cmd/gc: accept switches on comparable arrays.

The compiler is incorrectly rejecting switches on arrays of
comparable types. It also doesn't catch incomparable structs
when typechecking the switch, leading to unreadable errors
during typechecking of the generated code.

Fixes issue 3894.

R=rsc
CC=gobot, golang-dev, r, remy
http://codereview.appspot.com/6442074

1 files changed, 32 insertions, 0 deletions

diff --git a/test/switch.go b/test/switch.go
index 09bf4341a..a4242f257 100644
--- a/test/switch.go
+++ b/test/switch.go
@@ -284,6 +284,38 @@ func main() {
 	default:
 	}
 
+	// switch on interface.
+	switch i := interface{}("hello"); i {
+	case 42:
+		assert(false, `i should be "hello"`)
+	case "hello":
+		assert(true, "hello")
+	default:
+		assert(false, `i should be "hello"`)
+	}
+
+	// switch on array.
+	switch ar := [3]int{1, 2, 3}; ar {
+	case [3]int{1,2,3}:
+		assert(true, "[1 2 3]")
+	case [3]int{4,5,6}:
+		assert(false, "ar should be [1 2 3]")
+	default:
+		assert(false, "ar should be [1 2 3]")
+	}
+
+	// switch on channel
+	switch c1, c2 := make(chan int), make(chan int); c1 {
+	case nil:
+		assert(false, "c1 did not match itself")
+	case c2:
+		assert(false, "c1 did not match itself")
+	case c1:
+		assert(true, "chan")
+	default:
+		assert(false, "c1 did not match itself")
+	}
+
 	i := 0
 	switch x := 5; {
 		case i < x: