service: add backend to GetVersion response (#1641)

Implements #1640

service/api/types.go

@@ -415,6 +415,7 @@ type GetVersionIn struct {
 type GetVersionOut struct {
 	DelveVersion string
 	APIVersion   int
+	Backend      string // backend currently in use
 }
 
 // SetAPIVersionIn is the input for SetAPIVersion.

service/debugger/debugger.go

@@ -1207,6 +1207,27 @@ func (d *Debugger) ListDynamicLibraries() []api.Image {
 	return r
 }
 
+func (d *Debugger) GetVersion(out *api.GetVersionOut) error {
+	if d.config.CoreFile != "" {
+		if d.config.Backend == "rr" {
+			out.Backend = "rr"
+		} else {
+			out.Backend = "core"
+		}
+	} else {
+		if d.config.Backend == "default" {
+			if runtime.GOOS == "darwin" {
+				out.Backend = "lldb"
+			} else {
+				out.Backend = "native"
+			}
+		} else {
+			out.Backend = d.config.Backend
+		}
+	}
+	return nil
+}
+
 func go11DecodeErrorCheck(err error) error {
 	if _, isdecodeerr := err.(dwarf.DecodeError); !isdecodeerr {
 		return err

service/rpccommon/server.go

@@ -387,7 +387,7 @@ func (cb *RPCCallback) Return(out interface{}, err error) {
 func (s *RPCServer) GetVersion(args api.GetVersionIn, out *api.GetVersionOut) error {
 	out.DelveVersion = version.DelveVersion.String()
 	out.APIVersion = s.s.config.APIVersion
-	return nil
+	return s.s.debugger.GetVersion(out)
 }
 
 // Changes version of the API being served.