Enhance DirectiveListener to collect import/exports with combinators.

pkg/front_end/lib/src/incremental/file_state.dart

Index: pkg/front_end/lib/src/incremental/file_state.dart
diff --git a/pkg/front_end/lib/src/incremental/file_state.dart b/pkg/front_end/lib/src/incremental/file_state.dart
index 3f353897463840f6dab6be37cef2ee59734140aa..993d84a7f4f29fc159494e5e6af0d24314f68c1e 100644
--- a/pkg/front_end/lib/src/incremental/file_state.dart
+++ b/pkg/front_end/lib/src/incremental/file_state.dart
@@ -35,6 +35,7 @@ class FileState {
   List<int> _content;
   List<int> _contentHash;
 
+  List<NamespaceExport> _exports;
   List<FileState> _importedLibraries;
   List<FileState> _exportedLibraries;
   List<FileState> _partFiles;
@@ -61,6 +62,9 @@ class FileState {
   /// The list of the libraries exported by this library.
   List<FileState> get exportedLibraries => _exportedLibraries;
 
+  /// The list of the exported files with combinators.
+  List<NamespaceExport> get exports => _exports;
+
   @override
   int get hashCode => uri.hashCode;
 
@@ -123,16 +127,32 @@ class FileState {
     _importedLibraries = <FileState>[];
     _exportedLibraries = <FileState>[];
     _partFiles = <FileState>[];
-    await _addFileForRelativeUri(_importedLibraries, 'dart:core');
-    for (String uri in listener.imports) {
-      await _addFileForRelativeUri(_importedLibraries, uri);
+    _exports = <NamespaceExport>[];
+    {
+      FileState coreFile = await _getFileForRelativeUri('dart:core');
+      if (coreFile != null) {
+        _importedLibraries.add(coreFile);
+      }
+    }
+    for (ImportDirective import_ in listener.imports) {
+      FileState file = await _getFileForRelativeUri(import_.uri);
+      if (file != null) {
+        _importedLibraries.add(file);
+      }
     }
     await _addVmTargetImportsForCore();
-    for (String uri in listener.exports) {
-      await _addFileForRelativeUri(_exportedLibraries, uri);
+    for (ExportDirective export_ in listener.exports) {
+      FileState file = await _getFileForRelativeUri(export_.uri);
+      if (file != null) {
+        _exportedLibraries.add(file);
+        _exports.add(new NamespaceExport(file, export_.combinators));
+      }
     }
     for (String uri in listener.parts) {
-      await _addFileForRelativeUri(_partFiles, uri);
+      FileState file = await _getFileForRelativeUri(uri);
+      if (file != null) {
+        _partFiles.add(file);
+      }
     }
 
     // Compute referenced files.
@@ -152,11 +172,24 @@ class FileState {
     return fileUri.toString();
   }
 
-  /// Add the [FileState] for the given [relativeUri] to the [files].
-  /// Do nothing if the URI cannot be parsed, cannot correspond any file, etc.
-  Future<Null> _addFileForRelativeUri(
-      List<FileState> files, String relativeUri) async {
-    if (relativeUri.isEmpty) return;
+  /// Fasta unconditionally loads all VM libraries.  In order to be able to
+  /// serve them using the file system view, pretend that all of them were
+  /// imported into `dart:core`.
+  /// TODO(scheglov) Ask VM people whether all these libraries are required.

[Siggi Cherem (dart-lang), 2017/05/15 22:18:53]

I think it's safe to remove this.

The VM needs these libraries, but not from us :) - we want it to get them from a
platform.dill file that is built separately and not from the app. The VM now
supports this, but fasta still includes them because we haven't finished moving
over to just use the platform.dill for the VM tests and performance bots. As
Slava said on that email, in the future these platform.dill will be replaced
with a VM snapshot.

If those libraries get imported by the user, then yes we will need to be handle
them, but that's a regular import at that point.

[scheglov, 2017/05/16 00:14:24]

It's not safe to remove here.
TargetImplemenation.loadExtraRequiredLibraries() schedules all of them.
Maybe something else should also be changed in Fasta?

[Siggi Cherem (dart-lang), 2017/05/16 21:43:47]

I see, then yes :) we need to update fasta to stop doing it unless we pass a
flag with the list of libraries to enqueue

+  Future<Null> _addVmTargetImportsForCore() async {
+    if (uri.toString() != 'dart:core') return;
+    for (String uri in new VmTarget(null).extraRequiredLibraries) {
+      FileState file = await _getFileForRelativeUri(uri);
+      if (file != null) {
+        _importedLibraries.add(file);
+      }
+    }
+  }
+
+  /// Return the [FileState] for the given [relativeUri] or `null` if the URI
+  /// cannot be parsed, cannot correspond any file, etc.
+  Future<FileState> _getFileForRelativeUri(String relativeUri) async {
+    if (relativeUri.isEmpty) return null;
 
     // Resolve the relative URI into absolute.
     // The result is either:
@@ -166,23 +199,10 @@ class FileState {
     try {
       absoluteUri = fileUri.resolve(relativeUri);
     } on FormatException {
-      return;
+      return null;
     }
 
-    FileState file = await _fsState.getFile(absoluteUri);
-    if (file == null) return;
-    files.add(file);
-  }
-
-  /// Fasta unconditionally loads all VM libraries.  In order to be able to
-  /// serve them using the file system view, pretend that all of them were
-  /// imported into `dart:core`.
-  /// TODO(scheglov) Ask VM people whether all these libraries are required.
-  Future<Null> _addVmTargetImportsForCore() async {
-    if (uri.toString() != 'dart:core') return;
-    for (String uri in new VmTarget(null).extraRequiredLibraries) {
-      await _addFileForRelativeUri(_importedLibraries, uri);
-    }
+    return await _fsState.getFile(absoluteUri);
   }
 
   /// Scan the content of the file.
@@ -257,6 +277,30 @@ class LibraryCycle {
   }
 }
 
+/// Information about a single `export` directive.
+class NamespaceExport {
+  final FileState library;
+  final List<NamespaceCombinator> combinators;
+
+  NamespaceExport(this.library, this.combinators);
+
+  /// Return `true` if the [name] satisfies the sequence of the [combinators].
+  bool filter(String name) {

[Siggi Cherem (dart-lang), 2017/05/15 22:18:53]

nit: consider renaming this method. It might be just me, but when I read
`filter`, I think that "true" means that `name` is not visible.
Some ideas: `isIncluded`, `isVisible`, `isExported`, for example:

/// Whether [name] is exposed by the underlying export
/// after applying all [combinators].
bool isExposed(name) { ... }

[scheglov, 2017/05/16 00:14:24]

Done.

+    for (NamespaceCombinator combinator in combinators) {

[Siggi Cherem (dart-lang), 2017/05/15 22:18:53]

how much do we expect to use these functions? In practice do we expect these
combinator lists to be big?

I just wonder whether it is worth flattening the list of combinators to make
lookups efficient. For instance, I believe it can be shrink down to a boolean
(isShow/isHide) and a Set of names.

[scheglov, 2017/05/16 00:14:24]

I think usually there are zero combinators.
Sometimes one.
I have never seen more than one.
But this is still allowed by the specification.

I don't think we need flattening here.

+      if (combinator.isShow) {
+        if (!combinator.names.contains(name)) {
+          return false;
+        }
+      } else {
+        if (combinator.names.contains(name)) {
+          return false;
+        }
+      }
+    }
+    return true;
+  }
+}
+
 /// [DirectiveListener] that skips native clauses.
 class _DirectiveListenerWithNative extends DirectiveListener {
   @override