User-defined extended diagnostics

[CSchulz]

Which @angular/* package(s) are relevant/related to the feature request?

compiler-cli

Description

With great pleasure I looked at the new possibilities of extended diagnostics, but unfortunately I found out that there is no possibility to extend it myself.

For the moment I can patch the execution to inject some own checks but it feels not awesome.

Proposed solution

I think a good way to add some own rules would be a similar system like the builders schema.
You define within a checks.json file all supported rules, each rule can have a schema.json file to handle all configuration parameters.

{
  "checks": {
    "custom-check": {
      "implementation": "./custom-check",
      "schema": "./custom-check/schema.json",
      "description": "checks some custom stuff."
    },
    "custom-check-without-configuration": {
      "implementation": "./custom-check-without-configuration",
      "description": "checks some custom stuff."
    }
  }
}

The angular.json file contains a list of extending check sets on root level (same level as projects) and load all rules during build, serve, etc.

{
  "$schema": "./node_modules/@angular/cli/lib/config/schema.json",
  "version": 1,
  "projects": {
  },
  "extendedDiagnosticsExtensions": [
    "./local-provided-custom-checks",
    "@npm-provided/custom-checks"
  ]
}

The tsconfig.json file lists all checks also custom ones. If a custom one is not listed, it won't be enabled.

{
  "angularCompilerOptions": {
    "extendedDiagnostics": {
      // The categories to use for specific diagnostics.
      "checks": {
        // Maps check name to its category.
        "invalidBananaInBox": "suppress",
        "customCheck": "error",
        "customCheckWithoutConfiguration": "suppress",
      },

      // The category to use for any diagnostics not listed in `checks` above.
      "defaultCategory": "error"
    }
  }
}

Alternatives considered

to be considered

[angular-robot]

This feature request is now candidate for our backlog! In the next phase, the community has 60 days to upvote. If the request receives more than 20 upvotes, we'll move it to our consideration list.

You can find more details about the feature request process in our documentation.

[dgp1130]

We've discussed supporting custom extended diagnostics in the past, and I think we're generally interested in supporting that, though it has some usability and security considerations to work through and hasn't been prioritized. Please upvote if anyone is interested!

/cc @JamesHenry @piotrtomiak who've expressed interest.

[Harpush]

That's a great idea! I recently wanted to write an ESLint rule that involved component ts AST info and got stuck. Using extended diagnostic for it could be awesome.