Correct OutlineBorder gapStart when InputDecoration icon is specified (#18182)

bin/internal/goldens.version

-95f60c7e328b53dd65de18a608830a872a92e3cd
+17b9d558228edad27729a0c1823430d73cb26608

packages/flutter/lib/src/material/input_decorator.dart

@@ -1037,12 +1037,15 @@ class _RenderDecoration extends RenderBox {
     }
 
     if (label != null) {
+      final double labelX = _boxParentData(label).offset.dx;
       switch (textDirection) {
         case TextDirection.rtl:
-          decoration.borderGap.start = _boxParentData(label).offset.dx + label.size.width;
+          decoration.borderGap.start = labelX + label.size.width;
           break;
         case TextDirection.ltr:
-          decoration.borderGap.start = _boxParentData(label).offset.dx;
+          // The value of _InputBorderGap.start is relative to the origin of the
+          // _BorderContainer which is inset by the icon's width.
+          decoration.borderGap.start = labelX - _boxSize(icon).width;
           break;
       }
       decoration.borderGap.extent = label.size.width * 0.75;

packages/flutter/test/material/input_decorator_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:io' show Platform;
+
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -1428,4 +1430,52 @@ void main() {
       ),
     );
   });
+
+  testWidgets(
+    'InputDecorator OutlineBorder focused label with icon',
+    (WidgetTester tester) async {
+      // Regression test for https://github.com/flutter/flutter/issues/18111
+
+      Widget buildFrame(TextDirection textDirection) {
+        return new MaterialApp(
+          home: new Scaffold(
+            body: new Container(
+              padding: const EdgeInsets.all(16.0),
+              alignment: Alignment.center,
+              child: new Directionality(
+                textDirection: textDirection,
+                child: const RepaintBoundary(
+                  child: const InputDecorator(
+                    isFocused: true,
+                    isEmpty: true,
+                    decoration: const InputDecoration(
+                      icon: const Icon(Icons.insert_link),
+                      labelText: 'primaryLink',
+                      hintText: 'Primary link to story',
+                      border: const OutlineInputBorder(),
+                    ),
+                  ),
+                ),
+              ),
+            ),
+          ),
+        );
+      }
+
+      await tester.pumpWidget(buildFrame(TextDirection.ltr));
+      await expectLater(
+        find.byType(InputDecorator),
+        matchesGoldenFile('input_decorator.outline_icon_label.ltr.png'),
+        skip: !Platform.isLinux,
+      );
+
+      await tester.pumpWidget(buildFrame(TextDirection.rtl));
+      await expectLater(
+        find.byType(InputDecorator),
+        matchesGoldenFile('input_decorator.outline_icon_label.rtl.png'),
+        skip: !Platform.isLinux,
+      );
+    },
+    skip: !Platform.isLinux,
+  );
 }