Support StepInTarget

[davidanthoff]

This is really a combined question and feature request: my understanding is that currently VS Code doesn't use the StepInTarget stuff?

If so, it would be great if UI for that could be added, it seems super useful :)

[gjsjohnmurray]

@weinand please comment on current status and possible plans

[weinand]

Surfacing Debug Adapter Protocol features in the VS Code debugger UI is a continuous goal. But it has lower priority and we do not yet know in which milestone we'll add the feature.

[weinand]

In April we will investigate how we could support this feature in VS Code.

Original feature request
Pull request for adding the feature to DAP.

[weinand]

After reviewing the original request and the VS UI I suggest the following implementation in VS Code:

The UX is a context menu item "Step Into" with submenus actions for all available targets. The "Step Into" menu item is only available if there is a current stack frame selected in the CALL STACK view (and there is a yellow or green execution highlight in the the editor).
If there are no stepIn targets for the line, "Step Into" is disabled.

How this looks in VS:

How does the UI interact with the DAP:
Only if a DA has a true supportsStepInTargetsRequest capability, VS Code does the following:

• in the stopped state VS Code issues the stepInTargets request to find the possible "stepIn targets" for the current frame. The "current frame" is determined by the current stack frame selected in the CALL STACK view.
• If the stepInTargets request returns one or more targets, the targets show up as sub menu items of the "Step Into" menu. The target's label becomes the menu item's label and the target ID is used as the targetId argument for the stepIn request that is triggered if the menu item is selected. If stepInTargets does not returns any targets the "Step Into" menu should be disabled.

Ideally the stepInTargets request should be executed lazily, so that single stepping through some code does not trigger a stepInTargets request for every step. One approach to achieve this would be by running stepInTargets only if the context menu is about to open or when the "Step Into" menu item is selected and the submenu needs to be populated.

@isidorn does this make sense?

[isidorn]

@weinand this overall makes sense. Some comments / feedback:

• If supportsStepInTargetsRequest is false we show nothing in the context menu
• Once context menu is contstructed we can not do anything lazily. We also can not prevent the showing of context menu while the stepInTargets are being fetched, so imho there is only one way to make this work:
  • "Step Into Specific" action is always there when adapter supports this, and on click we fetch stepInTargets if there are mulitple targets we show them via quick pick, if only one we just execute it