Just panic on errors

Author: dtolnay

README.md

@@ -50,15 +50,15 @@ https://github.com/dtolnay/proc-macro-hack/tree/master/demo-hack-impl
 
 proc_macro_expr_impl! {
     /// Add one to an expression.
-    pub fn add_one_impl(input: &str) -> Result<String, String> {
-        Ok(format!("1 + {}", input))
+    pub fn add_one_impl(input: &str) -> String {
+        format!("1 + {}", input)
     }
 }
 
 proc_macro_item_impl! {
     /// A function that always returns 2.
-    pub fn two_fn_impl(input: &str) -> Result<String, String> {
-        Ok(format!("fn {}() -> u8 {{ 2 }}", input))
+    pub fn two_fn_impl(input: &str) -> String {
+        format!("fn {}() -> u8 {{ 2 }}", input)
     }
 }
 ```
@@ -84,7 +84,7 @@ proc-macro = true
 
 Users of your crate depend on your declaration crate and implementation crate,
 then use your procedural macros as though it were magic. They even get
-reasonable error messages if your procedural macro returns an error.
+reasonable error messages if your procedural macro panics.
 
 https://github.com/dtolnay/proc-macro-hack/tree/master/example
 

demo-hack-impl/src/lib.rs

@@ -5,14 +5,14 @@
 
 proc_macro_expr_impl! {
     /// Add one to an expression.
-    pub fn add_one_impl(input: &str) -> Result<String, String> {
-        Ok(format!("1 + {}", input))
+    pub fn add_one_impl(input: &str) -> String {
+        format!("1 + {}", input)
     }
 }
 
 proc_macro_item_impl! {
     /// A function that always returns 2.
-    pub fn two_fn_impl(input: &str) -> Result<String, String> {
-        Ok(format!("fn {}() -> u8 {{ 2 }}", input))
+    pub fn two_fn_impl(input: &str) -> String {
+        format!("fn {}() -> u8 {{ 2 }}", input)
     }
 }

src/lib.rs

@@ -31,7 +31,7 @@ macro_rules! proc_macro_item_decl {
 macro_rules! proc_macro_expr_impl {
     ($(
         $( #[$attr:meta] )*
-        pub fn $func:ident($input:ident: &str ) -> Result<String, String> $body:block
+        pub fn $func:ident($input:ident: &str) -> String $body:block
     )+) => {
         $(
             $( #[$attr] )*
@@ -47,22 +47,15 @@ macro_rules! proc_macro_expr_impl {
 
                 let tokens = &source[prefix.len() .. source.len() - suffix.len()];
 
-                fn func($input: &str) -> Result<String, String> $body
+                fn func($input: &str) -> String $body
 
-                let wrap = match func(tokens) {
-                    Ok(expr) => {
-                        format!("
-                            macro_rules! proc_macro_call {{
-                                () => {{
-                                    {}
-                                }}
-                            }}
-                        ", expr)
-                    }
-                    Err(msg) => panic!(msg)
-                };
-
-                wrap.parse().unwrap()
+                format!("
+                    macro_rules! proc_macro_call {{
+                        () => {{
+                            {}
+                        }}
+                    }}
+                ", func(tokens)).parse().unwrap()
             }
         )+
     }
@@ -72,7 +65,7 @@ macro_rules! proc_macro_expr_impl {
 macro_rules! proc_macro_item_impl {
     ($(
         $( #[$attr:meta] )*
-        pub fn $func:ident($input:ident: &str ) -> Result<String, String> $body:block
+        pub fn $func:ident($input:ident: &str) -> String $body:block
     )+) => {
         $(
             $( #[$attr] )*
@@ -88,9 +81,9 @@ macro_rules! proc_macro_item_impl {
 
                 let tokens = &source[prefix.len() .. source.len() - suffix.len()];
 
-                fn func($input: &str) -> Result<String, String> $body
+                fn func($input: &str) -> String $body
 
-                func(tokens).unwrap_or_else(|msg| panic!(msg)).parse().unwrap()
+                func(tokens).parse().unwrap()
             }
         )+
     }