dap: add 'clipboard' support, and truncate a long value

[hyangah]

• add 'clipboard' capability
• apply a larger string limit for 'hover' and 'clipboard' context
• truncate the string representation of a compound type (or pointer of a compound type) variable if the length of the value is larger than 256. But when a variable is returned as a result of Evaluate Request for hover or copy value feature (clipboard or variables context), do not truncate the value.

Updates golang/vscode-go#1318
Fixes golang/vscode-go#1435
Updates golang/vscode-go/issues/126

[hyangah]

Arbitrarily chosen 1K, Still 1K is too large for my taste.

Before:

After:

Still it's possible that we'd end up sending a large JSON message for variables response if the requested variable/scope contains many long variables. This PR doesn't mean to prevent that.

[derekparker]

Arbitrarily chosen 1K, Still 1K is too large for my taste.

Would you like time to live with it and possibly change this before it gets submitted?

[suzmue]

Arbitrarily chosen 1K, Still 1K is too large for my taste.

I agree I think that these strings become unnecessarily long.

When I was testing paging, this was the cause of some things being so slow that it was unusable for investigating the values.

I would say drop it to ~100 (or even less) especially if it has children to expand to get more information.

[hyangah]

Lowered the max limit to 256. Tried 128 and it broke some tests and some didn't look nice with 128 (e.g. slice of pointers to a compound type, ...) due to all the type info and len/cap info before the actual data. :-(
I think a better solution is to truncate more intelligently, but I don't want to go too deep into it now.

[hyangah]

@polinasok @suzmue, is this 256 limit ok? Or should we look into further to do better than SinglelineString and avoid truncating informational messages (e.g. failed load, or partial load...)?

I am not sure what you mean by "truncating information messages".

I do agree that 1K is too long and something shorter is sufficient as long as it can be expanded further. 256 seems ok.

I took a quick look at Python. They truncated my map at about 300+ characters, but it appeared to be based on the number of elements, not characters, and the output was {a, b, c, ...}, where entries were removed intelligently. But in any case, our number is in the similar ballpark.

[aarzilli]

LGTM, needs decision over the length constant.

[suzmue]

LGTM

[derekparker]

LGTM

I'll wait to merge until the length is sorted out and we get an ack from @polinasok.

[polinasok]

Could you remind me please what actions in the vscode UI generate evaluate requests with "hover" and "clipboard" context. I know that right click + "Copy to Value" is "variabels" and using Debug Console is "repl".

[polinasok]

The PR description needs updating.

[suzmue]

When the server declares the capability supportsClipboardContext, Copy Value from both the variable pane and WATCH use the clipboard context.

[hyangah]

@polinasok It looks like you accidentally edited my comment instead of responding to it.

I am not sure what you mean by "truncating information messages".

• information other than the variable's value such as len/cap of slice/array, or type information or address expression
• information that indicates the loading states, such as " ... 2 more", "- FAILED TO LOAD: some error", ...

Could you remind me please what actions in the vscode UI generate evaluate requests with "hover" and "clipboard" context. I know that right click + "Copy to Value" is "variabels" and using Debug Console is "repl".

"hover" -> when you hover over the variable from the editor.
"clipboard" -> "Copy Value" context menu from VARIABLES or WATCH view

[hyangah]

PR description is updated. Seems like we all agreed on 256 for now.
@suzmue has a prototype of removing type info and slice/array's len/cap info from the value presentation and making them available in a different way (type info is already supplied as the separate type attribute)

[polinasok]

"hover" -> when you hover over the variable from the editor.

I believe this is only true when you hover over the code, not in the Variables section.

@suzmue has a prototype of removing type info and slice/array's len/cap info from the value presentation
Should we consider smaller limit once the type info is dropped from the inlined value?

[polinasok]

@hyangah Oh and sorry for editing the comment instead of replying.

[hyangah]

"hover" -> when you hover over the variable from the editor.

I believe this is only true when you hover over the code, not in the Variables section.

fyi @polinasok 'editor' refers to the main area where code/document is presented in vscode. 'views' or 'viewlets' are the sections presented in the side bar area.