Fix convert to cascade

Closes #56788

GitOrigin-RevId: 7e35273
Change-Id: I49af5c39267d6b91cfca40b4feb42e1d921a4eeb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/386860
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Brian Wilkerson <[email protected]>
Reviewed-by: Samuel Rawlins <[email protected]>

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

@@ -30,8 +30,20 @@ class ConvertToCascade extends ResolvedCorrectionProducer {
     if (block is! Block) return;
 
     var previous = _getPrevious(block, node);
-    if (previous is! ExpressionStatement) return;
-    var previousOperator = _getTargetAndOperator(previous.expression)?.operator;
+    Token? previousOperator;
+    Token? semicolon;
+    if (previous is ExpressionStatement) {
+      semicolon = previous.semicolon;
+      previousOperator = _getTargetAndOperator(previous.expression)?.operator;
+    } else if (previous is VariableDeclarationStatement) {
+      // Single variable declaration.
+      if (previous.variables.variables.length != 1) {
+        return;
+      }
+      semicolon = previous.endToken;
+    } else {
+      return;
+    }
 
     var expression = node.expression;
     var target = _getTargetAndOperator(expression)?.target;
@@ -43,7 +55,9 @@ class ConvertToCascade extends ResolvedCorrectionProducer {
       if (previousOperator != null) {
         builder.addSimpleInsertion(previousOperator.offset, '.');
       }
-      builder.addDeletion(range.token(previous.semicolon!));
+      if (semicolon != null) {
+        builder.addDeletion(range.token(semicolon));
+      }
       builder.addSimpleReplacement(range.node(target), targetReplacement);
     });
   }

pkg/analysis_server/test/src/services/correction/fix/convert_to_cascade_test.dart

@@ -50,6 +50,27 @@ void f(A a) {
 ''');
   }
 
+  Future<void> test_declaration_method() async {
+    await resolveTestCode('''
+class A {
+  void m() {}
+}
+void f() {
+  final a = A();
+  a.m();
+}
+''');
+    await assertHasFix('''
+class A {
+  void m() {}
+}
+void f() {
+  final a = A()
+  ..m();
+}
+''');
+  }
+
   Future<void> test_method_method() async {
     await resolveTestCode('''
 class A {
@@ -96,6 +117,32 @@ void f(A a) {
 ''');
   }
 
+  Future<void> test_multipleDeclaration_first_method() async {
+    await resolveTestCode('''
+class A {
+  void m() {}
+}
+void f() {
+  final a = A(), a2 = A();
+  a.m();
+}
+''');
+    await assertNoFix();
+  }
+
+  Future<void> test_multipleDeclaration_last_method() async {
+    await resolveTestCode('''
+class A {
+  void m() {}
+}
+void f() {
+  final a = A(), a2 = A();
+  a2.m();
+}
+''');
+    await assertNoFix();
+  }
+
   Future<void> test_property_cascade() async {
     await resolveTestCode('''
 class A {