How to have a diagnostic WITHOUT associated file?

Imagine you compile a C# program without a 'main' entrypoint, and it generates the error message

CSC : error CS5001: Program does not contain a static 'Main' method suitable for an entry point [/Users/ljw/code/c/c.csproj]

It's impossible to report this error via LSP! That's because the publishDiagnostics message has a mandatory uri field -- but for errors like this, there's no uri that would make sense! And so the C# plugin for VSCode shows this message in the build output window, but simply doesn't report this error at all to VSCode diagnostics list. @DustinCampbell

I experimented with VSCode behavior:

• publishDiagnostics with uri = null -- this doesn't get shown in the diagnostics window at all
• publishDiagnostics with uri = "" -- this sometimes pops up the Chrome debugger in VSCode, and sometimes crashes VSCode completely with a "report this crash to Apple" system dialog.
• publishDiagnostics with uri = "file:///" or uri = "file:///some/directory -- this shows the error in the diagnostics window, and when you click on it, VSCode does some frenetic flickering of a new document tab before closing it again.

I think that "diagnostics not related to a particular file" are a real fact of life. LSP should be extended to cope with them. And VSCode should too.

My proposal: make the uri field optional. If it is absent/null, then treat it as a file-less diagnostic, and the range field inside each individual Diagnostic will be ignored.

Start with the publishDiagnostics message and the Diagnostic.range field described in the issue, then review the 21-comment discussion for protocol and client constraints. Done means the protocol clearly defines how diagnostics without an associated file are represented and how their ranges are handled.