internal/wayland: improve error handling

Note: wl_registry_add_listener is undocumented everywhere. Its implementation calls wl_proxy_add_listener which returns 0 on success or -1 on failure.
Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/wayland/wayland_test.go

@@ -0,0 +1,79 @@
+package wayland_test
+
+import (
+	"syscall"
+	"testing"
+
+	"hakurei.app/container/stub"
+	"hakurei.app/internal/wayland"
+)
+
+func TestError(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		err  wayland.Error
+		want string
+	}{
+		{"success", wayland.Error{
+			Cause: wayland.RSuccess,
+		}, "success"},
+
+		{"success errno", wayland.Error{
+			Cause: wayland.RSuccess,
+			Errno: stub.UniqueError(0),
+		}, "unique error 0 injected by the test suite"},
+
+		{"wl_display_connect_to_fd", wayland.Error{
+			Cause: wayland.RConnect,
+			Errno: stub.UniqueError(1),
+		}, "wl_display_connect_to_fd failed: unique error 1 injected by the test suite"},
+
+		{"wl_registry_add_listener", wayland.Error{
+			Cause: wayland.RListener,
+			Errno: stub.UniqueError(2),
+		}, "wl_registry_add_listener failed: unique error 2 injected by the test suite"},
+
+		{"wl_display_roundtrip", wayland.Error{
+			Cause: wayland.RRoundtrip,
+			Errno: stub.UniqueError(3),
+		}, "wl_display_roundtrip failed: unique error 3 injected by the test suite"},
+
+		{"not available", wayland.Error{
+			Cause: wayland.RNotAvail,
+		}, "compositor does not implement security_context_v1"},
+
+		{"not available errno", wayland.Error{
+			Cause: wayland.RNotAvail,
+			Errno: syscall.EAGAIN,
+		}, "compositor does not implement security_context_v1"},
+
+		{"socket", wayland.Error{
+			Cause: wayland.RSocket,
+			Errno: stub.UniqueError(4),
+		}, "unique error 4 injected by the test suite"},
+
+		{"socket invalid", wayland.Error{
+			Cause: wayland.RSocket,
+		}, "socket operation failed"},
+
+		{"invalid", wayland.Error{
+			Cause: 0xbad,
+		}, "impossible outcome"},
+
+		{"invalid errno", wayland.Error{
+			Cause: 0xbad,
+			Errno: stub.UniqueError(5),
+		}, "impossible outcome: unique error 5 injected by the test suite"},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := tc.err.Message(); got != tc.want {
+				t.Errorf("Message: %q, want %q", got, tc.want)
+			}
+		})
+	}
+}