Use onwarn and other options from svelte.config.js for every tool

Currently there are three places where I should configure ignores for svelte’s a11y warnings:

1. language server

   lspconfig.svelte.setup{
     cmd = { "yarn", "svelteserver", "--stdio" };
     on_attach = on_attach;
     settings = {
       svelte = {
         plugin = {
           svelte = {
             compilerWarnings = {
               ["a11y-no-onchange"] = "ignore"
             }
           }
         }
       }
     }
   }
   

2. svelte-check, which makes package.json look ugly when configured and this is only place to configure it

   {
     "val": "svelte-check --compiler-warnings a11y-no-onchange:ignore",
     "validate": "yarn val --threshold warning && yarn tsc --noEmit"
   }
   

3. eslint

   settings: {
     'svelte3/ignore-warnings': ({ code }) => code === 'a11y-no-onchange',
     // ...
   },
   

I would love to configure it in one place: svelte.config.js. It can’t be avoided because of svelte-preprocess and also these tools are reading it anyway for svelte-preprocess, why not use it for onwarn?

Also in the current situation I can’t make per-project configurations for language server.

Ideally, I would like to use svelte.config.js both in language tools and bundler and configure everything svelte-related there. This stuff too: https://github.com/sveltejs/language-tools/tree/master/packages/svelte-vscode#settings

[dummdidumm]

Candidates for harmonization of onwarn in my opinion are: language-server, svelte-check, rollup plugin, webpack plugin.

[Conduitry]

I’m rather concerned about adding svelte.config.js support to things that already have well established mechanisms for configuration. In ESLint, for example, plugins are just passed the configuration object that ESLint has already loaded. This could be the result of the merging of several hierarchical .eslintrc.js files (or JSON files, or YAML files, or the contents of the eslintConfig keys in package.json files), and I don’t think ESLint tells the plugin where any of these files were, so I don’t know where the plugin ought to look for svelte.config.js. There’s a single unified way for configuration to be handled, and ESLint core wants to be responsible for it.