Compact sample building for platform conflict description. (dart-lang…

…#344)

lib/src/messages.dart

@@ -51,3 +51,14 @@ String runningDartanalyzerFailed(bool usesFlutter, errorMsg) {
   return 'Running `${dict.dartanalyzerShortCmd}` failed with the following output:\n\n'
       '```\n$errorMsg\n```\n';
 }
+
+/// Build a list like "A, B and 3 more".
+String buildSample(Iterable<String> items) {
+  final total = items.length;
+  final fullCount = total <= 3 ? total : 2;
+  var sample = items.take(fullCount).join(', ');
+  if (total > fullCount) {
+    sample = '$sample and ${total - fullCount} more.';
+  }
+  return sample;
+}

lib/src/platform.dart

@@ -1,5 +1,6 @@
 library pana.platform;
 
+import 'messages.dart' show buildSample;
 import 'model.dart'
     show ComponentNames, DartPlatform, PlatformNames, PlatformUse;
 import 'pubspec.dart';
@@ -201,17 +202,16 @@ DartPlatform classifyPkgPlatform(
       transitiveLibs.keys ?? <String>[],
       value: (key) => classifyLibPlatform(transitiveLibs[key]));
 
+  String formatConflictSample(String s) {
+    final components = libraries[s].components.map((s) => '`$s`').join(', ');
+    return '`$s` (components: $components)';
+  }
+
   final conflicts =
       libraries.keys.where((key) => libraries[key].hasConflict).toList();
   if (conflicts.isNotEmpty) {
     conflicts.sort();
-    var sample = conflicts.take(3).map((s) {
-      final components = libraries[s].components.map((s) => '`$s`').join(', ');
-      return '`$s` (components: $components)';
-    }).join(', ');
-    if (conflicts.length > 3) {
-      sample = '$sample and ${conflicts.length - 3} more.';
-    }
+    final sample = buildSample(conflicts.map(formatConflictSample));
     return new DartPlatform.conflict('Conflicting libraries: $sample.');
   }
 
@@ -235,14 +235,7 @@ DartPlatform classifyPkgPlatform(
       );
     } else {
       flutterConflicts.sort();
-      var sample = flutterConflicts.take(3).map((s) {
-        final components =
-            libraries[s].components.map((s) => '`$s`').join(', ');
-        return '`$s` (components: $components)';
-      }).join(', ');
-      if (flutterConflicts.length > 3) {
-        sample = '$sample and ${flutterConflicts.length - 3} more.';
-      }
+      final sample = buildSample(flutterConflicts.map(formatConflictSample));
       return new DartPlatform.conflict(
           'References Flutter, but has conflicting libraries: $sample.');
     }

test/messages_test.dart

@@ -0,0 +1,39 @@
+// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:test/test.dart';
+
+import 'package:pana/src/messages.dart';
+
+void main() {
+  group('buildSample', () {
+    String format(int value) => '${value}x$value';
+
+    test('no items', () {
+      expect(buildSample(<int>[].map(format)), '');
+    });
+
+    test('1 item', () {
+      expect(buildSample(<int>[1].map(format)), '1x1');
+    });
+
+    test('2 items', () {
+      expect(buildSample(<int>[1, 2].map(format)), '1x1, 2x2');
+    });
+
+    test('3 items', () {
+      expect(buildSample(<int>[1, 2, 3].map(format)), '1x1, 2x2, 3x3');
+    });
+
+    test('4 items', () {
+      expect(
+          buildSample(<int>[1, 2, 3, 4].map(format)), '1x1, 2x2 and 2 more.');
+    });
+
+    test('10 items', () {
+      expect(buildSample(new List.generate(10, (i) => i + 1).map(format)),
+          '1x1, 2x2 and 8 more.');
+    });
+  });
+}