More efficient try!() alternative

serde_derive/src/de.rs

@@ -16,6 +16,7 @@ use bound;
 use fragment::{Expr, Fragment, Match, Stmts};
 use internals::ast::{Container, Data, Field, Style, Variant};
 use internals::{self, attr};
+use try;
 
 use std::collections::BTreeSet;
 
@@ -63,10 +64,12 @@ pub fn expand_derive_deserialize(input: &syn::DeriveInput) -> Result<Tokens, Str
         }
     };
 
+    let try_replacement = try::replacement();
     let generated = quote! {
         #[allow(non_upper_case_globals, unused_attributes, unused_qualifications)]
         const #dummy_const: () = {
             extern crate serde as _serde;
+            #try_replacement
             #impl_block
         };
     };

serde_derive/src/lib.rs

@@ -58,6 +58,7 @@ mod fragment;
 
 mod de;
 mod ser;
+mod try;
 
 #[proc_macro_derive(Serialize, attributes(serde))]
 pub fn derive_serialize(input: TokenStream) -> TokenStream {

serde_derive/src/ser.rs

@@ -15,6 +15,7 @@ use bound;
 use fragment::{Fragment, Match, Stmts};
 use internals::ast::{Container, Data, Field, Style, Variant};
 use internals::{attr, Ctxt};
+use try;
 
 use std::u32;
 
@@ -55,10 +56,12 @@ pub fn expand_derive_serialize(input: &syn::DeriveInput) -> Result<Tokens, Strin
         }
     };
 
+    let try_replacement = try::replacement();
     let generated = quote! {
         #[allow(non_upper_case_globals, unused_attributes, unused_qualifications)]
         const #dummy_const: () = {
             extern crate serde as _serde;
+            #try_replacement
             #impl_block
         };
     };

serde_derive/src/try.rs

@@ -0,0 +1,25 @@
+use quote::Tokens;
+use proc_macro2::{Op, Spacing};
+
+// None of our generated code requires the `From::from` error conversion
+// performed by the standard library's `try!` macro. With this simplified macro
+// we see a significant improvement in type checking and borrow checking time of
+// the generated code and a slight improvement in binary size.
+pub fn replacement() -> Tokens {
+    // Cannot pass `$expr` to `quote!` prior to Rust 1.17.0 so interpolate it.
+    let dollar = Op::new('$', Spacing::Alone);
+
+    quote! {
+        #[allow(unused_macros)]
+        macro_rules! try {
+            (#dollar __expr:expr) => {
+                match #dollar __expr {
+                    _serde::export::Ok(__val) => __val,
+                    _serde::export::Err(__err) => {
+                        return _serde::export::Err(__err);
+                    }
+                }
+            }
+        }
+    }
+}