[cfe] Apply a recovery step for 'const' for-in variables

Closes https://github.com/dart-lang/sdk/issues/48808

Change-Id: I68177a6eb7f0a5d64dee6eca9befa9957863f26c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/241604
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Chloe Stefantsova <cstefantsova@google.com>

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -6177,6 +6177,9 @@ class BodyBuilder extends StackListenerImpl
             fasta.messageForInLoopWithConstVariable,
             lvalue.fileOffset,
             lvalue.name!.length);
+        // As a recovery step, remove the const flag, to not confuse the
+        // constant evaluator further in the pipeline.
+        lvalue.isConst = false;
       }
     } else {
       VariableDeclaration variable = elements.syntheticVariableDeclaration =

pkg/front_end/testcases/general/issue48808.dart

@@ -0,0 +1,9 @@
+// Copyright (c) 2022, 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() {
+  for (const x in [1, 2, 3]) print(x);
+}
+
+main() {}

pkg/front_end/testcases/general/issue48808.dart.textual_outline.expect

@@ -0,0 +1,2 @@
+foo() {}
+main() {}

pkg/front_end/testcases/general/issue48808.dart.textual_outline_modelled.expect

@@ -0,0 +1,2 @@
+foo() {}
+main() {}

pkg/front_end/testcases/general/issue48808.dart.weak.expect

@@ -0,0 +1,23 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/issue48808.dart:6:14: Error: A for-in loop-variable can't be 'const'.
+// Try removing the 'const' modifier.
+//   for (const x in [1, 2, 3]) print(x);
+//              ^
+//
+import self as self;
+import "dart:core" as core;
+
+static method foo() → dynamic {
+  {
+    invalid-expression "pkg/front_end/testcases/general/issue48808.dart:6:14: Error: A for-in loop-variable can't be 'const'.
+Try removing the 'const' modifier.
+  for (const x in [1, 2, 3]) print(x);
+             ^";
+    for (core::int x in <core::int>[1, 2, 3])
+      core::print(x);
+  }
+}
+static method main() → dynamic {}

pkg/front_end/testcases/general/issue48808.dart.weak.modular.expect

@@ -0,0 +1,23 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/issue48808.dart:6:14: Error: A for-in loop-variable can't be 'const'.
+// Try removing the 'const' modifier.
+//   for (const x in [1, 2, 3]) print(x);
+//              ^
+//
+import self as self;
+import "dart:core" as core;
+
+static method foo() → dynamic {
+  {
+    invalid-expression "pkg/front_end/testcases/general/issue48808.dart:6:14: Error: A for-in loop-variable can't be 'const'.
+Try removing the 'const' modifier.
+  for (const x in [1, 2, 3]) print(x);
+             ^";
+    for (core::int x in <core::int>[1, 2, 3])
+      core::print(x);
+  }
+}
+static method main() → dynamic {}

pkg/front_end/testcases/general/issue48808.dart.weak.outline.expect

@@ -0,0 +1,7 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+
+static method foo() → dynamic
+  ;
+static method main() → dynamic
+  ;

pkg/front_end/testcases/general/issue48808.dart.weak.transformed.expect

@@ -0,0 +1,28 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/issue48808.dart:6:14: Error: A for-in loop-variable can't be 'const'.
+// Try removing the 'const' modifier.
+//   for (const x in [1, 2, 3]) print(x);
+//              ^
+//
+import self as self;
+import "dart:core" as core;
+
+static method foo() → dynamic {
+  {
+    invalid-expression "pkg/front_end/testcases/general/issue48808.dart:6:14: Error: A for-in loop-variable can't be 'const'.
+Try removing the 'const' modifier.
+  for (const x in [1, 2, 3]) print(x);
+             ^";
+    {
+      core::Iterator<core::int> :sync-for-iterator = core::_GrowableList::_literal3<core::int>(1, 2, 3).{core::Iterable::iterator}{core::Iterator<core::int>};
+      for (; :sync-for-iterator.{core::Iterator::moveNext}(){() → core::bool}; ) {
+        core::int x = :sync-for-iterator.{core::Iterator::current}{core::int};
+        core::print(x);
+      }
+    }
+  }
+}
+static method main() → dynamic {}