JS: fix parsing of for/for-of/for-in regarding LHSExpr vs Expr

js/parse.go

@@ -358,12 +358,15 @@ func (p *Parser) parseStmt(allowDeclaration bool) (stmt IStmt) {
 				}
 			}
 			init = varDecl
-		} else if p.tt != SemicolonToken {
+		} else if await {
 			init = p.parseExpression(OpLHS)
+		} else if p.tt != SemicolonToken {
+			init = p.parseExpression(OpExpr)
 		}
 		p.in = true
 
-		if p.tt == InToken {
+		isLHSExpr := isLHSExpr(init)
+		if isLHSExpr && p.tt == InToken {
 			if await {
 				p.fail("for statement", OfToken)
 				return
@@ -385,7 +388,7 @@ func (p *Parser) parseStmt(allowDeclaration bool) (stmt IStmt) {
 				varDecl.InForInOf = true
 			}
 			stmt = &ForInStmt{init, value, body}
-		} else if p.tt == OfToken {
+		} else if isLHSExpr && p.tt == OfToken {
 			p.next()
 			value := p.parseExpression(OpAssign)
 			if !p.consume("for statement", CloseParenToken) {
@@ -403,13 +406,7 @@ func (p *Parser) parseStmt(allowDeclaration bool) (stmt IStmt) {
 				varDecl.InForInOf = true
 			}
 			stmt = &ForOfStmt{await, init, value, body}
-		} else {
-			init = p.parseExpressionSuffix(init, OpExpr, OpLHS)
-			if p.tt != SemicolonToken {
-				p.fail("for statement", InToken, OfToken, SemicolonToken)
-				return
-			}
-
+		} else if p.tt == SemicolonToken {
 			var cond, post IExpr
 			if await {
 				p.fail("for statement", OfToken)
@@ -444,6 +441,12 @@ func (p *Parser) parseStmt(allowDeclaration bool) (stmt IStmt) {
 				varDecl.InFor = true
 			}
 			stmt = &ForStmt{init, cond, post, body}
+		} else if isLHSExpr {
+			p.fail("for statement", InToken, OfToken, SemicolonToken)
+			return
+		} else {
+			p.fail("for statement", SemicolonToken)
+			return
 		}
 		p.exitScope(parent)
 	case SwitchToken:

js/parse_test.go

@@ -69,8 +69,10 @@ func TestParse(t *testing.T) {
 		{"for (c && (a in b);;) {}", "Stmt(for (c&&((a in b))) ; ; Stmt({ }))"},
 		{"for (a in b) {}", "Stmt(for a in b Stmt({ }))"},
 		{"for (a = b;;) {}", "Stmt(for (a=b) ; ; Stmt({ }))"},
+		{"for (!a;;) {}", "Stmt(for (!a) ; ; Stmt({ }))"},
 		{"for (var [a] in b) {}", "Stmt(for Decl(var Binding([ Binding(a) ])) in b Stmt({ }))"},
-		{"for(async of b);", "Stmt(for async of b Stmt({ }))"},
+		{"for await (async of b);", "Stmt(for await async of b Stmt({ }))"},
+		{"for (async of => 5;;);", "Stmt(for (async Params(Binding(of)) => Stmt({ Stmt(return 5) })) ; ; Stmt({ }))"},
 		{"throw 5", "Stmt(throw 5)"},
 		{"try {} catch {b}", "Stmt(try Stmt({ }) catch Stmt({ Stmt(b) }))"},
 		{"try {} finally {c}", "Stmt(try Stmt({ }) finally Stmt({ Stmt(c) }))"},
@@ -460,6 +462,7 @@ func TestParseError(t *testing.T) {
 		{"for(var [a],b;", "unexpected ; in for statement"},
 		{"for(var [a]=5,{b};", "expected = instead of ; in var statement"},
 		{`for(let{[(`, `unexpected EOF in expression`},
+		{"for(async of b);", "expected => instead of b in arrow function"},
 		{"for await", "expected ( instead of EOF in for statement"},
 		{"function a(){for await", "expected ( instead of await in for statement"},
 		{"async function a(){ for await(a;", "expected of instead of ; in for statement"},

js/util.go

@@ -4,6 +4,14 @@ import (
 	"io"
 )
 
+func isLHSExpr(i IExpr) bool {
+	switch i.(type) {
+	case *CommaExpr, *CondExpr, *YieldExpr, *ArrowFunc, *BinaryExpr, *UnaryExpr:
+		return false
+	}
+	return true
+}
+
 // AsIdentifierName returns true if a valid identifier name is given.
 func AsIdentifierName(b []byte) bool {
 	if len(b) == 0 || !identifierStartTable[b[0]] {