Extract out a source_span package from source_maps.

pkg/source_span/lib/src/file.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.file;
+
+import 'dart:math' as math;
+import 'dart:typed_data';
+
+import 'package:path/path.dart' as p;
+
+import 'colors.dart' as colors;
+import 'location.dart';
+import 'span.dart';
+import 'span_mixin.dart';
+import 'utils.dart';
+
+// Constants to determine end-of-lines.
+const int _LF = 10;
+const int _CR = 13;
+
+/// A class representing a source file.
+///
+/// This doesn't necessarily have to correspond to a file on disk, just a chunk
+/// of text usually with a URL associated with it.
+class SourceFile {
+  /// The URL where the source file is located.
+  ///
+  /// This may be null, indicating that the URL is unknown or unavailable.
+  final Uri url;
+
+  /// An array of offsets for each line beginning in the file.
+  ///
+  /// Each offset refers to the first character *after* the newline. If the
+  /// source file has a trailing newline, the final offset won't actually be in
+  /// the file.
+  final _lineStarts = <int>[0];
+
+  /// The code points of the characters in the file.
+  final Uint32List _decodedChars;
+
+  /// The length of the file in characters.
+  int get length => _decodedChars.length;
+
+  /// The number of lines in the file.
+  int get lines => _lineStarts.length;
+
+  /// Creates a new source file from [text].
+  ///
+  /// [url] may be either a [String], a [Uri], or `null`.
+  SourceFile(String text, {url})
+      : this.decoded(text.runes, url: url);
+
+  /// Creates a new source file from a list of decoded characters.
+  ///
+  /// [url] may be either a [String], a [Uri], or `null`.
+  SourceFile.decoded(Iterable<int> decodedChars, {url})
+      : url = url is String ? Uri.parse(url) : url,
+        _decodedChars = new Uint32List.fromList(decodedChars.toList()) {
+    for (var i = 0; i < _decodedChars.length; i++) {
+      var c = _decodedChars[i];
+      if (c == _CR) {
+        // Return not followed by newline is treated as a newline
+        var j = i + 1;
+        if (j >= _decodedChars.length || _decodedChars[j] != _LF) c = _LF;
+      }
+      if (c == _LF) _lineStarts.add(i + 1);
+    }
+  }
+
+  /// Returns a span in [this] from [start] to [end] (exclusive).
+  ///
+  /// If [end] isn't passed, it defaults to the end of the file.
+  FileSpan span(int start, [int end]) {
+    if (end == null) end = length - 1;
+    return new FileSpan._(this, location(start), location(end));
+  }
+
+  /// Returns a location in [this] at [offset].
+  FileLocation location(int offset) => new FileLocation._(this, offset);
+
+  /// Gets the 0-based line corresponding to [offset].
+  int getLine(int offset) {
+    if (offset < 0) {
+      throw new RangeError("Offset may not be negative, was $offset.");
+    } else if (offset > length) {
+      throw new RangeError("Offset $offset must not be greater than the number "
+          "of characters in the file, $length.");
+    }
+    return binarySearch(_lineStarts, (o) => o > offset) - 1;
+  }
+
+  /// Gets the 0-based column corresponding to [offset].
+  ///
+  /// If [line] is passed, it's assumed to be the line containing [offset] and
+  /// is used to more efficiently compute the column.
+  int getColumn(int offset, {int line}) {
+    if (offset < 0) {
+      throw new RangeError("Offset may not be negative, was $offset.");
+    } else if (offset > length) {
+      throw new RangeError("Offset $offset must be not be greater than the "
+          "number of characters in the file, $length.");
+    }
+
+    if (line == null) {
+      line = getLine(offset);
+    } else if (line < 0) {
+      throw new RangeError("Line may not be negative, was $line.");
+    } else if (line >= lines) {
+      throw new RangeError("Line $line must be less than the number of "
+          "lines in the file, $lines.");
+    }
+
+    var lineStart = _lineStarts[line];
+    if (lineStart > offset) {
+      throw new RangeError("Line $line comes after offset $offset.");
+    }
+
+    return offset - lineStart;
+  }
+
+  /// Gets the offset for a [line] and [column].
+  ///
+  /// [column] defaults to 0.
+  int getOffset(int line, [int column]) {
+    if (column == null) column = 0;
+
+    if (line < 0) {
+      throw new RangeError("Line may not be negative, was $line.");
+    } else if (line >= lines) {
+      throw new RangeError("Line $line must be less than the number of "
+          "lines in the file, $lines.");
+    } else if (column < 0) {
+      throw new RangeError("Column may not be negative, was $column.");
+    }
+
+    var result = _lineStarts[line] + column;
+    if (result > length ||
+        (line + 1 < lines && result >= _lineStarts[line + 1])) {
+      throw new RangeError("Line $line doesn't have $column columns.");
+    }
+
+    return result;
+  }
+
+  /// Returns the text of the file from [start] to [end] (exclusive).
+  ///
+  /// If [end] isn't passed, it defaults to the end of the file.
+  String getText(int start, [int end]) =>
+      new String.fromCharCodes(_decodedChars.sublist(start, end));
+}
+
+/// A [SourceLocation] within a [SourceFile].
+///
+/// Unlike the base [SourceLocation], [FileLocation] lazily computes its line
+/// and column values based on its offset and the contents of [file].
+///
+/// A [FileLocation] can be created using [SourceFile.location].
+class FileLocation extends SourceLocation {
+  /// The [file] that [this] belongs to.
+  final SourceFile file;
+
+  Uri get sourceUrl => file.url;
+  int get line => file.getLine(offset);
+  int get column => file.getColumn(offset);
+
+  FileLocation._(this.file, int offset)
+      : super(offset) {
+    if (offset > file.length) {
+      throw new RangeError("Offset $offset must not be greater than the number "
+          "of characters in the file, ${file.length}.");
+    }
+  }
+
+  FileSpan pointSpan() => new FileSpan._(file, this, this);
+}
+
+/// A [SourceSpan] within a [SourceFile].
+///
+/// Unlike the base [SourceSpan], [FileSpan] lazily computes its line and column
+/// values based on its offset and the contents of [file]. [FileSpan.message] is
+/// also able to provide more context then [SourceSpan.message], and
+/// [FileSpan.union] will return a [FileSpan] if possible.
+///
+/// A [FileSpan] can be created using [SourceFile.span].
+class FileSpan extends SourceSpanMixin {
+  /// The [file] that [this] belongs to.
+  final SourceFile file;
+
+  final FileLocation start;
+  final FileLocation end;
+
+  String get text => file.getText(start.offset, end.offset);
+
+  FileSpan._(this.file, this.start, this.end) {
+    if (end.offset < start.offset) {
+      throw new ArgumentError('End $end must come after start $start.');
+    }
+  }
+
+  SourceSpan union(SourceSpan other) {
+    if (other is! FileSpan) return super.union(other);
+
+    var span = expand(other);
+    var beginSpan = span.start == this.start ? this : other;
+    var endSpan = span.end == this.end ? this : other;
+
+    if (beginSpan.end.compareTo(endSpan.start) < 0) {
+      throw new ArgumentError("Spans $this and $other are disjoint.");
+    }
+
+    return span;
+  }
+
+  /// Returns a new span that covers both [this] and [other].
+  ///
+  /// Unlike [union], [other] may be disjoint from [this]. If it is, the text
+  /// between the two will be covered by the returned span.
+  FileSpan expand(FileSpan other) {
+    if (sourceUrl != other.sourceUrl) {
+      throw new ArgumentError("Source URLs \"${sourceUrl}\" and "
+          " \"${other.sourceUrl}\" don't match.");
+    }
+
+    var start = min(this.start, other.start);
+    var end = max(this.end, other.end);
+    return new FileSpan._(file, start, end);    
+  }
+
+  String message(String message, {color}) {
+    if (color == true) color = colors.RED;
+    if (color == false) color = null;
+
+    var line = start.line;
+    var column = start.column;
+
+    var buffer = new StringBuffer();
+    buffer.write('line ${start.line + 1}, column ${start.column + 1}');
+    if (sourceUrl != null) buffer.write(' of ${p.prettyUri(sourceUrl)}');
+    buffer.write(': $message\n');
+
+    var textLine = file.getText(file.getOffset(line),
+        line == file.lines - 1 ? null : file.getOffset(line + 1));
+
+    column = math.min(column, textLine.length - 1);
+    var toColumn =
+        math.min(column + end.offset - start.offset, textLine.length);
+
+    if (color != null) {
+      buffer.write(textLine.substring(0, column));
+      buffer.write(color);
+      buffer.write(textLine.substring(column, toColumn));
+      buffer.write(colors.NONE);
+      buffer.write(textLine.substring(toColumn));
+    } else {
+      buffer.write(textLine);
+    }
+    if (!textLine.endsWith('\n')) buffer.write('\n');
+
+    buffer.write(' ' * column);
+    if (color != null) buffer.write(color);
+    buffer.write('^' * math.max(toColumn - column, 1));
+    if (color != null) buffer.write(colors.NONE);
+    return buffer.toString();
+  }
+}