Expression evaluation autocomplete overlay is positioned over the las…

…t `.` in the expression (#3449)

packages/devtools_app/lib/src/debugger/evaluate.dart

@@ -13,6 +13,7 @@ import '../globals.dart';
 import '../notifications.dart';
 import '../theme.dart';
 import '../ui/search.dart';
+import '../ui/utils.dart';
 import '../utils.dart';
 import 'debugger_controller.dart';
 
@@ -135,14 +136,28 @@ class _ExpressionEvalFieldState extends State<ExpressionEvalField>
               shouldRequestFocus: false,
               supportClearField: true,
               onSelection: _onSelection,
-              tracking: true,
               decoration: const InputDecoration(
                 contentPadding: EdgeInsets.all(denseSpacing),
                 border: OutlineInputBorder(),
                 focusedBorder: OutlineInputBorder(borderSide: BorderSide.none),
                 enabledBorder: OutlineInputBorder(borderSide: BorderSide.none),
                 labelText: 'Eval',
               ),
+              overlayXPositionBuilder:
+                  (String inputValue, TextStyle inputStyle) {
+                // X-coordinate is equivalent to the width of the input text
+                // up to the last "." or the insertion point (cursor):
+                final indexOfDot = inputValue.lastIndexOf('.');
+                final textSegment = indexOfDot != -1
+                    ? inputValue.substring(0, indexOfDot + 1)
+                    : inputValue;
+                return calculateTextSpanWidth(
+                  TextSpan(
+                    text: textSegment,
+                    style: inputStyle,
+                  ),
+                );
+              },
             ),
           ),
         ),

packages/devtools_app/lib/src/ui/search.dart

@@ -556,6 +556,13 @@ typedef ClearSearchField = Function(
   bool force,
 });
 
+/// Provided by clients to specify where the autocomplete overlay should be
+/// positioned relative to the input text.
+typedef OverlayXPositionBuilder = double Function(
+  String inputValue,
+  TextStyle inputStyle,
+);
+
 mixin SearchFieldMixin<T extends StatefulWidget> on State<T> {
   TextEditingController searchTextFieldController;
   FocusNode _searchFieldFocusNode;
@@ -601,9 +608,10 @@ mixin SearchFieldMixin<T extends StatefulWidget> on State<T> {
   /// [searchFieldKey]
   /// [searchFieldEnabled]
   /// [onSelection]
-  /// [onHilightDropdown] use to override default highlghter.
+  /// [onHighlightDropdown] use to override default highlghter.
   /// [decoration]
-  /// [tracking] if true displays pop-up to the right of the TextField's caret.
+  /// [overlayXPositionBuilder] callback function to determine where the
+  /// autocomplete overlay should be positioned relative to the input text.
   /// [supportClearField] if true clear TextField content if pop-up not visible. If
   /// pop-up is visible close the pop-up on first ESCAPE.
   /// [keyEventsToPropogate] a set of key events that should be propogated to
@@ -617,7 +625,7 @@ mixin SearchFieldMixin<T extends StatefulWidget> on State<T> {
     HighlightAutoComplete onHighlightDropdown,
     InputDecoration decoration,
     String label,
-    bool tracking = false,
+    OverlayXPositionBuilder overlayXPositionBuilder,
     bool supportClearField = false,
     Set<LogicalKeyboardKey> keyEventsToPropogate = const {},
     VoidCallback onClose,
@@ -633,7 +641,7 @@ mixin SearchFieldMixin<T extends StatefulWidget> on State<T> {
       searchTextFieldController: searchTextFieldController,
       decoration: decoration,
       label: label,
-      tracking: tracking,
+      overlayXPositionBuilder: overlayXPositionBuilder,
       onClose: onClose,
     );
 
@@ -718,6 +726,7 @@ class _SearchField extends StatelessWidget {
     this.tracking = false,
     this.decoration,
     this.onClose,
+    this.overlayXPositionBuilder,
   });
 
   final SearchControllerMixin controller;
@@ -731,30 +740,21 @@ class _SearchField extends StatelessWidget {
   final bool tracking;
   final InputDecoration decoration;
   final VoidCallback onClose;
+  final OverlayXPositionBuilder overlayXPositionBuilder;
 
   @override
   Widget build(BuildContext context) {
+    final textStyle = Theme.of(context).textTheme.subtitle1;
     final searchField = TextField(
       key: searchFieldKey,
       autofocus: true,
       enabled: searchFieldEnabled,
       focusNode: searchFieldFocusNode,
       controller: searchTextFieldController,
+      style: textStyle,
       onChanged: (value) {
-        if (tracking) {
-          // Use a TextPainter to calculate the width of the newly entered text.
-          // TODO(terry): The TextPainter's TextStyle is default (same as this
-          //              TextField) consider explicitly using a TextStyle of
-          //              this TextField if the TextField needs styling.
-          final painter = TextPainter(
-            textDirection: TextDirection.ltr,
-            text: TextSpan(text: value),
-          );
-          painter.layout();
-
-          // X coordinate of the pop-up, immediately to the right of the insertion
-          // point (caret).
-          controller.xPosition = painter.width;
+        if (overlayXPositionBuilder != null) {
+          controller.xPosition = overlayXPositionBuilder(value, textStyle);
         }
         controller.search = value;
       },