Add constant write node

Author: kddnewton

config.yml

@@ -873,19 +873,35 @@ nodes:
       - name: value
         type: node?
     comment: |
-      Represents writing to a constant.
+      Represents writing to a constant path.
 
-          Foo = 1
-          ^^^^^^^
+          ::Foo = 1
+          ^^^^^^^^^
 
           Foo::Bar = 1
           ^^^^^^^^^^^^
+
+          ::Foo::Bar = 1
+          ^^^^^^^^^^^^^^
   - name: ConstantReadNode
     comment: |
       Represents referencing a constant.
 
           Foo
           ^^^
+  - name: ConstantWriteNode
+    child_nodes:
+      - name: name_loc
+        type: location
+      - name: value
+        type: node?
+      - name: operator_loc
+        type: location?
+    comment: |
+      Represents writing to a constant.
+
+          Foo = 1
+          ^^^^^^^
   - name: DefNode
     child_nodes:
       - name: name_loc

src/yarp.c

@@ -1700,6 +1700,27 @@ yp_constant_read_node_create(yp_parser_t *parser, const yp_token_t *name) {
     return node;
 }
 
+// Allocate a new ConstantWriteNode node.
+static yp_constant_write_node_t *
+yp_constant_write_node_create(yp_parser_t *parser, yp_constant_read_node_t *target, const yp_token_t *operator, yp_node_t *value) {
+    yp_constant_write_node_t *node = YP_ALLOC_NODE(parser, yp_constant_write_node_t);
+
+    *node = (yp_constant_write_node_t) {
+        {
+            .type = YP_NODE_CONSTANT_WRITE_NODE,
+            .location = {
+                .start = target->base.location.start,
+                .end = value != NULL ? value->location.end : target->base.location.end
+            },
+        },
+        .name_loc = YP_LOCATION_NODE_VALUE((yp_node_t *) target),
+        .operator_loc = YP_OPTIONAL_LOCATION_TOKEN_VALUE(operator),
+        .value = value
+    };
+
+    return node;
+}
+
 // Allocate and initialize a new DefNode node.
 static yp_def_node_t *
 yp_def_node_create(
@@ -7540,8 +7561,9 @@ parse_target(yp_parser_t *parser, yp_node_t *target, yp_token_t *operator, yp_no
             return (yp_node_t *) write_node;
         }
         case YP_NODE_CONSTANT_PATH_NODE:
-        case YP_NODE_CONSTANT_READ_NODE:
             return (yp_node_t *) yp_constant_path_write_node_create(parser, target, operator, value);
+        case YP_NODE_CONSTANT_READ_NODE:
+            return (yp_node_t *) yp_constant_write_node_create(parser, (yp_constant_read_node_t *) target, operator, value);
         case YP_NODE_BACK_REFERENCE_READ_NODE:
         case YP_NODE_NUMBERED_REFERENCE_READ_NODE:
             yp_diagnostic_list_append(&parser->error_list, target->location.start, target->location.end, "Can't set variable");