Add warning message to session save when transcript isn't saved.

Somewhat recently, we made the change to hide the behavior to save LLDB
session history to the transcript buffer behind the flag
`interpreter.save-transcript`.

Author: Tom Yang

lldb/source/Commands/CommandObjectSession.cpp

@@ -19,7 +19,8 @@ class CommandObjectSessionSave : public CommandObjectParsed {
       : CommandObjectParsed(interpreter, "session save",
                             "Save the current session transcripts to a file.\n"
                             "If no file if specified, transcripts will be "
-                            "saved to a temporary file.",
+                            "saved to a temporary file.\n"
+                            "Note: transcripts will only be saved if interpreter.save-transcript is true.\n",
                             "session save [file]") {
     AddSimpleArgumentList(eArgTypePath, eArgRepeatOptional);
   }

lldb/source/Interpreter/CommandInterpreter.cpp

@@ -3308,6 +3308,8 @@ bool CommandInterpreter::SaveTranscript(
   result.SetStatus(eReturnStatusSuccessFinishNoResult);
   result.AppendMessageWithFormat("Session's transcripts saved to %s\n",
                                  output_file->c_str());
+  if (!GetSaveTranscript())
+    result.AppendError("Note: the setting interpreter.save-transcript is set to false, so the transcript might not have been recorded.");
 
   if (GetOpenTranscriptInEditor() && Host::IsInteractiveGraphicSession()) {
     const FileSpec file_spec;

lldb/source/Interpreter/InterpreterProperties.td

@@ -16,7 +16,7 @@ let Definition = "interpreter" in {
   def SaveSessionOnQuit: Property<"save-session-on-quit", "Boolean">,
     Global,
     DefaultFalse,
-    Desc<"If true, LLDB will save the session's transcripts before quitting.">;
+    Desc<"If true, LLDB will save the session's transcripts before quitting. Note: transcripts will only be saved if interpreter.save-transcript is true.">;
   def OpenTranscriptInEditor: Property<"open-transcript-in-editor", "Boolean">,
     Global,
     DefaultTrue,

lldb/test/API/commands/session/save/TestSessionSave.py

@@ -85,6 +85,8 @@ def test_session_save(self):
         interpreter.HandleCommand("session save", res)
         self.assertTrue(res.Succeeded())
         raw += self.raw_transcript_builder(cmd, res)
+        # Also check that we don't print an error message about an empty transcript.
+        self.assertNotIn("interpreter.save-transcript is set to false", res.GetError())
 
         with open(os.path.join(td.name, os.listdir(td.name)[0]), "r") as file:
             content = file.read()
@@ -93,6 +95,33 @@ def test_session_save(self):
             for line in lines:
                 self.assertIn(line, content)
 
+    @no_debug_info_test
+    def test_session_save_no_transcript_warning(self):
+        interpreter = self.dbg.GetCommandInterpreter()
+
+        self.runCmd("settings set interpreter.save-transcript false")
+
+        # These commands won't be saved, so are arbitrary.
+        commands = [
+            "p 1",
+            "settings set interpreter.save-session-on-quit true",
+            "fr v",
+            "settings set interpreter.echo-comment-commands true",
+        ]
+
+        for command in commands:
+            res = lldb.SBCommandReturnObject()
+            interpreter.HandleCommand(command, res)
+
+        output_file = self.getBuildArtifact('my-session')
+
+        res = lldb.SBCommandReturnObject()
+        interpreter.HandleCommand("session save " + output_file, res)
+        self.assertTrue(res.Succeeded())
+        # We should warn about the setting being false.
+        self.assertIn("interpreter.save-transcript is set to false", res.GetError())
+        self.assertTrue(os.path.getsize(output_file) == 0, "Output file should be empty since we didn't save the transcript.")
+
     @no_debug_info_test
     def test_session_save_on_quit(self):
         raw = ""