service/dap: add throw reason to exception info (#2524)

We can get the throw reason by looking at the argument "s" in runtime.throw. This is not currently working in Go 1.16 or Go 1.17 (see golang/go#46425), but does work in Go 1.15 and Go 1.14

_fixtures/fatalerror.go

@@ -0,0 +1,6 @@
+package main
+
+func main() {
+	var f func()
+	go f()
+}

service/dap/server.go

@@ -29,6 +29,7 @@ import (
 	"sync"
 
 	"github.com/go-delve/delve/pkg/gobuild"
+	"github.com/go-delve/delve/pkg/goversion"
 	"github.com/go-delve/delve/pkg/locspec"
 	"github.com/go-delve/delve/pkg/logflags"
 	"github.com/go-delve/delve/pkg/proc"
@@ -2509,14 +2510,36 @@ func (s *Server) onExceptionInfoRequest(request *dap.ExceptionInfoRequest) {
 	if bpState != nil && bpState.Breakpoint != nil && (bpState.Breakpoint.Name == proc.FatalThrow || bpState.Breakpoint.Name == proc.UnrecoveredPanic) {
 		switch bpState.Breakpoint.Name {
 		case proc.FatalThrow:
-			// TODO(suzmue): add the fatal throw reason to body.Description.
 			body.ExceptionId = "fatal error"
+			// Attempt to get the value of the throw reason.
+			// This is not currently working for Go 1.16 or 1.17: https://github.com/golang/go/issues/46425.
+			handleError := func(err error) {
+				if err != nil {
+					body.Description = fmt.Sprintf("Error getting throw reason: %s", err.Error())
+				}
+				if goversion.ProducerAfterOrEqual(s.debugger.TargetGoVersion(), 1, 16) {
+					body.Description = "Throw reason unavailable, see https://github.com/golang/go/issues/46425"
+				}
+			}
+
+			exprVar, err := s.debugger.EvalVariableInScope(goroutineID, 1, 0, "s", DefaultLoadConfig)
+			if err == nil {
+				if exprVar.Value != nil {
+					body.Description = exprVar.Value.String()
+				} else {
+					handleError(exprVar.Unreadable)
+				}
+			} else {
+				handleError(err)
+			}
 		case proc.UnrecoveredPanic:
 			body.ExceptionId = "panic"
 			// Attempt to get the value of the panic message.
 			exprVar, err := s.debugger.EvalVariableInScope(goroutineID, 0, 0, "(*msgs).arg.(data)", DefaultLoadConfig)
 			if err == nil {
 				body.Description = exprVar.Value.String()
+			} else {
+				body.Description = fmt.Sprintf("Error getting panic message: %s", err.Error())
 			}
 		}
 	} else {
@@ -2545,7 +2568,7 @@ func (s *Server) onExceptionInfoRequest(request *dap.ExceptionInfoRequest) {
 	}
 
 	frames, err := s.debugger.Stacktrace(goroutineID, s.args.stackTraceDepth, 0)
-	if err == nil && len(frames) > 0 {
+	if err == nil {
 		apiFrames, err := s.debugger.ConvertStacktrace(frames, nil)
 		if err == nil {
 			var buf bytes.Buffer
@@ -2562,6 +2585,8 @@ func (s *Server) onExceptionInfoRequest(request *dap.ExceptionInfoRequest) {
 			})
 			body.Details.StackTrace = buf.String()
 		}
+	} else {
+		body.Details.StackTrace = fmt.Sprintf("Error getting stack trace: %s", err.Error())
 	}
 	response := &dap.ExceptionInfoResponse{
 		Response: *newResponse(request.Request),

service/dap/server_test.go

@@ -3490,7 +3490,6 @@ func TestBadAccess(t *testing.T) {
 						if eInfo.Body.ExceptionId != "runtime error" || !strings.HasPrefix(eInfo.Body.Description, errorPrefix) {
 							t.Errorf("\ngot  %#v\nwant ExceptionId=\"runtime error\" Text=\"%s\"", eInfo, errorPrefix)
 						}
-
 					}
 
 					client.ContinueRequest(1)
@@ -3602,6 +3601,41 @@ func TestPanicBreakpointOnNext(t *testing.T) {
 }
 
 func TestFatalThrowBreakpoint(t *testing.T) {
+	runTest(t, "fatalerror", func(client *daptest.Client, fixture protest.Fixture) {
+		runDebugSessionWithBPs(t, client, "launch",
+			// Launch
+			func() {
+				client.LaunchRequest("exec", fixture.Path, !stopOnEntry)
+			},
+			// Set breakpoints
+			fixture.Source, []int{3},
+			[]onBreakpoint{{
+				execute: func() {
+					checkStop(t, client, 1, "main.main", 3)
+
+					client.ContinueRequest(1)
+					client.ExpectContinueResponse(t)
+
+					se := client.ExpectStoppedEvent(t)
+					if se.Body.ThreadId != 1 || se.Body.Reason != "exception" || se.Body.Description != "fatal error" {
+						t.Errorf("\ngot  %#v\nwant ThreadId=1 Reason=\"exception\" Description=\"fatal error\"", se)
+					}
+
+					// TODO(suzmue): Enable this test for 1.17 when https://github.com/golang/go/issues/46425 is fixed.
+					errorPrefix := "\"go of nil func value\""
+					if goversion.VersionAfterOrEqual(runtime.Version(), 1, 16) {
+						errorPrefix = "Throw reason unavailable, see https://github.com/golang/go/issues/46425"
+					}
+					client.ExceptionInfoRequest(1)
+					eInfo := client.ExpectExceptionInfoResponse(t)
+					if eInfo.Body.ExceptionId != "fatal error" || !strings.HasPrefix(eInfo.Body.Description, errorPrefix) {
+						t.Errorf("\ngot  %#v\nwant ExceptionId=\"runtime error\" Text=%s", eInfo, errorPrefix)
+					}
+
+				},
+				disconnect: true,
+			}})
+	})
 	runTest(t, "testdeadlock", func(client *daptest.Client, fixture protest.Fixture) {
 		runDebugSessionWithBPs(t, client, "launch",
 			// Launch
@@ -3621,6 +3655,10 @@ func TestFatalThrowBreakpoint(t *testing.T) {
 					if se.Body.Reason != "exception" || se.Body.Description != "fatal error" {
 						t.Errorf("\ngot  %#v\nwant Reason=\"exception\" Description=\"fatal error\"", se)
 					}
+
+					// TODO(suzmue): Get the exception info for the thread and check the description
+					// includes "all goroutines are asleep - deadlock!".
+					// Stopped events with no selected goroutines need to be supported to test deadlock.
 				},
 				disconnect: true,
 			}})

service/debugger/debugger.go

@@ -237,6 +237,12 @@ func (d *Debugger) checkGoVersion() error {
 	return goversion.Compatible(producer)
 }
 
+func (d *Debugger) TargetGoVersion() string {
+	d.targetMutex.Lock()
+	defer d.targetMutex.Unlock()
+	return d.target.BinInfo().Producer()
+}
+
 // Launch will start a process with the given args and working directory.
 func (d *Debugger) Launch(processArgs []string, wd string) (*proc.Target, error) {
 	if err := verifyBinaryFormat(processArgs[0]); err != nil {