Cast Result.root type from process() options

lib/lazy-result.d.ts

@@ -1,3 +1,4 @@
+import Document from './document.js'
 import { SourceMap } from './postcss.js'
 import Processor from './processor.js'
 import Result, { Message, ResultOptions } from './result.js'
@@ -18,7 +19,9 @@ declare namespace LazyResult {
  * const lazy = postcss([autoprefixer]).process(css)
  * ```
  */
-declare class LazyResult_ implements PromiseLike<Result> {
+declare class LazyResult_<RootNode = Document | Root>
+  implements PromiseLike<Result<RootNode>>
+{
   /**
    * Processes input CSS through synchronous and asynchronous plugins
    * and calls onRejected for each error thrown in any plugin.
@@ -33,7 +36,7 @@ declare class LazyResult_ implements PromiseLike<Result> {
    * })
    * ```
    */
-  catch: Promise<Result>['catch']
+  catch: Promise<Result<RootNode>>['catch']
 
   /**
    * Processes input CSS through synchronous and asynchronous plugins
@@ -47,7 +50,7 @@ declare class LazyResult_ implements PromiseLike<Result> {
    * })
    * ```
    */
-  finally: Promise<Result>['finally']
+  finally: Promise<Result<RootNode>>['finally']
 
   /**
    * Processes input CSS through synchronous and asynchronous plugins
@@ -62,7 +65,7 @@ declare class LazyResult_ implements PromiseLike<Result> {
    * })
    * ```
    */
-  then: Promise<Result>['then']
+  then: Promise<Result<RootNode>>['then']
 
   /**
    * @param processor Processor used for this transformation.
@@ -76,7 +79,7 @@ declare class LazyResult_ implements PromiseLike<Result> {
    *
    * @return Result with output content.
    */
-  async(): Promise<Result>
+  async(): Promise<Result<RootNode>>
 
   /**
    * An alias for the `css` property. Use it with syntaxes
@@ -145,7 +148,7 @@ declare class LazyResult_ implements PromiseLike<Result> {
    *
    * PostCSS runners should always use `LazyResult#then`.
    */
-  get root(): Root
+  get root(): RootNode
 
   /**
    * Returns the default string description of an object.
@@ -158,7 +161,7 @@ declare class LazyResult_ implements PromiseLike<Result> {
    *
    * @return Result with output content.
    */
-  sync(): Result
+  sync(): Result<RootNode>
 
   /**
    * Alias for the `LazyResult#css` property.
@@ -180,6 +183,8 @@ declare class LazyResult_ implements PromiseLike<Result> {
   warnings(): Warning[]
 }
 
-declare class LazyResult extends LazyResult_ {}
+declare class LazyResult<
+  RootNode = Document | Root
+> extends LazyResult_<RootNode> {}
 
 export = LazyResult

lib/no-work-result.d.ts

@@ -22,12 +22,12 @@ declare namespace NoWorkResult {
  * let root = noWorkResult.root // now css is parsed because we accessed the root
  * ```
  */
-declare class NoWorkResult_ implements LazyResult {
-  catch: Promise<Result>['catch']
-  finally: Promise<Result>['finally']
-  then: Promise<Result>['then']
+declare class NoWorkResult_ implements LazyResult<Root> {
+  catch: Promise<Result<Root>>['catch']
+  finally: Promise<Result<Root>>['finally']
+  then: Promise<Result<Root>>['then']
   constructor(processor: Processor, css: string, opts: ResultOptions)
-  async(): Promise<Result>
+  async(): Promise<Result<Root>>
   get content(): string
   get css(): string
   get map(): SourceMap
@@ -36,7 +36,7 @@ declare class NoWorkResult_ implements LazyResult {
   get processor(): Processor
   get root(): Root
   get [Symbol.toStringTag](): string
-  sync(): Result
+  sync(): Result<Root>
   toString(): string
   warnings(): Warning[]
 }

lib/postcss.d.ts

@@ -236,11 +236,11 @@ declare namespace postcss {
     (data: object[]): Node[]
   }
 
-  export interface Syntax {
+  export interface Syntax<RootNode = Document | Root> {
     /**
      * Function to generate AST by string.
      */
-    parse?: Parser
+    parse?: Parser<RootNode>
 
     /**
      * Class to generate string by AST.
@@ -304,7 +304,7 @@ declare namespace postcss {
     sourcesContent?: boolean
   }
 
-  export interface ProcessOptions {
+  export interface ProcessOptions<RootNode = Document | Root> {
     /**
      * The path of the CSS source file. You should always set `from`,
      * because it is used in source map generation and syntax error messages.
@@ -319,17 +319,17 @@ declare namespace postcss {
     /**
      * Function to generate AST by string.
      */
-    parser?: Parser | Syntax
+    parser?: Parser<RootNode> | Syntax<RootNode>
 
     /**
      * Class to generate string by AST.
      */
-    stringifier?: Stringifier | Syntax
+    stringifier?: Stringifier | Syntax<RootNode>
 
     /**
      * Object with parse and stringify.
      */
-    syntax?: Syntax
+    syntax?: Syntax<RootNode>
 
     /**
      * The path where you'll put the output CSS file. You should always set `to`

lib/processor.d.ts

@@ -1,3 +1,4 @@
+import Document from './document.js'
 import LazyResult from './lazy-result.js'
 import NoWorkResult from './no-work-result.js'
 import {
@@ -72,9 +73,12 @@ declare class Processor_ {
    * @return Promise proxy.
    */
   process(
-    css: { toString(): string } | LazyResult | Result | Root | string,
-    options?: ProcessOptions
+    css: { toString(): string } | LazyResult | Result | Root | string
   ): LazyResult | NoWorkResult
+  process<RootNode extends Document | Root = Root>(
+    css: { toString(): string } | LazyResult | Result | Root | string,
+    options: ProcessOptions<RootNode>
+  ): LazyResult<RootNode>
 
   /**
    * Adds a plugin to be used as a CSS processor.

lib/result.d.ts

@@ -60,7 +60,7 @@ declare namespace Result {
  * const result2 = postcss.parse(css).toResult()
  * ```
  */
-declare class Result_ {
+declare class Result_<RootNode = Document | Root> {
   /**
    * A CSS string representing of `Result#root`.
    *
@@ -141,14 +141,14 @@ declare class Result_ {
    * root.toResult().root === root
    * ```
    */
-  root: Document | Root
+  root: RootNode
 
   /**
    * @param processor Processor used for this transformation.
    * @param root      Root node after all transformations.
    * @param opts      Options from the `Processor#process` or `Root#toResult`.
    */
-  constructor(processor: Processor, root: Document | Root, opts: Result.ResultOptions)
+  constructor(processor: Processor, root: RootNode, opts: Result.ResultOptions)
 
   /**
    * An alias for the `Result#css` property.
@@ -201,6 +201,6 @@ declare class Result_ {
   warnings(): Warning[]
 }
 
-declare class Result extends Result_ {}
+declare class Result<RootNode = Document | Root> extends Result_<RootNode> {}
 
 export = Result

test/types.ts

@@ -1,4 +1,4 @@
-import postcss, { PluginCreator, Result } from '../lib/postcss.js'
+import postcss, { Document, PluginCreator } from '../lib/postcss.js'
 
 const plugin: PluginCreator<string> = prop => {
   return {
@@ -14,12 +14,20 @@ const plugin: PluginCreator<string> = prop => {
 
 plugin.postcss = true
 
-const processResult: Promise<Result> | Result = postcss([
-  plugin
-]).process('h1{color: black;}', { from: undefined })
+postcss([plugin])
+  .process('h1{color: black;}', {
+    from: undefined
+  })
+  .then(result => {
+    console.log(result.root.parent)
+    console.log(result.css)
+  })
 
-processResult.then((result: Result) => {
-  console.log(result.css)
-})
+function parseMarkdown(): Document {
+  return new Document()
+}
+
+let doc = postcss().process('a{}', { parser: parseMarkdown }).root
+console.log(doc.toString())
 
 export default plugin