duplicated top stackframe with old debug adapters

[weinand]

VSCode Version: Insider 1.14.0

• debug simple program with mono-debug

Observe: the stack frame is duplicated:

First VS Code asks for stackframes with startFrame = 0 and levels = 1.
Then mono-debug returns all frames (which happens to be exactly one).
Then VS Code asks for stackframes with startFrame = 0 and levels = 20 (probably because the first result did not return the "totalFrames" attribute and VS Code falls back to the old behavior).
Then mono-debug returns all frames again and VS Code adds them to the existing one instead of replacing the existing one.

Then I tried a program where the stacktrace has one additional level but this doesn't make a difference:

[weinand]

VS Code 1.13 uses the following heuristic to decide whether a DA supports loading stack frames ranges: it request a single frame (startFrame: 0, levels: 1). If the DA returns more frames, VS Code assumes that the DA does not support ranges.

This heuristic fails if there is only one frame available or if the DA honours 'levels' but not 'startFrame'. This latter case is the reason for the mono-debug problem.

Since we have not found a way to fix the heuristic in a robust way, we've decided to require that DAs opt-into the delayed loading of stack frames by introducing a new capability supportsDelayedStackTraceLoading.

@roblourens please enable the supportsDelayedStackTraceLoading for the inspector protocol.

[isidorn]

@delmyers @gregg-miskelly @MSLaguana @DanTup @devoncarew @WebFreak001 @roblourens @andysterland @hbenl @lukaszunity @svaarala @ramya-rao-a @vadimcn @felixfbecker @daviwil @rkeithhill @DonJayamanne @MSLaguana @rebornix in order to benefit from delayed stack trace loading your adapters now need to explicitly specify this capability supportsDelayedStackTraceLoading.

This is the original feature request, however we have now introduced a capability as @weinand mentions in the comment above. The capability is available in the preview version of the adapter npm module.

[DanTup]

@ishanarora @weinand Do we need to target a specific Code version to use supportsDelayedStackTraceLoading and if so, is it one that's already shipped or is this currently only usable in Insiders?