How to integrate custom build diagnostics (errors, warnings, etc) with the Swift-VSCode extension?

[josh-arnold-1]

Hello,

I am exploring using Bazel with VSCode for iOS development. Currently, I'm generating a compile_commands.json file that SourceKit-LSP is using to give me jump to definition, syntax highlighting, etc.

However, I wondering what the correct high level approach looks like for integrating bazel build errors into sourcekit-lsps diagnostics?

Would I need to manually write my own vscode language server extension that handles these build diagnostics, independently from SourceKit-LSP, or is there someway to "extend" or "hook into" either the VSCode-Swift extension, or SourceKit-LSP to integrate it with my bazel build diagnostics (errors, warnings, etc)?

Thank you so much, any help or guidance is much appreciated 🙏

[matthewbastien]

If you want problems from Bazel build to show up in the editor then you can set up a build task with a problem matcher. It would look something like:

{
    "label": "Bazel Build",
    "type": "shell",
    "command": "bazel",
    "args": ["build", "//some:target"],
    "group": "build",
    "problemMatcher": {
        "owner": "bazel",
        "pattern": [
            {
                // Insert pattern matcher here
            }
        ]
    }
}

I went looking for official VS Code documentation on the problem matchers, but I can't seem to find it... The only documentation I could find only showed how to use problem matchers that were already created via an extension: https://code.visualstudio.com/docs/debugtest/tasks

If you want to be able to re-use the problem matcher between tasks then I'm pretty sure you have to create an extension that defines it for you and then you can reference it like "$<id-from-extension>. For example, VS Code ships with an existing TypeScript problem matcher called tsc:

{
    // ...
    "problemMatcher": "$tsc"
}

Note that these will show up alongside any errors from SourceKit-LSP. If you wanted to go one step further and merge them with issues from SourceKit-LSP then that might require some changes to the Swift extension to expose the diagnostics. I can't remember off the top of my head whether or not VS Code has an API to listen for events from language servers created by other extensions.

[matthewbastien]

Another thing I forgot to mention: this will only show errors when you actually run the build task. If you wanted to have this done in real time then that would definitely require some sort of Bazel language server to do properly.

[josh-arnold-1]

Thanks so much, this is super helpful. The problem matcher is a quick way to get started, but it seems a custom language server is the best way to implement this for more robust support.