docker: set default standalone

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

src/buildx.ts

@@ -18,22 +18,10 @@ export class Buildx {
   private tmpdir = fs.mkdtempSync(path.join(os.tmpdir(), 'docker-actions-toolkit-')).split(path.sep).join(path.posix.sep);
 
   constructor(opts?: BuildxOpts) {
-    this.standalone = opts?.standalone ?? this.isStandalone();
+    this.standalone = opts?.standalone ?? !Docker.isAvailable();
     this.version = this.getVersion();
   }
 
-  private isStandalone(): boolean {
-    let dockerAvailable = false;
-    Docker.isAvailable()
-      .then((res: boolean) => {
-        dockerAvailable = res;
-      })
-      .catch(e => {
-        dockerAvailable = false;
-      });
-    return dockerAvailable;
-  }
-
   public getCommand(args: Array<string>) {
     return {
       command: this.standalone ? 'buildx' : 'docker',

src/docker.ts

@@ -2,26 +2,30 @@ import * as core from '@actions/core';
 import * as exec from '@actions/exec';
 
 export class Docker {
-  public static async isAvailable(): Promise<boolean> {
-    return await exec
+  public static isAvailable(): boolean {
+    let dockerAvailable = false;
+    exec
       .getExecOutput('docker', undefined, {
         ignoreReturnCode: true,
         silent: true
       })
       .then(res => {
         if (res.stderr.length > 0 && res.exitCode != 0) {
-          return false;
+          dockerAvailable = false;
+        } else {
+          dockerAvailable = res.exitCode == 0;
         }
-        return res.exitCode == 0;
       })
       // eslint-disable-next-line @typescript-eslint/no-unused-vars
       .catch(error => {
-        return false;
+        dockerAvailable = false;
       });
+    return dockerAvailable;
   }
 
   public static async info(standalone?: boolean) {
-    if (standalone) {
+    const dockerAvailable = standalone ?? !Docker.isAvailable();
+    if (dockerAvailable) {
       core.info(`Docker info skipped in standalone mode`);
     } else {
       await exec.exec('docker', ['version'], {