Minor cleanups and fixes

serde/src/private/de.rs

@@ -805,18 +805,18 @@ mod content {
     /// Not public API.
     pub struct TaggedContentVisitor<'de, T> {
         tag_name: &'static str,
-        tag_default: Option<T>,
+        default_variant: Option<T>,
         expecting: &'static str,
         value: PhantomData<TaggedContent<'de, T>>,
     }
 
     impl<'de, T> TaggedContentVisitor<'de, T> {
         /// Visitor for the content of an internally tagged enum with the given
         /// tag name.
-        pub fn new(name: &'static str, default_tag: Option<T>, expecting: &'static str) -> Self {
+        pub fn new(name: &'static str, default_variant: Option<T>, expecting: &'static str) -> Self {
             TaggedContentVisitor {
                 tag_name: name,
-                tag_default: default_tag,
+                default_variant: default_variant,
                 expecting: expecting,
                 value: PhantomData,
             }
@@ -853,16 +853,12 @@ mod content {
         where
             S: SeqAccess<'de>,
         {
-            let tag = match try!(seq.next_element()) {
-                Some(tag) => {
-                    tag
+            let tag = match seq.next_element()? {
+                Some(tag) => tag,
+                None => match self.default_variant {
+                    Some(variant) => variant,
+                    None => return Err(de::Error::missing_field(self.tag_name)),
                 },
-                None => {
-                    match self.tag_default {
-                        Some(default) => default,
-                        None => return Err(de::Error::missing_field(self.tag_name)),
-                    }
-                }
             };
             let rest = de::value::SeqAccessDeserializer::new(seq);
             Ok(TaggedContent {
@@ -892,7 +888,7 @@ mod content {
                 }
             }
             match tag {
-                None => match self.tag_default {
+                None => match self.default_variant {
                     Some(default) => {
                         Ok(TaggedContent {
                             tag: default,

serde_derive/src/de.rs

@@ -1344,14 +1344,6 @@ fn deserialize_internally_tagged_enum(
 ) -> Fragment {
     let (variants_stmt, variant_visitor) = prepare_enum_variant_enum(variants, cattrs);
 
-    let mut default_variant = quote! { None };
-    for (i, variant) in variants.iter().enumerate() {
-        if variant.attrs.default() {
-            let variant_name = field_i(i);
-            default_variant = quote!{ Some(__Field::#variant_name) };
-        }
-    }
-
     // Match arms to extract a variant from a string
     let variant_arms = variants
         .iter()
@@ -1374,6 +1366,10 @@ fn deserialize_internally_tagged_enum(
             }
         });
 
+    let default_variant = get_default_variant(variants).unwrap_or(quote! {
+        std::option::Option::None
+    });
+
     let expecting = format!("internally tagged enum {}", params.type_name());
     let expecting = cattrs.expecting().unwrap_or(&expecting);
 
@@ -1392,6 +1388,18 @@ fn deserialize_internally_tagged_enum(
     }
 }
 
+fn get_default_variant(variants: &[Variant]) -> Option<TokenStream> {
+    for (i, variant) in variants.iter().enumerate() {
+        if variant.attrs.default() {
+            let variant_name = field_i(i);
+            return Some(quote! {
+                std::option::Option::Some(__Field::#variant_name)
+            });
+        }
+    }
+    None
+}
+
 fn deserialize_adjacently_tagged_enum(
     params: &Parameters,
     variants: &[Variant],

serde_derive/src/internals/ast.rs

@@ -156,7 +156,6 @@ fn enum_from_ast<'a>(
         })
         .collect();
 
-    // Check only one enum arm is marked #[serde(default)]
     let mut has_default = false;
     for variant in &variants {
         if !variant.attrs.default() {