Don't make sdkPath required yet in implementations.

It would be a breaking change.
dart-lang/pub#2563 (comment)

Change-Id: Ia2b75b5ed863753629340e6d2a4e273adc84bad2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/155001
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: scheglov

pkg/analyzer/CHANGELOG.md

@@ -4,6 +4,9 @@
   find SDK, for example using `package:cli_util`.
 * Fixed `LintDriver` for the new way to access `WorkspacePackage`.
 * Deprecated `Scope.lookup()`, use `Scope.lookup2()` instead.
+* Updated implementations of `ContextBuilder.createContext()` and
+  `ContextLocator.locateContexts` to use the current SDK if `sdkPath`
+  is not provided.
 
 ## 0.39.13
 * Added 'dart/sdk/build_sdk_summary.dart' with `buildSdkSummary`.

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

@@ -22,6 +22,7 @@ import 'package:analyzer/src/dart/analysis/performance_logger.dart'
     show PerformanceLog;
 import 'package:analyzer/src/generated/sdk.dart' show DartSdkManager;
 import 'package:analyzer/src/generated/source.dart' show ContentCache;
+import 'package:cli_util/cli_util.dart';
 import 'package:meta/meta.dart';
 
 /// An implementation of a context builder.
@@ -44,8 +45,10 @@ class ContextBuilderImpl implements ContextBuilder {
       List<String> librarySummaryPaths,
       @deprecated PerformanceLog performanceLog,
       @deprecated AnalysisDriverScheduler scheduler,
-      @required String sdkPath,
+      String sdkPath,
       String sdkSummaryPath}) {
+    // TODO(scheglov) Remove this, and make `sdkPath` required.
+    sdkPath ??= getSdkPath();
     ArgumentError.checkNotNull(sdkPath, 'sdkPath');
 
     var byteStore = MemoryByteStore();

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

@@ -26,6 +26,7 @@ import 'package:analyzer/src/dart/analysis/performance_logger.dart'
 import 'package:analyzer/src/generated/sdk.dart' show DartSdkManager;
 import 'package:analyzer/src/task/options.dart';
 import 'package:analyzer/src/util/yaml.dart';
+import 'package:cli_util/cli_util.dart';
 import 'package:glob/glob.dart';
 import 'package:meta/meta.dart';
 import 'package:path/path.dart';
@@ -56,7 +57,9 @@ class ContextLocatorImpl implements ContextLocator {
       List<String> excludedPaths = const <String>[],
       String optionsFile,
       String packagesFile,
-      @required String sdkPath}) {
+      String sdkPath}) {
+    // TODO(scheglov) Remove this, and make `sdkPath` required.
+    sdkPath ??= getSdkPath();
     ArgumentError.checkNotNull(sdkPath, 'sdkPath');
 
     List<ContextRoot> roots = locateRoots(