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 #3894.

R=rsc
CC=gobot, golang-dev, r, remy
https://golang.org/cl/6442074

1 files changed, 32 insertions, 0 deletions

diff --git a/test/switch.go b/test/switch.go
index 09bf4341a0..a4242f2571 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: