Implements alias annotation and allow multiple deserialization renames.

test_suite/tests/ui/conflict/internal-tag-alias.rs

@@ -0,0 +1,12 @@
+use serde_derive::Serialize;
+
+#[derive(Serialize)]
+#[serde(tag = "conflict")]
+enum E {
+    A {
+        #[serde(alias = "conflict")]
+        x: (),
+    },
+}
+
+fn main() {}

test_suite/tests/ui/conflict/internal-tag-alias.stderr

@@ -0,0 +1,14 @@
+error: variant field name `conflict` conflicts with internal tag
+  --> $DIR/internal-tag-alias.rs:4:1
+   |
+4  | / #[serde(tag = "conflict")]
+5  | | enum E {
+6  | |     A {
+7  | |         #[serde(alias = "conflict")]
+8  | |         x: (),
+9  | |     },
+10 | | }
+   | |_^
+
+error: aborting due to previous error
+

test_suite/tests/ui/duplicate-attribute/rename-rename-de.rs

@@ -1,10 +0,0 @@
-use serde_derive::Serialize;
-
-#[derive(Serialize)]
-struct S {
-    #[serde(rename = "x")]
-    #[serde(rename(deserialize = "y"))]
-    x: (),
-}
-
-fn main() {}

test_suite/tests/ui/duplicate-attribute/rename-rename-de.stderr

@@ -1,8 +0,0 @@
-error: duplicate serde attribute `rename`
- --> $DIR/rename-rename-de.rs:6:13
-  |
-6 |     #[serde(rename(deserialize = "y"))]
-  |             ^^^^^^
-
-error: aborting due to previous error
-