QDirIterator: don't require NFD normalization on Darwin for validity

HFS+ filesystems do enforce NFD normalization, so the test worked for
those filesystems. But on APFS, the filesystem is normalization-
insensitive but preserves it, so our transformation caused valid files
to be rejected.

This commit also optimizes the solution for all systems too. Instead of
converting from 8-bit to UTF-16 then back to 8-bit (allocating memory in
both steps), we only convert to UTF-16. And if we detect the locale is
UTF-8, then we use the further optimized QUtf8::isValidUtf8 function
that doesn't allocate any memory at all (ditto for US-ASCII, the case of
someone running with LANG=C).

Fixes: QTBUG-76522
Change-Id: Ief874765cd7b43798de3fffd15aa0d81620ad317
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 44 insertions, 3 deletions

diff --git a/src/corelib/io/qfilesystemiterator_unix.cpp b/src/corelib/io/qfilesystemiterator_unix.cpp
index a9acf542d4..92ebdf0341 100644
--- a/src/corelib/io/qfilesystemiterator_unix.cpp
+++ b/src/corelib/io/qfilesystemiterator_unix.cpp
@@ -40,13 +40,54 @@
 #include "qplatformdefs.h"
 #include "qfilesystemiterator_p.h"
 
+#if QT_CONFIG(textcodec)
+#  include <qtextcodec.h>
+#  include <private/qutfcodec_p.h>
+#endif
+
 #ifndef QT_NO_FILESYSTEMITERATOR
 
+#include <memory>
+
 #include <stdlib.h>
 #include <errno.h>
 
 QT_BEGIN_NAMESPACE
 
+static bool checkNameDecodable(const char *d_name, qsizetype len)
+{
+    // This function is called in a loop from advance() below, but the loop is
+    // usually run only once.
+
+#if QT_CONFIG(textcodec)
+    // We identify the codecs by their RFC 2978 MIBenum values. In this
+    // function:
+    //  3   US-ASCII (ANSI X3.4-1986)
+    //  4   Latin1 (ISO-8859-1)
+    // 106  UTF-8
+    QTextCodec *codec = QTextCodec::codecForLocale();
+#  ifdef QT_LOCALE_IS_UTF8
+    int mibEnum = 106;
+#  else
+    int mibEnum = codec->mibEnum();
+#  endif
+    if (Q_LIKELY(mibEnum == 106))   // UTF-8
+        return QUtf8::isValidUtf8(d_name, len).isValidUtf8;
+    if (mibEnum == 3)               // US-ASCII
+        return QtPrivate::isAscii(QLatin1String(d_name, len));
+    if (mibEnum == 4)               // Latin 1
+        return true;
+
+    // fall back to generic QTextCodec
+    QTextCodec::ConverterState cs(QTextCodec::IgnoreHeader);
+    codec->toUnicode(d_name, len, &cs);
+    return cs.invalidChars == 0 && cs.remainingChars == 0;
+#else
+    // if we have no text codecs, then QString::fromLocal8Bit is fromLatin1
+    return true;
+#endif
+}
+
 QFileSystemIterator::QFileSystemIterator(const QFileSystemEntry &entry, QDir::Filters filters,
                                          const QStringList &nameFilters, QDirIterator::IteratorFlags flags)
     : nativePath(entry.nativeFilePath())
@@ -81,9 +122,9 @@ bool QFileSystemIterator::advance(QFileSystemEntry &fileEntry, QFileSystemMetaDa
         dirEntry = QT_READDIR(dir);
 
         if (dirEntry) {
-            // process entries with correct UTF-8 names only
-            if (QFile::encodeName(QFile::decodeName(dirEntry->d_name)) == dirEntry->d_name) {
-                fileEntry = QFileSystemEntry(nativePath + QByteArray(dirEntry->d_name), QFileSystemEntry::FromNativePath());
+            qsizetype len = strlen(dirEntry->d_name);
+            if (checkNameDecodable(dirEntry->d_name, len)) {
+                fileEntry = QFileSystemEntry(nativePath + QByteArray(dirEntry->d_name, len), QFileSystemEntry::FromNativePath());
                 metaData.fillFromDirEnt(*dirEntry);
                 return true;
             }