At master, the Go source below produces an error message about line 6:

/tmp/x.go:6: x repeated on left side of :=

However, the error actually originates on line 5, and this was correctly reported at least in Go 1.4.2.

package foo

func f() {
    select {
    case x, x := <-func() chan int {
            c := make(chan int)
            return c
    }():
    }
}

The problem is (*parser).case_ doesn't access p.op (which is storing the LCOLAS token's line number) until after the p.expr() call, which might invalidate p.op if it contains another LCOLAS or LASOP token.

Best fix seems to be to just save lineno before calling p.next() like case LCOLAS in (*parser).simple_stmt. Then _yylex doesn't need to save lexlineno in yylval.i either.

CC @griesemer