Make futures returned by AnalysisContext cancelable.

pkg/analyzer/test/generated/engine_test.dart

Index: pkg/analyzer/test/generated/engine_test.dart
diff --git a/pkg/analyzer/test/generated/engine_test.dart b/pkg/analyzer/test/generated/engine_test.dart
index 9c325f3d2cae762be868029f57eb5f25b2e4b356..2a8a6f8b8346f766b512b1a244879e07950d8314 100644
--- a/pkg/analyzer/test/generated/engine_test.dart
+++ b/pkg/analyzer/test/generated/engine_test.dart
@@ -10,6 +10,7 @@ library engine.engine_test;
 import 'dart:async';
 import 'dart:collection';
 
+import 'package:analyzer/src/cancelable_future.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ -1152,6 +1153,34 @@ main() {}''');
     });
   }
 
+  Future test_getResolvedCompilationUnitFuture_cancel() {
+    _context = AnalysisContextFactory.contextWithCore();
+    _sourceFactory = _context.sourceFactory;
+    Source source = _addSource("/lib.dart", "library lib;");
+    // Complete all pending analysis tasks and flush the AST so that it won't
+    // be available immediately.
+    while (_context.performAnalysisTask().hasMoreWork) {}

[Brian Wilkerson, 2014/12/15 19:49:26]

We have normally put in some limit on the number of times we will invoke
performAnalysisTask before failing in order to guard against infinite loops.

[Paul Berry, 2014/12/16 16:58:06]

Done.

+    DartEntry dartEntry = _context.getReadableSourceEntryOrNull(source);
+    dartEntry.flushAstStructures();
+    CancelableFuture<CompilationUnit> future =
+        _context.getResolvedCompilationUnitFuture(source, source);
+    bool completed = false;
+    future.then((CompilationUnit unit) {
+      fail('Future should have been canceled');
+    }, onError: (error) {
+      expect(error, new isInstanceOf<FutureCanceledError>());
+      completed = true;
+    });
+    expect(completed, isFalse);
+    expect(_context.pendingFutureSources_forTesting, isNotEmpty);
+    future.cancel();
+    expect(_context.pendingFutureSources_forTesting, isEmpty);
+    return pumpEventQueue().then((_) {
+      expect(completed, isTrue);
+      expect(_context.pendingFutureSources_forTesting, isEmpty);
+    });
+  }
+
   Future test_getResolvedCompilationUnitFuture_unrelatedLibrary() {
     _context = AnalysisContextFactory.contextWithCore();
     _sourceFactory = _context.sourceFactory;