go/types: close scope for each "select" case after its body

Classic Go pitfall: "defer" in a loop does not do what you might expect.

+ test case

Fixes issue 9570
Fixes issue 9569

Change-Id: Iec05420872ef71190083a7192f76c92f54f4a2a1
Reviewed-on: https://go-review.googlesource.com/2655
Reviewed-by: Robert Griesemer <gri@golang.org>

go/types/stmt.go

@@ -569,11 +569,11 @@ func (check *Checker) stmt(ctxt stmtContext, s ast.Stmt) {
 			}
 
 			check.openScope(s, "case")
-			defer check.closeScope()
 			if clause.Comm != nil {
 				check.stmt(inner, clause.Comm)
 			}
 			check.stmtList(inner, clause.Body)
+			check.closeScope()
 		}
 
 	case *ast.ForStmt:

go/types/testdata/stmt0.src

@@ -215,6 +215,17 @@ func selects() {
 	case x /* ERROR send or receive */ :
 	case a /* ERROR send or receive */ := ch:
 	}
+
+	// test for issue 9570: ch2 in second case falsely resolved to
+	// ch2 declared in body of first case
+	ch1 := make(chan int)
+	ch2 := make(chan int)
+	select {
+	case <-ch1:
+		var ch2 /* ERROR ch2 declared but not used */ chan bool
+	case i := <-ch2:
+		print(i + 1)
+	}
 }
 
 func gos() {