Revamp serde_codegen_internals error handling

serde_codegen/src/de.rs

@@ -5,11 +5,12 @@ use bound;
 use internals::ast::{Body, Field, Item, Style, Variant};
 use internals::{self, attr};
 
-pub fn expand_derive_deserialize(item: &syn::MacroInput) -> Tokens {
+pub fn expand_derive_deserialize(item: &syn::MacroInput) -> Result<Tokens, String> {
     let item = {
         let ctxt = internals::Ctxt::new();
         let item = Item::from_ast(&ctxt, item);
         check_no_str(&ctxt, &item);
+        try!(ctxt.check());
         item
     };
 
@@ -27,7 +28,7 @@ pub fn expand_derive_deserialize(item: &syn::MacroInput) -> Tokens {
 
     let dummy_const = aster::id(format!("_IMPL_DESERIALIZE_FOR_{}", item.ident));
 
-    quote! {
+    Ok(quote! {
         #[allow(non_upper_case_globals, unused_attributes, unused_qualifications)]
         const #dummy_const: () = {
             extern crate serde as _serde;
@@ -40,7 +41,7 @@ pub fn expand_derive_deserialize(item: &syn::MacroInput) -> Tokens {
                 }
             }
         };
-    }
+    })
 }
 
 // All the generics in the input, plus a bound `T: Deserialize` for each generic

serde_codegen/src/lib.rs

@@ -123,7 +123,7 @@ macro_rules! shim {
     ($name:ident $pkg:ident :: $func:ident) => {
         fn $func(
             cx: &mut ::syntax::ext::base::ExtCtxt,
-            _span: ::syntax::codemap::Span,
+            span: ::syntax::codemap::Span,
             meta_item: &::syntax::ast::MetaItem,
             annotatable: &::syntax::ext::base::Annotatable,
             push: &mut FnMut(::syntax::ext::base::Annotatable)
@@ -158,7 +158,13 @@ macro_rules! shim {
             let s = pprust::item_to_string(item);
 
             let syn_item = syn::parse_macro_input(&s).unwrap();
-            let expanded = $pkg::$func(&syn_item).to_string();
+            let expanded = match $pkg::$func(&syn_item) {
+                Ok(expanded) => expanded.to_string(),
+                Err(msg) => {
+                    cx.span_err(span, &msg);
+                    return;
+                }
+            };
 
             use syntax::parse;
             let name = stringify!($name).to_string();
@@ -174,21 +180,21 @@ shim!(Serialize ser::expand_derive_serialize);
 shim!(Deserialize de::expand_derive_deserialize);
 
 #[cfg(feature = "with-syn")]
-pub fn expand_single_item(item: &str) -> String {
+pub fn expand_single_item(item: &str) -> Result<String, String> {
     let syn_item = syn::parse_macro_input(item).unwrap();
     let (ser, de, syn_item) = strip_serde_derives(syn_item);
     let expanded_ser = if ser {
-        Some(ser::expand_derive_serialize(&syn_item))
+        Some(try!(ser::expand_derive_serialize(&syn_item)))
     } else {
         None
     };
     let expanded_de = if de {
-        Some(de::expand_derive_deserialize(&syn_item))
+        Some(try!(de::expand_derive_deserialize(&syn_item)))
     } else {
         None::<quote::Tokens>
     };
     let syn_item = strip_serde_attrs(syn_item);
-    return quote!(#expanded_ser #expanded_de #syn_item).to_string();
+    return Ok(quote!(#expanded_ser #expanded_de #syn_item).to_string());
 
     fn strip_serde_derives(item: syn::MacroInput) -> (bool, bool, syn::MacroInput) {
         let mut ser = false;

serde_codegen/src/ser.rs

@@ -5,8 +5,10 @@ use bound;
 use internals::ast::{Body, Field, Item, Style, Variant};
 use internals::{self, attr};
 
-pub fn expand_derive_serialize(item: &syn::MacroInput) -> Tokens {
+pub fn expand_derive_serialize(item: &syn::MacroInput) -> Result<Tokens, String> {
-    let item = Item::from_ast(&internals::Ctxt::new(), item);
+    let ctxt = internals::Ctxt::new();
+    let item = Item::from_ast(&ctxt, item);
+    try!(ctxt.check());
 
     let impl_generics = build_impl_generics(&item);
 
@@ -22,7 +24,7 @@ pub fn expand_derive_serialize(item: &syn::MacroInput) -> Tokens {
 
     let dummy_const = aster::id(format!("_IMPL_SERIALIZE_FOR_{}", item.ident));
 
-    quote! {
+    Ok(quote! {
         #[allow(non_upper_case_globals, unused_attributes, unused_qualifications)]
         const #dummy_const: () = {
             extern crate serde as _serde;
@@ -35,7 +37,7 @@ pub fn expand_derive_serialize(item: &syn::MacroInput) -> Tokens {
                 }
             }
         };
-    }
+    })
 }
 
 // All the generics in the input, plus a bound `T: Serialize` for each generic

serde_codegen_internals/src/ctxt.rs

@@ -1,29 +1,43 @@
 use std::fmt::Display;
-use std::cell::Cell;
+use std::cell::RefCell;
 
 #[derive(Default)]
 pub struct Ctxt {
-    err_count: Cell<usize>,
+    errors: RefCell<Option<Vec<String>>>,
 }
 
 impl Ctxt {
     pub fn new() -> Self {
-        Default::default()
+        Ctxt {
+            errors: RefCell::new(Some(Vec::new())),
+        }
     }
 
     pub fn error<T: Display>(&self, msg: T) {
-        println!("{}", msg);
+        self.errors.borrow_mut().as_mut().unwrap().push(msg.to_string());
-        self.err_count.set(self.err_count.get() + 1);
+    }
+
+    pub fn check(self) -> Result<(), String> {
+        let mut errors = self.errors.borrow_mut().take().unwrap();
+        match errors.len() {
+            0 => Ok(()),
+            1 => Err(errors.pop().unwrap()),
+            n => {
+                let mut msg = format!("{} errors:", n);
+                for err in errors {
+                    msg += "\n\t# ";
+                    msg += &err;
+                }
+                Err(msg)
+            }
+        }
     }
 }
 
 impl Drop for Ctxt {
     fn drop(&mut self) {
-        let err_count = self.err_count.get();
+        if self.errors.borrow().is_some() {
-        if err_count == 1 {
+            panic!("forgot to check for errors");
-            panic!("1 error");
-        } else if err_count > 1 {
-            panic!("{} errors", err_count);
         }
     }
 }

serde_derive/src/lib.rs

@@ -9,13 +9,17 @@ use rustc_macro::TokenStream;
 #[rustc_macro_derive(Serialize)]
 pub fn derive_serialize(input: TokenStream) -> TokenStream {
     let item = format!("#[derive(Serialize)]\n{}", input);
-    let expanded = serde_codegen::expand_single_item(&item);
+    match serde_codegen::expand_single_item(&item) {
-    expanded.parse().unwrap()
+        Ok(expanded) => expanded.parse().unwrap(),
+        Err(msg) => panic!(msg),
+    }
 }
 
 #[rustc_macro_derive(Deserialize)]
 pub fn derive_deserialize(input: TokenStream) -> TokenStream {
     let item = format!("#[derive(Deserialize)]\n{}", input);
-    let expanded = serde_codegen::expand_single_item(&item);
+    match serde_codegen::expand_single_item(&item) {
-    expanded.parse().unwrap()
+        Ok(expanded) => expanded.parse().unwrap(),
+        Err(msg) => panic!(msg),
+    }
 }