Merge pull request #9890 from Microsoft/cast_of_await

Allow `await` in a simple unary expression

Author: Andy

src/compiler/parser.ts

@@ -3417,6 +3417,7 @@ namespace ts {
          *      6) - UnaryExpression[?yield]
          *      7) ~ UnaryExpression[?yield]
          *      8) ! UnaryExpression[?yield]
+         *      9) [+Await] await UnaryExpression[?yield]
          */
         function parseSimpleUnaryExpression(): UnaryExpression {
             switch (token()) {
@@ -3431,6 +3432,8 @@ namespace ts {
                     return parseTypeOfExpression();
                 case SyntaxKind.VoidKeyword:
                     return parseVoidExpression();
+                case SyntaxKind.AwaitKeyword:
+                    return parseAwaitExpression();
                 case SyntaxKind.LessThanToken:
                     // This is modified UnaryExpression grammar in TypeScript
                     //  UnaryExpression (modified):

tests/baselines/reference/castOfAwait.js

@@ -0,0 +1,28 @@
+//// [castOfAwait.ts]
+async function f() {
+    <number> await 0;
+    typeof await 0;
+    void await 0;
+    await void <string> typeof <number> void await 0;
+    await await 0;
+}
+
+
+//// [castOfAwait.js]
+var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
+    return new (P || (P = Promise))(function (resolve, reject) {
+        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
+        function rejected(value) { try { step(generator.throw(value)); } catch (e) { reject(e); } }
+        function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
+        step((generator = generator.apply(thisArg, _arguments)).next());
+    });
+};
+function f() {
+    return __awaiter(this, void 0, void 0, function* () {
+        yield 0;
+        typeof yield 0;
+        void yield 0;
+        yield void typeof void yield 0;
+        yield yield 0;
+    });
+}

tests/baselines/reference/castOfAwait.symbols

@@ -0,0 +1,11 @@
+=== tests/cases/compiler/castOfAwait.ts ===
+async function f() {
+>f : Symbol(f, Decl(castOfAwait.ts, 0, 0))
+
+    <number> await 0;
+    typeof await 0;
+    void await 0;
+    await void <string> typeof <number> void await 0;
+    await await 0;
+}
+

tests/baselines/reference/castOfAwait.types

@@ -0,0 +1,35 @@
+=== tests/cases/compiler/castOfAwait.ts ===
+async function f() {
+>f : () => Promise<void>
+
+    <number> await 0;
+><number> await 0 : number
+>await 0 : number
+>0 : number
+
+    typeof await 0;
+>typeof await 0 : string
+>await 0 : number
+>0 : number
+
+    void await 0;
+>void await 0 : undefined
+>await 0 : number
+>0 : number
+
+    await void <string> typeof <number> void await 0;
+>await void <string> typeof <number> void await 0 : any
+>void <string> typeof <number> void await 0 : undefined
+><string> typeof <number> void await 0 : string
+>typeof <number> void await 0 : string
+><number> void await 0 : number
+>void await 0 : undefined
+>await 0 : number
+>0 : number
+
+    await await 0;
+>await await 0 : number
+>await 0 : number
+>0 : number
+}
+

tests/baselines/reference/castOfYield.errors.txt

@@ -0,0 +1,12 @@
+tests/cases/compiler/castOfYield.ts(4,14): error TS1109: Expression expected.
+
+
+==== tests/cases/compiler/castOfYield.ts (1 errors) ====
+    function* f() {
+        <number> (yield 0);
+        // Unlike await, yield is not allowed to appear in a simple unary expression.
+        <number> yield 0;
+                 ~~~~~
+!!! error TS1109: Expression expected.
+    }
+    

tests/baselines/reference/castOfYield.js

@@ -0,0 +1,15 @@
+//// [castOfYield.ts]
+function* f() {
+    <number> (yield 0);
+    // Unlike await, yield is not allowed to appear in a simple unary expression.
+    <number> yield 0;
+}
+
+
+//// [castOfYield.js]
+function f() {
+    (yield 0);
+    // Unlike await, yield is not allowed to appear in a simple unary expression.
+    ;
+    yield 0;
+}

tests/cases/compiler/castOfAwait.ts

@@ -0,0 +1,8 @@
+// @target: es6
+async function f() {
+    <number> await 0;
+    typeof await 0;
+    void await 0;
+    await void <string> typeof <number> void await 0;
+    await await 0;
+}

tests/cases/compiler/castOfYield.ts

@@ -0,0 +1,5 @@
+function* f() {
+    <number> (yield 0);
+    // Unlike await, yield is not allowed to appear in a simple unary expression.
+    <number> yield 0;
+}