cmd/dlv: delete trace directory when we delete the built executable (#856)

Mozilla RR will create a trace directory that can be reused with the
replay verb, however if we delete the executable file the trace
directory will become useless, so delete that too before exit.

Users that wish to reuse a recording should build the executable
themselves and then use either dlv exec or rr record to do the
recording.

cmd/dlv/cmds/commands.go

@@ -383,7 +383,7 @@ func testCmd(cmd *cobra.Command, args []string) {
 		defer os.Remove("./" + testdebugname)
 		processArgs := append([]string{"./" + testdebugname}, targetArgs...)
 
-		return execute(0, processArgs, conf, "", executingOther)
+		return execute(0, processArgs, conf, "", executingGeneratedTest)
 	}()
 	os.Exit(status)
 }
@@ -433,6 +433,7 @@ type executeKind int
 const (
 	executingExistingFile = executeKind(iota)
 	executingGeneratedFile
+	executingGeneratedTest
 	executingOther
 )
 
@@ -507,6 +508,13 @@ func execute(attachPid int, processArgs []string, conf *config.Config, coreFile
 	} else {
 		// Create and start a terminal
 		client := rpc2.NewClient(listener.Addr().String())
+		if client.Recorded() && (kind == executingGeneratedFile || kind == executingGeneratedTest) {
+			// When using the rr backend remove the trace directory if we built the
+			// executable
+			if tracedir, err := client.TraceDirectory(); err == nil {
+				defer SafeRemoveAll(tracedir)
+			}
+		}
 		term := terminal.New(client, conf)
 		term.InitFile = InitFile
 		status, err = term.Run()
@@ -601,3 +609,28 @@ func splitQuotedFields(in string) []string {
 
 	return r
 }
+
+// SafeRemoveAll removes dir and its contents but only as long as dir does
+// not contain directories.
+func SafeRemoveAll(dir string) {
+	dh, err := os.Open(dir)
+	if err != nil {
+		return
+	}
+	defer dh.Close()
+	fis, err := dh.Readdir(-1)
+	if err != nil {
+		return
+	}
+	for _, fi := range fis {
+		if fi.IsDir() {
+			return
+		}
+	}
+	for _, fi := range fis {
+		if err := os.Remove(filepath.Join(dir, fi.Name())); err != nil {
+			return
+		}
+	}
+	os.Remove(dir)
+}