Validate that root paths are absolute and normalized.

pkg/analyzer/lib/src/util/absolute_path.dart

 // Copyright (c) 2015, 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.util.absolute_path;
 
-/// The class for manipulating absolute paths.
+/// The class for manipulating absolute, normalized paths.
 class AbsolutePathContext {
-  final String separator;
+  static const int _COLON = 0x3A;
+  static const int _PERIOD = 0x2e;
+  static const int _LOWER_A = 0x61;
+  static const int _LOWER_Z = 0x7A;
+  static const int _UPPER_A = 0x41;
+  static const int _UPPER_Z = 0x5A;
 
+  final bool _isWindows;
+  String separator;
   int _separatorChar;
 
-  AbsolutePathContext(this.separator) {
-    if (separator.length != 1) {
-      throw new ArgumentError.value(
-          separator, 'separator', 'must be exactly one character long');
-    }
+  AbsolutePathContext(this._isWindows) {
+    separator = _isWindows ? r'\' : '/';
     _separatorChar = separator.codeUnitAt(0);
   }
 
   /// Append the given relative [suffix] to the given absolute [parent].
   ///
   ///     context.append('/path/to', 'foo'); // -> '/path/to/foo'
   ///
   /// The given [suffix] cannot be an absolute path or use `..`.
   String append(String parent, String suffix) {
     return '$parent$separator$suffix';
@@ skipping 20 matching lines @@
   ///     context.dirname(r'C:\path');          // -> 'C:\'
   ///     context.dirname(r'C:\');              // -> 'C:\'
   String dirname(String path) {
     int firstIndex = path.indexOf(separator);
     int lastIndex = path.lastIndexOf(separator);
     return lastIndex == firstIndex
         ? path.substring(0, firstIndex + 1)
         : path.substring(0, lastIndex);
   }
 
+  /// Return `true` if the given [path] is valid.
+  ///
+  ///     context.isNormalized('/foo/bar');        // -> true
+  ///     context.isNormalized('/foo/bar/../baz'); // -> false
+  bool isValid(String path) {
+    return _isAbsolute(path) && _isNormalized(path);
+  }
+
   /// Return `true` if [child] is a path beneath [parent], and `false`
   /// otherwise. Both the [child] and [parent] paths must be absolute paths.
   ///
   ///     context.isWithin('/root/path', '/root/path/a'); // -> true
   ///     context.isWithin('/root/path', '/root/other');  // -> false
   ///     context.isWithin('/root/path', '/root/path');   // -> false
   bool isWithin(String parent, String child) {
     int parentLength = parent.length;
     int childLength = child.length;
     if (parentLength >= childLength) {
@@ skipping 19 matching lines @@
   ///     context.relative('/root/path', '/root/path/a/b.dart'); // -> 'a/b.dart'
   ///     context.relative('/root/path', '/root/other.dart');    // -> null
   String suffix(String parent, String child) {
     String parentPrefix = parent + separator;
     if (child.startsWith(parentPrefix)) {
       return child.substring(parentPrefix.length);
     }
     return null;
   }
 
+  /// Return `true` if the given [path] is absolute.
+  ///
+  ///     _isAbsolute('/foo/bar');   // -> true
+  ///     _isAbsolute('/');          // -> true
+  ///     _isAbsolute('foo/bar');    // -> false
+  ///     _isAbsolute('C:\foo\bar'); // -> true
+  ///     _isAbsolute('C:\');        // -> true
+  ///     _isAbsolute('foo\bar');    // -> false
+  bool _isAbsolute(String path) {
+    if (_isWindows) {
+      return path.length >= 3 &&
+          _isAlphabetic(path.codeUnitAt(0)) &&
+          path.codeUnitAt(1) == _COLON &&
+          path.codeUnitAt(2) == _separatorChar;
+    } else {
+      return path.isNotEmpty && path.codeUnitAt(0) == _separatorChar;
+    }
+  }
+
+
+  /// Return `true` if the given absolute [path] is normalized.
+  ///
+  ///     _isAbsolute('/foo/bar');         // -> true
+  ///     _isAbsolute('/foo/..bar');       // -> true
+  ///     _isAbsolute('/');                // -> true
+  ///     _isAbsolute('/foo/bar/../baz');  // -> false
+  ///     _isAbsolute('/foo/bar/..');      // -> false

[Brian Wilkerson, 2015/12/09 22:58:20]

Wrong method name in examples.

+  bool _isNormalized(String path) {
+    int periodCount = 0;
+    for (int c in path.codeUnits) {
+      if (c == _PERIOD) {
+        periodCount++;
+        continue;
+      }
+      if (c == _separatorChar) {
+        if (periodCount == 1 || periodCount == 2) {
+          return false;
+        }
+      }
+      periodCount = 0;
+    }
+    return periodCount != 1 && periodCount != 2;
+  }
+
+  /// Returns whether [char] is the code for an ASCII letter (uppercase or
+  /// lowercase).
+  static bool _isAlphabetic(int char) {
+    return char >= _UPPER_A && char <= _UPPER_Z ||
+        char >= _LOWER_A && char <= _LOWER_Z;
+  }
+
   /// Return `true` if [str] starts with the given [prefix].
   ///
   /// The check is done from the end of [prefix], because absolute paths
   /// usually have the same prefix, e.g. the user's home directory.
   static bool _startsWithUnsafe(String str, String prefix) {
     int len = prefix.length;
     for (int i = len - 1; i >= 0; i--) {
       if (str.codeUnitAt(i) != prefix.codeUnitAt(i)) {
         return false;
       }
     }
     return true;
   }
 }