perf(register): cache readDefaultTsConfig results (#918)

Previously, readDefaultTsConfig would read the tsconfig.json file every
time it was called, which would be at least once for every file being
compiled. By caching the results so that the tsconfig.json file only
needs to be read once, build times can be dramatically reduced, bringing
them in-line with build times when using a hardcoded config.

As an example, on a personal project, this shaves around 25 seconds off
of a 40 second build, meaning it speeds up the build by more than two
times.

Author: mogzol

packages/register/read-default-tsconfig.ts

@@ -8,6 +8,8 @@ import * as ts from 'typescript'
 
 const debug = debugFactory('@swc-node')
 
+const configCache: Record<string, Partial<ts.CompilerOptions & { fallbackToTs: (path: string) => boolean }>> = {}
+
 export function readDefaultTsConfig(
   tsConfigPath = process.env.SWC_NODE_PROJECT ?? process.env.TS_NODE_PROJECT ?? join(process.cwd(), 'tsconfig.json'),
 ) {
@@ -25,6 +27,10 @@ export function readDefaultTsConfig(
 
   const fullTsConfigPath = resolve(tsConfigPath)
 
+  if (fullTsConfigPath in configCache) {
+    return configCache[fullTsConfigPath]
+  }
+
   if (!existsSync(fullTsConfigPath)) {
     return compilerOptions
   }
@@ -50,6 +56,8 @@ export function readDefaultTsConfig(
     console.info(yellow(`Read ${tsConfigPath} failed: ${(e as Error).message}`))
   }
 
+  configCache[fullTsConfigPath] = compilerOptions
+
   return compilerOptions
 }
 
@@ -128,7 +136,7 @@ export function tsCompilerOptionsToSwcConfig(options: ts.CompilerOptions, filena
     keepClassNames: true,
     externalHelpers: Boolean(options.importHelpers),
     react:
-      options.jsxFactory ?? options.jsxFragmentFactory ?? options.jsx ?? options.jsxImportSource
+      (options.jsxFactory ?? options.jsxFragmentFactory ?? options.jsx ?? options.jsxImportSource)
         ? {
             pragma: options.jsxFactory,
             pragmaFrag: options.jsxFragmentFactory,