[CFE] Error when library and part(s) doesn't agree on language version

From the feature spec: "Part files must be marked with the same version
as their library. They must always be treated the same way as the
library they belong to, so it is a compile-time error if a part file has
a different language level override than its library. It is also a
compile-time error if a part file has no language version marker,
and the importing library does".

Change-Id: I29805e261e63b89a7d8832770ed2b007fb6df37f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/112247
Commit-Queue: Jens Johansen <jensj@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>

Author: jensjoha

pkg/front_end/lib/src/fasta/fasta_codes_generated.dart

@@ -6580,6 +6580,16 @@ const MessageCode messageLanguageVersionInvalidInDotPackages = const MessageCode
     message:
         r"""The language version is not specified correctly in the .packages file.""");
 
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeLanguageVersionMismatchInPart =
+    messageLanguageVersionMismatchInPart;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageLanguageVersionMismatchInPart = const MessageCode(
+    "LanguageVersionMismatchInPart",
+    message:
+        r"""The language version override has to be the same in the library and its part(s).""");
+
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Template<
     Message Function(

pkg/front_end/lib/src/fasta/source/source_library_builder.dart

@@ -98,6 +98,7 @@ import '../fasta_codes.dart'
         messageGenericFunctionTypeUsedAsActualTypeArgument,
         messageIncorrectTypeArgumentVariable,
         messageLanguageVersionInvalidInDotPackages,
+        messageLanguageVersionMismatchInPart,
         messagePartExport,
         messagePartExportContext,
         messagePartInPart,
@@ -901,6 +902,21 @@ class SourceLibraryBuilder extends LibraryBuilder {
       }
       return false;
     }
+
+    // Language versions have to match.
+    if ((this.languageVersionExplicitlySet !=
+            part.languageVersionExplicitlySet) ||
+        (this.library.languageVersionMajor !=
+                part.library.languageVersionMajor ||
+            this.library.languageVersionMinor !=
+                part.library.languageVersionMinor)) {
+      // This is an error, but the part is not removed from the list of
+      // parts, so that metadata annotations can be associated with it.
+      addProblem(
+          messageLanguageVersionMismatchInPart, partOffset, noLength, fileUri);
+      return false;
+    }
+
     part.validatePart(this, usedParts);
     NameIterator partDeclarations = part.nameIterator;
     while (partDeclarations.moveNext()) {

pkg/front_end/messages.status

@@ -336,6 +336,8 @@ InvalidVoid/script1: Fail
 InvalidVoid/script2: Fail
 LanguageVersionInvalidInDotPackages/analyzerCode: Fail
 LanguageVersionInvalidInDotPackages/part_wrapped_script: Fail # Importing file in the (now) part.
+LanguageVersionMismatchInPart/analyzerCode: Fail
+LanguageVersionMismatchInPart/part_wrapped_script: Fail # Part in (now) part.
 LanguageVersionTooHigh/analyzerCode: Fail
 LanguageVersionTooHigh/part_wrapped_script: Fail # Content comes after "part of [...]" meaning it's not actually a language version specification.
 LibraryDirectiveNotFirst/part_wrapped_script1: Fail # Defining library name in the (now) part.

pkg/front_end/messages.yaml

@@ -3624,4 +3624,16 @@ LanguageVersionInvalidInDotPackages:
   script:
     main.dart: "import 'package:foo/foo.dart';"
     lib/foo.dart: "// blah blah blah"
-    .packages: "foo:lib/#dart=arglebargle"
+    .packages: "foo:lib/#dart=arglebargle"
+
+LanguageVersionMismatchInPart:
+  template: "The language version override has to be the same in the library and its part(s)."
+  script:
+    main.dart: >
+      // @dart = 2.4
+
+      part 'part.dart';
+    part.dart: >
+      // @dart = 2.3
+
+      part of 'main.dart';

pkg/front_end/test/language_versioning/data/parts_disagreeing/main.dart

@@ -0,0 +1,13 @@
+// Copyright (c) 2019, 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.
+
+// @dart = 2.5
+
+part /*error: LanguageVersionMismatchInPart*/ 'part.dart';
+
+/*library: languageVersion=2.5*/
+
+main() {
+  /*error: MethodNotFound*/ foo();
+}

pkg/front_end/test/language_versioning/data/parts_disagreeing/part.dart

@@ -0,0 +1,9 @@
+// Copyright (c) 2019, 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.
+
+// @dart = 2.4
+
+part of 'main.dart';
+
+foo() {}

pkg/front_end/test/language_versioning/data/parts_disagreeing_has_package/.packages

@@ -0,0 +1 @@
+foo:lib/#dart=2.5

pkg/front_end/test/language_versioning/data/parts_disagreeing_has_package/lib/foo.dart

@@ -0,0 +1,16 @@
+// Copyright (c) 2019, 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 library and its part is both technically at language version 2.5,
+// but one is explicitly set, the other is not. That's an error.
+
+// @dart = 2.5
+
+part /*error: LanguageVersionMismatchInPart*/ 'part.dart';
+
+/*library: languageVersion=2.5*/
+
+foo() {
+  /*error: MethodNotFound*/ bar();
+}

pkg/front_end/test/language_versioning/data/parts_disagreeing_has_package/lib/part.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2019, 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.
+
+part of 'foo.dart';
+
+bar() {}

pkg/front_end/test/language_versioning/data/parts_disagreeing_has_package/main.dart

@@ -0,0 +1,16 @@
+// Copyright (c) 2019, 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.
+
+// Set version of this file (not technically in package) explicitly to test as
+// much as possibly separately.
+
+// @dart = 2.4
+
+import 'package:foo/foo.dart';
+
+/*library: languageVersion=2.4*/
+
+main() {
+  main();
+}