auto-start ADB if it's not running

src/adbclient.js

@@ -87,6 +87,29 @@ ADBClient.prototype = {
             });
     },
 
+    test_adb_connection : function(o) {
+        var x = {o:o||{},deferred:$.Deferred()};
+        this.proxy_connect()
+            .then(function() {
+                return this.dexcmd('cn');
+            })
+            .then(function(data) {
+                this.fd = data;
+                return this.dexcmd('dc', this.fd);
+            })
+            .then(function() {
+                return this.proxy_disconnect();
+            })
+            .then(function() {
+                x.deferred.resolveWith(x.o.ths||this, [null, x.o.extra]);
+            })
+            .fail(function(err) {
+                // if we fail, still resolve the deferred, passing the error
+                x.deferred.resolveWith(x.o.ths||this, [err, x.o.extra]);
+            });
+        return x.deferred;
+    },
+
     list_devices : function(o) {
         var x = {o:o||{},deferred:$.Deferred()};
         this.proxy_connect()

src/debugMain.js

@@ -307,8 +307,23 @@ class AndroidDebugSession extends DebugSession {
                 if (!launchActivity)
                     if (!(launchActivity = this.apk_file_info.launcher))
                         return fail_launch('No valid launch activity found in AndroidManifest.xml or launch.json');
-                return this.findSuitableDevice(args.targetDevice);
+
+                return new ADBClient().test_adb_connection()
+                    .then(err => {
+                        // if adb is not running, see if we can start it ourselves using ANDROID_HOME (and a sensible port number)
+                        var adbport = ws_proxy.adbport;
+                        if (err && process.env.ANDROID_HOME && typeof adbport === 'number' && adbport > 0 && adbport < 65536) {
+                            var adbpath = path.join(process.env.ANDROID_HOME, 'platform-tools', /^win/.test(process.platform)?'adb.exe':'adb');
+                            var adbargs = ['-P',''+adbport,'start-server'];
+                            try {
+                                this.LOG([adbpath, ...adbargs].join(' '));
+                                var stdout = require('child_process').execFileSync(adbpath, adbargs, {cwd:process.env.ANDROID_HOME, encoding:'utf8'});
+                                this.LOG(stdout);
+                            } catch (ex) {} // if we fail, it doesn't matter - the device query will fail and the user will have to work it out themselves
+                        }
+                    })
             })
+            .then(() => this.findSuitableDevice(args.targetDevice))
             .then(device => {
                 this._device = device;
                 this._device.adbclient = new ADBClient(this._device.serial);