Fix #2485. Updateas and is expressions tests with a function type (#2538)

Update`as` and `is` expressions tests with a function type

Author: sgrekhov

Language/Expressions/Constants/as_type_A01_t02.dart

@@ -74,7 +74,7 @@ main() {
 
   const f1 = foo as void Function();
   const f2 = as as void Function();
-  const f3 = bar<int> as int Function(int);
+  const f3 = (bar<int>) as int Function(int);
 
   const d = 2 as dynamic;
 

Language/Expressions/Constants/is_not_type_A01_t02.dart

@@ -72,7 +72,7 @@ main() {
   const fo7 = IntET2(1) is! FutureOr<IntET1Alias>;
 
   const f1 = foo is! void Function();
-  const f2 = bar<int> is! int Function(int);
+  const f2 = (bar<int>) is! int Function(int);
 
   const d = 2 is! dynamic;
 

Language/Expressions/Constants/is_type_A01_t02.dart

@@ -73,7 +73,7 @@ main() {
   const fo7 = IntET2(1) is FutureOr<IntET1Alias>;
 
   const f1 = foo is void Function();
-  const f2 = bar<int> is int Function<int>(int);
+  const f2 = (bar<int>) is int Function(int);
 
   const d = 2 is dynamic;
 

LanguageFeatures/Constructor-tear-offs/ambiguities_A36_t04.dart

@@ -0,0 +1,84 @@
+// 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.
+
+/// @assertion This new syntax also introduces new ambiguities in the grammar, 
+/// similar to the one we introduced with generic functions. Examples include:
+/// 
+/// f(a<b,c>(d)); // Existing ambiguity, resolved to a generic method call.
+/// f(x.a<b,c>[d]); // f((x.a<b, c>)[d]) or f((x.a < b), (c > [d]))
+/// f(x.a<b,c>-d);  // f((x.a<b, c>)-d) or f((x.a < b), (c > -d]))
+/// The x.a<b,c> can be an explicitly instantiated generic function tear-off or 
+/// an explicitly instantiated type literal named using a prefix, which is new. 
+/// While neither type objects nor functions declare operator- or operator[], 
+/// such could be added using extension methods.
+/// 
+/// We will disambiguate such situations heuristically based on the token 
+/// following the > that matches the < we are ambiguous about. In the existing 
+/// ambiguity we treat ( as a sign that the < starts a generic invocation. We 
+/// extend the number of tokens which, when following a potential type argument 
+/// list, makes us choose to parse the previous tokens as that type argument 
+/// list.
+/// 
+/// There is a number of tokens which very consistently end an expression, and 
+/// we include all those:
+/// 
+/// ), }, ], ;, :, ,
+/// 
+/// Then we include tokens which we predict will continue a generic instantiation:
+/// 
+/// ( . == !=
+/// 
+/// The first six are tokens which cannot possibly start an expression, and 
+/// therefore cannot occur after a greater-than infix operator. The last four 
+/// tokens can continue an expression, and of those only ( can also start an 
+/// expression, and we already decided how to disambiguate that).
+/// 
+/// There are many other tokens which currently cannot continue an expression 
+/// (and therefore cannot validly follow a type argument list) or which cannot 
+/// start an expression (and therefore cannot validly follow a greater-than 
+/// operator), but in the service of keeping our future options open, we choose 
+/// a design that does not rely on those restrictions. For example we omit most 
+/// infix operators from being "continuation tokens", even though they currently 
+/// cannot start a new expression, and therefore cannot follow a > infix 
+/// operator. This leaves us open to allowing some of those operators as prefix 
+/// operators in the future, like we currently allow the - operator.
+///
+/// @description Checks that it is a syntax error if function with type argument
+/// specified is part of `as`, `as!` or `is` expressions
+/// @author [email protected]
+
+int bar<T>(T t) => 42;
+void foo<T1, T2, T3>() {}
+
+main() {
+  const c1 = bar<int> as int Function(int);
+//           ^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  const c2 = bar<int> is! int Function(int);
+//           ^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  const c3 = bar<int> is int Function(int);
+//           ^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  const c4 = foo<int, String, bool> as void Function();
+//           ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  const c5 = foo<int, String, bool> is! void Function();
+//           ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  const c6 = foo<int, String, bool> is void Function();
+//           ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}