Add unit test for serde attribute processing

schemars_derive/src/preprocess.rs

@@ -1,9 +1,7 @@
-use proc_macro2::TokenStream;
 use quote::ToTokens;
 use serde_derive_internals::Ctxt;
 use std::collections::BTreeSet;
 use syn::parse::Parser;
-use syn::spanned::Spanned;
 use syn::{
     Attribute, Data, DeriveInput, Field, GenericParam, Generics, Ident, Meta, NestedMeta, Variant,
 };
@@ -18,7 +16,7 @@ pub fn add_trait_bounds(generics: &mut Generics) {
 
 // If a struct/variant/field has any #[schemars] attributes, then rename them
 // to #[serde] so that serde_derive_internals will parse them for us.
-pub fn process_serde_attrs(input: &mut DeriveInput) -> Result<(), TokenStream> {
+pub fn process_serde_attrs(input: &mut DeriveInput) -> Result<(), String> {
     let ctxt = Ctxt::new();
     process_attrs(&ctxt, &mut input.attrs);
     match input.data {
@@ -27,11 +25,7 @@ pub fn process_serde_attrs(input: &mut DeriveInput) -> Result<(), TokenStream> {
         Data::Union(ref mut u) => process_serde_field_attrs(&ctxt, u.fields.named.iter_mut()),
     };
 
-    ctxt.check().map_err(|message| {
-        quote_spanned! {input.span()=>
-            compile_error!(#message);
-        }
-    })
+    ctxt.check()
 }
 
 fn process_serde_variant_attrs<'a>(ctxt: &Ctxt, variants: impl Iterator<Item = &'a mut Variant>) {
@@ -118,3 +112,48 @@ fn get_meta_ident(ctxt: &Ctxt, meta: &NestedMeta) -> Result<Ident, ()> {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pretty_assertions::assert_eq;
+    use syn::DeriveInput;
+
+    #[test]
+    fn test_process_serde_attrs() {
+        let mut input: DeriveInput = parse_quote! {
+            #[serde(container, container2 = "blah")]
+            #[serde(container3(foo, bar))]
+            #[schemars(container2 = "overridden", container4)]
+            #[misc]
+            struct MyStruct {
+                #[serde(field, field2)]
+                field1: i32,
+                #[serde(field, field2)]
+                #[schemars(field = "overridden")]
+                field2: i32,
+                #[schemars(field)]
+                field3: i32,
+            }
+        };
+        let expected: DeriveInput = parse_quote! {
+            #[serde(container2 = "overridden", container4)]
+            #[serde(container, container3(foo, bar))]
+            struct MyStruct {
+                #[serde(field, field2)]
+                field1: i32,
+                #[serde(field = "overridden")]
+                #[serde(field2)]
+                field2: i32,
+                #[serde(field)]
+                field3: i32,
+            }
+        };
+
+        if let Err(e) = process_serde_attrs(&mut input) {
+            panic!("process_serde_attrs returned error: {}", e)
+        };
+
+        assert_eq!(input, expected);
+    }
+}