service/dap: include selected goroutine in threads request

service/dap/server.go

@@ -193,7 +193,11 @@ const (
 	// what is presented. A common use case of a call injection is to
 	// stringify complex data conveniently.
 	maxStringLenInCallRetVars = 1 << 10 // 1024
+)
+
+var (
 	// Max number of goroutines that we will return.
+	// This is a var for testing
 	maxGoroutines = 1 << 10
 )
 
@@ -1358,8 +1362,8 @@ func (s *Server) onThreadsRequest(request *dap.ThreadsRequest) {
 	if s.debugger != nil {
 		gs, next, err = s.debugger.Goroutines(0, maxGoroutines)
 	}
-	threads := make([]dap.Thread, len(gs))
 
+	var threads []dap.Thread
 	if err != nil {
 		switch err.(type) {
 		case proc.ErrProcessExited:
@@ -1375,16 +1379,41 @@ func (s *Server) onThreadsRequest(request *dap.ThreadsRequest) {
 				}})
 		}
 		threads = []dap.Thread{{Id: 1, Name: "Dummy"}}
-	} else if len(threads) == 0 {
+	} else if len(gs) == 0 {
 		threads = []dap.Thread{{Id: 1, Name: "Dummy"}}
 	} else {
-		if next >= 0 {
-			s.logToConsole(fmt.Sprintf("Too many goroutines, only loaded %d", len(gs)))
-		}
 		state, err := s.debugger.State( /*nowait*/ true)
 		if err != nil {
 			s.log.Debug("Unable to get debugger state: ", err)
 		}
+
+		if next >= 0 {
+			s.logToConsole(fmt.Sprintf("Too many goroutines, only loaded %d", len(gs)))
+
+			// Make sure the selected goroutine is included in the list of threads
+			// to return.
+			if state != nil && state.SelectedGoroutine != nil {
+				var selectedFound bool
+				for _, g := range gs {
+					if g.ID == state.SelectedGoroutine.ID {
+						selectedFound = true
+						break
+					}
+				}
+				if !selectedFound {
+					g, err := s.debugger.FindGoroutine(state.SelectedGoroutine.ID)
+					if err != nil {
+						s.log.Debug("Error getting selected goroutine: ", err)
+					} else {
+						// TODO(suzmue): Consider putting the selected goroutine at the top.
+						// To be consistent we may want to do this for all threads requests.
+						gs = append(gs, g)
+					}
+				}
+			}
+		}
+
+		threads = make([]dap.Thread, len(gs))
 		s.debugger.LockTarget()
 		defer s.debugger.UnlockTarget()
 

service/dap/server_test.go

@@ -922,6 +922,63 @@ func TestStackTraceRequest(t *testing.T) {
 	})
 }
 
+func TestSelectedThreadsRequest(t *testing.T) {
+	runTest(t, "goroutinestackprog", func(client *daptest.Client, fixture protest.Fixture) {
+		runDebugSessionWithBPs(t, client, "launch",
+			// Launch
+			func() {
+				client.LaunchRequest("exec", fixture.Path, !stopOnEntry)
+			},
+			// Set breakpoints
+			fixture.Source, []int{20},
+			[]onBreakpoint{{
+				execute: func() {
+					checkStop(t, client, 1, "main.main", 20)
+
+					defaultMaxGoroutines := maxGoroutines
+					defer func() { maxGoroutines = defaultMaxGoroutines }()
+
+					maxGoroutines = 1
+					client.SetBreakpointsRequest(fixture.Source, []int{8})
+					client.ExpectSetBreakpointsResponse(t)
+
+					client.ContinueRequest(1)
+					client.ExpectContinueResponse(t)
+
+					se := client.ExpectStoppedEvent(t)
+					if se.Body.Reason != "breakpoint" || se.Body.ThreadId == 1 {
+						t.Errorf("got %#v, want Reason=%q, ThreadId!=1", se, "breakpoint")
+					}
+
+					client.ThreadsRequest()
+					oe := client.ExpectOutputEvent(t)
+					if !strings.HasPrefix(oe.Body.Output, "Too many goroutines") {
+						t.Errorf("got %#v, expected Output=\"Too many goroutines...\"\n", oe)
+
+					}
+					tr := client.ExpectThreadsResponse(t)
+
+					if len(tr.Body.Threads) != 2 {
+						t.Errorf("got %d threads, expected 2\n", len(tr.Body.Threads))
+					}
+
+					var selectedFound bool
+					for _, thread := range tr.Body.Threads {
+						if thread.Id == se.Body.ThreadId {
+							selectedFound = true
+							break
+						}
+					}
+					if !selectedFound {
+						t.Errorf("got %#v, want ThreadId=%d\n", tr.Body.Threads, se.Body.ThreadId)
+					}
+				},
+				disconnect: true,
+			}})
+
+	})
+}
+
 // TestScopesAndVariablesRequests executes to a breakpoint and tests different
 // configurations of 'scopes' and 'variables' requests.
 func TestScopesAndVariablesRequests(t *testing.T) {