Remove factory body in *.fromEnvironment, and implement this same behavior

pkg/compiler/lib/src/diagnostics/messages.dart

 // Copyright (c) 2011, 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.
 
 /// The messages in this file should follow the [Guide for Writing
 /// Diagnostics](../../../../front_end/lib/src/fasta/diagnostics.md).
 ///
 /// Other things to keep in mind:
 ///
 /// An INFO message should always be preceded by a non-INFO message, and the
@@ skipping 137 matching lines @@
   EXTRA_CATCH_DECLARATION,
   EXTRA_FORMALS,
   EXTRANEOUS_MODIFIER,
   EXTRANEOUS_MODIFIER_REPLACE,
   FACTORY_REDIRECTION_IN_NON_FACTORY,
   FINAL_FUNCTION_TYPE_PARAMETER,
   FINAL_WITHOUT_INITIALIZER,
   FORIN_NOT_ASSIGNABLE,
   FORMAL_DECLARED_CONST,
   FORMAL_DECLARED_STATIC,
+  FROM_ENVIRONMENT_MUST_BE_CONST,
   FUNCTION_TYPE_FORMAL_WITH_DEFAULT,
   FUNCTION_WITH_INITIALIZER,
   GENERIC,
   GETTER_MISMATCH,
   UNDEFINED_INSTANCE_GETTER_BUT_SETTER,
   HEX_DIGIT_EXPECTED,
   HIDDEN_HINTS,
   HIDDEN_IMPLICIT_IMPORT,
   HIDDEN_IMPORT,
   HIDDEN_WARNINGS,
@@ skipping 903 matching lines @@
           const MessageTemplate(
               MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_FIELD,
               "This non-final field prevents using const constructors."),
 
       MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_CONSTRUCTOR:
           const MessageTemplate(
               MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_CONSTRUCTOR,
               "This const constructor is not allowed due to "
               "non-final fields."),
 
+      MessageKind.FROM_ENVIRONMENT_MUST_BE_CONST: const MessageTemplate(
+          MessageKind.FROM_ENVIRONMENT_MUST_BE_CONST,
+          "#{className}.fromEnvironment can only be used as a "
+          "const constructor.",
+          howToFix: "Try replacing `new` with `const`.",
+          examples: const ["main() { new bool.fromEnvironment('X'); }"]),
+
       MessageKind.INITIALIZING_FORMAL_NOT_ALLOWED: const MessageTemplate(
           MessageKind.INITIALIZING_FORMAL_NOT_ALLOWED,
           "Initializing formal parameter only allowed in generative "
           "constructor."),
 
       MessageKind.INVALID_PARAMETER: const MessageTemplate(
           MessageKind.INVALID_PARAMETER, "Cannot resolve parameter."),
 
       MessageKind.NOT_INSTANCE_FIELD: const MessageTemplate(
           MessageKind.NOT_INSTANCE_FIELD,
@@ skipping 2701 matching lines @@
   static String convertToString(value) {
     if (value is ErrorToken) {
       // Shouldn't happen.
       return value.assertionMessage;
     } else if (value is Token) {
       value = value.lexeme;
     }
     return '$value';
   }
 }