Use different SDKs based on option settings

pkg/analyzer/lib/src/generated/sdk.dart

Index: pkg/analyzer/lib/src/generated/sdk.dart
diff --git a/pkg/analyzer/lib/src/generated/sdk.dart b/pkg/analyzer/lib/src/generated/sdk.dart
index a2b6325a0ab50b5b6079f26de68e663487a1f362..42351c41c980482f72e07d8c24c416bd71eb7b76 100644
--- a/pkg/analyzer/lib/src/generated/sdk.dart
+++ b/pkg/analyzer/lib/src/generated/sdk.dart
@@ -8,11 +8,17 @@ import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
-import 'package:analyzer/src/generated/engine.dart' show AnalysisContext;
+import 'package:analyzer/src/generated/engine.dart'
+    show AnalysisContext, AnalysisOptions;
 import 'package:analyzer/src/generated/source.dart'
     show ContentCache, Source, UriKind;
 
 /**
+ * A function used to create a new DartSdk
+ */
+typedef DartSdk SdkCreator();
+
+/**
  * A Dart SDK installed in a specified location.
  */
 abstract class DartSdk {
@@ -79,6 +85,54 @@ abstract class DartSdk {
 }
 
 /**
+ * Manages the DartSdk's that

[Paul Berry, 2016/02/09 18:21:18]

Incomplete comment

+ */
+class DartSdkManager {
+  /**
+   * The function used to create new SDK's.
+   */
+  final SdkCreator sdkCreator;
+
+  /**
+   * A table mapping (an encoding of) analysis options to the SDK that has been
+   * configured with those options.
+   */
+  Map<int, DartSdk> sdkMap = new HashMap<int, DartSdk>();
+
+  /**
+   * Initialize a newly created manager.
+   */
+  DartSdkManager(this.sdkCreator);
+
+  /**
+   * Return any SDK that has been created, or `null` if no SDKs have been
+   * created.
+   */
+  DartSdk get anySdk {
+    if (sdkMap.isEmpty) {
+      return null;
+    }
+    return sdkMap.values.first;
+  }
+
+  /**
+   * Return the Dart SDK that is appropriate for the given analysis [options].
+   * If such an SDK has not yet been created, then the [sdkCreator] will be
+   * invoked to create it.
+   */
+  DartSdk getSdkForOptions(AnalysisOptions options) {
+    int encoding = options.encodeCrossContextOptions();
+    DartSdk sdk = sdkMap[encoding];
+    if (sdk == null) {
+      sdk = sdkCreator();
+      sdkMap[encoding] = sdk;
+      sdk.context.analysisOptions.setCrossContextOptionsFrom(options);
+    }
+    return sdk;
+  }
+}
+
+/**
  * A map from Dart library URI's to the [SdkLibraryImpl] representing that
  * library.
  */