Add cache for known plugins (#301)

* Add cache for known plugins

We have to call `require.resolve(…)` ~10 times per call to `parse(…)`. These calls generally take microseconds however if you call `prettier.format(…)` several thousand times the times add up. It also adds up for embedded documents which call `parse(…)` a large number of times.

This adds a cache for these calls because generally only a few will ever be installed and Node.js will not cache misses internally.

* Update src/plugins.ts

Co-authored-by: Robin Malfait <malfait.robin@gmail.com>

* Update changelog

---------

Co-authored-by: Robin Malfait <malfait.robin@gmail.com>

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 
 - Add support for `prettier-plugin-multiline-arrays` ([#299](https://github.com/tailwindlabs/prettier-plugin-tailwindcss/pull/299))
+- Add resolution cache for known plugins ([#301](https://github.com/tailwindlabs/prettier-plugin-tailwindcss/pull/301))
 
 ## [0.6.5] - 2024-06-17
 

src/config.ts

@@ -18,6 +18,7 @@ import loadConfigFallback from 'tailwindcss/loadConfig'
 import resolveConfigFallback from 'tailwindcss/resolveConfig'
 import type { RequiredConfig } from 'tailwindcss/types/config.js'
 import { expiringMap } from './expiring-map.js'
+import { resolveIn } from './resolve'
 import type { ContextContainer } from './types'
 
 let localRequire = createRequire(import.meta.url)
@@ -106,10 +107,7 @@ async function loadTailwindConfig(
   let tailwindConfig: RequiredConfig = { content: [] }
 
   try {
-    let pkgFile = localRequire.resolve('tailwindcss/package.json', {
-      paths: [baseDir],
-    })
-
+    let pkgFile = resolveIn('tailwindcss/package.json', [baseDir])
     let pkgDir = path.dirname(pkgFile)
 
     try {
@@ -155,9 +153,7 @@ async function loadV4(
   entryPoint: string | null,
 ) {
   // Import Tailwind — if this is v4 it'll have APIs we can use directly
-  let pkgPath = localRequire.resolve('tailwindcss', {
-    paths: [baseDir],
-  })
+  let pkgPath = resolveIn('tailwindcss', [baseDir])
   let tw = await import(pathToFileURL(pkgPath).toString())
 
   // This is not Tailwind v4

src/plugins.ts

@@ -1,4 +1,3 @@
-import { createRequire as req } from 'node:module'
 import type { Parser, ParserOptions, Plugin, Printer } from 'prettier'
 import './types'
 import * as prettierParserAcorn from 'prettier/plugins/acorn'
@@ -9,26 +8,22 @@ import * as prettierParserHTML from 'prettier/plugins/html'
 import * as prettierParserMeriyah from 'prettier/plugins/meriyah'
 import * as prettierParserPostCSS from 'prettier/plugins/postcss'
 import * as prettierParserTypescript from 'prettier/plugins/typescript'
+import { loadIfExists, maybeResolve } from './resolve'
 
 interface PluginDetails {
   parsers: Record<string, Parser<any>>
   printers: Record<string, Printer<any>>
 }
 
 async function loadIfExistsESM(name: string): Promise<Plugin<any>> {
-  try {
-    if (req(import.meta.url).resolve(name)) {
-      let mod = await import(name)
-      return mod.default ?? mod
-    }
+  let mod = await loadIfExists<Plugin<any>>(name)
 
-    throw new Error('unreachable')
-  } catch (e) {
-    return {
-      parsers: {},
-      printers: {},
-    }
+  mod ??= {
+    parsers: {},
+    printers: {},
   }
+
+  return mod
 }
 
 export async function loadPlugins() {
@@ -46,14 +41,6 @@ export async function loadPlugins() {
     ...thirdparty.printers,
   }
 
-  function maybeResolve(name: string) {
-    try {
-      return req(import.meta.url).resolve(name)
-    } catch (err) {
-      return null
-    }
-  }
-
   function findEnabledPlugin(
     options: ParserOptions<any>,
     name: string,

src/resolve.ts

@@ -0,0 +1,47 @@
+import { createRequire as req } from 'node:module'
+import { expiringMap } from './expiring-map'
+
+const localRequire = req(import.meta.url)
+
+// This is a long-lived cache for resolved modules whether they exist or not
+// Because we're compatible with a large number of plugins, we need to check
+// for the existence of a module before attempting to import it. This cache
+// is used to mitigate the cost of that check because Node.js does not cache
+// failed module resolutions making repeated checks very expensive.
+const resolveCache = expiringMap<string, string | null>(30_000)
+
+export function resolveIn(id: string, paths: string[]) {
+  return localRequire.resolve(id, {
+    paths,
+  })
+}
+
+export function maybeResolve(name: string) {
+  let modpath = resolveCache.get(name)
+
+  if (modpath === undefined) {
+    modpath = freshMaybeResolve(name)
+    resolveCache.set(name, modpath)
+  }
+
+  return modpath
+}
+
+export async function loadIfExists<T>(name: string): Promise<T | null> {
+  let modpath = maybeResolve(name)
+
+  if (modpath) {
+    let mod = await import(name)
+    return mod.default ?? mod
+  }
+
+  return null
+}
+
+function freshMaybeResolve(name: string) {
+  try {
+    return localRequire.resolve(name)
+  } catch (err) {
+    return null
+  }
+}