Extend front_end API to accept patch files

pkg/front_end/lib/kernel_generator.dart

Index: pkg/front_end/lib/kernel_generator.dart
diff --git a/pkg/front_end/lib/kernel_generator.dart b/pkg/front_end/lib/kernel_generator.dart
index 348d1f9021571c70c7bdbc8b1044a7b91e038f31..40920a652767f2bbd8da968f5e6c5061179635e8 100644
--- a/pkg/front_end/lib/kernel_generator.dart
+++ b/pkg/front_end/lib/kernel_generator.dart
@@ -37,6 +37,17 @@ import 'package:source_span/source_span.dart' show SourceSpan;
 /// needed to access the contents of method bodies).
 Future<Program> kernelForProgram(Uri source, CompilerOptions options) async {
   var loader = await _createLoader(options, entry: source);
+  // TODO(sigmund): delete this. At this time we have no need to explicitly list
+  // VM libraries, since they are normally found by chasing dependencies.
+  // `dart:_builtin` is an exception because it is used by the kernel
+  // transformers to inform the VM about where the main entrypoint is. This is
+  // expected to change, and we should be able to remove these lines at that
+  // point. We check for the presense of `dart:developer` in the targetPatches
+  // to ensure we only load this library while running on the VM.
+  if (options.compileSdk &&
+      options.targetPatches.containsKey(Uri.parse('dart:developer'))) {
+    loader.loadLibrary(Uri.parse('dart:_builtin'));

[Siggi Cherem (dart-lang), 2017/01/27 21:55:51]

this came up in the context of my other CL where I'm running the
kernel-service.dart through the frontend. 

I thought we were going to need to pass in a list of core libraries to load, but
I'm not certain at this point that it will be needed, so I opted for this
temporary exception until we figure that out.

+  }
   // TODO(sigmund): merge what we have in loadEverything and the logic below in
   // kernelForBuildUnit so there is a single place where we crawl for
   // dependencies.
@@ -131,8 +142,18 @@ Future<DartLoader> _createLoader(CompilerOptions options,
   var packages = await createPackages(
       _uriToPath(options.packagesFileUri, options),
       discoveryPath: entry?.path);
-  return new DartLoader(
+  var loader = new DartLoader(
       repository ?? new Repository(), kernelOptions, packages);
+  var patchPaths = {};
+
+  String resolve(Uri patch) =>
+    options.fileSystem.context.fromUri(options.sdkRoot.resolveUri(patch));

[Siggi Cherem (dart-lang), 2017/01/27 21:55:51]

you'll see in the other CL that this is not used yet, I'm using only absolute
URIs, the reason is that none of the VM patches are shipped with the SDK today.
That needs to change in the future.

[Paul Berry, 2017/01/27 22:49:19]

Add a TODO comment here: we should switch this code over to using
ProcessedOptions so that we can resolve the URIs correctly even if the SDK root
is not directly specified (in some cases it will be automatically inferred).

You can assign the TODO to me if you want.

[Siggi Cherem (dart-lang), 2017/01/27 23:00:19]

Done.

+
+  options.targetPatches.forEach((uri, patches) {
+    patchPaths['$uri'] = patches.map(resolve).toList();
+  });
+  loader.context.analysisOptions.patchPaths = patchPaths;
+  return loader;
 }
 
 DartOptions _convertOptions(CompilerOptions options) {
@@ -144,6 +165,7 @@ DartOptions _convertOptions(CompilerOptions options) {
       sdkSummary:
           options.compileSdk ? null : _uriToPath(options.sdkSummary, options),
       packagePath: _uriToPath(options.packagesFileUri, options),
+      customUriMappings: options.uriOverride,
       declaredVariables: options.declaredVariables);
 }