[parser] Parse import.meta

Summary:
Allows parsing of `import.meta`, which is in the latest standard (from ES2020). While we don't type-check it or other `MetaProperty`s (e.g. `new.target`), at least it's not a parse error so someone can just use `$FlowFixMe` now.

There was a PR for this but it was 3 years old, didn't have parser tests, so I just implemented from scratch myself here instead.

Fixes #6913
Closes #6958

Changelog: [feature] Added parser support for `import.meta`

Reviewed By: mroch

Differential Revision: D30716916

fbshipit-source-id: eb5c5ec53d34d46c228e89137d6a4da8d0839e84

src/parser/expression_parser.ml

@@ -69,6 +69,14 @@ module Expression
             comments = _;
           } ) ->
       false
+    | ( _,
+        MetaProperty
+          {
+            MetaProperty.meta = (_, { Identifier.name = "import"; comments = _ });
+            property = (_, { Identifier.name = "meta"; comments = _ });
+            comments = _;
+          } ) ->
+      false
     (* #sec-static-semantics-static-semantics-isvalidsimpleassignmenttarget *)
     | (_, Array _)
     | (_, Identifier _)
@@ -258,6 +266,14 @@ module Expression
             comments = _;
           } ) ->
       false
+    | ( _,
+        MetaProperty
+          {
+            MetaProperty.meta = (_, { Identifier.name = "import"; comments = _ });
+            property = (_, { Identifier.name = "meta"; comments = _ });
+            comments = _;
+          } ) ->
+      false
     (* #sec-static-semantics-static-semantics-isvalidsimpleassignmenttarget *)
     | (_, Identifier _)
     | (_, Member _)
@@ -677,17 +693,32 @@ module Expression
     with_loc
       (fun env ->
         let leading = Peek.comments env in
+        let start_loc = Peek.loc env in
         Expect.token env T_IMPORT;
-        let leading_arg = Peek.comments env in
-        Expect.token env T_LPAREN;
-        let argument = add_comments (assignment (with_no_in false env)) ~leading:leading_arg in
-        Expect.token env T_RPAREN;
-        let trailing = Eat.trailing_comments env in
-        Expression.Import
-          {
-            Expression.Import.argument;
-            comments = Flow_ast_utils.mk_comments_opt ~leading ~trailing ();
-          })
+        if Eat.maybe env T_PERIOD then (
+          (* import.meta *)
+          let import_ident = Flow_ast_utils.ident_of_source (start_loc, "import") in
+          let meta_loc = Peek.loc env in
+          Expect.identifier env "meta";
+          let meta_ident = Flow_ast_utils.ident_of_source (meta_loc, "meta") in
+          let trailing = Eat.trailing_comments env in
+          Expression.MetaProperty
+            {
+              Expression.MetaProperty.meta = import_ident;
+              property = meta_ident;
+              comments = Flow_ast_utils.mk_comments_opt ~leading ~trailing ();
+            }
+        ) else
+          let leading_arg = Peek.comments env in
+          Expect.token env T_LPAREN;
+          let argument = add_comments (assignment (with_no_in false env)) ~leading:leading_arg in
+          Expect.token env T_RPAREN;
+          let trailing = Eat.trailing_comments env in
+          Expression.Import
+            {
+              Expression.Import.argument;
+              comments = Flow_ast_utils.mk_comments_opt ~leading ~trailing ();
+            })
       env
 
   and call_cover ?(allow_optional_chain = true) ?(in_optional_chain = false) env start_loc left =

src/parser/parser_flow.ml

@@ -135,7 +135,9 @@ module rec Parse : PARSER = struct
       error_on_decorators env decorators;
       let statement =
         match Peek.ith_token ~i:1 env with
-        | T_LPAREN -> Statement.expression env
+        | T_LPAREN (* import(...) *)
+        | T_PERIOD (* import.meta *) ->
+          Statement.expression env
         | _ -> Statement.import_declaration env
       in
       statement

src/parser/test/flow/meta_property/import_meta.js

@@ -0,0 +1 @@
+import.meta;

src/parser/test/flow/meta_property/import_meta.tree.json

@@ -0,0 +1,35 @@
+{
+  "type":"Program",
+  "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":12}},
+  "range":[0,12],
+  "body":[
+    {
+      "type":"ExpressionStatement",
+      "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":12}},
+      "range":[0,12],
+      "expression":{
+        "type":"MetaProperty",
+        "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":11}},
+        "range":[0,11],
+        "meta":{
+          "type":"Identifier",
+          "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":6}},
+          "range":[0,6],
+          "name":"import",
+          "typeAnnotation":null,
+          "optional":false
+        },
+        "property":{
+          "type":"Identifier",
+          "loc":{"source":null,"start":{"line":1,"column":7},"end":{"line":1,"column":11}},
+          "range":[7,11],
+          "name":"meta",
+          "typeAnnotation":null,
+          "optional":false
+        }
+      },
+      "directive":null
+    }
+  ],
+  "comments":[]
+}

src/parser/test/flow/meta_property/import_meta_assign.js

@@ -0,0 +1 @@
+import.meta = 1;

src/parser/test/flow/meta_property/import_meta_assign.tree.json

@@ -0,0 +1,54 @@
+{
+  "errors":[
+    {
+      "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":11}},
+      "message":"Invalid left-hand side in assignment"
+    }
+  ],
+  "type":"Program",
+  "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":16}},
+  "range":[0,16],
+  "body":[
+    {
+      "type":"ExpressionStatement",
+      "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":16}},
+      "range":[0,16],
+      "expression":{
+        "type":"AssignmentExpression",
+        "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":15}},
+        "range":[0,15],
+        "operator":"=",
+        "left":{
+          "type":"MetaProperty",
+          "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":11}},
+          "range":[0,11],
+          "meta":{
+            "type":"Identifier",
+            "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":6}},
+            "range":[0,6],
+            "name":"import",
+            "typeAnnotation":null,
+            "optional":false
+          },
+          "property":{
+            "type":"Identifier",
+            "loc":{"source":null,"start":{"line":1,"column":7},"end":{"line":1,"column":11}},
+            "range":[7,11],
+            "name":"meta",
+            "typeAnnotation":null,
+            "optional":false
+          }
+        },
+        "right":{
+          "type":"Literal",
+          "loc":{"source":null,"start":{"line":1,"column":14},"end":{"line":1,"column":15}},
+          "range":[14,15],
+          "value":1,
+          "raw":"1"
+        }
+      },
+      "directive":null
+    }
+  ],
+  "comments":[]
+}

src/parser/test/flow/meta_property/import_not_meta.js

@@ -0,0 +1 @@
+import.foo;

src/parser/test/flow/meta_property/import_not_meta.tree.json

@@ -0,0 +1,41 @@
+{
+  "errors":[
+    {
+      "loc":{"source":null,"start":{"line":1,"column":7},"end":{"line":1,"column":10}},
+      "message":"Unexpected identifier, expected the identifier `meta`"
+    }
+  ],
+  "type":"Program",
+  "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":11}},
+  "range":[0,11],
+  "body":[
+    {
+      "type":"ExpressionStatement",
+      "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":11}},
+      "range":[0,11],
+      "expression":{
+        "type":"MetaProperty",
+        "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":10}},
+        "range":[0,10],
+        "meta":{
+          "type":"Identifier",
+          "loc":{"source":null,"start":{"line":1,"column":0},"end":{"line":1,"column":6}},
+          "range":[0,6],
+          "name":"import",
+          "typeAnnotation":null,
+          "optional":false
+        },
+        "property":{
+          "type":"Identifier",
+          "loc":{"source":null,"start":{"line":1,"column":7},"end":{"line":1,"column":10}},
+          "range":[7,10],
+          "name":"meta",
+          "typeAnnotation":null,
+          "optional":false
+        }
+      },
+      "directive":null
+    }
+  ],
+  "comments":[]
+}