Fix deriving for single-variant enums

src/libsyntax/ext/deriving.rs

@@ -698,26 +698,30 @@ fn expand_deriving_eq_enum_method(cx: ext_ctxt,
         };
         other_arms.push(move matching_arm);
 
-        // Create the nonmatching pattern.
-        let nonmatching_pat = @{
-            id: cx.next_id(),
-            node: pat_wild,
-            span: span
-        };
-
-        // Create the nonmatching pattern body.
-        let nonmatching_expr = build::mk_bool(cx, span, !is_eq);
-        let nonmatching_body_block = build::mk_simple_block(cx,
-                                                            span,
-                                                            nonmatching_expr);
-
-        // Create the nonmatching arm.
-        let nonmatching_arm = {
-            pats: ~[ nonmatching_pat ],
-            guard: None,
-            body: move nonmatching_body_block
-        };
-        other_arms.push(move nonmatching_arm);
+        // Maybe generate a non-matching case. If there is only one
+        // variant then there will always be a match.
+        if enum_definition.variants.len() > 1 {
+            // Create the nonmatching pattern.
+            let nonmatching_pat = @{
+                id: cx.next_id(),
+                node: pat_wild,
+                span: span
+            };
+
+            // Create the nonmatching pattern body.
+            let nonmatching_expr = build::mk_bool(cx, span, !is_eq);
+            let nonmatching_body_block = build::mk_simple_block(cx,
+                                                                span,
+                                                                nonmatching_expr);
+
+            // Create the nonmatching arm.
+            let nonmatching_arm = {
+                pats: ~[ nonmatching_pat ],
+                guard: None,
+                body: move nonmatching_body_block
+            };
+            other_arms.push(move nonmatching_arm);
+        }
 
         // Create the self pattern.
         let self_pat = create_enum_variant_pattern(cx,

src/test/run-pass/deriving-enum-single-variant.rs

+type task_id = int;
+
+#[deriving_eq]
+pub enum Task {
+    TaskHandle(task_id)
+}
+
+fn main() { }