[flow] Part 2 Issue 3658 - Forward IfNullSet let expressions in the CFE.

This is a small change that allows forwarding let expressions for IfNullSets in the CFE.

Since we now store the promotion information for a written expression in an if-statement, the CFE builds a let expression and it's not recognized by flow analysis. To fix this, we add a forward so flow analysis recognizes that it's the same expression that it's trying to find.

language/inference_update_4/assignment_promotion_in_if_statement_test passes from this change.

Bug: dart-lang/language#3658
Change-Id: I4ec99de036498869b0d9c5c652ca748d9f5e570a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/391861
Reviewed-by: Johnni Winther <[email protected]>
Reviewed-by: Paul Berry <[email protected]>
Commit-Queue: Kallen Tu <[email protected]>

pkg/front_end/lib/src/type_inference/inference_visitor.dart

@@ -6002,6 +6002,12 @@ class InferenceVisitorImpl extends InferenceVisitorBase
       replacement = new Let(readVariable, conditional)
         ..fileOffset = node.fileOffset;
     }
+
+    // Forward the expression in cases where flow analysis needs to use the
+    // expression information. For example, for keeping the promotion in the
+    // following if statement in `if ((x ??= 2) == null) { ... }`.
+    flowAnalysis.forwardExpression(replacement, writeResult.expression);
+
     return createNullAwareExpressionInferenceResult(
         inferredType, replacement, nullAwareGuards);
   }

pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart

@@ -0,0 +1,53 @@
+// Copyright (c) 2024, 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.
+
+// Tests the promotion of assignment expressions in if statements as described
+// by https://github.com/dart-lang/language/issues/3658
+
+int? nullableInt() => 1;
+
+notEqualNull_assignIfNull() {
+  int? x = null;
+  if ((x ??= nullableInt()) != null) {
+    x.isEven; // x promoted to int
+  }
+}
+
+notEqualNullNull_eq() {
+  int? x = null;
+  if ((x = nullableInt()) != null) {
+    x.isEven; // x promoted to int
+  }
+}
+
+is_eq() {
+  int? x = null;
+  if ((x = nullableInt()) is int) {
+    x.isEven; // x promoted to int
+  }
+}
+
+is_plusEq() {
+  num x = 2;
+  if ((x += 1) is int) {
+    x.isEven; // x promoted to int
+  }
+}
+
+is_postfix() {
+  num x = 2;
+  if ((x++) is int) {
+    // No promotion because the value being is checked is the value of `x`
+    // before the increment, and that value isn't relevant after the increment
+    // occurs.
+    x.isEven; // Error.
+  }
+}
+
+is_prefix() {
+  num x = 2;
+  if ((++x) is int) {
+    x.isEven; // x promoted to int
+  }
+}

pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart.strong.expect

@@ -0,0 +1,53 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart:44:7: Error: The getter 'isEven' isn't defined for the class 'num'.
+// Try correcting the name to the name of an existing getter, or defining a getter or field named 'isEven'.
+//     x.isEven; // Error.
+//       ^^^^^^
+//
+import self as self;
+import "dart:core" as core;
+
+static method nullableInt() → core::int?
+  return 1;
+static method notEqualNull_assignIfNull() → dynamic {
+  has-declared-initializer core::int? x = null;
+  if(!((let final core::int? #t1 = x in #t1 == null ?{core::int?} x = self::nullableInt() : #t1{core::int}) == null)) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method notEqualNullNull_eq() → dynamic {
+  has-declared-initializer core::int? x = null;
+  if(!((x = self::nullableInt()) == null)) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method is_eq() → dynamic {
+  has-declared-initializer core::int? x = null;
+  if((x = self::nullableInt()) is core::int) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method is_plusEq() → dynamic {
+  core::num x = 2;
+  if((x = x.{core::num::+}(1){(core::num) → core::num}) is core::int) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method is_postfix() → dynamic {
+  core::num x = 2;
+  if((let final core::num #t2 = x in let final core::num #t3 = x = #t2.{core::num::+}(1){(core::num) → core::num} in #t2) is core::int) {
+    invalid-expression "pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart:44:7: Error: The getter 'isEven' isn't defined for the class 'num'.
+Try correcting the name to the name of an existing getter, or defining a getter or field named 'isEven'.
+    x.isEven; // Error.
+      ^^^^^^" in x{<unresolved>}.isEven;
+  }
+}
+static method is_prefix() → dynamic {
+  core::num x = 2;
+  if((x = x.{core::num::+}(1){(core::num) → core::num}) is core::int) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}

pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart.strong.modular.expect

@@ -0,0 +1,53 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart:44:7: Error: The getter 'isEven' isn't defined for the class 'num'.
+// Try correcting the name to the name of an existing getter, or defining a getter or field named 'isEven'.
+//     x.isEven; // Error.
+//       ^^^^^^
+//
+import self as self;
+import "dart:core" as core;
+
+static method nullableInt() → core::int?
+  return 1;
+static method notEqualNull_assignIfNull() → dynamic {
+  has-declared-initializer core::int? x = null;
+  if(!((let final core::int? #t1 = x in #t1 == null ?{core::int?} x = self::nullableInt() : #t1{core::int}) == null)) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method notEqualNullNull_eq() → dynamic {
+  has-declared-initializer core::int? x = null;
+  if(!((x = self::nullableInt()) == null)) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method is_eq() → dynamic {
+  has-declared-initializer core::int? x = null;
+  if((x = self::nullableInt()) is core::int) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method is_plusEq() → dynamic {
+  core::num x = 2;
+  if((x = x.{core::num::+}(1){(core::num) → core::num}) is core::int) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method is_postfix() → dynamic {
+  core::num x = 2;
+  if((let final core::num #t2 = x in let final core::num #t3 = x = #t2.{core::num::+}(1){(core::num) → core::num} in #t2) is core::int) {
+    invalid-expression "pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart:44:7: Error: The getter 'isEven' isn't defined for the class 'num'.
+Try correcting the name to the name of an existing getter, or defining a getter or field named 'isEven'.
+    x.isEven; // Error.
+      ^^^^^^" in x{<unresolved>}.isEven;
+  }
+}
+static method is_prefix() → dynamic {
+  core::num x = 2;
+  if((x = x.{core::num::+}(1){(core::num) → core::num}) is core::int) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}

pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart.strong.outline.expect

@@ -0,0 +1,18 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+static method nullableInt() → core::int?
+  ;
+static method notEqualNull_assignIfNull() → dynamic
+  ;
+static method notEqualNullNull_eq() → dynamic
+  ;
+static method is_eq() → dynamic
+  ;
+static method is_plusEq() → dynamic
+  ;
+static method is_postfix() → dynamic
+  ;
+static method is_prefix() → dynamic
+  ;

pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart.strong.transformed.expect

@@ -0,0 +1,53 @@
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart:44:7: Error: The getter 'isEven' isn't defined for the class 'num'.
+// Try correcting the name to the name of an existing getter, or defining a getter or field named 'isEven'.
+//     x.isEven; // Error.
+//       ^^^^^^
+//
+import self as self;
+import "dart:core" as core;
+
+static method nullableInt() → core::int?
+  return 1;
+static method notEqualNull_assignIfNull() → dynamic {
+  has-declared-initializer core::int? x = null;
+  if(!((let final core::int? #t1 = x in #t1 == null ?{core::int?} x = self::nullableInt() : #t1{core::int}) == null)) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method notEqualNullNull_eq() → dynamic {
+  has-declared-initializer core::int? x = null;
+  if(!((x = self::nullableInt()) == null)) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method is_eq() → dynamic {
+  has-declared-initializer core::int? x = null;
+  if((x = self::nullableInt()) is core::int) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method is_plusEq() → dynamic {
+  core::num x = 2;
+  if((x = x.{core::num::+}(1){(core::num) → core::num}) is core::int) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method is_postfix() → dynamic {
+  core::num x = 2;
+  if((let final core::num #t2 = x in let final core::num #t3 = x = #t2.{core::num::+}(1){(core::num) → core::num} in #t2) is core::int) {
+    invalid-expression "pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart:44:7: Error: The getter 'isEven' isn't defined for the class 'num'.
+Try correcting the name to the name of an existing getter, or defining a getter or field named 'isEven'.
+    x.isEven; // Error.
+      ^^^^^^" in x{<unresolved>}.isEven;
+  }
+}
+static method is_prefix() → dynamic {
+  core::num x = 2;
+  if((x = x.{core::num::+}(1){(core::num) → core::num}) is core::int) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}

pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart.textual_outline.expect

@@ -0,0 +1,13 @@
+int? nullableInt() => 1;
+
+notEqualNull_assignIfNull() {}
+
+notEqualNullNull_eq() {}
+
+is_eq() {}
+
+is_plusEq() {}
+
+is_postfix() {}
+
+is_prefix() {}

pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart.textual_outline_modelled.expect

@@ -0,0 +1,13 @@
+int? nullableInt() => 1;
+
+is_eq() {}
+
+is_plusEq() {}
+
+is_postfix() {}
+
+is_prefix() {}
+
+notEqualNullNull_eq() {}
+
+notEqualNull_assignIfNull() {}

pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart.weak.expect

@@ -0,0 +1,94 @@
+//
+// Problems in component:
+//
+// sdk/lib/core/core.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/async/async.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/collection/collection.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/_internal/vm_shared/lib/compact_hash.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/concurrent/concurrent.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/convert/convert.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/developer/developer.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/ffi/ffi.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/internal/internal.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/isolate/isolate.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/math/math.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/mirrors/mirrors.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/typed_data/typed_data.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/_internal/vm/bin/vmservice_io.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/vmservice/vmservice.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/_internal/vm/bin/builtin.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/html/dartium/nativewrappers.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/io/io.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+// sdk/lib/cli/cli.dart: Error: Loaded library is compiled with sound null safety and cannot be used in compilation for unsound null safety.
+//
+library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart:44:7: Error: The getter 'isEven' isn't defined for the class 'num'.
+// Try correcting the name to the name of an existing getter, or defining a getter or field named 'isEven'.
+//     x.isEven; // Error.
+//       ^^^^^^
+//
+import self as self;
+import "dart:core" as core;
+
+static method nullableInt() → core::int?
+  return 1;
+static method notEqualNull_assignIfNull() → dynamic {
+  has-declared-initializer core::int? x = null;
+  if(!((let final core::int? #t1 = x in #t1 == null ?{core::int?} x = self::nullableInt() : #t1{core::int}) == null)) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method notEqualNullNull_eq() → dynamic {
+  has-declared-initializer core::int? x = null;
+  if(!((x = self::nullableInt()) == null)) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method is_eq() → dynamic {
+  has-declared-initializer core::int? x = null;
+  if((x = self::nullableInt()) is core::int) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method is_plusEq() → dynamic {
+  core::num x = 2;
+  if((x = x.{core::num::+}(1){(core::num) → core::num}) is core::int) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}
+static method is_postfix() → dynamic {
+  core::num x = 2;
+  if((let final core::num #t2 = x in let final core::num #t3 = x = #t2.{core::num::+}(1){(core::num) → core::num} in #t2) is core::int) {
+    invalid-expression "pkg/front_end/testcases/inference_update_4/assignment_promotion_in_if_statement.dart:44:7: Error: The getter 'isEven' isn't defined for the class 'num'.
+Try correcting the name to the name of an existing getter, or defining a getter or field named 'isEven'.
+    x.isEven; // Error.
+      ^^^^^^" in x{<unresolved>}.isEven;
+  }
+}
+static method is_prefix() → dynamic {
+  core::num x = 2;
+  if((x = x.{core::num::+}(1){(core::num) → core::num}) is core::int) {
+    x{core::int}.{core::int::isEven}{core::bool};
+  }
+}