Issue 13239. Add the 'Encapsulate Field' refactoring.

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

Index: pkg/analysis_server/lib/src/services/correction/assist_internal.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
index d213c4725c3572d0329a8c32eab736c3d9da3874..3575bae454643f22e997ecc82c03358c0243e828 100644
--- a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
@@ -85,6 +85,7 @@ class AssistProcessor {
     _addProposal_convertToIsNot_onIs();
     _addProposal_convertToIsNot_onNot();
     _addProposal_convertToIsNotEmpty();
+    _addProposal_encapsulateField();
     _addProposal_exchangeOperands();
     _addProposal_importAddShow();
     _addProposal_introduceLocalTestedType();
@@ -660,6 +661,7 @@ class AssistProcessor {
         isEmptyAccess.parent as PrefixExpression;
     // should be !
     if (prefixExpression.operator.type != TokenType.BANG) {
+      _coverageMarker();
       return;
     }
     // do replace
@@ -669,6 +671,49 @@ class AssistProcessor {
     _addAssist(AssistKind.CONVERT_INTO_IS_NOT_EMPTY, []);
   }
 
+  void _addProposal_encapsulateField() {
+    // find FieldDeclaration
+    FieldDeclaration fieldDeclaraton =
+        node.getAncestor((x) => x is FieldDeclaration);
+    if (fieldDeclaraton == null) {
+      _coverageMarker();
+      return;
+    }
+    // has a parse error
+    VariableDeclarationList variableList = fieldDeclaraton.fields;
+    if (variableList.keyword == null && variableList.type == null) {
+      _coverageMarker();
+      return;
+    }
+    // should have exactly one field
+    List<VariableDeclaration> fields = variableList.variables;
+    if (fields.length != 1) {
+      _coverageMarker();
+      return;
+    }
+    VariableDeclaration field = fields.first;
+    SimpleIdentifier nameNode = field.name;
+    // should have a public name
+    String name = nameNode.name;
+    if (Identifier.isPrivateName(name)) {
+      _coverageMarker();
+      return;
+    }
+    // prepare change
+    String eol2 = eol + eol;
+    _addReplaceEdit(rangeNode(nameNode), '_$name');
+    String typeNameCode =
+        variableList.type != null ? _getNodeText(variableList.type) + ' ' : '';
+    String getterCode = '$eol2  ${typeNameCode}get $name => _$name;';
+    String setterCode = '$eol2'
+        '  void set $name(${typeNameCode}$name) {$eol'
+        '    _$name = $name;$eol'
+        '  }';
+    _addInsertEdit(fieldDeclaraton.end, getterCode + setterCode);
+    // add proposal
+    _addAssist(AssistKind.ENCAPSULATE_FIELD, []);
+  }
+
   void _addProposal_exchangeOperands() {
     // check that user invokes quick assist on binary expression
     if (node is! BinaryExpression) {