Permit impl item to end with semicolon (#118)

* Add test with semicolons after an impl signature

* Permit impl item to end with semicolon

* Regenerate parser

Author: dtolnay

corpus/declarations.txt

@@ -970,6 +970,31 @@ unsafe impl Foo {
 
 (source_file (impl_item (type_identifier) (declaration_list)))
 
+===========================================
+Trait impl signature
+===========================================
+
+impl<K: Debug + Ord> Debug for OccupiedError<K>;
+impl<K: Debug + Ord> Display for OccupiedError<K>;
+
+---
+
+(source_file
+  (impl_item
+    (type_parameters
+      (constrained_type_parameter
+        (type_identifier)
+          (trait_bounds (type_identifier) (type_identifier))))
+    (type_identifier)
+    (generic_type (type_identifier) (type_arguments (type_identifier))))
+  (impl_item
+    (type_parameters
+      (constrained_type_parameter
+        (type_identifier)
+        (trait_bounds (type_identifier) (type_identifier))))
+    (type_identifier)
+    (generic_type (type_identifier) (type_arguments (type_identifier)))))
+
 ===========================================
 Impls with default functions
 ===========================================

grammar.js

@@ -464,7 +464,7 @@ module.exports = grammar({
       )),
       field('type', $._type),
       optional($.where_clause),
-      field('body', $.declaration_list)
+      choice(field('body', $.declaration_list), ';')
     ),
 
     trait_item: $ => seq(

src/grammar.json

@@ -2602,12 +2602,21 @@
           ]
         },
         {
-          "type": "FIELD",
-          "name": "body",
-          "content": {
-            "type": "SYMBOL",
-            "name": "declaration_list"
-          }
+          "type": "CHOICE",
+          "members": [
+            {
+              "type": "FIELD",
+              "name": "body",
+              "content": {
+                "type": "SYMBOL",
+                "name": "declaration_list"
+              }
+            },
+            {
+              "type": "STRING",
+              "value": ";"
+            }
+          ]
         }
       ]
     },

src/node-types.json

@@ -2113,7 +2113,7 @@
     "fields": {
       "body": {
         "multiple": false,
-        "required": true,
+        "required": false,
         "types": [
           {
             "type": "declaration_list",