Don't wipe out items on an error in #[cast_to]

Author: dynaxis

macros/src/lib.rs

@@ -2,8 +2,7 @@ extern crate proc_macro;
 
 use proc_macro::TokenStream;
 
-use syn::parse_macro_input;
-use syn::{DeriveInput, ItemImpl};
+use syn::{parse, parse_macro_input, DeriveInput, ItemImpl};
 
 use args::{Casts, Flag, Targets};
 use gen_caster::generate_caster;
@@ -46,13 +45,19 @@ mod item_type;
 /// ```
 #[proc_macro_attribute]
 pub fn cast_to(args: TokenStream, input: TokenStream) -> TokenStream {
-    let Targets { flags, paths } = parse_macro_input!(args as args::Targets);
-    let expanded = if paths.is_empty() {
-        item_impl::process(&flags, parse_macro_input!(input as ItemImpl))
-    } else {
-        item_type::process(&flags, paths, parse_macro_input!(input as DeriveInput))
-    };
-    expanded.into()
+    match parse::<Targets>(args) {
+        Ok(Targets { flags, paths }) => {
+            if paths.is_empty() {
+                item_impl::process(&flags, parse_macro_input!(input as ItemImpl))
+            } else {
+                item_type::process(&flags, paths, parse_macro_input!(input as DeriveInput))
+            }
+        }
+        Err(err) => vec![err.to_compile_error(), input.into()]
+            .into_iter()
+            .collect(),
+    }
+    .into()
 }
 
 /// Declare target traits for casting implemented by a type.

tests/ui/duplicate-flags.rs

@@ -0,0 +1,27 @@
+use intertrait::cast::*;
+use intertrait::*;
+use std::sync::Arc;
+
+#[cast_to([sync, sync] Greet)]
+struct Data;
+
+trait Source: CastFromSync {}
+
+trait Greet {
+    fn greet(&self);
+}
+
+impl Greet for Data {
+    fn greet(&self) {
+        println!("Hello");
+    }
+}
+
+impl Source for Data {}
+
+fn main() {
+    let data = Arc::new(Data);
+    let source: Arc<dyn Source> = data;
+    let greet = source.cast::<dyn Greet>();
+    greet.unwrap_or_else(|_| panic!("can't happen")).greet();
+}

tests/ui/duplicate-flags.stderr

@@ -0,0 +1,5 @@
+error: Duplicated flag: sync
+ --> $DIR/duplicate-flags.rs:5:18
+  |
+5 | #[cast_to([sync, sync] Greet)]
+  |                  ^^^^

tests/ui/unknown-flag.rs

@@ -0,0 +1,27 @@
+use intertrait::cast::*;
+use intertrait::*;
+use std::sync::Arc;
+
+#[cast_to([sync, send] Greet)]
+struct Data;
+
+trait Source: CastFromSync {}
+
+trait Greet {
+    fn greet(&self);
+}
+
+impl Greet for Data {
+    fn greet(&self) {
+        println!("Hello");
+    }
+}
+
+impl Source for Data {}
+
+fn main() {
+    let data = Arc::new(Data);
+    let source: Arc<dyn Source> = data;
+    let greet = source.cast::<dyn Greet>();
+    greet.unwrap_or_else(|_| panic!("can't happen")).greet();
+}

tests/ui/unknown-flag.stderr

@@ -0,0 +1,5 @@
+error: Unknown flag: send
+ --> $DIR/unknown-flag.rs:5:18
+  |
+5 | #[cast_to([sync, send] Greet)]
+  |                  ^^^^