[cfe] Deem all intersection types syntactically not nullable

Closes #44362.

Bug: #44362
Change-Id: Id54de1848e6af1108956476e241bab5c0ed96a4b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/177124
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Dmitry Stefantsov <[email protected]>

Author: Dmitry Stefantsov

pkg/front_end/testcases/nnbd/issue44362.dart

@@ -0,0 +1,13 @@
+// Copyright (c) 2020, 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.
+
+foo<X>(X? x) {
+  if (x is int) {
+    bar(x);
+  }
+}
+
+bar<Y>(dynamic y) {}
+
+main() {}

pkg/front_end/testcases/nnbd/issue44362.dart.outline.expect

@@ -0,0 +1,10 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method foo<X extends core::Object? = dynamic>(self::foo::X? x) → dynamic
+  ;
+static method bar<Y extends core::Object? = dynamic>(dynamic y) → dynamic
+  ;
+static method main() → dynamic
+  ;

pkg/front_end/testcases/nnbd/issue44362.dart.strong.expect

@@ -0,0 +1,11 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method foo<X extends core::Object? = dynamic>(self::foo::X? x) → dynamic {
+  if(x is{ForNonNullableByDefault} core::int) {
+    self::bar<dynamic>(x{self::foo::X? & core::int /* '?' & '!' = '!' */});
+  }
+}
+static method bar<Y extends core::Object? = dynamic>(dynamic y) → dynamic {}
+static method main() → dynamic {}

pkg/front_end/testcases/nnbd/issue44362.dart.strong.transformed.expect

@@ -0,0 +1,11 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method foo<X extends core::Object? = dynamic>(self::foo::X? x) → dynamic {
+  if(x is{ForNonNullableByDefault} core::int) {
+    self::bar<dynamic>(x{self::foo::X? & core::int /* '?' & '!' = '!' */});
+  }
+}
+static method bar<Y extends core::Object? = dynamic>(dynamic y) → dynamic {}
+static method main() → dynamic {}

pkg/front_end/testcases/nnbd/issue44362.dart.textual_outline.expect

@@ -0,0 +1,3 @@
+foo<X>(X? x) {}
+bar<Y>(dynamic y) {}
+main() {}

pkg/front_end/testcases/nnbd/issue44362.dart.textual_outline_modelled.expect

@@ -0,0 +1,3 @@
+bar<Y>(dynamic y) {}
+foo<X>(X? x) {}
+main() {}

pkg/front_end/testcases/nnbd/issue44362.dart.weak.expect

@@ -0,0 +1,11 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method foo<X extends core::Object? = dynamic>(self::foo::X? x) → dynamic {
+  if(x is{ForNonNullableByDefault} core::int) {
+    self::bar<dynamic>(x{self::foo::X? & core::int /* '?' & '!' = '!' */});
+  }
+}
+static method bar<Y extends core::Object? = dynamic>(dynamic y) → dynamic {}
+static method main() → dynamic {}

pkg/front_end/testcases/nnbd/issue44362.dart.weak.transformed.expect

@@ -0,0 +1,11 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "dart:core" as core;
+
+static method foo<X extends core::Object? = dynamic>(self::foo::X? x) → dynamic {
+  if(x is{ForNonNullableByDefault} core::int) {
+    self::bar<dynamic>(x{self::foo::X? & core::int /* '?' & '!' = '!' */});
+  }
+}
+static method bar<Y extends core::Object? = dynamic>(dynamic y) → dynamic {}
+static method main() → dynamic {}

pkg/kernel/lib/type_algebra.dart

@@ -1067,6 +1067,10 @@ bool isTypeParameterTypeWithoutNullabilityMarker(
 /// and Null are nullable, but aren't considered applications of the nullable
 /// type constructor.
 bool isNullableTypeConstructorApplication(DartType type) {
+  if (type is TypeParameterType && type.promotedBound != null) {
+    // Promoted types are never considered applications of ?.
+    return false;
+  }
   return type.declaredNullability == Nullability.nullable &&
       type is! DynamicType &&
       type is! VoidType &&