Feature request: allow language services to validate breakpoint locations

[gregg-miskelly]

Note

I am opening this feature request based on dotnet/vscode-csharp#5267
Original opener: @cateyes99

Overview

In full Visual Studio, when the user tries to set a breakpoint, the UI will ask the language service to validate the breakpoint request. This allows the language service to decide if a given location is a valid location for a breakpoint. For example, a comment isn't a valid location.

Visual Studio has an LSP extension for this -- textDocument/validateBreakableRange.

[weinand]

Neither VS Code nor DAP knows anything about LSP. So this feature request sounds like a private communication between a specific DAP and LSP.

[gregg-miskelly]

No. This doesn't have anything to do with DAP - it can't, as it needs to happen when we aren't debugging.

[dbaeumer]

VS handles breakpoint placement different than VS Code does. @weinand correct me if I am wrong: in VS Code breakpoints are placed and only validated when a debugger runs. In VS a language server can validate a breakpoint. This makes sense where a language server knows enough about the generated code (which is the case in C#). To support that VS as an LSP extension that send a request to a language server to validate such a breakpoint.

I guess @gregg-miskelly is asking to support such a validation model in VS Code as well.

[vscodenpa]

This feature request is now a candidate for our backlog. The community has 60 days to upvote the issue. If it receives 20 upvotes we will move it to our backlog. If not, we will close it. To learn more about how we handle feature requests, please see our documentation.

Happy Coding!

[weinand]

@gregg-miskelly @dbaeumer thanks for clarifying.

This feature request is similar to the "inline value" and "debug hover" support because the feature is debug-related but the "data provider" lives on the language extension side.

Similar to the corresponding InlineValuesProvider and EvaluatableExpressionProvider extension APIs we would need something like a BreakpointLocationValidator extension API that the C# extension could implement for C# via the LSP extension textDocument/validateBreakableRange.

VS Code's generic debugger UI would use the BreakpointValidator to validate breakpoint creation. One problem in VS Code is that breakpoints are not typed (or bound to a specific source language). Users can set them at any time in any file and any debugger can make use of them. So if a C# breakpoint validator thinks that a breakpoint in a C# comment isn't valid, there might be another debugger that sees this differently. I don't really know how the UI for breakpoint validations would look like (actually some users use breakpoints as bookmarks and they would be surprised if some validator would kick in and prevent them from creating bookmarks in "invalid" locations).

Since I don't think that invalid breakpoint locations are a big pain point in VS Code, I don't see that this feature request gets high priority on our backlog...

[gregg-miskelly]

I opened this issue because @cateyes99 requested it on the C# extension, and it seemed reasonable for there to be a place for users to '+1' the suggestion. But personally, I am not bothered that VS Code lets you set breakpoints in invalid places. So, I don't disagree.

So if a C# breakpoint validator thinks that a breakpoint in a C# comment isn't valid, there might be another debugger that sees this differently.

In theory this shouldn't be a problem, and we haven't found it to be a problem in Visual Studio. This is because the validator isn't saying "this location will definitely bind" but rather "I know this line can't have a breakpoint because this isn't code".