Vetur config file RFC

rfcs/001-vetur-config-file.md

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+- Start Date: 2020-10-14
+- Target Major Version: 2.x & 3.x
+- Reference Issues: https://github.com/vuejs/vetur/issues/2325, https://github.com/vuejs/vetur/issues/2243, https://github.com/vuejs/vetur/issues/1635, https://github.com/vuejs/vetur/issues/815, https://github.com/vuejs/vetur/issues/424
+- Implementation PR: (leave this empty)
+
+# Summery
+A new configuration file for Vetur and VTI
+
+# Basic example
+
+```javascript
+// vetur.config.js
+/** @type {import('vti').VeturConfig} */
+module.exports = {
+  // **optional** default: `{}`
+  // override vscode settings part
+  // Notice: It only affects the settings used by Vetur.
+  settings: {
+    "vetur.useWorkspaceDependencies": true,
+    "vetur.experimental.templateInterpolationService": true
+  },
+  // **optional** default: `[{ root: './' }]`
+  // support monorepos
+  projects: [
+    './packages/repo2', // shorthand for only root.
+    {
+      // **required**
+      // Where is your project?
+      // It is relative to `vetur.config.js`.
+      root: './packages/repo1',
+      // **optional** default: `'package.json'`
+      // Where is `package.json` in the project?
+      // We use it to determine the version of vue.
+      // It is relative to root property.
+      package: './package.json',
+      // **optional**
+      // Where is TypeScript config file in the project?
+      // It is relative to root property.
+      tsconfig: './tsconfig.json',
+      // **optional** default: `[]`
+      // Register globally Vue component glob.
+      // If you set it, you can get completion by that components.
+      // It is relative to root property.
+      // Notice: It won't actually do it. You need to use `require.context` or `Vue.component`
+      globalComponents: [
+        './src/components/**/*.vue'
+      ]
+    }
+  ]
+}
+```
+
+# Motivation
+- The VTI need some method to set configuration.
+- The monorepo need a baseline or logic.
+- VSCode workspace config is own by vscode. I don't want to commit it in git.
+- Shared settings required for team projects.
+- Register global vue component.
+
+# Detailed design
+
+## Noun
+- Vetur: a VSCode extension for Vue support.
+- VTI: a CLI for Vue file type-check, diagnostics or some feature.
+- VLS: vue language server, The core of everything. It is base on [language server protocol](https://microsoft.github.io/language-server-protocol/).
+
+## Config file spec
+- All path formats are used with `/`.
+  > Helpful for cross-platform use project.
+- Only support commonjs format.
+  > We can use it quickly and directly.
+- Use pure JavaScript.
+  > Same as above.
+  > You can get typings like `@JSDoc`.
+- UTF-8 charset
+
+## How to use
+
+### VTI
+You can use it to override VTI default settings.
+```bash
+vti `action`
+vti -c vetur.config.js `action`
+vti --config vetur.config.js `action`
+```
+
+### Vetur
+This profile takes precedence over vscode setting.
+It will find it when Vetur initialization.
+If it isn't exist, It will use `{ settings: {}, projects: ['./'] }`.
+This will ensure consistency with past behavior.
+
+### How to find `vetur.config.js`
+- Start from the root and work your way up until the file is found.
+- The root is set `process.cwd()` value in VTI and you can set file path in CLI params.
+
+PS. Each root can have its own vetur.config.js in VSCode Multi root feature.
+
+## Property detail
+
+### Definition
+```typescript
+type Glob = string
+
+export interface VeturConfig {
+  settings?: { [key: string]: boolean | string | Enum },
+  projects?: Array<string | {
+    root: string,
+    package?: string,
+    tsconfig?: string,
+    globalComponents?: Array<Glob | { name: string, path: string }>
+  }>
+}
+```
+
+### `settings`
+Incoming to vue language server config.
+
+In VLS, it will merge (vscode setting or VTL default config) and vetur.config.js `settings`.
+```typescript
+import _ from 'lodash'
+
+// original vscode config or VTI default config
+const config: VLSFullConfig = params.initializationOptions?.config
+  ? _.merge(getDefaultVLSConfig(), params.initializationOptions.config)
+  : getDefaultVLSConfig();
+
+// From vetur.config.js
+const veturConfig = getVeturConfigInWorkspace()
+// Merge vetur.config.js
+Object.keys(veturConfig.setting).forEach((key) => {
+  _.set(config, key, veturConfig.setting[key])
+})
+```
+
+Notice: It only affects the settings used by Vetur.
+For example, we use `typescript.preferences.quoteStyle` in Vetur. so you can set it.
+But it don't affect original TypeScript support in VSCode.
+
+### `projects`
+The monorepo need a baseline or logic.
+Possible options are `package.json` or `tsconfig.js`.
+But both are used for node and typescript projects.
+We're likely to waste unnecessary resources on things we don't need.
+So I figured the best way to do it was through the setup.
+
+For detailed discussion, see this [RFC](https://github.com/vuejs/vetur/pull/2377).
+
+if `projects[]` is only a string, It is a shorthand when you only need to define `root`.
+
+### `projects[].root`
+All runtime dependencies is base on value of this property.
+Like `typescript`, `prettier`, `@prettier/pug`.
+Also Vetur find `./package.json` and `./tsconfig.js` by default.
+
+### `projects[].package`
+We can get the project name or dependency info from here.
+But We only use it to determine the version of vue now.
+But it doesn't rule out the use of more.
+
+### `projects[].tsconfig`
+Typescript project profile.
+It's the key to helping us support JavaScript and TypeScript.
+We also use it for support template interpolation.
+
+#### Why isn't array?
+If you are familiar with typescript, You know TypeScript allow support multiple discrete `tsconfig`.
+But in the vue ecosystem, It's almost completely unsupported.
+For example, We often use webpack to compile Vue projects.
+The `vue-loader` call `ts-loader` for support typescript.
+But `ts-loader` is only support only one `tsconfig.json`.
+
+For these reasons, we also don't support it.
+It can reduce development and maintenance costs.
+
+PS. `jsconfig.json` is also support it.
+
+### `projects[].globalComponents`
+We have some amazing features, Like `template interpolation`.
+But it only work when register component in component.
+For example:
+```javascript
+import Comp from '@/components/Comp.vue'
+
+export default {
+  components: {
+    Comp
+  }
+}
+```
+
+With this property available, we will parse vue component files that match the glob on vls startup.
+You can support `template interpolation` for that components anywhere in the project.
+
+This property allow two type values in array.
+- Glob (`string`) [format](https://github.com/mrmlnc/fast-glob#pattern-syntax)
+  Vetur will call glob lib with `projects[].root` for loading component when value is string.
+  It use `path.basename(fileName, path.extname(fileName))` as component name.
+- Object (`{ name: string, path: string }`)
+  Vetur use this data directly.
+  It's the most flexible way.
+  If this is a relative path, It is based on `projects[].root`.
+
+Notice: It won't actually do it. You need to use `require.context` and `Vue.component` in your project. [more](https://vuejs.org/v2/guide/components-registration.html#Automatic-Global-Registration-of-Base-Components)
+
+# Drawbacks
+- We need to guide the user through the new settings.
+- Monorepo's support is not so automatic.
+- Maintenance required to read configuration file code
+- Working with multiple profiles may confuse users.
+
+# Alternatives
+- Use vscode configuration file.
+- Put configuration to `vue.config.js`.
+  > Additional communication with `vue-cli` maintainer is required.
+- Use more cli params in VTI.
+
+# Adoption strategy
+No any breaking change on it.
+
+To guide user,
+We can add a dialog when open project,
+Or open a help page when vetur extensions install,
+and add help in the document in Vetur.
+
+# Unresolved questions
+- How to achieve Monorepo support?
+  > Another RFC. https://github.com/vuejs/vetur/pull/2377