disallow the "await x ** 2" edge case

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+* Fix a commonly-missed corner case with `await` inside `**`
+
+    I recently discovered an interesting discussion about JavaScript syntax entitled ["Most implementations seem to have missed that `await x ** 2` is not legal"](https://github.com/tc39/ecma262/issues/2197). Indeed esbuild has missed this, but this is not surprising because V8 has missed this as well and I usually test esbuild against V8 to test if esbuild is conformant with the JavaScript standard. Regardless, it sounds like the result of the discussion is that the specification should stay the same and implementations should be fixed. This release fixes this bug in esbuild's parser. The syntax `await x ** 2` is no longer allowed and parentheses are now preserved for the syntax `(await x) ** 2`.
+
 ## 0.8.34
 
 * Fix a parser bug about suffix expressions after an arrow function body ([#701](https://github.com/evanw/esbuild/issues/701))

internal/js_parser/js_parser.go

@@ -2375,7 +2375,11 @@ func (p *parser) parsePrefix(level js_ast.L, errors *deferredErrors, flags exprF
 					if p.fnOrArrowDataParse.arrowArgErrors != nil {
 						p.fnOrArrowDataParse.arrowArgErrors.invalidExprAwait = nameRange
 					}
-					return js_ast.Expr{Loc: loc, Data: &js_ast.EAwait{Value: p.parseExpr(js_ast.LPrefix)}}
+					value := p.parseExpr(js_ast.LPrefix)
+					if p.lexer.Token == js_lexer.TAsteriskAsterisk {
+						p.lexer.Unexpected()
+					}
+					return js_ast.Expr{Loc: loc, Data: &js_ast.EAwait{Value: value}}
 				}
 			}
 

internal/js_parser/js_parser_test.go

@@ -229,6 +229,49 @@ func TestExponentiation(t *testing.T) {
 	expectParseError(t, "void x.y() ** 2", "<stdin>: error: Unexpected \"**\"\n")
 	expectParseError(t, "delete x.y() ** 2", "<stdin>: error: Unexpected \"**\"\n")
 	expectParseError(t, "typeof x.y() ** 2", "<stdin>: error: Unexpected \"**\"\n")
+
+	// https://github.com/tc39/ecma262/issues/2197
+	expectParseError(t, "delete x ** 0", "<stdin>: error: Unexpected \"**\"\n")
+	expectParseError(t, "delete x.prop ** 0", "<stdin>: error: Unexpected \"**\"\n")
+	expectParseError(t, "delete x[0] ** 0", "<stdin>: error: Unexpected \"**\"\n")
+	expectParseError(t, "delete x?.prop ** 0", "<stdin>: error: Unexpected \"**\"\n")
+	expectParseError(t, "void x ** 0", "<stdin>: error: Unexpected \"**\"\n")
+	expectParseError(t, "typeof x ** 0", "<stdin>: error: Unexpected \"**\"\n")
+	expectParseError(t, "+x ** 0", "<stdin>: error: Unexpected \"**\"\n")
+	expectParseError(t, "-x ** 0", "<stdin>: error: Unexpected \"**\"\n")
+	expectParseError(t, "~x ** 0", "<stdin>: error: Unexpected \"**\"\n")
+	expectParseError(t, "!x ** 0", "<stdin>: error: Unexpected \"**\"\n")
+	expectParseError(t, "await x ** 0", "<stdin>: error: Unexpected \"**\"\n")
+	expectParseError(t, "await -x ** 0", "<stdin>: error: Unexpected \"**\"\n")
+	expectPrinted(t, "(delete x) ** 0", "(delete x) ** 0;\n")
+	expectPrinted(t, "(delete x.prop) ** 0", "(delete x.prop) ** 0;\n")
+	expectPrinted(t, "(delete x[0]) ** 0", "(delete x[0]) ** 0;\n")
+	expectPrinted(t, "(delete x?.prop) ** 0", "(delete x?.prop) ** 0;\n")
+	expectPrinted(t, "(void x) ** 0", "(void x) ** 0;\n")
+	expectPrinted(t, "(typeof x) ** 0", "(typeof x) ** 0;\n")
+	expectPrinted(t, "(+x) ** 0", "(+x) ** 0;\n")
+	expectPrinted(t, "(-x) ** 0", "(-x) ** 0;\n")
+	expectPrinted(t, "(~x) ** 0", "(~x) ** 0;\n")
+	expectPrinted(t, "(!x) ** 0", "(!x) ** 0;\n")
+	expectPrinted(t, "(await x) ** 0", "(await x) ** 0;\n")
+	expectPrinted(t, "(await -x) ** 0", "(await -x) ** 0;\n")
+}
+
+func TestAwait(t *testing.T) {
+	expectPrinted(t, "await x", "await x;\n")
+	expectPrinted(t, "await +x", "await +x;\n")
+	expectPrinted(t, "await -x", "await -x;\n")
+	expectPrinted(t, "await ~x", "await ~x;\n")
+	expectPrinted(t, "await !x", "await !x;\n")
+	expectPrinted(t, "await --x", "await --x;\n")
+	expectPrinted(t, "await ++x", "await ++x;\n")
+	expectPrinted(t, "await x--", "await x--;\n")
+	expectPrinted(t, "await x++", "await x++;\n")
+	expectPrinted(t, "await void x", "await void x;\n")
+	expectPrinted(t, "await delete x", "await delete x;\n")
+	expectPrinted(t, "await typeof x", "await typeof x;\n")
+	expectPrinted(t, "await (x * y)", "await (x * y);\n")
+	expectPrinted(t, "await (x ** y)", "await (x ** y);\n")
 }
 
 func TestRegExp(t *testing.T) {

internal/js_parser/ts_parser_test.go

@@ -1283,6 +1283,12 @@ func TestTSNew(t *testing.T) {
 	expectParseError(t, "new Foo!()", "<stdin>: error: Unexpected \"!\"\n")
 }
 
+func TestTSExponentiation(t *testing.T) {
+	// More info: https://github.com/microsoft/TypeScript/issues/41755
+	expectParseErrorTS(t, "await x! ** 2", "<stdin>: error: Unexpected \"**\"\n")
+	expectPrintedTS(t, "await x as any ** 2", "(await x) ** 2;\n")
+}
+
 func TestTSImport(t *testing.T) {
 	expectPrintedTS(t, "import {x} from 'foo'", "")
 	expectPrintedTS(t, "import {x} from 'foo'; log(x)", "import {x} from \"foo\";\nlog(x);\n")

internal/js_printer/js_printer.go

@@ -1939,7 +1939,7 @@ func (p *printer) printExpr(expr js_ast.Expr, level js_ast.L, flags int) {
 		p.printSpaceBeforeIdentifier()
 		p.print("await")
 		p.printSpace()
-		p.printExpr(e.Value, js_ast.LPrefix, 0)
+		p.printExpr(e.Value, js_ast.LPrefix-1, 0)
 
 		if wrap {
 			p.print(")")
@@ -2038,6 +2038,8 @@ func (p *printer) printExpr(expr js_ast.Expr, level js_ast.L, flags int) {
 			// "**" can't contain certain unary expressions
 			if left, ok := e.Left.Data.(*js_ast.EUnary); ok && left.Op.UnaryAssignTarget() == js_ast.AssignTargetNone {
 				leftLevel = js_ast.LCall
+			} else if _, ok := e.Left.Data.(*js_ast.EAwait); ok {
+				leftLevel = js_ast.LCall
 			} else if _, ok := e.Left.Data.(*js_ast.EUndefined); ok {
 				// Undefined is printed as "void 0"
 				leftLevel = js_ast.LCall