Create parser plugin "topLevelAwait" (#10449)

* Create parser plugin "topLevelAwait"

* Update test262 whitelist

* Update ts typings

* Fix "sourceType: unambiguous" with TLA

* Ambiguous tokens after await

* Update await %x(0)

* typo [skip ci]

* Typo [skip ci]

Co-Authored-By: Brian Ng <bng412@gmail.com>

packages/babel-parser/src/parser/base.js

@@ -13,6 +13,7 @@ export default class BaseParser {
   plugins: PluginsMap;
   filename: ?string;
   sawUnambiguousESM: boolean = false;
+  ambiguousScriptDifferentAst: boolean = false;
 
   // Initialized by Tokenizer
   state: State;

packages/babel-parser/src/parser/expression.js

@@ -2208,6 +2208,7 @@ export default class ExpressionParser extends LValParser {
   isAwaitAllowed(): boolean {
     if (this.scope.inFunction) return this.scope.inAsync;
     if (this.options.allowAwaitOutsideFunction) return true;
+    if (this.hasPlugin("topLevelAwait")) return this.inModule;
     return false;
   }
 
@@ -2234,9 +2235,33 @@ export default class ExpressionParser extends LValParser {
       );
     }
 
+    if (!this.scope.inFunction && !this.options.allowAwaitOutsideFunction) {
+      if (
+        this.hasPrecedingLineBreak() ||
+        // All the following expressions are ambiguous:
+        //   await + 0, await - 0, await ( 0 ), await [ 0 ], await / 0 /u, await ``
+        this.match(tt.plusMin) ||
+        this.match(tt.parenL) ||
+        this.match(tt.bracketL) ||
+        this.match(tt.backQuote) ||
+        // Sometimes the tokenizer generates tt.slash for regexps, and this is
+        // handler by parseExprAtom
+        this.match(tt.regexp) ||
+        this.match(tt.slash) ||
+        // This code could be parsed both as a modulo operator or as an intrinsic:
+        //   await %x(0)
+        (this.hasPlugin("v8intrinsic") && this.match(tt.modulo))
+      ) {
+        this.ambiguousScriptDifferentAst = true;
+      } else {
+        this.sawUnambiguousESM = true;
+      }
+    }
+
     if (!this.state.soloAwait) {
       node.argument = this.parseMaybeUnary();
     }
+
     return this.finishNode(node, "AwaitExpression");
   }
 

packages/babel-parser/src/parser/statement.js

@@ -495,11 +495,7 @@ export default class StatementParser extends ExpressionParser {
     this.state.labels.push(loopLabel);
 
     let awaitAt = -1;
-    if (
-      (this.scope.inAsync ||
-        (!this.scope.inFunction && this.options.allowAwaitOutsideFunction)) &&
-      this.eatContextual("await")
-    ) {
+    if (this.isAwaitAllowed() && this.eatContextual("await")) {
       awaitAt = this.state.lastTokStart;
     }
     this.scope.enter(SCOPE_OTHER);