QUrl: Keep one trailing slash when normalizing "file:///b/."

Removing the slash would be a drastic change in behavior. We can expect
many people to rely on the trailing slash to string-append further path
segments without inserting an extra slash.

Amends commit e7bcf41c0b23d83cfb31f966454945c705589a99.

Pick-to: 6.7 6.5
Fixes: QTBUG-128940
Change-Id: I71dfc957f383e4648b3b47a40aeb796d7237fb00
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 2addfa635d2f666d18ffc818f76eb673a6c787d1)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/io/qdir.cpp

@@ -2215,11 +2215,17 @@ bool QDir::match(const QString &filter, const QString &fileName)
     3) a sequence of "//" is treated as multiple path levels ("a/b//.." becomes
        "a/b/" and "a/b//../.." becomes "a/"), which matches the behavior
        observed in web browsers.
+
+    However, QUrl also uses local path mode for local URLs; with one exception:
+    Even in local mode we leave one trailing slash for paths ending in "/." if
+    the KeepLocalTrailingSlash flag is given. This reflects how QUrl needs to
+    treat local URLs due to compatibility constraints.
 */
 bool qt_normalizePathSegments(QString *path, QDirPrivate::PathNormalizations flags)
 {
     const bool allowUncPaths = flags.testAnyFlag(QDirPrivate::AllowUncPaths);
     const bool isRemote = flags.testAnyFlag(QDirPrivate::RemotePath);
+    const bool keepLocalTrailingSlash = flags.testAnyFlags(QDirPrivate::KeepLocalTrailingSlash);
     const qsizetype prefixLength = rootLength(*path, allowUncPaths);
 
     // RFC 3986 says: "The input buffer is initialized with the now-appended
@@ -2331,11 +2337,25 @@ bool qt_normalizePathSegments(QString *path, QDirPrivate::PathNormalizations fla
         }
 
         if (out > start) {
-            // backtrack one or all the slashes (so "/tmp///" -> "/tmp/")
+            // Always backtrack one slash
             if (out[-1] == u'/' && in != end)
                 --out;
-            while (!isRemote && out > start && out[-1] == u'/')
-                --out;
+
+            if (!isRemote) {
+                bool removedAnySlashes = false;
+
+                // Backtrack all slashes ...
+                while (out > start && out[-1] == u'/') {
+                    --out;
+                    removedAnySlashes = true;
+                }
+
+                // ... except a trailing one if it exists and flag given
+                if (removedAnySlashes && keepLocalTrailingSlash && out > start) {
+                    ++out;
+                    break;
+                }
+            }
         }
         if (out == start) {
             // We've reached the root. Make sure we don't turn a relative path

src/corelib/io/qdir_p.h

@@ -30,7 +30,8 @@ public:
     enum PathNormalization {
         DefaultNormalization = 0x00,
         AllowUncPaths = 0x01,
-        RemotePath = 0x02
+        RemotePath = 0x02,
+        KeepLocalTrailingSlash = 0x04,
     };
     Q_DECLARE_FLAGS(PathNormalizations, PathNormalization)
     Q_FLAGS(PathNormalizations)

src/corelib/io/qurl.cpp

@@ -911,7 +911,9 @@ inline void QUrlPrivate::appendPath(QString &appendTo, QUrl::FormattingOptions o
 {
     QString thePath = path;
     if (options & QUrl::NormalizePathSegments) {
-        qt_normalizePathSegments(&thePath, isLocalFile() ? QDirPrivate::DefaultNormalization : QDirPrivate::RemotePath);
+        qt_normalizePathSegments(
+                &thePath,
+                isLocalFile() ? QDirPrivate::KeepLocalTrailingSlash : QDirPrivate::RemotePath);
     }
 
     QStringView thePathView(thePath);
@@ -2712,7 +2714,9 @@ QUrl QUrl::resolved(const QUrl &relative) const
     else
         t.d->sectionIsPresent &= ~QUrlPrivate::Fragment;
 
-    qt_normalizePathSegments(&t.d->path, isLocalFile() ? QDirPrivate::DefaultNormalization : QDirPrivate::RemotePath);
+    qt_normalizePathSegments(
+            &t.d->path,
+            isLocalFile() ? QDirPrivate::KeepLocalTrailingSlash : QDirPrivate::RemotePath);
     if (!t.d->hasAuthority())
         fixupNonAuthorityPath(&t.d->path);
 

tests/auto/corelib/io/qurl/tst_qurl.cpp

@@ -1497,7 +1497,9 @@ void tst_QUrl::fromLocalFileNormalize_data()
     QTest::newRow("relative-dot-dot") << QString::fromLatin1("././a.txt") << QString::fromLatin1("file:././a.txt") << QString::fromLatin1("file:a.txt");
     QTest::newRow("relative-path-dotdot") << QString::fromLatin1("b/../a.txt") << QString::fromLatin1("file:b/../a.txt") << QString::fromLatin1("file:a.txt");
     QTest::newRow("absolute-path-dotdot") << QString::fromLatin1("/b/../a.txt") << QString::fromLatin1("file:///b/../a.txt") << QString::fromLatin1("file:///a.txt");
-    QTest::newRow("absolute-path-dot") << QString::fromLatin1("/b/.") << QString::fromLatin1("file:///b/.") << QString::fromLatin1("file:///b");
+    QTest::newRow("absolute-path-slash") << QString::fromLatin1("/b/") << QString::fromLatin1("file:///b/") << QString::fromLatin1("file:///b/");
+    QTest::newRow("absolute-path-slahs-dot") << QString::fromLatin1("/b/.") << QString::fromLatin1("file:///b/.") << QString::fromLatin1("file:///b/");
+    QTest::newRow("absolute-path-slahs-dot-slash") << QString::fromLatin1("/b/./") << QString::fromLatin1("file:///b/./") << QString::fromLatin1("file:///b/");
 }
 
 void tst_QUrl::fromLocalFileNormalize()