Display the sizes of the largest library cycles in the diagnostic pages

I know there it has been hypothesized that large library cycles might
be causing some of the performance issues that users are seeing. This
CL adds a way for users to be able to tell us how big their library
cycles really are, which might help us determine whether that's true.

Change-Id: I5cb53f175823dd20a7ff678468b19a6187584b71
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/423206
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Brian Wilkerson <[email protected]>

Author: bwilkerson

pkg/analysis_server/lib/src/status/diagnostics.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 import 'dart:convert' show JsonEncoder;
 import 'dart:developer' as developer;
 import 'dart:io';
+import 'dart:math' as math;
 
 import 'package:analysis_server/protocol/protocol_constants.dart'
     show PROTOCOL_VERSION;
@@ -33,6 +34,8 @@ import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/src/context/source.dart';
 import 'package:analyzer/src/dart/analysis/analysis_options_map.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
+import 'package:analyzer/src/dart/analysis/file_state.dart';
+import 'package:analyzer/src/dart/analysis/library_graph.dart';
 import 'package:analyzer/src/dart/sdk/sdk.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/source/package_map_resolver.dart';
@@ -1014,7 +1017,8 @@ class ContextsPage extends DiagnosticPageWithNav {
         'contexts',
         'Contexts',
         description:
-            'An analysis context defines the options and the set of sources being analyzed.',
+            'An analysis context defines a set of sources for which URIs are '
+            'all resolved in the same way.',
       );
 
   @override
@@ -1190,6 +1194,41 @@ class ContextsPage extends DiagnosticPageWithNav {
     buf.write('<p class="scroll-table">');
     writeMap(info.templateMap);
     buf.write('</p>');
+
+    h3('Largest library cycles');
+    Set<LibraryCycle> cycles = {};
+    var contextRoot = driver.analysisContext!.contextRoot;
+    for (var filePath in contextRoot.analyzedFiles()) {
+      var fileState = driver.fsState.getFileForPath(filePath);
+      var kind = fileState.kind;
+      if (kind is LibraryFileKind) {
+        cycles.add(kind.libraryCycle);
+      }
+    }
+    var sortedCycles =
+        cycles.toList()..sort((first, second) => second.size - first.size);
+    var cyclesToDisplay = math.min(sortedCycles.length, 10);
+    var initialPathLength = contextRoot.root.path.length + 1;
+    buf.write('<p>There are ${sortedCycles.length} library cycles. ');
+    buf.write('The $cyclesToDisplay largest contain</p>');
+    buf.write('<ul>');
+    for (var i = 0; i < cyclesToDisplay; i++) {
+      var cycle = sortedCycles[i];
+      var libraries = cycle.libraries;
+      var cycleSize = cycle.size;
+      var libraryCount = math.min(cycleSize, 8);
+      buf.write('<li>$cycleSize libraries, including');
+      buf.write('<ul>');
+      for (var j = 0; j < libraryCount; j++) {
+        var library = libraries[j];
+        buf.write('<li>');
+        buf.write(library.file.path.substring(initialPathLength));
+        buf.write('</li>');
+      }
+      buf.write('</ul>');
+      buf.write('</li>');
+    }
+    buf.write('</ul>');
   }
 
   void writeList<E>(List<E> list) {
@@ -2360,6 +2399,11 @@ class _CollectedOptionsData {
   final Set<String> plugins = <String>{};
 }
 
+extension on LibraryCycle {
+  /// The number of libraries in the cycle.
+  int get size => libraries.length;
+}
+
 extension on String {
   String get wordBreakOnSlashes => splitMapJoin('/', onMatch: (_) => '/<wbr>');
 }