Improve suggestion completions for debug breakpoints

[cdce8p]

Is your feature request related to a problem? Please describe.
At the moment suggestion completions for debug breakpoint expressions are quite limited. As far as I can tell those only work for the first word (on a module level). A common simplified use case, at least for me, is the following example

class Test:
  var: int = 42

def main():
  # set breakpoint here
  ...

If I want to debug main for a specific value, I would set the breakpoint condition to

Test.var == 42

Describe the solution you'd like
It would be nice if pyright could support at least MemberAccess completions, since those are the most common.

Additional context

[erictraut]

Breakpoints are not handled by pyright. They're handled by VS Code and the core python extension.

Transferring issue accordingly.

[cdce8p]

@erictraut I tried debugging this issue before I opened it. Although I didn't get far, I noticed that getCompletionsForPositions is also called for breakpoint completions. That's why I opened it in the pyright repo. It seems to be the ParseTree that's causing the issue.

Regularly the current node type in this case is Error (if I remember correctly) which would fall down to _getMemberAccessCompletions. However for the breakpoint it is Module which only calls _getStatementCompletions.

I don't know enough about the internals to know what's causing this issue. Just wanted to let you know my observations. Maybe it helps.

[erictraut]

The onCompletion handler is being called in the Pyright LSP when I type into the breakpoint expression text box, but it is being called on the document, which is not being modified when you're editing a breakpoint expression. Pyright appears to have no access to the text you're typing into the breakpoint box, which makes it impossible to provide accurate type completions. Instead, it's being asked to provide completions within the document at the start of the line where the breakpoint is located.

I'm not sure how this interaction is supposed to work. @jakebailey do you have any insights here?

[brettcannon]

Thank you for the suggestion! We have marked this issue as "needs decision" to make sure we have a conversation about your idea. We plan to leave this feature request open for at least a month to see how many 👍 votes the opening comment gets to help us make our decision.

[jakebailey]

I don't really know how this is supposed to work, no. It surprises me that VS Code would be attempting to use the zero position to effectively as for a completion, but as you build the expression, even using the correct context wouldn't work as there's no text doc for this. IIRC VS has something similar in a way (since it has a repl) that had special tie-ins with MPLS. I didn't know this sort of thing existed for VS Code and had assumed that in this context, it would only try and do something while the debugger was running, but thinking about it, it doesn't make sense that it would attempt to live-evaluate any random expression you put in that box...

[cdce8p]

I wouldn't agree. There are some (all be it limited) cases where it does make sense. A few use cases:

1. You might be new to a large codebase and don't know all the classes and their structure quite yet. Having suggestions, even just for member access, would help you find what you're looking for more efficiently. (That was the case when I first started working on pyright)
2. An extension / language server could perform some basic sanity checks. Eg. check for assignment vs equals. When I first used breakpoints, I just assumed it would always do equal checks (even with only one =) since assignments didn't make any sense to be. I know it now, but this could have easily been caught. This would especially be useful for someone who frequently changes the project and/or language they are working in, like most (often new) open source contributors.
3. An extension could add some basic syntax highlighting

I hope those examples show why I believe this would be a useful addition. Of course a more experienced programmer might not care enough, but it would lower the barrier for beginners.

[jakebailey]

Sorry, the above isn't at all about whether or not this should work, but trying to figure out how this is working at the moment and how it is supposed to fit into the language server specification, as things seem to be behaving strangely and we don't get enough info to properly handle things.

[luabud]

Thanks for the suggestion! We talked about it with the team and we have unfortunately decided we will not be moving forward with this idea. We think there isn't an enough widespread need for this to warrant the maintenance cost for the feature.