[parser] forbid reserved types in opaque type

Summary: `opaque type string = number` would overwrite the `string` builtin. reserved types should be disallowed.

Reviewed By: samwgoldman

Differential Revision: D6199767

fbshipit-source-id: f0f5bdf44d8cff0d444381747f0ebb5a94df3ffa

src/parser/statement_parser.ml

@@ -558,7 +558,7 @@ module Statement
     Expect.token env T_OPAQUE;
     Expect.token env T_TYPE;
     Eat.push_lex_mode env Lex_mode.TYPE;
-    let id = Parse.identifier env in
+    let id = Type.type_identifier env in
     let typeParameters = Type.type_parameter_declaration_with_defaults env in
     let supertype = match Peek.token env with
     | T_COLON ->

src/parser/test/flow/types/opaque_aliases/invalid/reserved_type.js

@@ -0,0 +1 @@
+opaque type string = number;

src/parser/test/flow/types/opaque_aliases/invalid/reserved_type.tree.json

@@ -0,0 +1,34 @@
+{
+  "errors":[
+    {
+      "loc":{"source":null,"start":{"line":1,"column":12},"end":{"line":1,"column":18}},
+      "message":"Unexpected reserved type"
+    }
+  ],
+  "type":"Program",
+  "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":28}},
+  "range":[0,28],
+  "body":[
+    {
+      "type":"OpaqueType",
+      "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":28}},
+      "range":[0,28],
+      "id":{
+        "type":"Identifier",
+        "loc":{"source":null,"start":{"line":1,"column":12},"end":{"line":1,"column":18}},
+        "range":[12,18],
+        "name":"string",
+        "typeAnnotation":null,
+        "optional":false
+      },
+      "typeParameters":null,
+      "impltype":{
+        "type":"NumberTypeAnnotation",
+        "loc":{"source":null,"start":{"line":1,"column":21},"end":{"line":1,"column":27}},
+        "range":[21,27]
+      },
+      "supertype":null
+    }
+  ],
+  "comments":[]
+}

src/parser/test/flow/types/opaque_aliases/valid/reserved_value.js

@@ -0,0 +1 @@
+opaque type switch = number;

src/parser/test/flow/types/opaque_aliases/valid/reserved_value.tree.json

@@ -0,0 +1,28 @@
+{
+  "type":"Program",
+  "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":28}},
+  "range":[0,28],
+  "body":[
+    {
+      "type":"OpaqueType",
+      "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":28}},
+      "range":[0,28],
+      "id":{
+        "type":"Identifier",
+        "loc":{"source":null,"start":{"line":1,"column":12},"end":{"line":1,"column":18}},
+        "range":[12,18],
+        "name":"switch",
+        "typeAnnotation":null,
+        "optional":false
+      },
+      "typeParameters":null,
+      "impltype":{
+        "type":"NumberTypeAnnotation",
+        "loc":{"source":null,"start":{"line":1,"column":21},"end":{"line":1,"column":27}},
+        "range":[21,27]
+      },
+      "supertype":null
+    }
+  ],
+  "comments":[]
+}