Add improved types

*   Add better support for different compile results, if you have custom
    results, add them to `CompileResultMap`
*   Better input/output of functions
*   Infer plugins better
*   Redo all docs

lib/index.js

@@ -8,12 +8,12 @@
  * @typedef {import('../index.js').Parser} Parser
  * @typedef {import('../index.js').Pluggable} Pluggable
  * @typedef {import('../index.js').PluggableList} PluggableList
+ * @typedef {import('../index.js').PluginTuple} PluginTuple
  * @typedef {import('../index.js').Plugin} Plugin
  * @typedef {import('../index.js').Preset} Preset
  * @typedef {import('../index.js').ProcessCallback} ProcessCallback
  * @typedef {import('../index.js').Processor} Processor
  * @typedef {import('../index.js').RunCallback} RunCallback
- * @typedef {import('../index.js').Transformer} Transformer
  */
 
 import structuredClone from '@ungap/structured-clone'
@@ -52,7 +52,6 @@ function base() {
 
   // Plugins.
   processor.attachers = attachers
-  // @ts-expect-error: overloads are handled.
   processor.use = use
 
   // API.
@@ -75,7 +74,8 @@ function base() {
     let index = -1
 
     while (++index < attachers.length) {
-      destination.use(...attachers[index])
+      const attacher = attachers[index]
+      destination.use(...attacher)
     }
 
     destination.data(structuredClone(namespace))
@@ -129,7 +129,6 @@ function base() {
         options[0] = undefined
       }
 
-      /** @type {Transformer | void} */
       const transformer = attacher.call(processor, ...options)
 
       if (typeof transformer === 'function') {
@@ -144,7 +143,7 @@ function base() {
   }
 
   /**
-   * @param {Pluggable | null | undefined} [value]
+   * @param {Exclude<Pluggable, PluginTuple> | PluggableList | null | undefined} [value]
    * @param {...unknown} options
    * @returns {Processor}
    */
@@ -176,15 +175,16 @@ function base() {
     return processor
 
     /**
-     * @param {import('../index.js').Pluggable<Array<unknown>>} value
-     * @returns {void}
+     * @param {import('../index.js').Pluggable} value
+     * @returns {undefined}
      */
     function add(value) {
       if (typeof value === 'function') {
         addPlugin(value)
       } else if (typeof value === 'object') {
         if (Array.isArray(value)) {
-          const [plugin, ...options] = value
+          const [plugin, ...options] =
+            /** @type {[Plugin, ...Array<unknown>]} */ (value)
           addPlugin(plugin, ...options)
         } else {
           addPreset(value)
@@ -196,7 +196,7 @@ function base() {
 
     /**
      * @param {Preset} result
-     * @returns {void}
+     * @returns {undefined}
      */
     function addPreset(result) {
       if (!('plugins' in result) && !('settings' in result)) {
@@ -215,7 +215,7 @@ function base() {
 
     /**
      * @param {PluggableList | null | undefined} [plugins]
-     * @returns {void}
+     * @returns {undefined}
      */
     function addList(plugins) {
       let index = -1
@@ -235,7 +235,7 @@ function base() {
     /**
      * @param {Plugin} plugin
      * @param {...unknown} [value]
-     * @returns {void}
+     * @returns {undefined}
      */
     function addPlugin(plugin, value) {
       let index = -1
@@ -299,7 +299,7 @@ function base() {
    * @param {Node} node
    * @param {RunCallback | VFileCompatible} [doc]
    * @param {RunCallback} [callback]
-   * @returns {Promise<Node> | void}
+   * @returns {Promise<Node> | undefined}
    */
   function run(node, doc, callback) {
     assertNode(node)
@@ -316,10 +316,11 @@ function base() {
 
     executor(undefined, callback)
 
+    // Note: `void`s needed for TS.
     /**
-     * @param {((node: Node) => void) | undefined} resolve
-     * @param {(error: Error) => void} reject
-     * @returns {void}
+     * @param {((node: Node) => undefined | void) | undefined} resolve
+     * @param {(error: Error) => undefined | void} reject
+     * @returns {undefined}
      */
     function executor(resolve, reject) {
       // @ts-expect-error: `doc` can’t be a callback anymore, we checked.
@@ -329,7 +330,7 @@ function base() {
        * @param {Error | undefined} error
        * @param {Node} tree
        * @param {VFile} file
-       * @returns {void}
+       * @returns {undefined}
        */
       function done(error, tree, file) {
         tree = tree || node
@@ -362,7 +363,7 @@ function base() {
     /**
      * @param {Error | undefined} [error]
      * @param {Node} [tree]
-     * @returns {void}
+     * @returns {undefined}
      */
     function done(error, tree) {
       bail(error)
@@ -387,10 +388,11 @@ function base() {
 
     executor(undefined, callback)
 
+    // Note: `void`s needed for TS.
     /**
-     * @param {((file: VFile) => void) | undefined} resolve
-     * @param {(error?: Error | undefined) => void} reject
-     * @returns {void}
+     * @param {((file: VFile) => undefined | void) | undefined} resolve
+     * @param {(error?: Error | undefined) => undefined | void} reject
+     * @returns {undefined}
      */
     function executor(resolve, reject) {
       const file = vfile(doc)
@@ -417,7 +419,7 @@ function base() {
       /**
        * @param {Error | undefined} [error]
        * @param {VFile | undefined} [file]
-       * @returns {void}
+       * @returns {undefined}
        */
       function done(error, file) {
         if (error || !file) {
@@ -432,7 +434,7 @@ function base() {
     }
   }
 
-  /** @type {Processor['processSync']} */
+  /** @type {import('../index.js').Processor['processSync']} */
   function processSync(doc) {
     /** @type {boolean | undefined} */
     let complete
@@ -451,7 +453,7 @@ function base() {
 
     /**
      * @param {Error | undefined} [error]
-     * @returns {void}
+     * @returns {undefined}
      */
     function done(error) {
       complete = true

package.json

@@ -67,7 +67,7 @@
     "xo": "^0.55.0"
   },
   "scripts": {
-    "build": "tsc --build --clean && tsc --build && type-coverage",
+    "build": "tsc --build --clean && tsc --build && type-coverage && tsd",
     "format": "remark . --frail --output --quiet && prettier . --log-level warn --write && xo --fix",
     "prepack": "npm run build && npm run format",
     "test": "npm run build && npm run format && npm run test-coverage",
@@ -95,10 +95,6 @@
     "atLeast": 100,
     "detail": true,
     "ignoreCatch": true,
-    "#": "`type-coverage` currently barfs on inferring nodes in plugins, while TS gets it",
-    "ignoreFiles": [
-      "test/**/*.js"
-    ],
     "strict": true
   },
   "xo": {
@@ -109,6 +105,7 @@
         ],
         "rules": {
           "@typescript-eslint/ban-types": "off",
+          "@typescript-eslint/consistent-type-definitions": "off",
           "@typescript-eslint/naming-convention": "off"
         }
       }

readme.md

@@ -460,7 +460,8 @@ Parse text to a syntax tree.
 
 ###### Parameters
 
-*   `file` ([`VFile`][vfile]) — any value accepted  as `x` in `new VFile(x)`
+*   `file` ([`VFile`][vfile]) — file to parse; typically `string`; any value
+    accepted as `x` in `new VFile(x)`
 
 ###### Returns
 
@@ -497,14 +498,15 @@ Yields:
 #### `processor.Parser`
 
 A **parser** handles the parsing of text to a syntax tree.
+
 It is used in the [parse phase][overview] and is called with a `string` and
 [`VFile`][vfile] of the document to parse.
 
 `Parser` can be a normal function, in which case it must return the syntax
 tree representation of the given file ([`Node`][node]).
 
-`Parser` can also be a constructor function (a function with a `parse` field, or
-other fields, in its `prototype`), in which case it is constructed with `new`.
+`Parser` can also be a constructor function (a function with a `parse` field in
+its `prototype`), in which case it is constructed with `new`.
 Instances must have a `parse` method that is called without arguments and must
 return a [`Node`][node].
 
@@ -521,8 +523,8 @@ Compile a syntax tree.
 ###### Parameters
 
 *   `tree` ([`Node`][node]) — tree to compile
-*   `file` ([`VFile`][vfile], optional) — any value accepted as `x` in
-    `new VFile(x)`
+*   `file` ([`VFile`][vfile], optional) — file associated with `node`; any
+    value accepted as `x` in `new VFile(x)`
 
 ###### Returns
 
@@ -562,14 +564,15 @@ Yields:
 
 A **compiler** handles the compiling of a syntax tree to something else (in
 most cases, text).
+
 It is used in the [stringify phase][overview] and called with a [`Node`][node]
 and [`VFile`][file] representation of the document to compile.
 
 `Compiler` can be a normal function, in which case it should return the textual
 representation of the given tree (`string`).
 
 `Compiler` can also be a constructor function (a function with a `compile`
-field, or other fields, in its `prototype`), in which case it is constructed
+field in its `prototype`), in which case it is constructed
 with `new`.
 Instances must have a `compile` method that is called without arguments and
 should return a `string`.
@@ -599,7 +602,7 @@ Run *[transformers][transformer]* on a syntax tree.
 
 ###### Returns
 
-Nothing if `done` is given (`void`).
+Nothing if `done` is given (`undefined`).
 A [`Promise`][promise] otherwise.
 The promise is rejected with a fatal error or resolved with the transformed
 tree ([`Node`][node]).
@@ -639,6 +642,7 @@ Yields:
 #### `function done(err[, tree, file])`
 
 Callback called when transformers are done.
+
 Called with either an error or results.
 
 ###### Parameters
@@ -679,12 +683,13 @@ Process the given file as configured on the processor.
 
 ###### Parameters
 
-*   `file` ([`VFile`][vfile]) — any value accepted as `x` in `new VFile(x)`
+*   `file` ([`VFile`][vfile]) — file; any value accepted as `x` in
+    `new VFile(x)`
 *   `done` ([`Function`][process-done], optional) — callback
 
 ###### Returns
 
-Nothing if `done` is given (`void`).
+Nothing if `done` is given (`undefined`).
 A [`Promise`][promise] otherwise.
 The promise is rejected with a fatal error or resolved with the processed
 file ([`VFile`][vfile]).
@@ -742,6 +747,7 @@ Yields:
 #### `function done(err, file)`
 
 Callback called when the process is done.
+
 Called with either an error or a result.
 
 ###### Parameters
@@ -905,6 +911,7 @@ processor.data() // => {charlie: 'delta'}
 ### `processor.freeze()`
 
 Freeze a processor.
+
 Frozen processors are meant to be extended and not to be configured directly.
 
 When a processor is frozen it cannot be unfrozen.
@@ -1073,6 +1080,7 @@ Optional transform ([`Transformer`][transformer]).
 ### `function transformer(tree, file[, next])`
 
 Transformers handle syntax trees and files.
+
 They are functions that are called each time a syntax tree and file are passed
 through the [run phase][overview].
 When an error occurs in them (either because it’s thrown, returned, rejected,
@@ -1084,16 +1092,18 @@ exact semantics of these functions.
 ###### Parameters
 
 *   `tree` ([`Node`][node]) — tree to handle
-*   `file` ([`VFile`][vfile]) —file to handle
-*   `next` ([`Function`][next], optional)
+*   `file` ([`VFile`][vfile]) — file to handle
+*   `next` ([`Function`][next], optional) — callback
 
 ###### Returns
 
-*   `void` — the next transformer keeps using same tree
+If you accept `next`, nothing.
+Otherwise:
+
 *   `Error` — fatal error to stop the process
-*   [`Node`][node] — new, changed, tree
-*   `Promise<Node>` — resolved with a new, changed, tree or rejected with an
-    `Error`
+*   `Promise<undefined>` or `undefined` — the next transformer keeps using same
+    tree
+*   `Promise<Node>` or [`Node`][node] — new, changed, tree
 
 #### `function next(err[, tree[, file]])`
 
@@ -1109,6 +1119,7 @@ may perform asynchronous operations, and must call `next()`.
 ## `Preset`
 
 Presets are sharable configuration.
+
 They can contain plugins and settings.
 
 ###### Example