derive: Refactor to use syn::Error::to_compile_error

Author: tesaguri

oauth1-request-derive/src/ctxt.rs

@@ -1,40 +1,41 @@
+use core::fmt::Display;
 use std::mem;
 
-use proc_macro2::{Span, TokenStream};
-use quote::ToTokens;
-
-use crate::util::error;
+use proc_macro2::Span;
+use syn::Error;
 
 pub struct Ctxt {
-    errors: Option<TokenStream>,
+    error: Option<Error>,
 }
 
 impl Ctxt {
     pub fn new() -> Self {
-        Self {
-            errors: Some(TokenStream::new()),
+        Self { error: None }
+    }
+
+    pub fn add_error(&mut self, error: Error) {
+        if let Some(ref mut e) = self.error {
+            e.combine(error);
+        } else {
+            self.error = Some(error);
         }
     }
 
-    pub fn error(&mut self, msg: &str, span: Span) {
-        error(msg, span).to_tokens(self.errors.as_mut().unwrap());
+    pub fn add_error_message<T: Display>(&mut self, span: Span, msg: T) {
+        self.add_error(Error::new(span, msg));
     }
 
-    pub fn emit_errors(mut self) -> Option<TokenStream> {
-        let errors = self.errors.take().unwrap();
+    pub fn take_error(mut self) -> Option<Error> {
+        let error = self.error.take();
         mem::forget(self);
-        if errors.is_empty() {
-            None
-        } else {
-            Some(errors)
-        }
+        error
     }
 }
 
 impl Drop for Ctxt {
     fn drop(&mut self) {
         if !std::thread::panicking() {
-            panic!("must call `Ctxt::emit_errors`");
+            panic!("must call `Ctxt::take_error`");
         }
     }
 }

oauth1-request-derive/src/lib.rs

@@ -28,7 +28,6 @@ mod util;
 use proc_macro2::{Span, TokenStream};
 use proc_macro_crate::FoundCrate;
 use quote::{quote, quote_spanned};
-use syn::spanned::Spanned;
 use syn::{
     parse_macro_input, parse_quote, Data, DataStruct, DeriveInput, Fields, GenericParam, Generics,
     Ident,
@@ -38,7 +37,6 @@ use self::container::ContainerMeta;
 use self::ctxt::Ctxt;
 use self::field::Field;
 use self::method_body::MethodBody;
-use self::util::error;
 
 /// A derive macro for [`oauth1_request::Request`][Request] trait.
 ///
@@ -59,7 +57,10 @@ fn expand_derive_oauth1_authorize(input: DeriveInput) -> TokenStream {
             fields: Fields::Named(fields),
             ..
         }) => fields,
-        _ => return error("expected a struct with named fields", input.span()),
+        _ => {
+            return syn::Error::new_spanned(input, "expected a struct with named fields")
+                .into_compile_error()
+        }
     };
 
     let mut cx = Ctxt::new();
@@ -81,7 +82,7 @@ fn expand_derive_oauth1_authorize(input: DeriveInput) -> TokenStream {
         let name = f.name();
         let (name, span) = (name.string_value(), name.span());
         if name == prev_name {
-            cx.error(&format!("duplicate parameter \"{}\"", name), span);
+            cx.add_error_message(span, format!("duplicate parameter \"{}\"", name));
         }
         name
     });
@@ -105,7 +106,10 @@ fn expand_derive_oauth1_authorize(input: DeriveInput) -> TokenStream {
                 &*krate
             }
             Err(proc_macro_crate::Error::CargoManifestDirNotSet) => "oauth1_request",
-            Err(e) => panic!("{:?}", e),
+            Err(e) => {
+                cx.add_error_message(Span::call_site(), e);
+                "oauth1_request"
+            }
         };
         let krate = Ident::new(krate, Span::call_site());
         quote! {
@@ -116,7 +120,8 @@ fn expand_derive_oauth1_authorize(input: DeriveInput) -> TokenStream {
     add_trait_bounds(&mut generics);
     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
-    if let Some(mut tokens) = cx.emit_errors() {
+    if let Some(e) = cx.take_error() {
+        let mut tokens = e.into_compile_error();
         tokens.extend(quote! {
             const _: () = {
                 #use_oauth1_request

oauth1-request-derive/src/meta.rs

@@ -31,14 +31,14 @@ macro_rules! def_meta {
                     let meta_list = match attr.parse_args_with(parser) {
                         Ok(list) => list,
                         Err(e) => {
-                            cx.error(&e.to_string(), e.span());
+                            cx.add_error(e);
                             continue;
                         }
                     };
 
                     for meta in meta_list {
                         if let Err(e) = ret.add_meta(meta) {
-                            cx.error(&e.to_string(), e.span());
+                            cx.add_error(e);
                         }
                     }
                 }

oauth1-request-derive/src/util.rs

@@ -3,7 +3,7 @@ mod oauth_parameter;
 pub use oauth_parameter::OAuthParameter;
 
 use proc_macro2::{Ident, Span, TokenStream, TokenTree};
-use quote::{quote_spanned, ToTokens};
+use quote::ToTokens;
 
 impl OAuthParameter {
     fn serialize_method_name(self) -> Option<&'static str> {
@@ -30,9 +30,3 @@ impl ToTokens for OAuthParameter {
         tokens.extend(::core::iter::once(TokenTree::Ident(ident)));
     }
 }
-
-pub fn error(msg: &str, span: Span) -> TokenStream {
-    quote_spanned!(span=>
-        compile_error!(#msg);
-    )
-}