feat: Support for opt-in caching

README.md

@@ -111,6 +111,7 @@ Please note that no options are required. However, depending on your configurati
 | `dotenvOptions`            | `{}`                                       | Provides options for [`dotenv`](https://github.com/motdotla/dotenv#options). Note that this plugin only accepts a `string` value for `path`. |
 | `postcssOptions`           | `{}`                                       | See [`postcssOptions`](#postcssOptions) below.                                                                                               |
 | `rendererOptions`          | `{}`                                       | See [`rendererOptions`](#rendererOptions) below.                                                                                             |
+| `caching`                  | `"never"`                                  | See [`caching`](#caching) below                                                                                                              |
 
 ```json
 {
@@ -240,6 +241,19 @@ This is experimental, and may not always work as expected. It currently supports
 
 > For convenience, `loadPaths` for Sass are extended, not replaced. The defaults are the path of the current file, and `'node_modules'`.
 
+#### `caching`
+
+Enables or disables caching.
+
+`"always"` will cache everything. This is overly agressive, and will cause stale types when CSS imported by CSS is modified.
+The cache key is the filename of the CSS file directly imported by TypeScript. Restarting the TypeScript server will clear the cache.
+
+`"never"` (default) regenerates types for every CSS file, every time any file is changed. This causes significant latency in editor
+operations (autocomplete, import suggestions, etc) in large projects, even when editing non-CSS files.
+
+Unfortunately, there's no balanced option or correct invalidation possible, due to typescript and the various CSS tools having
+different module loading systems.
+
 ### Visual Studio Code
 
 #### Recommended usage

src/index.ts

@@ -11,6 +11,7 @@ import { getDtsSnapshot } from './helpers/getDtsSnapshot';
 import { createLogger } from './helpers/logger';
 import { getProcessor } from './helpers/getProcessor';
 import { filterPlugins } from './helpers/filterPlugins';
+import { IScriptSnapshot } from 'typescript/lib/tsserverlibrary';
 
 const getPostCssConfigPlugins = (directory: string) => {
   try {
@@ -35,6 +36,7 @@ const init: tsModule.server.PluginModuleFactory = ({ typescript: ts }) => {
     const logger = createLogger(info);
     const directory = info.project.getCurrentDirectory();
     const compilerOptions = info.project.getCompilerOptions();
+    const scriptSnapshotCache = new WeakMap<IScriptSnapshot, IScriptSnapshot>();
 
     const languageServiceHost = {} as Partial<tsModule.LanguageServiceHost>;
 
@@ -132,8 +134,16 @@ const init: tsModule.server.PluginModuleFactory = ({ typescript: ts }) => {
     };
 
     languageServiceHost.getScriptSnapshot = (fileName) => {
-      if (isCSS(fileName) && fs.existsSync(fileName)) {
-        return getDtsSnapshot(
+      const existingSnapshot =
+        info.languageServiceHost.getScriptSnapshot(fileName);
+      if (!isCSS(fileName) || !fs.existsSync(fileName)) return existingSnapshot;
+
+      const cachedSnapshot =
+        existingSnapshot && scriptSnapshotCache.get(existingSnapshot);
+      if (cachedSnapshot && options.caching === 'always') {
+        return cachedSnapshot;
+      } else {
+        const newSnapshot = getDtsSnapshot(
           ts,
           processor,
           fileName,
@@ -142,8 +152,10 @@ const init: tsModule.server.PluginModuleFactory = ({ typescript: ts }) => {
           compilerOptions,
           directory,
         );
+        if (existingSnapshot)
+          scriptSnapshotCache.set(existingSnapshot, newSnapshot);
+        return newSnapshot;
       }
-      return info.languageServiceHost.getScriptSnapshot(fileName);
     };
 
     const createModuleResolver =

src/options.ts

@@ -35,8 +35,11 @@ export interface Options {
   /** @deprecated To align with naming in other projects. */
   postCssOptions?: PostcssOptions;
   rendererOptions?: RendererOptions;
+  caching?: CachingOptions;
 }
 
+export type CachingOptions = 'always' | 'never';
+
 export type ClassnameTransformOptions =
   | 'asIs'
   | 'camelCase'