[flutter_tool] Misc. fixes for Fuchsia (#33466)

packages/flutter_tools/lib/src/fuchsia/fuchsia_dev_finder.dart

@@ -23,7 +23,8 @@ class FuchsiaDevFinder {
   /// formatted as follows:
   /// 192.168.42.172 scare-cable-skip-joy
   Future<List<String>> list() async {
-    if (fuchsiaArtifacts.devFinder == null) {
+    if (fuchsiaArtifacts.devFinder == null ||
+        !fuchsiaArtifacts.devFinder.existsSync()) {
       throwToolExit('Fuchsia dev_finder tool not found.');
     }
     final List<String> command = <String>[
@@ -45,7 +46,8 @@ class FuchsiaDevFinder {
   /// The string [deviceName] should be the name of the device from the
   /// 'list' command, e.g. 'scare-cable-skip-joy'.
   Future<String> resolve(String deviceName) async {
-    if (fuchsiaArtifacts.devFinder == null) {
+    if (fuchsiaArtifacts.devFinder == null ||
+        !fuchsiaArtifacts.devFinder.existsSync()) {
       throwToolExit('Fuchsia dev_finder tool not found.');
     }
     final List<String> command = <String>[

packages/flutter_tools/lib/src/fuchsia/fuchsia_device.dart

@@ -378,7 +378,7 @@ class FuchsiaDevice extends Device {
     const String findCommand = 'find /hub -name vmservice-port';
     final RunResult findResult = await shell(findCommand);
     if (findResult.exitCode != 0) {
-      throwToolExit("'$findCommand' on device $id failed");
+      throwToolExit("'$findCommand' on device $id failed. stderr: '${findResult.stderr}'");
       return null;
     }
     final String findOutput = findResult.stdout;

packages/flutter_tools/lib/src/fuchsia/fuchsia_sdk.dart

@@ -46,7 +46,8 @@ class FuchsiaSdk {
   ///    $ dev_finder list -full
   ///    > 192.168.42.56 paper-pulp-bush-angel
   Future<String> listDevices() async {
-    if (fuchsiaArtifacts.devFinder == null) {
+    if (fuchsiaArtifacts.devFinder == null ||
+        !fuchsiaArtifacts.devFinder.existsSync()) {
       return null;
     }
     final List<String> devices = await fuchsiaDevFinder.list();
@@ -64,7 +65,8 @@ class FuchsiaSdk {
           StreamController<String>(onCancel: () {
         process.kill();
       });
-      if (fuchsiaArtifacts.sshConfig == null) {
+      if (fuchsiaArtifacts.sshConfig == null ||
+          !fuchsiaArtifacts.sshConfig.existsSync()) {
         printError('Cannot read device logs: No ssh config.');
         printError('Have you set FUCHSIA_SSH_CONFIG or FUCHSIA_BUILD_DIR?');
         return null;
@@ -91,7 +93,7 @@ class FuchsiaSdk {
     } catch (exception) {
       printTrace('$exception');
     }
-    return null;
+    return const Stream<String>.empty();
   }
 }
 

packages/flutter_tools/test/fuchsia/fuchsa_device_test.dart

@@ -240,6 +240,8 @@ void main() {
         when(mockProcess.stderr).thenAnswer((Invocation _) => stderr.stream);
         devFinder = MockFile();
         sshConfig = MockFile();
+        when(devFinder.existsSync()).thenReturn(true);
+        when(sshConfig.existsSync()).thenReturn(true);
         when(devFinder.absolute).thenReturn(devFinder);
         when(sshConfig.absolute).thenReturn(sshConfig);
       });