Fixes terse doctor output when no devices available. (#22108)

packages/flutter_tools/lib/src/doctor.dart

@@ -124,12 +124,20 @@ class Doctor {
     for (DoctorValidator validator in validators) {
       final ValidationResult result = await validator.validate();
       buffer.write('${result.leadingBox} ${validator.title} is ');
-      if (result.type == ValidationType.missing)
+      switch (result.type) {
-        buffer.write('not installed.');
+        case ValidationType.missing:
-      else if (result.type == ValidationType.partial)
+          buffer.write('not installed.');
-        buffer.write('partially installed; more components are available.');
+          break;
-      else
+        case ValidationType.partial:
-        buffer.write('fully installed.');
+          buffer.write('partially installed; more components are available.');
+          break;
+        case ValidationType.notAvailable:
+          buffer.write('not available.');
+          break;
+        case ValidationType.installed:
+          buffer.write('fully installed.');
+          break;
+      }
 
       if (result.statusInfo != null)
         buffer.write(' (${result.statusInfo})');
@@ -171,11 +179,17 @@ class Doctor {
       }
       status.stop();
 
-      if (result.type == ValidationType.missing) {
+      switch (result.type) {
-        doctorResult = false;
+        case ValidationType.missing:
-      }
+          doctorResult = false;
-      if (result.type != ValidationType.installed) {
+          issues += 1;
-        issues += 1;
+          break;
+        case ValidationType.partial:
+        case ValidationType.notAvailable:
+          issues += 1;
+          break;
+        case ValidationType.installed:
+          break;
       }
 
       if (result.statusInfo != null)
@@ -238,7 +252,8 @@ abstract class Workflow {
 enum ValidationType {
   missing,
   partial,
-  installed
+  notAvailable,
+  installed,
 }
 
 abstract class DoctorValidator {
@@ -286,6 +301,7 @@ class GroupedValidator extends DoctorValidator {
             mergedType = ValidationType.partial;
           }
           break;
+        case ValidationType.notAvailable:
         case ValidationType.partial:
           mergedType = ValidationType.partial;
           break;
@@ -322,6 +338,7 @@ class ValidationResult {
         return '[✗]';
       case ValidationType.installed:
         return '[✓]';
+      case ValidationType.notAvailable:
       case ValidationType.partial:
         return '[!]';
     }
@@ -600,7 +617,7 @@ class IntelliJValidatorOnMac extends IntelliJValidator {
 }
 
 class DeviceValidator extends DoctorValidator {
-  DeviceValidator() : super('Connected devices');
+  DeviceValidator() : super('Connected device');
 
   @override
   Future<ValidationResult> validate() async {
@@ -619,7 +636,7 @@ class DeviceValidator extends DoctorValidator {
     }
 
     if (devices.isEmpty) {
-      return ValidationResult(ValidationType.partial, messages);
+      return ValidationResult(ValidationType.notAvailable, messages);
     } else {
       return ValidationResult(ValidationType.installed, messages, statusInfo: '${devices.length} available');
     }

packages/flutter_tools/test/commands/doctor_test.dart

@@ -148,13 +148,16 @@ void main() {
               '[✗] Missing Validator\n'
               '    ✗ A useful error message\n'
               '    ! A hint message\n'
+              '[!] Not Available Validator\n'
+              '    ✗ A useful error message\n'
+              '    ! A hint message\n'
               '[!] Partial Validator with only a Hint\n'
               '    ! There is a hint here\n'
               '[!] Partial Validator with Errors\n'
               '    ✗ A error message indicating partial installation\n'
               '    ! Maybe a hint will help the user\n'
               '\n'
-              '! Doctor found issues in 3 categories.\n'
+              '! Doctor found issues in 4 categories.\n'
       ));
     });
 
@@ -170,6 +173,11 @@ void main() {
               '    • A message that is not an error\n'
               '    ! A hint message\n'
               '\n'
+              '[!] Not Available Validator\n'
+              '    ✗ A useful error message\n'
+              '    • A message that is not an error\n'
+              '    ! A hint message\n'
+              '\n'
               '[!] Partial Validator with only a Hint\n'
               '    ! There is a hint here\n'
               '    • But there is no error\n'
@@ -179,7 +187,7 @@ void main() {
               '    ! Maybe a hint will help the user\n'
               '    • An extra message with some verbose details\n'
               '\n'
-              '! Doctor found issues in 3 categories.\n'
+              '! Doctor found issues in 4 categories.\n'
       ));
     });
   });
@@ -301,6 +309,19 @@ class MissingValidator extends DoctorValidator {
   }
 }
 
+class NotAvailableValidator extends DoctorValidator {
+  NotAvailableValidator(): super('Not Available Validator');
+
+  @override
+  Future<ValidationResult> validate() async {
+    final List<ValidationMessage> messages = <ValidationMessage>[];
+    messages.add(ValidationMessage.error('A useful error message'));
+    messages.add(ValidationMessage('A message that is not an error'));
+    messages.add(ValidationMessage.hint('A hint message'));
+    return ValidationResult(ValidationType.notAvailable, messages);
+  }
+}
+
 class PartialValidatorWithErrors extends DoctorValidator {
   PartialValidatorWithErrors() : super('Partial Validator with Errors');
 
@@ -336,6 +357,7 @@ class FakeDoctor extends Doctor {
       _validators = <DoctorValidator>[];
       _validators.add(PassingValidator('Passing Validator'));
       _validators.add(MissingValidator());
+      _validators.add(NotAvailableValidator());
       _validators.add(PartialValidatorWithHintsOnly());
       _validators.add(PartialValidatorWithErrors());
     }