Add checks to make sure new front_end package dependencies are not added.

pkg/front_end/test/subpackage_relationships_test.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:front_end/compiler_options.dart';
 import 'package:front_end/dependency_grapher.dart';
 import 'package:path/path.dart' as pathos;
 
 main() async {
   exit(await new _SubpackageRelationshipsTest().run());
 }
 
+/// List of packages that front_end is allowed to directly depend on.
+///
+/// TODO(paulberry): remove dependencies on analyzer.
+final allowedPackageDependencies = [

[Siggi Cherem (dart-lang), 2017/06/15 17:45:57]

do we need to also make the distinction between dev and non-dev dependencies?

[Paul Berry, 2017/06/15 17:58:27]

This script only checks files in pkg/front_end/lib, so this list excludes dev
dependencies.

I've updated the comment to clarify this.

+  'analyzer',
+  'charcode',
+  'convert',
+  'crypto',
+  'kernel',
+  'meta',
+  'package_config',
+  'path',
+  'source_span',
+  'testing',
+];
+
 /// Map from subpackage name to the rules for what the subpackage is allowed to
 /// depend directly on.
 ///
 /// Each listed directory is considered a subpackage.  Each package contains all
 /// of its descendant files that are not in a more deeply nested subpackage.
 ///
 /// TODO(paulberry): stuff in lib/src shouldn't depend on lib; lib should just
 /// re-export stuff in lib/src.
 /// TODO(paulberry): remove dependencies on analyzer.
 final subpackageRules = {
@@ skipping 145 matching lines @@
       this.allowedDependencies: const []});
 }
 
 class _SubpackageRelationshipsTest {
   /// File uri of the front_end package's "lib" directory.
   final frontEndLibUri = Platform.script.resolve('../lib/');
 
   /// Indicates whether any problems have been reported yet.
   bool problemsReported = false;
 
+  /// Package dependencies that were actually discovered
+  final actualPackageDependencies = <String>[];
+
   /// Check for problems resulting from URI [src] having a direct dependency on
   /// URI [dst].
   void checkDependency(Uri src, Uri dst) {
     if (dst.scheme == 'dart') return;
     if (dst.scheme != 'package') {
       problem('$src depends on $dst, which is neither a package: or dart: URI');
       return;
     }
+    if (src.scheme == 'package' &&
+        src.pathSegments[0] == 'front_end' &&
+        dst.scheme == 'package' &&
+        dst.pathSegments[0] != 'front_end') {
+      if (allowedPackageDependencies.contains(dst.pathSegments[0])) {
+        actualPackageDependencies.add(dst.pathSegments[0]);
+      } else {
+        problem('$src depends on package "${dst.pathSegments[0]}", which is '
+            'not found in allowedPackageDependencies');
+      }
+    }
     var srcSubpackage = subpackageForUri(src);
     if (srcSubpackage == null) return;
     var srcSubpackageRules = subpackageRules[srcSubpackage];
     if (srcSubpackageRules == null) {
       problem('$src is in subpackage "$srcSubpackage", which is not found in '
           'subpackageRules');
       return;
     }
     srcSubpackageRules.actuallyContainsFiles = true;
     if (dst.pathSegments[0] == 'analyzer') {
@@ skipping 47 matching lines @@
         new CompilerOptions()
           ..packagesFileUri = packagesFileUri
           ..chaseDependencies = true);
     for (var i = 0; i < graph.topologicallySortedCycles.length; i++) {
       for (var library in graph.topologicallySortedCycles[i].libraries.values) {
         for (var dependency in library.dependencies) {
           checkDependency(library.uri, dependency.uri);
         }
       }
     }
+    for (var package in allowedPackageDependencies) {
+      if (!actualPackageDependencies.contains(package)) {
+        problem(
+            '$package is listed in allowedPackageDependencies, but is not used');

[Siggi Cherem (dart-lang), 2017/06/15 17:45:57]

nit: maybe split line

[Paul Berry, 2017/06/15 17:58:27]

Done.

+      }
+    }
     subpackageRules.forEach((subpackage, rule) {
       if (!rule.actuallyContainsFiles) {
         problem("$subpackage contains no files");
       }
       if (rule.mayImportAnalyzer && !rule.actuallyImportsAnalyzer) {
         problem("$subpackage is allowed to import analyzer, but doesn't");
       }
       if (rule.allowSubdirs && !rule.actuallyHasSubdirs) {
         problem("$subpackage is allowed to have subdirectories, but doesn't");
       }
@@ skipping 31 matching lines @@
       if (subpackageRules[subpackage].allowSubdirs) {
         subpackageRules[subpackage].actuallyHasSubdirs = true;
       } else {
         problem('Uri $src is in a subfolder of $subpackage, but that '
             'subpackage does not allow dart files in subdirectories.');
       }
     }
     return subpackage;
   }
 }