Add minimal yaml support to the engine

pkg/analyzer/lib/src/task/yaml.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.
+
+library analyzer.src.task.yaml;
+
+import 'package:analyzer/src/context/cache.dart';
+import 'package:analyzer/src/generated/engine.dart' hide AnalysisTask;
+import 'package:analyzer/src/generated/error.dart';
+import 'package:analyzer/src/generated/java_engine.dart';
+import 'package:analyzer/src/generated/scanner.dart';
+import 'package:analyzer/src/generated/source.dart';
+import 'package:analyzer/src/task/general.dart';
+import 'package:analyzer/task/general.dart';
+import 'package:analyzer/task/model.dart';
+import 'package:analyzer/task/yaml.dart';
+import 'package:source_span/source_span.dart';
+import 'package:yaml/yaml.dart';
+
+/**
+ * A task that scans the content of a YAML file, producing a YAML document.
+ */
+class ParseYamlTask extends SourceBasedAnalysisTask {
+  /**
+   * The name of the input whose value is the content of the file.
+   */
+  static const String CONTENT_INPUT_NAME = 'CONTENT_INPUT_NAME';
+
+  /**
+   * The task descriptor describing this kind of task.
+   */
+  static final TaskDescriptor DESCRIPTOR = new TaskDescriptor(
+      'ParseYamlTask',
+      createTask,
+      buildInputs,
+      <ResultDescriptor>[YAML_DOCUMENT, YAML_ERRORS, YAML_LINE_INFO]);
+
+  /**
+   * Initialize a newly created task to access the content of the source
+   * associated with the given [target] in the given [context].
+   */
+  ParseYamlTask(InternalAnalysisContext context, AnalysisTarget target)
+      : super(context, target);
+
+  @override
+  TaskDescriptor get descriptor => DESCRIPTOR;
+
+  @override
+  void internalPerform() {
+    Source source = target.source;
+    String uri = source.uri.toString();
+    String content = getRequiredInput(CONTENT_INPUT_NAME);
+
+    if (context.getModificationStamp(source) < 0) {
+      String message = 'Content could not be read';
+      if (context is InternalAnalysisContext) {
+        CacheEntry entry =
+            (context as InternalAnalysisContext).getCacheEntry(target);
+        CaughtException exception = entry.exception;
+        if (exception != null) {
+          message = exception.toString();
+        }
+      }
+      //
+      // Record outputs.
+      //
+      outputs[YAML_DOCUMENT] = loadYamlDocument('', sourceUrl: uri);
+      outputs[YAML_ERRORS] = <AnalysisError>[
+        new AnalysisError(
+            source, 0, 0, ScannerErrorCode.UNABLE_GET_CONTENT, [message])
+      ];
+      outputs[YAML_LINE_INFO] = new LineInfo(<int>[0]);
+    } else {
+      YamlDocument document;
+      List<AnalysisError> errors = <AnalysisError>[];
+      try {
+        document = loadYamlDocument(content, sourceUrl: uri);
+      } on YamlException catch (exception) {
+        SourceSpan span = exception.span;
+        int offset = span.start.offset;
+        int length = span.end.offset - offset;
+        errors.add(new AnalysisError(source, offset, length,
+            YamlErrorCode.PARSE_ERROR, [exception.message]));
+      } catch (exception, stackTrace) {
+        throw new AnalysisException('Error while parsing ${source.fullName}',
+            new CaughtException(exception, stackTrace));
+      }
+      //
+      // Record outputs.
+      //
+      outputs[YAML_DOCUMENT] = document;
+      outputs[YAML_ERRORS] = errors;
+      outputs[YAML_LINE_INFO] = new LineInfo.fromContent(content);
+    }
+  }
+
+  /**
+   * Return a map from the names of the inputs of this kind of task to the task
+   * input descriptors describing those inputs for a task with the given
+   * [source].
+   */
+  static Map<String, TaskInput> buildInputs(Source source) {
+    return <String, TaskInput>{CONTENT_INPUT_NAME: CONTENT.of(source)};
+  }
+
+  /**
+   * Create a [ParseYamlTask] based on the given [target] in the given [context].
+   */
+  static ParseYamlTask createTask(
+      AnalysisContext context, AnalysisTarget target) {
+    return new ParseYamlTask(context, target);
+  }
+}
+
+/**
+ * The error codes used for errors in YAML files.
+ */
+class YamlErrorCode extends ErrorCode {
+  // TODO(brianwilkerson) Move this class to error.dart.
+
+  /**
+   * An error code indicating that there is a syntactic error in the file.
+   *
+   * Parameters:
+   * 0: the error message from the parse error
+   */
+  static const YamlErrorCode PARSE_ERROR =
+      const YamlErrorCode('PARSE_ERROR', '{0}');
+
+  /**
+   * Initialize a newly created error code to have the given [name]. The message
+   * associated with the error will be created from the given [message]
+   * template. The correction associated with the error will be created from the
+   * given [correction] template.
+   */
+  const YamlErrorCode(String name, String message, [String correction])
+      : super(name, message, correction);
+
+  @override
+  ErrorSeverity get errorSeverity => ErrorSeverity.ERROR;
+
+  @override
+  ErrorType get type => ErrorType.COMPILE_TIME_ERROR;
+}