fix: use webpack loader context to implement addWatchFile (#359)

Author: devongovett

src/webpack/context.ts

@@ -6,7 +6,23 @@ import type { Compilation } from 'webpack'
 import { Parser } from 'acorn'
 import type { UnpluginBuildContext } from '../types'
 
-export function createContext(compilation?: Compilation): UnpluginBuildContext {
+interface ContextOptions {
+  addWatchFile(file: string): void
+  getWatchFiles(): string[]
+}
+
+export function contextOptionsFromCompilation(compilation: Compilation): ContextOptions {
+  return {
+    addWatchFile(file) {
+      (compilation.fileDependencies ?? compilation.compilationDependencies).add(file)
+    },
+    getWatchFiles() {
+      return Array.from(compilation.fileDependencies ?? compilation.compilationDependencies)
+    },
+  }
+}
+
+export function createContext(options: ContextOptions, compilation?: Compilation): UnpluginBuildContext {
   return {
     parse(code: string, opts: any = {}) {
       return Parser.parse(code, {
@@ -17,11 +33,7 @@ export function createContext(compilation?: Compilation): UnpluginBuildContext {
       })
     },
     addWatchFile(id) {
-      if (!compilation)
-        throw new Error('unplugin/webpack: addWatchFile outside supported hooks (buildStart, buildEnd, load, transform, watchChange)');
-      (compilation.fileDependencies ?? compilation.compilationDependencies).add(
-        resolve(process.cwd(), id),
-      )
+      options.addWatchFile(resolve(process.cwd(), id))
     },
     emitFile(emittedFile) {
       const outFileName = emittedFile.fileName || emittedFile.name
@@ -45,11 +57,7 @@ export function createContext(compilation?: Compilation): UnpluginBuildContext {
       }
     },
     getWatchFiles() {
-      if (!compilation)
-        throw new Error('unplugin/webpack: getWatchFiles outside supported hooks (buildStart, buildEnd, load, transform, watchChange)')
-      return Array.from(
-        compilation.fileDependencies ?? compilation.compilationDependencies,
-      )
+      return options.getWatchFiles()
     },
   }
 }

src/webpack/index.ts

@@ -5,7 +5,7 @@ import VirtualModulesPlugin from 'webpack-virtual-modules'
 import type { ResolvePluginInstance, Resolver } from 'webpack'
 import type { ResolvedUnpluginOptions, UnpluginContext, UnpluginContextMeta, UnpluginFactory, UnpluginInstance, WebpackCompiler } from '../types'
 import { normalizeAbsolutePath, shouldLoad, toArray, transformUse } from '../utils'
-import { createContext } from './context'
+import { contextOptionsFromCompilation, createContext } from './context'
 
 const TRANSFORM_LOADER = resolve(
   __dirname,
@@ -89,7 +89,18 @@ export function getWebpackPlugin<UserOptions = Record<string, never>>(
                     const isEntry = requestContext.issuer === ''
 
                     // call hook
-                    const context = createContext()
+                    // resolveContext.fileDependencies is typed as a WriteOnlySet, so make our own copy here
+                    // so we can return it from getWatchFiles.
+                    const fileDependencies = new Set<string>()
+                    const context = createContext({
+                      addWatchFile(file) {
+                        fileDependencies.add(file)
+                        resolveContext.fileDependencies?.add(file)
+                      },
+                      getWatchFiles() {
+                        return Array.from(fileDependencies)
+                      },
+                    })
                     let error: Error | undefined
                     const pluginContext: UnpluginContext = {
                       error(msg: string | Error) {
@@ -178,7 +189,7 @@ export function getWebpackPlugin<UserOptions = Record<string, never>>(
 
           if (plugin.watchChange || plugin.buildStart) {
             compiler.hooks.make.tapPromise(plugin.name, async (compilation) => {
-              const context = createContext(compilation)
+              const context = createContext(contextOptionsFromCompilation(compilation), compilation)
               if (plugin.watchChange && (compiler.modifiedFiles || compiler.removedFiles)) {
                 const promises: Promise<void>[] = []
                 if (compiler.modifiedFiles) {
@@ -201,7 +212,7 @@ export function getWebpackPlugin<UserOptions = Record<string, never>>(
 
           if (plugin.buildEnd) {
             compiler.hooks.emit.tapPromise(plugin.name, async (compilation) => {
-              await plugin.buildEnd!.call(createContext(compilation))
+              await plugin.buildEnd!.call(createContext(contextOptionsFromCompilation(compilation), compilation))
             })
           }
 

src/webpack/loaders/load.ts

@@ -21,7 +21,14 @@ export default async function load(this: LoaderContext<any>, source: string, map
     id = decodeURIComponent(id.slice(plugin.__virtualModulePrefix.length))
 
   const res = await plugin.load.call(
-    { ...this._compilation && createContext(this._compilation) as any, ...context },
+    { ...createContext({
+      addWatchFile: (file) => {
+        this.addDependency(file)
+      },
+      getWatchFiles: () => {
+        return this.getDependencies()
+      },
+    }, this._compilation), ...context },
     normalizeAbsolutePath(id),
   )
 

src/webpack/loaders/transform.ts

@@ -24,7 +24,14 @@ export default async function transform(this: LoaderContext<{ unpluginName: stri
     warn: error => this.emitWarning(typeof error === 'string' ? new Error(error) : error),
   }
   const res = await plugin.transform.call(
-    { ...this._compilation && createContext(this._compilation) as any, ...context },
+    { ...createContext({
+      addWatchFile: (file) => {
+        this.addDependency(file)
+      },
+      getWatchFiles: () => {
+        return this.getDependencies()
+      },
+    }, this._compilation), ...context },
     source,
     this.resource,
   )