Initial API for the Dart front_end package.

pkg/front_end/lib/compilation_error.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Defines the API for the front end to communicate information about
+/// compilation errors to clients.
+library front_end.compilation_error;
+
+import 'source_location.dart';

[Brian Wilkerson, 2016/10/13 23:37:01]

I'm not seeing this file in the CL. Did you forget to include a file, or did you
mean 'source_span.dart'?

[Paul Berry, 2016/10/14 00:09:35]

Whoops, you're correct.  Thanks.

+
+/// A single error that occurred during compilation, and information about where
+/// it occurred.
+///
+/// TODO(paulberry): add a reference to the analyzer error code.

[Brian Wilkerson, 2016/10/13 23:37:01]

We also need the correction message and support for properties.

Is there a reason why we're not using AnalysisError, which already has this
additional support?

[Paul Berry, 2016/10/14 00:09:35]

I'm not convinced that we need these--they sound like analyzer-centric use cases
so they shouldn't be exposed through this API.  But maybe I don't understand
what they're used for.  Let's talk about it these questions in person tomorrow.
AnalysisError has a bunch of static methods that don't seem like they belong in
the front end API, as well as the correction message and properties mentioned
above.  Unless we're certain that all of the features of AnalysisError make
sense for back ends other than analyzer, I'd rather not presume to put them in
this API.

However, I see no problem making AnalysisError *implement* this API.

[Paul Berry, 2016/10/14 21:32:34]

After further discussion this morning, I'm ok adding the correction message once
most errors actually use it (which Brian says he hopes to have implemented
soon).  The properties are currently only used for analyzer's use case, so I'm
leaving them out of this API for now; if they wind up being needed by
compilation back-ends, we can always add them.

+abstract class CompilationError {
+  /// A text description of the compile error.
+  String get message;
+
+  /// The source location where the error occurred.
+  SourceLocation get location;
+}