#3057. Add more flow analysis tests, fix existing (#3117)

Add more flow analysis tests, fix existing

Author: sgrekhov

TypeSystem/flow-analysis/reachability_A13_t01.dart

@@ -0,0 +1,19 @@
+// Copyright (c) 2025, 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.
+
+/// @assertion type cast If `N` is an expression of the form `E1 as S` where the
+/// static type of `E1` is `T` then:
+/// - Let `before(E1) = before(N)`
+/// - Let `after(N) = promote(E1, S, after(E1))`
+///
+/// @description Checks that `after(N) = promote(E1, S, after(E1))`.
+/// @author [email protected]
+
+import '../../Utils/static_type_helper.dart';
+
+main() {
+  int? i = 2 > 1 ? 42 : null;
+  i as int;
+  i.expectStaticType<Exactly<int>>();
+}

TypeSystem/flow-analysis/reachability_A13_t02.dart

@@ -0,0 +1,40 @@
+// Copyright (c) 2025, 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.
+
+/// @assertion type cast If `N` is an expression of the form `E1 as S` where the
+/// static type of `E1` is `T` then:
+/// - Let `before(E1) = before(N)`
+/// - Let `after(N) = promote(E1, S, after(E1))`
+///
+/// @description Checks that `after(N) = promote(E1, S, after(E1))`. Test that
+/// after promotion to `Never` `after(N)` became unreachable.
+/// @author [email protected]
+
+test1(x) {
+  late int i;
+  if (1 > 2) {
+    x as Never;
+    i = 42;
+  }
+  i; // Definitely unassigned
+//^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+test2(x) {
+  late int i;
+  if (1 > 2) {
+    i = 42;
+    x as Never;
+  }
+  i; // Definitely unassigned
+//^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  test1(42);
+}

TypeSystem/flow-analysis/reachability_conditional_A01_t05.dart

@@ -0,0 +1,46 @@
+// Copyright (c) 2025, 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.
+
+/// @assertion Conditional statement: If `N` is a conditional statement of the
+/// form `if (E) S1 else S2` then:
+/// - Let `before(E) = before(N)`.
+/// - Let `before(S1) = split(true(E))`.
+/// - Let `before(S2) = split(false(E))`.
+/// - Let `after(N) = merge(after(S1), after(S2))`.
+///
+/// @description Checks that if `after(S1)` or `after(S2)` is unreachable then
+/// an assignment in the appropriate branch is omitted by the `join`.
+/// @author [email protected]
+
+Never foo() => throw "Never";
+
+void test1() {
+  late int i;
+  if (2 > 1) {
+    i = 0;
+    foo();
+  }
+  i; // Definitely unassigned
+//^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+void test2(Never n) {
+  late int i;
+  if (2 > 1) {
+  } else {
+    i = 0;
+    n;
+  }
+  i; // Definitely unassigned
+//^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  print(test1);
+  print(test2);
+}

TypeSystem/flow-analysis/reachability_for_in_A01_t04.dart

@@ -53,10 +53,7 @@ test4() {
   if (2 > 1) {
     for (i in <Never>[]) {}
   }
-  i; // Definitely unassigned.
-//^
-// [analyzer] unspecified
-// [cfe] unspecified
+  i; // Not definitely unassigned.
 }
 
 main() {

TypeSystem/flow-analysis/reachability_for_in_A01_t05.dart

@@ -61,10 +61,7 @@ test4() {
       i = 42;
     }
   }
-  i; // Definitely unassigned.
-//^
-// [analyzer] unspecified
-// [cfe] unspecified
+  i; // Not definitely unassigned.
 }
 
 main() {

TypeSystem/flow-analysis/reachability_for_in_A01_t06.dart

@@ -57,10 +57,7 @@ test4() {
     for (var j in <Never>[]) {}
     i = 42;
   }
-  i; // Definitely unassigned.
-//^
-// [analyzer] unspecified
-// [cfe] unspecified
+  i; // Not definitely unassigned.
 }
 
 main() {

TypeSystem/flow-analysis/reachability_for_in_A02_t07.dart

@@ -0,0 +1,29 @@
+// Copyright (c) 2025, 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.
+
+/// @assertion for each statement: If `N` is a for statement of the form
+/// `for (T X in E) S`, `for (var X in E) S`, or `for (X in E) S`, then:
+/// - Let `before(E) = before(N)`
+/// - Let `before(S) = conservativeJoin(after(E), assignedIn(N), capturedIn(N))`
+/// - Let `after(N) = join(before(S), break(S))`
+///
+/// @description Checks that
+/// `before(S) = conservativeJoin(after(E), assignedIn(N), capturedIn(N))`. Test
+/// that if a promoted variable is assigned in `X` then it preserves the
+/// promoted type.
+/// @author [email protected]
+
+test(int? n) {
+  if (n != null) { // n promoted to `int`
+    for (n in [42]) { // n is not promoted not demoted here
+      n.isEven; // n is still `int`
+    }
+    n.isEven;
+  }
+}
+
+main() {
+  test(42);
+  test(null);
+}