go/parser: accept parenthesized receive operations in select statements

R=rsc
CC=golang-dev
https://golang.org/cl/4439082

src/pkg/go/parser/parser.go

@@ -1780,10 +1780,6 @@ func (p *parser) parseCommClause() *ast.CommClause {
 				rhs = lhs[0]
 				lhs = nil // there is no lhs
 			}
-			if x, isUnary := rhs.(*ast.UnaryExpr); !isUnary || x.Op != token.ARROW {
-				p.errorExpected(rhs.Pos(), "send or receive operation")
-				rhs = &ast.BadExpr{rhs.Pos(), rhs.End()}
-			}
 			if lhs != nil {
 				comm = &ast.AssignStmt{lhs, pos, tok, []ast.Expr{rhs}}
 			} else {

src/pkg/go/parser/parser_test.go

@@ -51,6 +51,7 @@ var validPrograms = []interface{}{
 	`package p; type T []int; func f() { for _ = range []int{T{42}[0]} {} };`,
 	`package p; var a = T{{1, 2}, {3, 4}}`,
 	`package p; func f() { select { case <- c: case c <- d: case c <- <- d: case <-c <- d: } };`,
+	`package p; func f() { select { case x := (<-c): } };`,
 	`package p; func f() { if ; true {} };`,
 	`package p; func f() { switch ; {} };`,
 }