Debugger requirement: language-specific slot hiding

[mlvdv]

The debugger needs to decide which stack frame slots to display during normal debugging. What's needed is a language-specific recommendation on whether the name and value of any given slot would be sensible (useful) to a guest language programmer.

The debugger might display such slots anyway, for example in a special mode for language implementors.

@mickjordan reports that this would be useful for current work

[entlicher]

What if we change Object FrameSlot.getInfo(), which says nothing from the API point of view and serves to a particular language implementor only, who know what info they put into DrameDescriptor.addFrameSlot(), to a better typed FrameSlotInfo FrameSlot.getInfo()?
FrameSlotInfo can have then <T> T FrameSlot.getCapability(Class<T> capability) (inspired by TruffleRuntime).
This would add a flexibility to functionally evolve the APIs.
We could also have a more generic CapabilityProvider interface instead of FrameSlotInfo, that could be reused on more places.
Thoughts?

[jtulach]

Using getCapability is useful if you want to tunnel through some API - e.g. create a teleinterface. I may be wrong, but I don't think we need that for slots.

[chumer]

Yes I liked the FrameFormat SPI idea that is implemented by the language can be passed into the FrameDescriptor.

FrameFormat#isVisible(FrameSlot)
FrameFormat#isReadable(FrameSlot)
FrameFormat#isWritable(FrameSlot)
FrameFormat#getName(FrameSlot)
...

The FrameFormat can be null for a descriptor which means nothing is visible, nothing is readable/writable and an obfuscated name (like arg0, arg1).

I dislike FrameSlotInfo because it requires an additional allocation for each slot whereas FrameFormat could be shared accross a language.

[lukasstadler]

how about the following heuristic: only frame slots with String identifiers are visible in the debugger.

[chumer]

Some languages might not want to use String identifiers. I also think we should be conservative if a variable is not explicitly exported.

[entlicher]

Is there some example of such non-String identifiers and an idea of how should debugger treat them?
Debugger needs to convert everything to a String in the end to display it meaningfully.

[mlvdv]

how about the following heuristic: only frame slots with String identifiers are visible in the debugger.

This would conflate two separate issues:

• naming (and how names should be displayed to users)
• whether a particular slot (or frame, or anything else) should be displayed during ordinary operation.

The debugger should be able to display all slots when in special modes (not for guest language programmers), and names could be very helpful in those modes.

[chumer]

Tracked elsewhere: GR-89