*) | ||
| } | ||
| })) | ||
| } | ||
|
|
||
| fn find_error_msg(attrs: &[syn::Attribute]) -> Option<syn::MetaList> { | ||
| let mut error_msg = None; | ||
| for attr in attrs { | ||
| if let Some(meta) = attr.interpret_meta() { | ||
| if meta.name() == "fail" { | ||
| if error_msg.is_some() { | ||
| panic!("Cannot have two display attributes") | ||
| } else if let syn::Meta::List(list) = meta { | ||
| error_msg = Some(list); | ||
| } else { | ||
| panic!("fail attribute must take a list in parentheses") | ||
| } | ||
| } | ||
| } | ||
| } | ||
| error_msg | ||
| } | ||
|
|
||
| #[allow(unknown_lints, trivially_copy_pass_by_ref)] | ||
| fn is_backtrace(bi: &&BindingInfo) -> bool { | ||
| match bi.ast().ty { | ||
| syn::Type::Path(syn::TypePath { | ||
| qself: None, | ||
| path: syn::Path { | ||
| segments: ref path, .. | ||
| }, | ||
| }) => path.last().map_or(false, |s| { | ||
| s.value().ident == "Backtrace" && s.value().arguments.is_empty() | ||
| }), | ||
| _ => false, | ||
| } | ||
| } | ||
|
|
||
| #[allow(unknown_lints, trivially_copy_pass_by_ref)] | ||
| fn is_cause(bi: &&BindingInfo) -> bool { | ||
| let mut found_cause = false; | ||
| for attr in &bi.ast().attrs { | ||
| if let Some(meta) = attr.interpret_meta() { | ||
| if meta.name() == "cause" { | ||
| if found_cause { | ||
| panic!("Cannot have two `cause` attributes"); | ||
| } | ||
| found_cause = true; | ||
| } | ||
| if meta.name() == "fail" { | ||
| if let syn::Meta::List(ref list) = meta { | ||
| if let Some(ref pair) = list.nested.first() { | ||
| if let syn::NestedMeta::Meta(syn::Meta::Word(ref word)) = pair.value() { | ||
| if word == "cause" { | ||
| if found_cause { | ||
| panic!("Cannot have two `cause` attributes"); | ||
| } | ||
| found_cause = true; | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
| found_cause | ||
| } |
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