Use pre-installed Gradle when version matches

By executing Gradle on the PATH, we can avoid downloading and installing
a Gradle version that is already available on the runner.

Fixes #270

.github/workflows/integ-test-execution.yml

@@ -24,9 +24,6 @@ jobs:
       fail-fast: false
       matrix:
         os: ${{fromJSON(inputs.runner-os)}}
-        include:
-          - os: windows-latest
-            script-suffix: '.bat'
     runs-on: ${{ matrix.os }}
     steps:
     - name: Checkout sources

.github/workflows/integ-test-provision-gradle-versions.yml

@@ -25,9 +25,6 @@ jobs:
       fail-fast: false
       matrix:
         os: ${{fromJSON(inputs.runner-os)}}
-        include:
-          - os: windows-latest
-            script-suffix: '.bat'
     runs-on: ${{ matrix.os }}
     steps:
     - name: Checkout sources

sources/src/execution/provision.ts

@@ -1,9 +1,11 @@
 import * as fs from 'fs'
 import * as os from 'os'
 import * as path from 'path'
+import which from 'which'
 import * as httpm from '@actions/http-client'
 import * as core from '@actions/core'
 import * as cache from '@actions/cache'
+import * as exec from '@actions/exec'
 import * as toolCache from '@actions/tool-cache'
 
 import * as gradlew from './gradlew'
@@ -95,6 +97,12 @@ async function findGradleVersionDeclaration(version: string): Promise<GradleVers
 
 async function installGradleVersion(versionInfo: GradleVersionInfo): Promise<string> {
     return core.group(`Provision Gradle ${versionInfo.version}`, async () => {
+        const preInstalledGradle = await findGradleVersionOnPath(versionInfo)
+        if (preInstalledGradle !== undefined) {
+            core.info(`Gradle version ${versionInfo.version} is already available on PATH. Not installing.`)
+            return preInstalledGradle
+        }
+
         return locateGradleAndDownloadIfRequired(versionInfo)
     })
 }
@@ -184,3 +192,15 @@ interface GradleVersionInfo {
     version: string
     downloadUrl: string
 }
+
+async function findGradleVersionOnPath(versionInfo: GradleVersionInfo): Promise<string | undefined> {
+    const gradleExecutable = await which('gradle', {nothrow: true})
+    if (gradleExecutable) {
+        const output = await exec.getExecOutput(gradleExecutable, ['-v'], {silent: true})
+        if (output.stdout.includes(`Gradle ${versionInfo.version}`)) {
+            return gradleExecutable
+        }
+    }
+
+    return undefined
+}