Extract shorten() into string utils.

R=brianwilkerson@google.com

Bug:
Change-Id: I68d17461b4b5b478df5713cadb120a130f492406
Reviewed-on: https://dart-review.googlesource.com/16602
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/analysis_server/lib/src/services/correction/flutter_util.dart

@@ -2,6 +2,7 @@
 // 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:analysis_server/src/services/correction/strings.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ -187,13 +188,13 @@ String getWidgetPresentationText(InstanceCreationExpression node) {
   if (_isExactWidget(
       element, 'Icon', 'package:flutter/src/widgets/icon.dart')) {
     String text = arguments[0].toString();
-    String arg = _shortenText(text, 32);
+    String arg = shorten(text, 32);
     return 'Icon($arg)';
   }
   if (_isExactWidget(
       element, 'Text', 'package:flutter/src/widgets/text.dart')) {
     String text = arguments[0].toString();
-    String arg = _shortenText(text, 32);
+    String arg = shorten(text, 32);
     return 'Text($arg)';
   }
   return element.name;
@@ -257,11 +258,3 @@ bool _isExactWidget(ClassElement element, String type, String uri) {
       element.name == type &&
       element.source.uri.toString() == uri;
 }
-
-String _shortenText(String text, int limit) {
-  if (text.length > limit) {
-    int half = limit ~/ 2 - 2;
-    return text.substring(0, half) + '...' + text.substring(text.length - half);
-  }
-  return text;
-}

pkg/analysis_server/lib/src/services/correction/strings.dart

@@ -218,6 +218,20 @@ String repeat(String s, int n) {
   return sb.toString();
 }
 
+/**
+ * If the [text] length is above the [limit], replace the middle with `...`.
+ */
+String shorten(String text, int limit) {
+  if (text.length > limit) {
+    int headLength = limit ~/ 2 - 1;
+    int tailLength = limit - headLength - 3;
+    return text.substring(0, headLength) +
+        '...' +
+        text.substring(text.length - tailLength);
+  }
+  return text;
+}
+
 /**
  * Gets the substring after the last occurrence of a separator.
  * The separator is not returned.

pkg/analysis_server/test/services/correction/flutter_util_test.dart

@@ -60,7 +60,7 @@ var w = const Text('${'abc' * 100}');
 ''');
     var w = _getTopVariableCreation('w');
     expect(
-        getWidgetPresentationText(w), "Text('abcabcabcabca...cabcabcabcabc')");
+        getWidgetPresentationText(w), "Text('abcabcabcabcab...cabcabcabcabc')");
   }
 
   test_getFlutterWidgetPresentationText_unresolved() async {

pkg/analysis_server/test/services/correction/strings_test.dart

@@ -154,6 +154,18 @@ class StringsTest {
     expect(repeat('abc', 3), 'abcabcabc');
   }
 
+  void test_shorten() {
+    expect(shorten('', 10), '');
+    expect(shorten('0', 10), '0');
+    expect(shorten('012', 10), '012');
+    expect(shorten('0123456789', 10), '0123456789');
+    expect(shorten('0123456789abcd', 10), '0123...bcd');
+    expect(shorten('0123456789abcde', 10), '0123...cde');
+    expect(shorten('0123456789abcdef', 10), '0123...def');
+    expect(shorten('0123456789abcdef', 11), '0123...cdef');
+    expect(shorten('0123456789abcdef', 12), '01234...cdef');
+  }
+
   void test_substringAfterLast() {
     expect(substringAfterLast('', '/'), '');
     expect(substringAfterLast('abc', ''), '');