Address comments

packages/cache/src/internal/cacheUtils.ts

@@ -7,7 +7,11 @@ import * as path from 'path'
 import * as semver from 'semver'
 import * as util from 'util'
 import {v4 as uuidV4} from 'uuid'
-import {CacheFilename, CompressionMethod} from './constants'
+import {
+  CacheFilename,
+  CompressionMethod,
+  GnuTarPathOnWindows
+} from './constants'
 
 // From https://github.com/actions/toolkit/blob/main/packages/tool-cache/src/tool-cache.ts#L23
 export async function createTempDirectory(): Promise<string> {
@@ -90,7 +94,7 @@ async function getVersion(app: string): Promise<string> {
 
 // Use zstandard if possible to maximize cache performance
 export async function getCompressionMethod(): Promise<CompressionMethod> {
-  if (process.platform === 'win32' && !(await isGnuTarInstalled())) {
+  if (process.platform === 'win32' && !(await getGnuTarPathOnWindows())) {
     // Disable zstd due to bug https://github.com/actions/cache/issues/301
     return CompressionMethod.Gzip
   }
@@ -116,12 +120,12 @@ export function getCacheFileName(compressionMethod: CompressionMethod): string {
     : CacheFilename.Zstd
 }
 
-export async function isGnuTarInstalled(): Promise<boolean> {
-  const gnuTar = `${process.env['PROGRAMFILES']}\\Git\\usr\\bin\\tar.exe`
+export async function getGnuTarPathOnWindows(): Promise<string> {
+  if (fs.existsSync(GnuTarPathOnWindows)) {
+    return GnuTarPathOnWindows
+  }
   const versionOutput = await getVersion('tar')
-  return (
-    versionOutput.toLowerCase().includes('gnu tar') || fs.existsSync(gnuTar)
-  )
+  return versionOutput.toLowerCase().includes('gnu tar') ? io.which('tar') : ''
 }
 
 export function assertDefined<T>(name: string, value?: T): T {

packages/cache/src/internal/constants.ts

@@ -21,3 +21,6 @@ export const DefaultRetryDelay = 5000
 // over the socket during this period, the socket is destroyed and the download
 // is aborted.
 export const SocketTimeout = 5000
+
+// The default path of GNUtar on hosted Windows runners
+export const GnuTarPathOnWindows = 'C:\\Program Files\\Git\\usr\\bin\\tar.exe'

packages/cache/src/internal/tar.ts

@@ -14,19 +14,12 @@ async function getTarPath(
   let tarPath = await io.which('tar', true)
   switch (process.platform) {
     case 'win32': {
-      const gnuTar = `${process.env['PROGRAMFILES']}\\Git\\usr\\bin\\tar.exe`
+      const gnuTar = await utils.getGnuTarPathOnWindows()
       const systemTar = `${process.env['windir']}\\System32\\tar.exe`
-      if (existsSync(gnuTar)) {
+      if (gnuTar) {
         // Use GNUtar as default on windows
         args.push('--force-local')
         tarPath = gnuTar
-      } else if (
-        compressionMethod !== CompressionMethod.Gzip ||
-        (await utils.isGnuTarInstalled())
-      ) {
-        // We only use zstandard compression on windows when gnu tar is installed due to
-        // a bug with compressing large files with bsdtar + zstd
-        args.push('--force-local')
       } else if (existsSync(systemTar)) {
         tarPath = systemTar
       }