service/dap: support evaluate for hover context (#2496)

We can support evaluate for hover context in order to provide more
useful hover info for our users.

Updates go-delve/delve#2491
Updates golang/vscode-go#1510

service/dap/daptest/client.go

@@ -102,6 +102,7 @@ func (c *Client) ExpectInitializeResponseAndCapabilities(t *testing.T) *dap.Init
 		SupportTerminateDebuggee:         true,
 		SupportsExceptionInfoRequest:     true,
 		SupportsFunctionBreakpoints:      true,
+		SupportsEvaluateForHovers:        true,
 	}
 	if !reflect.DeepEqual(initResp.Body, wantCapabilities) {
 		t.Errorf("capabilities in initializeResponse: got %+v, want %v", pretty(initResp.Body), pretty(wantCapabilities))

service/dap/server.go

@@ -677,6 +677,7 @@ func (s *Server) onInitializeRequest(request *dap.InitializeRequest) {
 	response.Body.SupportTerminateDebuggee = true
 	response.Body.SupportsFunctionBreakpoints = true
 	response.Body.SupportsExceptionInfoRequest = true
+	response.Body.SupportsEvaluateForHovers = true
 	// TODO(polina): support this to match vscode-go functionality
 	response.Body.SupportsSetVariable = false
 	// TODO(polina): support these requests in addition to vscode-go feature parity
@@ -1755,7 +1756,7 @@ func (s *Server) convertVariableWithOpts(v *proc.Variable, qualifiedNameOrExpr s
 // variables, so consider also adding the following:
 // -- print {expression} - return the result as a string like from dlv cli
 func (s *Server) onEvaluateRequest(request *dap.EvaluateRequest) {
-	showErrorToUser := request.Arguments.Context != "watch" && request.Arguments.Context != "repl"
+	showErrorToUser := request.Arguments.Context != "watch" && request.Arguments.Context != "repl" && request.Arguments.Context != "hover"
 	if s.debugger == nil {
 		s.sendErrorResponseWithOpts(request.Request, UnableToEvaluateExpression, "Unable to evaluate expression", "debugger is nil", showErrorToUser)
 		return

service/dap/server_test.go

@@ -2560,6 +2560,16 @@ func TestEvaluateRequest(t *testing.T) {
 					if erres.Body.Error.Format != "Unable to evaluate expression: could not find symbol value for a1" {
 						t.Errorf("\ngot %#v\nwant Format=\"Unable to evaluate expression: could not find symbol value for a1\"", erres)
 					}
+					client.EvaluateRequest("a1", 1002, "repl")
+					erres = client.ExpectInvisibleErrorResponse(t)
+					if erres.Body.Error.Format != "Unable to evaluate expression: could not find symbol value for a1" {
+						t.Errorf("\ngot %#v\nwant Format=\"Unable to evaluate expression: could not find symbol value for a1\"", erres)
+					}
+					client.EvaluateRequest("a1", 1002, "hover")
+					erres = client.ExpectInvisibleErrorResponse(t)
+					if erres.Body.Error.Format != "Unable to evaluate expression: could not find symbol value for a1" {
+						t.Errorf("\ngot %#v\nwant Format=\"Unable to evaluate expression: could not find symbol value for a1\"", erres)
+					}
 				},
 				disconnect: false,
 			}})