Possibility to add data breakpoints

[britalmeida]

Please add a feature to "Add data breakpoint" (at least?) for the C and C++ language.

Ideally, this would be available both by:

• entering an address or variable name in the breakpoints panel, and
• right-click a variable within the code and "Add data breakpoint".

[weinand]

We will start exploring this in November

[weinand]

corresponding DAP proposal: microsoft/debug-adapter-protocol#20

[weinand]

What we plan to do:

• we support a new breakpoint type "data" which will be shown in the breakpoints view with a new icon
• a data breakpoint can be created via a context menu action in the Variables and Watches view
• data breakpoints have condition, hit count, and logPoints attributes (and the implementation provides information about what attributes are supported).
• hitting a data breakpoint stops the program and the reason is shown in the Stacktrace.
• initially a data breakpoint is defined by an expression and as such has no source location (in this respect it is similar to a function breakpoint). In the future it might become possible to set data breakpoints directly in the source and to show them in the gutter.

[britalmeida]

The plan sounds great!

Regarding the UX:

• it would be nice to be able to add a data breakpoint for a variable, also by right-clicking it on the source code directly. Otherwise, there is an extra step of having to add the variable to the Watches first.
• it would also be nice to be able to enter an address manually, instead of just a variable name. This action is usually available on the breakpoints panel.
• I can't immediately see a case where it would be helpful to see data breakpoints in the gutter. I would expect to see breaks for the flow there, but a data breakpoint would potentially show in many places. A common case of setting a data breakpoint is because it is not known when/where the data is changing, or it may be getting trampled by something else.

Data breakpoints with a condition, hit count and log:

• this sounds super powerful! I can already see the use of checking when a variable is cleared or set to a specific value ^^
• mind that logpoints are currently not working in C++ -> Conditional breakpoints and log points cause execution to stop as if it were a normal breakpoint. vscode-cpptools#2862

[weinand]

@britalmeida thanks for the feedback.

• if you read my proposal carefully, you will find that I already mention "setting data breakpoints directly".
• VS Code will never deal with "addresses". It only sends strings to the backend and the backend can decide what to do with it.
• VS Code provides the UI, but not the implementation in the backend. So the conditions, hit counts and log points are only powerful, if a debugger extension is able to implement them. So please don't hold your breath...