LLDB never finishes importing Swift modules/setting up Swift reflection

[z2oh]

These notifications in VS Code never go away during a debugging session. It's possible there's an issue on the client side, but I'm thinking the issue is in LLDB.

The Progress object which reports the reflection status is set up here: https://github.com/apple/llvm-project/blob/00c794fb25f1085c060d5c46e34cbb6145837f1f/lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntime.cpp#L505

This ctor takes an optional total parameter, which, as Progress::increment is called, is compared against to see when the operation is complete. When it's not set, the docs indicate that an indeterminate progress indicator should be displayed, but as far as I can tell, there's no way to report completion of this (which is normally triggered when Progress::m_completed == Progress::m_total).

It looks like the reflection progress object used to be constructed with a total, and with the following patch, I am no longer seeing the permanent "Setting up swift reflection" indicator:

diff --git a/lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntime.cpp b/lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntime.cpp
index 76a65ead7ff9..d3b83c784571 100644
--- a/lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntime.cpp
+++ b/lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntime.cpp
@@ -502,7 +502,7 @@ void SwiftLanguageRuntimeImpl::ProcessModulesToAdd() {

   auto &target = m_process.GetTarget();
   auto exe_module = target.GetExecutableModule();
-  Progress progress("Setting up Swift reflection");
+  Progress progress("Setting up Swift reflection", {}, modules_to_add_snapshot.GetSize());
   size_t completion = 0;

   // Add all defered modules to reflection context that were added to

The preferred total is less obvious for the "Importing Swift modules" progress events (here and here). Any ideas on what these totals should be?

cc @chelcassanova, it looks like you've been driving the improvements to the lldb reporting feature

[chelcassanova]

Hey Jeremy, thanks for tagging me in this and also for the patch! The "Setting up Swift reflection" report is indeed missing a total and your patch is correct, if you're able to put that patch up for review and add me as a reviewer that would be great 👍🏾 .

For the "Importing Swift modules" report, we actually have that as an indeterminate report so it doesn't have a total. The multiple reports you're seeing for "Importing Swift modules" is a bug that I'm looking into, thanks again for bringing this up!

[z2oh]

I appreciate you looking into this @chelcassanova! PR with the aforementioned patch is up here #8584

(I don't think I have the right repo privileges to manually specify reviewers)

[chelcassanova]

Fixed in #8623

[z2oh]

I finally got around to updating my Swift toolchain to a version which includes #8623, but I'm still seeing these persistent notifications when debugging a Swift project in VS Code:

If I understand the Progress semantics correctly, completion is only signaled upon one of:

1. if a total was set in the constructor, when Increment reaches that total
2. Progress object destructor is run

If we don't know the number of modules up front, is there a way to clean up the Progress object once we've completed?

[z2oh]

cc @chelcassanova, I'll look into resolving this soon and would love to hear your thoughts before digging in!

[chelcassanova]

Hey Jeremy, so sorry for my late response and thanks for looking into this! The Progress destructor should get run once the object is out of scope due to RAII, and since we create the progress report for Swift imports through a callback we also clear that callback on scope exit.

One of the original reasons that those spurious reports were coming in was because we cleared the callback by creating a new Progress object which will print the message it was initialized with, so the patch I merged just cleared it to an empty function. Just curious, are all of those reports just showing up with a title and no details?

[z2oh]

Just curious, are all of those reports just showing up with a title and no details?

Yes, as far as I can tell. Here's a screenshot from just now:

swift --version reports compnerd.org Swift version 6.0-dev (LLVM 57177aa1b91540b, Swift 6debc331289f02d), and this includes #8623 (https://github.com/apple/llvm-project/commits/57177aa1b91540b).

I let this spin for quite a bit (10+ minutes) and never saw them go away, so I assume that the std::unique_ptr<Progress> is being kept alive somehow, though I haven't confirmed this.

More than happy to provide as much detail as I can on this!

[chelcassanova]

The unique_ptr staying alive is also one of the main culprits I can think of, the other being that the reports are getting created but no details are being displayed which would indicate that the message that's supposed to get displayed with progress->Increment isn't being displayed at all, or that these reports are created but progress->Increment itself isn't being called so no details are added to the report. 🤔