Clang: Pass on file paths with native separators

libclang 3.8 seems to be sensitive to file paths separators [1]. On Windows,
this led to not updated document annotations and/or crashes after reparsing.

When passing file paths to libclang, convert to native separators.
When getting file paths from libclang, convert back.

This handles:
 * main file path
 * file paths of the unsaved files
 * -I<DIR> arguments, the resource path (for builtins) and the paths to the
   wrapped qt headers
 * included header files from libclang
 * source locations from libclang

Also, minimize the conversion in SourceLocation to a minimum by making
filePath() lazy.

[1] https://llvm.org/bugs/show_bug.cgi?id=28381

Change-Id: If5866f34a6fdc6b34b16c022d3988e8e6eae2a0a
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/tools/clangbackend/ipcsource/clangfilepath.cpp

@@ -0,0 +1,87 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#include "clangfilepath.h"
+
+#include <utf8string.h>
+
+#include <QByteArray>
+
+// Parameterized QDir::toNativeSeparators/-fromNativeSeparators for QByteArray
+static inline QByteArray replace(const QByteArray &pathName, char toReplace, char replacement)
+{
+    int i = pathName.indexOf(toReplace);
+    if (i != -1) {
+        QByteArray n(pathName);
+
+        char * const data = n.data();
+        data[i++] = replacement;
+
+        for (; i < n.length(); ++i) {
+            if (data[i] == toReplace)
+                data[i] = replacement;
+        }
+
+        return n;
+    }
+
+    return pathName;
+}
+
+static QByteArray fromNativeSeparatorsForQByteArray(const QByteArray &pathName)
+{
+#if defined(Q_OS_WIN)
+    return replace(pathName, '\\', '/');
+#else
+    return pathName;
+#endif
+}
+
+static QByteArray toNativeSeparatorsForQByteArray(const QByteArray &pathName)
+{
+#if defined(Q_OS_WIN)
+    return replace(pathName, '/', '\\');
+#else
+    return pathName;
+#endif
+}
+
+namespace ClangBackEnd {
+
+Utf8String FilePath::fromNativeSeparators(const Utf8String &pathName)
+{
+    const QByteArray pathNameAsByteArray = pathName.toByteArray();
+
+    return Utf8String::fromUtf8(fromNativeSeparatorsForQByteArray(pathNameAsByteArray));
+}
+
+Utf8String FilePath::toNativeSeparators(const Utf8String &pathName)
+{
+    const QByteArray pathNameAsByteArray = pathName.toByteArray();
+
+    return Utf8String::fromUtf8(toNativeSeparatorsForQByteArray(pathNameAsByteArray));
+}
+
+} // namespace ClangBackEnd