From 7ff5e3654d37834033fbd0936b1ef486d5e74926 Mon Sep 17 00:00:00 2001
From: Alexander Markov <alexmarkov@google.com>
Date: Tue, 2 Jun 2026 05:42:19 -0700
Subject: [PATCH] [tfa] Fix handling of late local variables with static type
 Never

Initializers of late local variables are wrapped into closures.
The result type of a closure is a static type of the variable.
So initializer of a late variable with static type Never have a call
to a closure with static result type Never.

TFA summary collector handles calls with static result type Never
specially, treating all subsequent code as unreachable (by setting
control-dependent condition to empty). As a result, all subsequent
code after late variable with static type Never (and initializer) is
tree-shaken.

The fix is to avoid propagating control-dependent condition out of
the late variable initializers.

TEST=pkg/vm/testcases/transformations/type_flow/transformer/regress_63478.dart
Fixes https://github.com/dart-lang/sdk/issues/63478

Change-Id: If41221777c9d249dd21ce5827c586b0f531cbce8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/508363
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>
---
 .../type_flow/summary_collector.dart          |  6 ++++
 .../type_flow/transformer/regress_63478.dart  | 24 +++++++++++++++
 .../transformer/regress_63478.dart.expect     | 30 +++++++++++++++++++
 3 files changed, 60 insertions(+)
 create mode 100644 pkg/vm/testcases/transformations/type_flow/transformer/regress_63478.dart
 create mode 100644 pkg/vm/testcases/transformations/type_flow/transformer/regress_63478.dart.expect

diff --git a/pkg/vm/lib/transformations/type_flow/summary_collector.dart b/pkg/vm/lib/transformations/type_flow/summary_collector.dart
index f1714649e07..ad55e732e32 100644
--- a/pkg/vm/lib/transformations/type_flow/summary_collector.dart
+++ b/pkg/vm/lib/transformations/type_flow/summary_collector.dart
@@ -2817,6 +2817,7 @@ class SummaryCollector extends RecursiveResultVisitor<TypeExpr?> {
     final variable = node.variable;
     variable.annotations.forEach(_visitAnnotation);
     final initializer = variable.initializer;
+    final savedCondition = _currentCondition;
     final TypeExpr initialValue = initializer == null
         ? ((variable.type.nullability == Nullability.nonNullable ||
                   variable.isLate)
@@ -2824,6 +2825,11 @@ class SummaryCollector extends RecursiveResultVisitor<TypeExpr?> {
               : _nullType)
         : _visit(initializer);
     _declareVariable(variable, initialValue);
+    if (variable.isLate) {
+      // Restore condition as initializer of a late variable
+      // is not evaluated immediately.
+      _currentCondition = savedCondition;
+    }
     return null;
   }
 
diff --git a/pkg/vm/testcases/transformations/type_flow/transformer/regress_63478.dart b/pkg/vm/testcases/transformations/type_flow/transformer/regress_63478.dart
new file mode 100644
index 00000000000..96ff6dd079c
--- /dev/null
+++ b/pkg/vm/testcases/transformations/type_flow/transformer/regress_63478.dart
@@ -0,0 +1,24 @@
+// Copyright (c) 2026, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+// Regression test for https://github.com/dart-lang/sdk/issues/63478.
+// Verifies that initializer of a late variable doesn't affect
+// subsequent statements.
+
+void test1() {
+  late var x = throw "error";
+  print("reachable");
+}
+
+Never sayNever() => throw 'Never';
+
+void test2() {
+  late Never y = sayNever();
+  print("reachable");
+}
+
+void main() {
+  test1();
+  test2();
+}
diff --git a/pkg/vm/testcases/transformations/type_flow/transformer/regress_63478.dart.expect b/pkg/vm/testcases/transformations/type_flow/transformer/regress_63478.dart.expect
new file mode 100644
index 00000000000..980722e091e
--- /dev/null
+++ b/pkg/vm/testcases/transformations/type_flow/transformer/regress_63478.dart.expect
@@ -0,0 +1,30 @@
+library #lib;
+import self as self;
+import "dart:core" as core;
+
+
+[@vm.inferred-return-type.metadata=dart.core::Null? (value: null)]
+static method test1() → void {
+  function #x#initializer() → Never
+    return throw "error";
+  late Never x = [@vm.inferred-type.metadata=? (receiver not int)] #x#initializer(){() → Never};
+  core::print("reachable");
+}
+
+[@vm.inferred-return-type.metadata=!]
+static method sayNever() → Never
+  return throw "Never";
+
+[@vm.inferred-return-type.metadata=dart.core::Null? (value: null)]
+static method test2() → void {
+  function #y#initializer() → Never
+    return self::sayNever();
+  late Never y = [@vm.inferred-type.metadata=? (receiver not int)] #y#initializer(){() → Never};
+  core::print("reachable");
+}
+
+[@vm.inferred-return-type.metadata=dart.core::Null? (value: null)]
+static method main() → void {
+  self::test1();
+  self::test2();
+}