Fix line number cache

lib/src/line_number_cache.dart

@@ -8,6 +8,7 @@ import 'dart:collection';
 import 'dart:io';
 
 import 'package:dartdoc/src/tuple.dart';
+import 'package:path/path.dart' as path;
 
 String _getNewlineChar(String contents) {
   if (contents.contains("\r\n")) {
@@ -22,12 +23,14 @@ String _getNewlineChar(String contents) {
 SplayTreeMap<int, int> _createLineNumbersMap(String contents) {
   var newlineChar = _getNewlineChar(contents);
   var offset = 0;
-  var lineNumber = 0;
+  var lineNumber = 1;
   var result = SplayTreeMap<int, int>();
 
   do {
     result[offset] = lineNumber;
-    offset = contents.indexOf(newlineChar, offset + 1);
+    offset = (offset + 1 <= contents.length)
+        ? contents.indexOf(newlineChar, offset + 1)
+        : -1;
     lineNumber += 1;
   } while (offset != -1);
 
@@ -36,22 +39,19 @@ SplayTreeMap<int, int> _createLineNumbersMap(String contents) {
 
 final LineNumberCache lineNumberCache = LineNumberCache();
 
-// TODO(kevmoo): this could use some testing
 class LineNumberCache {
-  final Map<String, String> __fileContents = <String, String>{};
   final Map<String, SplayTreeMap<int, int>> _lineNumbers =
       <String, SplayTreeMap<int, int>>{};
 
   Tuple2<int, int> lineAndColumn(String file, int offset) {
+    file = path.canonicalize(file);
     var lineMap = _lineNumbers.putIfAbsent(
-        file, () => _createLineNumbersMap(_fileContents(file)));
+        file, () => _createLineNumbersMap(File(file).readAsStringSync()));
     var lastKey = lineMap.lastKeyBefore(offset);
     if (lastKey != null) {
-      return Tuple2(lineMap[lastKey] + 1, offset - lastKey);
+      return Tuple2(lineMap[lastKey], offset - lastKey);
+    } else {
+      return Tuple2(lineMap[0], offset);
     }
-    return null;
   }
-
-  String _fileContents(String file) =>
-      __fileContents.putIfAbsent(file, () => File(file).readAsStringSync());
 }

test/line_number_cache_test.dart

@@ -0,0 +1,65 @@
+// Copyright (c) 2019, 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 dartdoc.cache_test;
+
+import 'dart:io';
+
+import 'package:dartdoc/src/line_number_cache.dart';
+import 'package:dartdoc/src/tuple.dart';
+import 'package:path/path.dart' as path;
+import 'package:test/test.dart';
+
+void main() {
+  group('Verify basic line cache behavior', () {
+    Directory _tempDir;
+
+    setUp(() {
+      _tempDir = Directory.systemTemp.createTempSync('line_number_cache');
+    });
+
+    tearDown(() {
+      _tempDir.deleteSync(recursive: true);
+    });
+
+    test('validate empty file behavior', () {
+      File emptyFile = File(path.join(_tempDir.path, 'empty_file'))
+        ..writeAsStringSync('');
+      LineNumberCache cache = LineNumberCache();
+      expect(cache.lineAndColumn(emptyFile.path, 0), equals(Tuple2(1, 0)));
+    });
+
+    test('single line without newline', () {
+      File singleLineWithoutNewline =
+          File(path.join(_tempDir.path, 'single_line'))
+            ..writeAsStringSync('a single line');
+      LineNumberCache cache = LineNumberCache();
+      expect(cache.lineAndColumn(singleLineWithoutNewline.path, 2),
+          equals(Tuple2(1, 2)));
+      expect(cache.lineAndColumn(singleLineWithoutNewline.path, 0),
+          equals(Tuple2(1, 0)));
+    });
+
+    test('multiple line without trailing newline', () {
+      File multipleLine = File(path.join(_tempDir.path, 'multiple_line'))
+        ..writeAsStringSync('This is the first line\nThis is the second line');
+      LineNumberCache cache = LineNumberCache();
+      expect(cache.lineAndColumn(multipleLine.path, 60), equals(Tuple2(2, 38)));
+      expect(cache.lineAndColumn(multipleLine.path, 30), equals(Tuple2(2, 8)));
+      expect(cache.lineAndColumn(multipleLine.path, 5), equals(Tuple2(1, 5)));
+      expect(cache.lineAndColumn(multipleLine.path, 0), equals(Tuple2(1, 0)));
+    });
+
+    test('multiple lines with trailing newline', () {
+      File multipleLine = File(path.join(_tempDir.path, 'multiple_line'))
+        ..writeAsStringSync(
+            'This is the first line\nThis is the second line\n');
+      LineNumberCache cache = LineNumberCache();
+      expect(cache.lineAndColumn(multipleLine.path, 60), equals(Tuple2(3, 14)));
+      expect(cache.lineAndColumn(multipleLine.path, 30), equals(Tuple2(2, 8)));
+      expect(cache.lineAndColumn(multipleLine.path, 5), equals(Tuple2(1, 5)));
+      expect(cache.lineAndColumn(multipleLine.path, 0), equals(Tuple2(1, 0)));
+    });
+  });
+}