Move exception support to its own library

pkg/analyzer/lib/exception/exception.dart

Index: pkg/analyzer/lib/exception/exception.dart
diff --git a/pkg/analyzer/lib/exception/exception.dart b/pkg/analyzer/lib/exception/exception.dart
new file mode 100644
index 0000000000000000000000000000000000000000..801411589cf89ea1023cf172616f00869cedcc58
--- /dev/null
+++ b/pkg/analyzer/lib/exception/exception.dart
@@ -0,0 +1,99 @@
+// Copyright (c) 2014, 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.exception.exception;
+
+/**
+ * An exception that occurred during the analysis of one or more sources.
+ */
+class AnalysisException implements Exception {
+  /**
+   * The message that explains why the exception occurred.
+   */
+  final String message;
+
+  /**
+   * The exception that caused this exception, or `null` if this exception was
+   * not caused by another exception.
+   */
+  final CaughtException cause;
+
+  /**
+   * Initialize a newly created exception to have the given [message] and
+   * [cause].
+   */
+  AnalysisException([this.message = 'Exception', this.cause = null]);
+
+  String toString() {
+    StringBuffer buffer = new StringBuffer();
+    buffer.write("AnalysisException: ");
+    buffer.writeln(message);
+    if (cause != null) {
+      buffer.write('Caused by ');
+      cause._writeOn(buffer);
+    }
+    return buffer.toString();
+  }
+}
+
+/**
+ * An exception that was caught and has an associated stack trace.
+ */
+class CaughtException implements Exception {
+  /**
+   * The exception that was caught.
+   */
+  final Object exception;
+
+  /**
+   * The stack trace associated with the exception.
+   */
+  StackTrace stackTrace;
+
+  /**
+   * Initialize a newly created caught exception to have the given [exception]
+   * and [stackTrace].
+   */
+  CaughtException(this.exception, stackTrace) {
+    if (stackTrace == null) {
+      try {
+        throw this;
+      } catch (_, st) {
+        stackTrace = st;
+      }
+    }
+    this.stackTrace = stackTrace;
+  }
+
+  @override
+  String toString() {
+    StringBuffer buffer = new StringBuffer();
+    _writeOn(buffer);
+    return buffer.toString();
+  }
+
+  /**
+   * Write a textual representation of the caught exception and its associated
+   * stack trace.
+   */
+  void _writeOn(StringBuffer buffer) {
+    if (exception is AnalysisException) {
+      AnalysisException analysisException = exception;
+      buffer.writeln(analysisException.message);
+      if (stackTrace != null) {
+        buffer.writeln(stackTrace.toString());
+      }
+      CaughtException cause = analysisException.cause;
+      if (cause != null) {
+        buffer.write('Caused by ');
+        cause._writeOn(buffer);
+      }
+    } else {
+      buffer.writeln(exception.toString());
+      if (stackTrace != null) {
+        buffer.writeln(stackTrace.toString());
+      }
+    }
+  }
+}