Add missing type declaration for getCombinedSourcemap (#3431)

* Add missing type declaration for getCombinedSourcemap

* Only add getCombinedSourcemap to transform hook

Co-authored-by: Lukas Taegert-Atkinson <lukas.taegert-atkinson@tngtech.com>
Co-authored-by: Lukas Taegert-Atkinson <lukastaegert@users.noreply.github.com>

docs/05-plugin-development.md

@@ -478,7 +478,7 @@ Structurally equivalent to `this.warn`, except that it will also abort the bundl
 
 #### `this.getCombinedSourcemap() => SourceMap`
 
-Get the combined source maps of all previous plugins. This context function can only be used in [`transform`](guide/en/#transform) plugin hook.
+Get the combined source maps of all previous plugins. This context function can only be used in the [`transform`](guide/en/#transform) plugin hook.
 
 #### `this.getFileName(referenceId: string) => string`
 

src/rollup/types.d.ts

@@ -228,10 +228,14 @@ type LoadResult = SourceDescription | string | null | undefined;
 
 export type LoadHook = (this: PluginContext, id: string) => Promise<LoadResult> | LoadResult;
 
+export interface TransformPluginContext extends PluginContext {
+	getCombinedSourcemap: () => SourceMap;
+}
+
 export type TransformResult = string | null | undefined | SourceDescription;
 
 export type TransformHook = (
-	this: PluginContext,
+	this: TransformPluginContext,
 	code: string,
 	id: string
 ) => Promise<TransformResult> | TransformResult;

src/utils/transform.ts

@@ -10,6 +10,7 @@ import {
 	RollupWarning,
 	SourceDescription,
 	TransformModuleJSON,
+	TransformPluginContext,
 	TransformResult
 } from '../rollup/types';
 import { collapseSourcemap } from './collapseSourcemaps';
@@ -81,7 +82,7 @@ export default function transform(
 			'transform',
 			[curSource, id],
 			transformReducer,
-			(pluginContext, plugin) => {
+			(pluginContext, plugin): TransformPluginContext => {
 				curPlugin = plugin;
 				return {
 					...pluginContext,