Introduce QDir::isEmpty()

A directory is empty when it doesn't contain files or folders.
We can exploit QDirIterator::hasNext() to check whether this is the
case. This is efficient since it doesn't list the whole folder (in the
non-empty case).

Test cases are added for both the empty and non-empty cases.

Change-Id: I0f7e26782c0f97f9c16f928dab6cae37927875d8
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

3 files changed, 45 insertions, 0 deletions

diff --git a/src/corelib/io/qdir.cpp b/src/corelib/io/qdir.cpp
index 437f774547..37795ae5c4 100644
--- a/src/corelib/io/qdir.cpp
+++ b/src/corelib/io/qdir.cpp
@@ -1843,6 +1843,26 @@ bool QDir::exists(const QString &name) const
 }
 
 /*!
+    Returns whether the directory is empty.
+
+    Equivalent to \c{count() == 0} with filters
+    \c{QDir::AllEntries | QDir::NoDotAndDotDot}, but faster as it just checks
+    whether the directory contains at least one entry.
+
+    \note Unless you set the \p filters flags to include \c{QDir::NoDotAndDotDot}
+          (as the default value does), no directory is empty.
+
+    \sa count(), entryList(), setFilter()
+    \since 5.9
+*/
+bool QDir::isEmpty(Filters filters) const
+{
+    const auto d = d_ptr.constData();
+    QDirIterator it(d->dirEntry.filePath(), d->nameFilters, filters);
+    return !it.hasNext();
+}
+
+/*!
     Returns a list of the root directories on this system.
 
     On Windows this returns a list of QFileInfo objects containing "C:/",
diff --git a/src/corelib/io/qdir.h b/src/corelib/io/qdir.h
index ef7ec2c701..950a26f327 100644
--- a/src/corelib/io/qdir.h
+++ b/src/corelib/io/qdir.h
@@ -144,6 +144,8 @@ public:
     void setSorting(SortFlags sort);
 
     uint count() const;
+    bool isEmpty(Filters filters = Filters(AllEntries | NoDotAndDotDot)) const;
+
     QString operator[](int) const;
 
     static QStringList nameFiltersFromString(const QString &nameFilter);
diff --git a/tests/auto/corelib/io/qdir/tst_qdir.cpp b/tests/auto/corelib/io/qdir/tst_qdir.cpp
index b86c6e4dfa..49ee8eb32c 100644
--- a/tests/auto/corelib/io/qdir/tst_qdir.cpp
+++ b/tests/auto/corelib/io/qdir/tst_qdir.cpp
@@ -211,6 +211,9 @@ private slots:
     void cdBelowRoot_data();
     void cdBelowRoot();
 
+    void emptyDir();
+    void nonEmptyDir();
+
 private:
 #ifdef BUILTIN_TESTDATA
     QString m_dataPath;
@@ -2281,6 +2284,26 @@ void tst_QDir::cdBelowRoot()
     QCOMPARE(dir.path(), rootPath);
 }
 
+void tst_QDir::emptyDir()
+{
+    const QString tempDir = QDir::currentPath() + "/tmpdir/";
+    QVERIFY(QDir().mkdir(tempDir));
+    QVERIFY(QDir(tempDir).mkdir("emptyDirectory"));
+
+    QDir testDir(tempDir + "emptyDirectory");
+    QVERIFY(testDir.isEmpty());
+    QVERIFY(!testDir.isEmpty(QDir::AllEntries));
+    QVERIFY(!testDir.isEmpty(QDir::AllEntries | QDir::NoDot));
+    QVERIFY(!testDir.isEmpty(QDir::AllEntries | QDir::NoDotDot));
+    QVERIFY(QDir(tempDir).removeRecursively());
+}
+
+void tst_QDir::nonEmptyDir()
+{
+    const QDir dir(m_dataPath);
+    QVERIFY(!dir.isEmpty());
+}
+
 QTEST_MAIN(tst_QDir)
 #include "tst_qdir.moc"