Extract out a source_span package from source_maps.

pkg/source_span/lib/src/location.dart

+// 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 source_span.location;
+
+import 'span.dart';
+
+// A class that describes a single location within a source file.
+class SourceLocation implements Comparable<SourceLocation> {
+  /// URL of the source containing this location.
+  ///
+  /// This may be null, indicating that the source URL is unknown or
+  /// unavailable.
+  final Uri sourceUrl;
+
+  /// The 0-based offset of this location in the source.
+  final int offset;
+
+  /// The 0-based line of this location in the source.
+  final int line;
+
+  /// The 0-based column of this location in the source
+  final int column;
+
+  /// Returns a representation of this location in the `source:line:column`
+  /// format used by text editors.
+  ///
+  /// This prints 1-based lines and columns.
+  String get toolString {
+    var source = sourceUrl == null ? 'unknown source' : sourceUrl;
+    return '$source:${line + 1}:${column + 1}';
+  }
+
+  /// Creates a new location indicating [offset] within [sourceUrl].
+  ///
+  /// [line] and [column] default to assuming the source is a single line. This
+  /// means that [line] defaults to 0 and [column] defaults to [offset].
+  ///
+  /// [sourceUrl] may be either a [String], a [Uri], or `null`.
+  SourceLocation(int offset, {sourceUrl, int line, int column})
+      : sourceUrl = sourceUrl is String ? Uri.parse(sourceUrl) : sourceUrl,
+        offset = offset,
+        line = line == null ? 0 : line,
+        column = column == null ? offset : column {
+    if (this.offset < 0) {
+      throw new RangeError("Offset may not be negative, was $offset.");
+    } else if (this.line < 0) {
+      throw new RangeError("Line may not be negative, was $line.");
+    } else if (this.column < 0) {
+      throw new RangeError("Column may not be negative, was $column.");
+    }
+  }
+
+  /// Returns the distance in characters between [this] and [other].
+  ///
+  /// This always returns a non-negative value.
+  int distance(SourceLocation other) {
+    if (sourceUrl != other.sourceUrl) {
+      throw new ArgumentError("Source URLs \"${sourceUrl}\" and "
+          "\"${other.sourceUrl}\" don't match.");
+    }
+    return (offset - other.offset).abs();
+  }
+
+  /// Returns a span that covers only a single point: this location.
+  SourceSpan pointSpan() => new SourceSpan(this, this, "");
+
+  /// Compares two locations.
+  ///
+  /// [other] must have the same source URL as [this].
+  int compareTo(SourceLocation other) {
+    if (sourceUrl != other.sourceUrl) {
+      throw new ArgumentError("Source URLs \"${sourceUrl}\" and "
+          "\"${other.sourceUrl}\" don't match.");
+    }
+    return offset - other.offset;
+  }
+
+  bool operator ==(SourceLocation other) =>
+      sourceUrl == other.sourceUrl && offset == other.offset;
+
+  int get hashCode => sourceUrl.hashCode + offset;
+
+  String toString() => '<$runtimeType: $offset $toolString>';
+}