Make LibraryCycle more null safe.

Change-Id: I1298651fcac80ec20db6c68b9b969da8c6320bde
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/215486
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

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

@@ -80,7 +80,7 @@ import 'package:meta/meta.dart';
 /// TODO(scheglov) Clean up the list of implicitly analyzed files.
 class AnalysisDriver implements AnalysisDriverGeneric {
   /// The version of data format, should be incremented on every format change.
-  static const int DATA_VERSION = 182;
+  static const int DATA_VERSION = 183;
 
   /// The number of exception contexts allowed to write. Once this field is
   /// zero, we stop writing any new exception contexts in this process.

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

@@ -140,7 +140,6 @@ class FileState {
   Set<FileState>? _directReferencedLibraries;
 
   LibraryCycle? _libraryCycle;
-  String? _transitiveSignature;
 
   /// The flag that shows whether the file has an error or warning that
   /// might be fixed by a change to another file.
@@ -320,10 +319,12 @@ class FileState {
 
   /// Return the signature of the file, based on API signatures of the
   /// transitive closure of imported / exported files.
+  /// TODO(scheglov) Remove it.
   String get transitiveSignature {
-    libraryCycle; // sets _transitiveSignature
-    _transitiveSignature ??= _invalidTransitiveSignature;
-    return _transitiveSignature!;
+    var librarySignatureBuilder = ApiSignature()
+      ..addString(uriStr)
+      ..addString(libraryCycle.transitiveSignature);
+    return librarySignatureBuilder.toHex();
   }
 
   /// The [UnlinkedUnit2] of the file.
@@ -335,13 +336,6 @@ class FileState {
   /// Return the [uri] string.
   String get uriStr => uri.toString();
 
-  String get _invalidTransitiveSignature {
-    return (ApiSignature()
-          ..addString(path)
-          ..addBytes(unlinkedSignature))
-        .toHex();
-  }
-
   @override
   bool operator ==(Object other) {
     return other is FileState && other.uri == uri;
@@ -357,14 +351,8 @@ class FileState {
     return bytes;
   }
 
-  void internal_setLibraryCycle(LibraryCycle? cycle, String? signature) {
-    if (cycle == null) {
-      _libraryCycle = null;
-      _transitiveSignature = null;
-    } else {
-      _libraryCycle = cycle;
-      _transitiveSignature = signature;
-    }
+  void internal_setLibraryCycle(LibraryCycle? cycle) {
+    _libraryCycle = cycle;
   }
 
   /// Return a new parsed unresolved [CompilationUnit].

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

@@ -121,7 +121,7 @@ class LibraryContext {
         }
       }
 
-      var resolutionKey = cycle.transitiveSignature! + '.linked_bundle';
+      var resolutionKey = cycle.transitiveSignature + '.linked_bundle';
       var resolutionBytes = byteStore.get(resolutionKey) as Uint8List?;
 
       if (resolutionBytes == null) {

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

@@ -20,10 +20,10 @@ void computeLibraryCycle(Uint32List salt, FileState file) {
 /// Information about libraries that reference each other, so form a cycle.
 class LibraryCycle {
   /// The libraries that belong to this cycle.
-  final List<FileState> libraries = [];
+  final List<FileState> libraries;
 
   /// The library cycles that this cycle references directly.
-  final Set<LibraryCycle> directDependencies = <LibraryCycle>{};
+  final Set<LibraryCycle> directDependencies;
 
   /// The cycles that use this cycle, used to [invalidate] transitively.
   final List<LibraryCycle> _directUsers = [];
@@ -34,7 +34,17 @@ class LibraryCycle {
   /// transitive signatures of the cycles that the [libraries] reference
   /// directly.  So, indirectly it is based on the transitive closure of all
   /// files that [libraries] reference (but we don't compute these files).
-  String? transitiveSignature;
+  String transitiveSignature;
+
+  LibraryCycle({
+    required this.libraries,
+    required this.directDependencies,
+    required this.transitiveSignature,
+  }) {
+    for (var directDependency in directDependencies) {
+      directDependency._directUsers.add(this);
+    }
+  }
 
   /// Invalidate this cycle and any cycles that directly or indirectly use it.
   ///
@@ -42,12 +52,14 @@ class LibraryCycle {
   /// [libraries] that share this [LibraryCycle] instance.
   void invalidate() {
     for (var library in libraries) {
-      library.internal_setLibraryCycle(null, null);
+      library.internal_setLibraryCycle(null);
     }
-    for (var user in _directUsers) {
+    for (var user in _directUsers.toList()) {
       user.invalidate();
     }
-    _directUsers.clear();
+    for (var directDependency in directDependencies) {
+      directDependency._directUsers.remove(this);
+    }
   }
 
   @override
@@ -87,8 +99,6 @@ class _LibraryWalker extends graph.DependencyWalker<_LibraryNode> {
 
   @override
   void evaluateScc(List<_LibraryNode> scc) {
-    var cycle = LibraryCycle();
-
     var signature = ApiSignature();
     signature.addUint32List(_salt);
 
@@ -100,17 +110,20 @@ class _LibraryWalker extends graph.DependencyWalker<_LibraryNode> {
     });
 
     // Append direct referenced cycles.
+    var directDependencies = <LibraryCycle>{};
     for (var node in scc) {
       var file = node.file;
       _appendDirectlyReferenced(
-          cycle, signature, file.importedFiles.whereNotNull().toList());
-      _appendDirectlyReferenced(
-          cycle, signature, file.exportedFiles.whereNotNull().toList());
+        directDependencies,
+        signature,
+        file.directReferencedLibraries.whereNotNull().toList(),
+      );
     }
 
     // Fill the cycle with libraries.
+    var libraries = <FileState>[];
     for (var node in scc) {
-      cycle.libraries.add(node.file);
+      libraries.add(node.file);
 
       signature.addLanguageVersion(node.file.packageLanguageVersion);
       signature.addString(node.file.uriStr);
@@ -122,20 +135,16 @@ class _LibraryWalker extends graph.DependencyWalker<_LibraryNode> {
       }
     }
 
-    // Compute the general library cycle signature.
-    cycle.transitiveSignature = signature.toHex();
+    // Create the LibraryCycle instance for the cycle.
+    var cycle = LibraryCycle(
+      libraries: libraries,
+      directDependencies: directDependencies,
+      transitiveSignature: signature.toHex(),
+    );
 
-    // Compute library specific signatures.
+    // Set the instance into the libraries.
     for (var node in scc) {
-      var librarySignatureBuilder = ApiSignature()
-        ..addString(node.file.uriStr)
-        ..addString(cycle.transitiveSignature!);
-      var librarySignature = librarySignatureBuilder.toHex();
-
-      node.file.internal_setLibraryCycle(
-        cycle,
-        librarySignature,
-      );
+      node.file.internal_setLibraryCycle(cycle);
     }
   }
 
@@ -144,7 +153,7 @@ class _LibraryWalker extends graph.DependencyWalker<_LibraryNode> {
   }
 
   void _appendDirectlyReferenced(
-    LibraryCycle cycle,
+    Set<LibraryCycle> directDependencies,
     ApiSignature signature,
     List<FileState> directlyReferenced,
   ) {
@@ -155,9 +164,8 @@ class _LibraryWalker extends graph.DependencyWalker<_LibraryNode> {
       // We get null when the library is a part of the cycle being build.
       if (referencedCycle == null) continue;
 
-      if (cycle.directDependencies.add(referencedCycle)) {
-        referencedCycle._directUsers.add(cycle);
-        signature.addString(referencedCycle.transitiveSignature!);
+      if (directDependencies.add(referencedCycle)) {
+        signature.addString(referencedCycle.transitiveSignature);
       }
     }
   }