Initial implementation of AnalysisDriver.

pkg/analyzer/lib/src/dart/analysis/driver.dart

Index: pkg/analyzer/lib/src/dart/analysis/driver.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/driver.dart b/pkg/analyzer/lib/src/dart/analysis/driver.dart
index 2a86589a75ede9649358534072c2c6ad302cfbdb..0b2bbf18912ec8ac14a1f565e04103e92ef3b57f 100644
--- a/pkg/analyzer/lib/src/dart/analysis/driver.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/driver.dart
@@ -3,11 +3,36 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:collection';
+import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/error/error.dart';
+import 'package:analyzer/error/listener.dart';
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer/src/context/context.dart';
+import 'package:analyzer/src/context/source.dart';
 import 'package:analyzer/src/dart/analysis/byte_store.dart';
+import 'package:analyzer/src/dart/error/todo_codes.dart';
+import 'package:analyzer/src/dart/scanner/reader.dart';
+import 'package:analyzer/src/dart/scanner/scanner.dart';
+import 'package:analyzer/src/generated/engine.dart'
+    show AnalysisContext, AnalysisEngine, AnalysisOptions, ChangeSet;
+import 'package:analyzer/src/generated/parser.dart';
 import 'package:analyzer/src/generated/source.dart';
+import 'package:analyzer/src/generated/utilities_dart.dart';
+import 'package:analyzer/src/summary/api_signature.dart';
+import 'package:analyzer/src/summary/flat_buffers.dart' as fb;
+import 'package:analyzer/src/summary/format.dart';
+import 'package:analyzer/src/summary/idl.dart';
+import 'package:analyzer/src/summary/link.dart';
+import 'package:analyzer/src/summary/package_bundle_reader.dart';
+import 'package:analyzer/src/summary/summarize_ast.dart';
+import 'package:analyzer/src/summary/summarize_elements.dart';
+import 'package:analyzer/src/util/fast_uri.dart';
+import 'package:convert/convert.dart';
+import 'package:crypto/crypto.dart';
 
 /**
  * This class computes [AnalysisResult]s for Dart files.
@@ -47,6 +72,13 @@ import 'package:analyzer/src/generated/source.dart';
  * TODO(scheglov) Clean up the list of implicitly analyzed files.
  */
 class AnalysisDriver {
+  final PerformanceLog _logger;
+
+  /**
+   * The resource provider for working with files.
+   */
+  final ResourceProvider _resourceProvider;
+
   /**
    * The byte storage to get and put serialized data.
    *
@@ -55,18 +87,60 @@ class AnalysisDriver {
   final ByteStore _byteStore;
 
   /**
+   * This [ContentCache] is consulted for a file content before reading
+   * the content from the file.
+   */
+  final ContentCache _contentCache;
+
+  /**
    * The [SourceFactory] is used to resolve URIs to paths and restore URIs
    * from file paths.
    */
   final SourceFactory _sourceFactory;
 
   /**
-   * This [ContentCache] is consulted for a file content before reading
-   * the content from the file.
+   * The analysis options to analyze with.
    */
-  final ContentCache _contentCache;
+  final AnalysisOptions _analysisOptions;
+
+  /**
+   * The combined unlinked and linked package for the SDK, extracted from
+   * the given [_sourceFactory].
+   */
+  PackageBundle _sdkBundle;
+
+  /**
+   * The mapping from the files for which analysis was requested using
+   * [getResult] to the [Completer]s to report the result.
+   */
+  final _requestedFiles = <String, Completer<AnalysisResult>>{};
+
+  /**
+   * The set of explicitly analyzed files.
+   */
+  final _explicitFiles = new LinkedHashSet<String>();
 
-  AnalysisDriver(this._byteStore, this._sourceFactory, this._contentCache);
+  /**
+   * The set of files that are currently scheduled for analysis.
+   */
+  final _filesToAnalyze = new LinkedHashSet<String>();
+
+  /**
+   * The current file state.
+   *
+   * It maps file paths to MD5 hash of the file content.
+   */
+  final _fileContentHashMap = <String, String>{};
+
+  /**
+   * TODO(scheglov) document and improve
+   */
+  final _hasWorkStreamController = new StreamController<String>();
+
+  AnalysisDriver(this._logger, this._resourceProvider, this._byteStore,
+      this._contentCache, this._sourceFactory, this._analysisOptions) {
+    _sdkBundle = _sourceFactory.dartSdk.getLinkedBundle();
+  }
 
   /**
    * Set the list of files that the driver should try to analyze sooner.
@@ -101,7 +175,28 @@ class AnalysisDriver {
    * using [addFile], for example when [getResult] was called for a file.
    */
   Stream<AnalysisResult> get results async* {
-    // TODO(scheglov) implement
+    try {
+      while (true) {
+        // TODO(scheglov) implement state transitioning
+        await for (String why in _hasWorkStreamController.stream) {
+          // Analyze the first file in the general queue.
+          if (_filesToAnalyze.isNotEmpty) {
+            _logger.runTimed('Analyzed ${_filesToAnalyze.length} files', () {
+              while (_filesToAnalyze.isNotEmpty) {
+                String path = _filesToAnalyze.first;
+                _filesToAnalyze.remove(path);
+                _File file = _fileForPath(path);
+                _computeAndPrintErrors(file);
+                // TODO(scheglov) yield the result
+              }
+            });
+          }
+        }
+        // TODO(scheglov) implement
+      }
+    } finally {
+      print('The stream was cancelled.');
+    }
   }
 
   /**
@@ -112,7 +207,9 @@ class AnalysisDriver {
    * The results of analysis are eventually produced by the [results] stream.
    */
   void addFile(String path) {
-    // TODO(scheglov) implement
+    _explicitFiles.add(path);
+    _filesToAnalyze.add(path);
+    _hasWorkStreamController.add('do it!');
   }
 
   /**
@@ -134,7 +231,12 @@ class AnalysisDriver {
    * [changeFile] invocation.
    */
   void changeFile(String path) {
-    // TODO(scheglov) implement
+    // TODO(scheglov) Don't clear, schedule API signature validation.
+    _fileContentHashMap.clear();
+    _filesToAnalyze.add(path);
+    _filesToAnalyze.addAll(_explicitFiles);
+    // TODO(scheglov) name?!
+    _hasWorkStreamController.add('do it!');
   }
 
   /**
@@ -152,8 +254,9 @@ class AnalysisDriver {
    * transitions to "idle".
    */
   Future<AnalysisResult> getResult(String path) {
-    // TODO(scheglov) implement
-    throw new UnimplementedError();
+    var completer = new Completer<AnalysisResult>();
+    _requestedFiles[path] = completer;

[Paul Berry, 2016/10/24 11:46:21]

There's a bug here.  If the client calls getResult() twice for the same path
without waiting for the first call to complete, the old completer will be
discarded and never signaled.

[scheglov, 2016/10/24 17:23:48]

Fixed.
We need a list of completers here.
Every of the will complete with the same value at the time when we manage to
compute the result.

+    return completer.future;

[Paul Berry, 2016/10/24 11:46:21]

I'm surprised not to see a call to `_hasWorkStreamController.add(...)` or
`_filesToAnalyze.add(path)` here.  Don't we need to do something to trigger the
file to be analyzed?

[scheglov, 2016/10/24 17:23:48]

Done.

Yes, we need to add a value to the "has work" stream.
We don't need to add to `_filesToAnalyze` because `_requestedFiles` are handled
before we look into `_filesToAnalyze`.

   }
 
   /**
@@ -166,7 +269,310 @@ class AnalysisDriver {
    * but does not guarantee this.
    */
   void removeFile(String path) {
-    // TODO(scheglov) implement
+    _explicitFiles.remove(path);
+    _filesToAnalyze.remove(path);
+  }
+
+  /**
+   * TODO(scheglov) replace with actual [AnalysisResult] computing.
+   */
+  List<String> _computeAndPrintErrors(_File file) {
+    List<String> errorStrings = _logger.run('Compute errors $file', () {
+      LibraryContext libraryContext = _createLibraryContext(file);
+
+      String errorsKey;
+      {
+        ApiSignature signature = new ApiSignature();
+        signature.addString(libraryContext.node.linkedHash);
+        signature.addString(file.contentHash);
+        errorsKey = '${signature.toHex()}.errors';
+      }
+
+      {
+        List<int> bytes = _byteStore.get(errorsKey);
+        if (bytes != null) {
+          fb.BufferContext bp = new fb.BufferContext.fromBytes(bytes);
+          int table = bp.derefObject(0);
+          return const fb.ListReader<String>(const fb.StringReader())
+              .vTableGet(bp, table, 0);
+        }
+      }
+
+      AnalysisContext analysisContext = _createAnalysisContext(libraryContext);
+      analysisContext.resolveCompilationUnit2(
+          libraryContext.file.source, libraryContext.file.source);
+      try {
+        List<AnalysisError> errors;
+        try {
+          errors = _logger.runTimed('Computed errors', () {
+            return analysisContext.computeErrors(file.source);
+          });
+        } catch (e, st) {
+          // TODO(scheglov) why does it fail?
+          // Caused by Bad state: Unmatched TypeParameterElementImpl T

[Paul Berry, 2016/10/24 11:46:21]

This exception is usually caused by a bug in type inference, where it creates a
type pointing to a type parameter that is not in scope.  If you want to send me
repro instructions I'd be happy to investigate.

[scheglov, 2016/10/24 17:23:47]

I will try to come up with a repro today.

[scheglov, 2016/10/24 17:29:31]

Hm...
Cannot reproduce now.
I will remove try/catch and see if it happens again.

+          errors = [];
+        }
+        List<String> errorStrings = errors
+            .where((error) => error.errorCode is! TodoCode)
+            .map((error) => error.toString())
+            .toList();
+        {
+          fb.Builder fbBuilder = new fb.Builder();
+          var exportedOffset = fbBuilder.writeList(errorStrings
+              .map((errorStr) => fbBuilder.writeString(errorStr))
+              .toList());
+          fbBuilder.startTable();
+          fbBuilder.addOffset(0, exportedOffset);
+          var offset = fbBuilder.endTable();
+          List<int> bytes = fbBuilder.finish(offset, 'CErr');
+          _byteStore.put(errorsKey, bytes);
+        }
+
+        return errorStrings;
+      } finally {
+        analysisContext.dispose();
+      }
+    });
+
+    if (errorStrings.isNotEmpty) {
+      errorStrings.forEach((errorString) => print('\t$errorString'));
+    } else {
+      print('\tNO ERRORS');
+    }
+    return errorStrings;
+  }
+
+  AnalysisContext _createAnalysisContext(LibraryContext libraryContext) {
+    AnalysisContextImpl analysisContext =
+        AnalysisEngine.instance.createAnalysisContext();
+
+    analysisContext.sourceFactory =
+        new SourceFactory((_sourceFactory as SourceFactoryImpl).resolvers);
+    analysisContext.resultProvider =
+        new InputPackagesResultProvider(analysisContext, libraryContext.store);
+    analysisContext
+        .applyChanges(new ChangeSet()..addedSource(libraryContext.file.source));
+    return analysisContext;
+  }
+
+  /**
+   * Return the content in which the library represented by the given

[Paul Berry, 2016/10/24 11:46:21]

s/content/context/

[scheglov, 2016/10/24 17:23:48]

Done.

+   * [libraryFile] should be analyzed it.
+   *
+   * TODO(scheglov) We often don't need [SummaryDataStore], only linked hash.
+   */
+  LibraryContext _createLibraryContext(_File libraryFile) {
+    Map<String, _LibraryNode> nodes = <String, _LibraryNode>{};
+
+    return _logger.run('Create library context', () {
+      SummaryDataStore store = new SummaryDataStore(const <String>[]);
+      store.addBundle(null, _sdkBundle);
+
+      void createLibraryNodes(_File libraryFile) {
+        Uri libraryUri = libraryFile.uri;
+        if (libraryUri.scheme == 'dart') {
+          return;

[Paul Berry, 2016/10/24 11:46:21]

Why?  Is this because we always get "dart:" stuff from the SDK summary?  If so
it would be good to have a comment documenting this.

[scheglov, 2016/10/24 17:23:48]

Done.

+        }
+        String uriStr = libraryUri.toString();
+        if (!nodes.containsKey(uriStr)) {
+          _LibraryNode node = new _LibraryNode(this, nodes, libraryUri);
+          nodes[uriStr] = node;
+          ReferencedUris referenced = _getReferencedUris(libraryFile);
+
+          // Append unlinked bundles.
+          for (String uri in referenced.parted) {
+            _File file = libraryFile.resolveUri(uri);
+            PackageBundle unlinked = _getUnlinked(file);
+            node.unlinkedBundles.add(unlinked);
+            store.addBundle(null, unlinked);
+          }
+
+          // Create nodes for referenced libraries.
+          for (String uri in referenced.imported) {
+            _File file = libraryFile.resolveUri(uri);
+            createLibraryNodes(file);
+          }
+          for (String uri in referenced.exported) {
+            _File file = libraryFile.resolveUri(uri);
+            createLibraryNodes(file);
+          }
+        }
+      }
+
+      _logger.runTimed2(() {
+        createLibraryNodes(libraryFile);
+      }, () => 'Computed ${nodes.length} nodes');
+      _LibraryNode libraryNode = nodes[libraryFile.uri.toString()];

[Paul Berry, 2016/10/24 11:46:21]

Nit: how about if we change createLibraryNodes() so that it returns the library
node corresponding to its argument?  Then we can just do:

_LibraryNode libraryNode = _logger.runTimed2(() =>
createLibraryNodes(libraryFile), ...);

[scheglov, 2016/10/24 17:23:48]

Done.

+
+      Set<String> libraryUrisToLink = new Set<String>();
+      int numberOfNodesWithLinked = 0;
+      _logger.runTimed2(() {
+        for (_LibraryNode node in nodes.values) {
+          String key = '${node.linkedHash}.linked';
+          List<int> bytes = _byteStore.get(key);
+          if (bytes != null) {
+            PackageBundle linked = new PackageBundle.fromBuffer(bytes);
+            node.linked = linked;
+            store.addBundle(null, linked);
+            numberOfNodesWithLinked++;
+          } else {
+            libraryUrisToLink.add(node.uri.toString());
+          }
+        }
+      }, () => 'Loaded $numberOfNodesWithLinked linked bundles');
+
+      Map<String, LinkedLibraryBuilder> linkedLibraries = {};
+      _logger.runTimed2(() {
+        linkedLibraries = link(libraryUrisToLink, (String uri) {
+          LinkedLibrary linkedLibrary = store.linkedMap[uri];
+          if (linkedLibrary == null) {
+            throw new StateError('No linked library for: $uri');
+          }
+          return linkedLibrary;
+        }, (String uri) {
+          UnlinkedUnit unlinkedUnit = store.unlinkedMap[uri];
+          if (unlinkedUnit == null) {
+            throw new StateError('No unlinked unit for: $uri');
+          }
+          return unlinkedUnit;
+        }, (_) => null, _analysisOptions.strongMode);
+      }, () => 'Linked ${linkedLibraries.length} bundles');
+
+      linkedLibraries.forEach((uri, linkedBuilder) {
+        _LibraryNode node = nodes[uri];
+        String key = '${node.linkedHash}.linked';
+        List<int> bytes;
+        {
+          PackageBundleAssembler assembler = new PackageBundleAssembler();
+          assembler.addLinkedLibrary(uri, linkedBuilder);
+          bytes = assembler.assemble().toBuffer();
+        }
+        PackageBundle linked = new PackageBundle.fromBuffer(bytes);
+        node.linked = linked;
+        store.addBundle(null, linked);
+        _byteStore.put(key, bytes);
+      });
+
+      return new LibraryContext(libraryFile, libraryNode, store);
+    });
+  }
+
+  /**
+   * Return the [_File] for the given [path] in [_sourceFactory].
+   */
+  _File _fileForPath(String path) {
+    Source fileSource = _resourceProvider.getFile(path).createSource();
+    Uri uri = _sourceFactory.restoreUri(fileSource);
+    Source source = _resourceProvider.getFile(path).createSource(uri);
+    return new _File(this, source);
+  }
+
+  /**
+   * TODO(scheglov) It would be nice to get URIs of "parts" from unlinked.
+   */
+  ReferencedUris _getReferencedUris(_File file) {
+    // Try to get from the store.
+    {
+      String key = '${file.contentHash}.uris';
+      List<int> bytes = _byteStore.get(key);
+      if (bytes != null) {
+        fb.BufferContext bp = new fb.BufferContext.fromBytes(bytes);
+        int table = bp.derefObject(0);
+        const fb.ListReader<String> stringListReader =
+            const fb.ListReader<String>(const fb.StringReader());
+        bool isLibrary = const fb.BoolReader().vTableGet(bp, table, 0);
+        List<String> imported = stringListReader.vTableGet(bp, table, 1);
+        List<String> exported = stringListReader.vTableGet(bp, table, 2);
+        List<String> parted = stringListReader.vTableGet(bp, table, 3);
+        ReferencedUris referencedUris = new ReferencedUris();
+        referencedUris.isLibrary = isLibrary;
+        referencedUris.imported.addAll(imported);
+        referencedUris.exported.addAll(exported);
+        referencedUris.parted.addAll(parted);
+        return referencedUris;
+      }
+    }
+
+    // Compute URIs.
+    ReferencedUris referencedUris = new ReferencedUris();
+    referencedUris.parted.add(file.uri.toString());
+    for (Directive directive in file.unit.directives) {
+      if (directive is PartOfDirective) {
+        referencedUris.isLibrary = false;
+      } else if (directive is UriBasedDirective) {
+        String uri = directive.uri.stringValue;
+        if (directive is ImportDirective) {
+          referencedUris.imported.add(uri);
+        } else if (directive is ExportDirective) {
+          referencedUris.exported.add(uri);
+        } else if (directive is PartDirective) {
+          referencedUris.parted.add(uri);
+        }
+      }
+    }
+
+    // Serialize into bytes.
+    List<int> bytes;
+    {
+      fb.Builder fbBuilder = new fb.Builder();
+      var importedOffset = fbBuilder.writeList(referencedUris.imported
+          .map((uri) => fbBuilder.writeString(uri))
+          .toList());
+      var exportedOffset = fbBuilder.writeList(referencedUris.exported
+          .map((uri) => fbBuilder.writeString(uri))
+          .toList());
+      var partedOffset = fbBuilder.writeList(referencedUris.parted
+          .map((uri) => fbBuilder.writeString(uri))
+          .toList());
+      fbBuilder.startTable();
+      fbBuilder.addBool(0, referencedUris.isLibrary);
+      fbBuilder.addOffset(1, importedOffset);
+      fbBuilder.addOffset(2, exportedOffset);
+      fbBuilder.addOffset(3, partedOffset);
+      var offset = fbBuilder.endTable();
+      bytes = fbBuilder.finish(offset, 'SoRU');
+    }
+
+    // We read the content and recomputed the hash.
+    // So, we need to update the key.
+    String key = '${file.contentHash}.uris';
+    _byteStore.put(key, bytes);
+
+    return referencedUris;
+  }
+
+  /**
+   * Return the unlinked bundle of [file] for the current file state.
+   *
+   * That is, if there is an existing bundle for the current content hash
+   * of the [file] in the [_byteStore], then it is returned. Otherwise, the
+   * [file] content is read, the content hash is computed and the current file
+   * state is updated accordingly. That the content is parsed into the
+   * [CompilationUnit] and serialized into a new unlinked bundle. The bundle
+   * is then put into the [_byteStore] and returned.
+   */
+  PackageBundle _getUnlinked(_File file) {
+    // Try to get bytes for file's unlinked bundle.
+    List<int> bytes;
+    {
+      String key = '${file.contentHash}.unlinked';
+      bytes = _byteStore.get(key);
+    }
+    // If no cached unlinked bundle, compute it.
+    if (bytes == null) {
+      _logger.runTimed('Create unlinked for $file', () {
+        // We read the content and recomputed the hash.
+        // So, we need to update the key.
+        String key = '${file.contentHash}.unlinked';
+        UnlinkedUnitBuilder unlinkedUnit = serializeAstUnlinked(file.unit);
+        PackageBundleAssembler assembler = new PackageBundleAssembler();
+        assembler.addUnlinkedUnitWithHash(
+            file.uri.toString(), unlinkedUnit, key);
+        bytes = assembler.assemble().toBuffer();
+        _byteStore.put(key, bytes);
+      });
+    }
+    return new PackageBundle.fromBuffer(bytes);
   }
 }
 
@@ -217,3 +623,299 @@ class AnalysisResult {
   AnalysisResult(this.path, this.uri, this.content, this.contentHash, this.unit,
       this.errors);
 }
+
+class LibraryContext {

[Paul Berry, 2016/10/24 11:46:21]

Please add doc comments to this class and its public members (or make it
private).

Same with PerformanceLog and ReferencedURIs.

[scheglov, 2016/10/24 17:23:48]

Done.

+  final _File file;
+  final _LibraryNode node;
+  final SummaryDataStore store;
+  LibraryContext(this.file, this.node, this.store);
+}
+
+class PerformanceLog {
+  final StringSink sink;
+  int _level = 0;
+
+  PerformanceLog(this.sink);
+
+  /*=T*/ run/*<T>*/(String msg, /*=T*/ f()) {
+    Stopwatch timer = new Stopwatch()..start();
+    try {
+      writeln('+++ $msg.');
+      _level++;
+      return f();
+    } finally {
+      _level--;
+      int ms = timer.elapsedMilliseconds;
+      writeln('--- $msg in $ms ms.');
+    }
+  }
+
+  /*=T*/ runTimed/*<T>*/(String msg, /*=T*/ f()) {

[Paul Berry, 2016/10/24 11:46:21]

I'm not comfortable with the duplication between run() and runTimed().  It's not
clear when callers should use one vs. the other.

AFAICT, run() has a strict superset of the functionality of runTimed(), so I
would just drop this method and have all callers use run().

[scheglov, 2016/10/24 17:23:48]

Acknowledged.

+    _level++;
+    Stopwatch timer = new Stopwatch()..start();
+    try {
+      return f();
+    } finally {
+      _level--;
+      int ms = timer.elapsedMilliseconds;
+      writeln('$msg in $ms ms.');
+    }
+  }
+
+  runTimed2(f(), String getMsg()) {

[Paul Berry, 2016/10/24 11:46:21]

Similar concern here.  I would recommend getting rid of runTimed2(), and
changing callers that look like this:

logger.runTimed2(() {
    ...computation...
  }, () => ...computed message...);

To look like this instead:

logger.run("generic message"), () {
    ...computation...
    logger.writeln(...computed message...);
  });

It will make the log slightly less pretty, IMHO it's more important to have a
clean and simple logging API.

[scheglov, 2016/10/24 17:23:48]

Acknowledged.
I completely agree.
I changed the log to have only run().

+    _level++;
+    Stopwatch timer = new Stopwatch()..start();
+    try {
+      return f();
+    } finally {
+      _level--;
+      int ms = timer.elapsedMilliseconds;
+      String msg = getMsg();
+      writeln('$msg in $ms ms.');
+    }
+  }
+
+  void writeln(String msg) {
+    String indent = '\t' * _level;
+    sink.writeln('$indent$msg');
+  }
+}
+
+class ReferencedUris {
+  bool isLibrary = true;
+  final List<String> imported = <String>[];
+  final List<String> exported = <String>[];
+  final List<String> parted = <String>[];
+}
+
+/**
+ * Information about a file being analyzed, explicitly or implicitly.
+ *
+ * It keeps a consistent view on its [content], [contentHash] and [unit].
+ */
+class _File {
+  /**
+   * The driver instance that is used to access [SourceFactory] and caches.
+   */
+  final AnalysisDriver driver;
+
+  /**
+   * The [Source] this [_File] instance represent.

[Brian Wilkerson, 2016/10/26 06:31:48]

nit: "represent" --> "represents"

+   */
+  final Source source;
+
+  String _content;
+  String _contentHash;
+  CompilationUnit _unit;
+
+  _File(this.driver, this.source);
+
+  /**
+   * Return the current content of the file.
+   *
+   * If the [_content] field if it is still `null`, get the content from the
+   * content cache or from the [source]. If the content cannot be accessed
+   * because of an exception, it considers to be an empty string.
+   *
+   * When a new content is read, the new [_contentHash] is computed and the
+   * current file state is updated.
+   */
+  String get content {
+    if (_content == null) {
+      _readContentAndComputeHash();
+    }
+    return _content;
+  }
+
+  /**
+   * Ensure that the [contentHash] is filled.
+   *
+   * If the hash is already in the current file state, return the current
+   * value. Otherwise, read the [content], compute the hash, put it into
+   * the current file state, and update the [contentHash] field.
+   *
+   * The client cannot remember values of this property, because its value

[Paul Berry, 2016/10/24 11:46:21]

Change "cannot" to either "should not" or "cannot safely".

("cannot" implies that it's impossible; what we're trying to communicate is that
it's a bad idea)

[scheglov, 2016/10/24 17:23:48]

Done.

+   * might change when [content] is read and the hash is recomputed.
+   */
+  String get contentHash {
+    _contentHash ??= driver._fileContentHashMap[path];
+    if (_contentHash == null) {
+      _readContentAndComputeHash();
+    }
+    return _contentHash;
+  }
+
+  String get path => source.fullName;
+
+  /**
+   * Return the [CompilationUnit] of the file.
+   *
+   * Current this unit is resolved, it is used to compute unlinked summaries

[Paul Berry, 2016/10/24 11:46:21]

I had trouble understanding this paragraph.  Do you perhaps mean something like
this?

"Currently method returns an *unresolved* unit, since it is only used to compute
unlinked summaries and URIs.  (Performing resolution and computing errors is
done in a separate analysis context).  But this might change in the future."

[scheglov, 2016/10/24 17:23:48]

I changed the documentation comments for this getter and _File.

+   * and and URIs. We use a separate analysis context to perform resolution
+   * and computing errors. But this might change in the future.
+   */
+  CompilationUnit get unit {
+    AnalysisErrorListener errorListener = AnalysisErrorListener.NULL_LISTENER;
+
+    CharSequenceReader reader = new CharSequenceReader(content);
+    Scanner scanner = new Scanner(source, reader, errorListener);
+    scanner.scanGenericMethodComments = driver._analysisOptions.strongMode;
+    Token token = scanner.tokenize();
+    LineInfo lineInfo = new LineInfo(scanner.lineStarts);
+
+    Parser parser = new Parser(source, errorListener);
+    parser.parseGenericMethodComments = driver._analysisOptions.strongMode;
+    _unit = parser.parseCompilationUnit(token);
+    _unit.lineInfo = lineInfo;
+
+    return _unit;
+  }
+
+  Uri get uri => source.uri;
+
+  /**
+   * Return the [_File] for the [uri] referenced in this file.
+   */
+  _File resolveUri(String uri) {
+    Source uriSource = driver._sourceFactory.resolveUri(source, uri);
+    return new _File(driver, uriSource);
+  }
+
+  @override
+  String toString() => uri.toString();
+
+  /**
+   * Fill the [_content] and [_contentHash] fields.
+   *
+   * If the [_content] field if it is still `null`, get the content from the

[Paul Berry, 2016/10/24 11:46:21]

Drop the words "if it".

[scheglov, 2016/10/24 17:23:48]

Done.

+   * content cache or from the [source]. If the content cannot be accessed
+   * because of an exception, it considers to be an empty string.
+   *
+   * When a new content is read, the new [_contentHash] should be computed and
+   * the current file state should be updated.
+   */
+  void _readContentAndComputeHash() {
+    try {
+      _content = driver._contentCache.getContents(source);
+      _content ??= source.contents.data;
+    } catch (_) {
+      _content = '';

[Paul Berry, 2016/10/24 11:46:21]

Do we need to record the fact that we couldn't read the file contents somewhere
(in order to ensure that the user will see an appropriate error message when
trying to import a non-existing file)?

[scheglov, 2016/10/24 17:23:48]

I don't know yet.
There is a bug with not existing source.
I will add TODO and fix it soon.

Then I suspect that we will get error messages automatically during
DartParseTask in the context.
OTOH, if/when we decide to push parsed unresolved units into analysis context,
we might lose this feature.
Something to cover with a test to prevent a regression.

+    }
+    // Compute the content hash.
+    List<int> textBytes = UTF8.encode(_content);
+    List<int> hashBytes = md5.convert(textBytes).bytes;
+    _contentHash = hex.encode(hashBytes);
+    // Update the current file state.
+    driver._fileContentHashMap[path] = _contentHash;
+  }
+}
+
+class _LibraryNode {
+  final AnalysisDriver driver;
+  final Map<String, _LibraryNode> nodes;
+  final Uri uri;
+  final List<PackageBundle> unlinkedBundles = <PackageBundle>[];
+
+  Set<_LibraryNode> transitiveDependencies;
+  List<_LibraryNode> _dependencies;
+  String _linkedHash;
+
+  List<int> linkedNewBytes;
+  PackageBundle linked;
+
+  _LibraryNode(this.driver, this.nodes, this.uri);
+
+  /**
+   * Retrieve the dependencies of this node.
+   */
+  List<_LibraryNode> get dependencies {
+    if (_dependencies == null) {
+      Set<_LibraryNode> dependencies = new Set<_LibraryNode>();
+
+      void appendDependency(String uriStr) {
+        Uri uri = FastUri.parse(uriStr);
+        if (uri.scheme == 'dart') {
+          // Dependency on the SDK is implicit and always added.
+          // The SDK linked bundle is precomputed before linking packages.
+        } else {
+          if (!uri.isAbsolute) {
+            uri = resolveRelativeUri(this.uri, uri);
+            uriStr = uri.toString();
+          }
+          _LibraryNode node = nodes[uriStr];
+          if (node == null) {
+            throw new StateError('No node for: $uriStr');
+          }
+          dependencies.add(node);
+        }
+      }
+
+      for (PackageBundle unlinkedBundle in unlinkedBundles) {
+        for (UnlinkedUnit unit in unlinkedBundle.unlinkedUnits) {
+          for (UnlinkedImport import in unit.imports) {
+            if (!import.isImplicit) {
+              appendDependency(import.uri);
+            }
+          }
+          for (UnlinkedExportPublic export in unit.publicNamespace.exports) {
+            appendDependency(export.uri);
+          }
+        }
+      }
+
+      _dependencies = dependencies.toList();
+    }
+    return _dependencies;
+  }
+
+  @override
+  int get hashCode => uri.hashCode;
+
+  bool get isReady => linked != null;

[Paul Berry, 2016/10/24 11:46:21]

It's not obvious to me why "ready" means "linked".  Maybe rename this method to
"isLinked"?

[scheglov, 2016/10/24 17:23:48]

I removed this and couple other fields later.

+
+  String get linkedHash {

[Paul Berry, 2016/10/24 11:46:21]

The name "linkedHash" sounds like it means a hash of the data in "linked", and
therefore "linkedHash" should always be called after linking.

But it's actually the opposite situation--we call "linkedHash" prior to linking
in order to figure out whether we already have the linked data in the cache
somewhere.

How about renaming this to something like "dependencySignature"?

[scheglov, 2016/10/24 17:23:48]

Done.

+    if (_linkedHash == null) {
+      if (transitiveDependencies == null) {
+        computeTransitiveDependencies();
+      }
+
+      // Add all unlinked API signatures.
+      List<String> signatures = <String>[];
+      signatures.add(driver._sdkBundle.apiSignature);
+      transitiveDependencies
+          .map((node) => node.unlinkedBundles)
+          .expand((bundles) => bundles)
+          .map((bundle) => bundle.apiSignature)
+          .forEach(signatures.add);
+      signatures.sort();
+
+      // Combine into a single hash.
+      ApiSignature signature = new ApiSignature();
+      signature.addString(uri.toString());
+      signatures.forEach(signature.addString);
+      _linkedHash = signature.toHex();
+    }
+    return _linkedHash;
+  }
+
+  bool operator ==(other) {
+    return other is _LibraryNode && other.uri == uri;
+  }
+
+  void computeTransitiveDependencies() {
+    if (transitiveDependencies == null) {
+      transitiveDependencies = new Set<_LibraryNode>();
+
+      void appendDependencies(_LibraryNode node) {
+        if (transitiveDependencies.add(node)) {
+          node.dependencies.forEach(appendDependencies);
+        }
+      }
+
+      appendDependencies(this);
+    }
+  }
+
+  @override
+  String toString() => uri.toString();
+}