Add QTemporaryDir::errorString()

[ChangeLog][QtCore][QTemporaryDir] Added errorString() method that
returns the string explaining why creating the temporary directory
failed.

Change-Id: Ib306f8f647014b399b87ffff13f0a1f3c89e0a2c
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: David Faure <david.faure@kdab.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

src/corelib/io/qtemporarydir.cpp

@@ -38,6 +38,7 @@
 #include "qdiriterator.h"
 #include "qplatformdefs.h"
 #include <QDebug>
+#include <QPair>
 
 #if defined(QT_BUILD_CORE_LIB)
 #include "qcoreapplication.h"
@@ -59,7 +60,7 @@ public:
 
     void create(const QString &templateName);
 
-    QString path;
+    QString pathOrError;
     bool autoRemove;
     bool success;
 };
@@ -97,7 +98,7 @@ static int nextRand(int &v)
     return r;
 }
 
-static char *q_mkdtemp(char *templateName)
+QPair<QString, bool> q_mkdtemp(char *templateName)
 {
     static const char letters[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 
@@ -105,8 +106,7 @@ static char *q_mkdtemp(char *templateName)
 
     char *XXXXXX = templateName + length - 6;
 
-    if ((length < 6u) || strncmp(XXXXXX, "XXXXXX", 6))
-        return 0;
+    Q_ASSERT((length >= 6u) && strncmp(XXXXXX, "XXXXXX", 6) == 0);
 
     for (int i = 0; i < 256; ++i) {
         int v = qrand();
@@ -133,17 +133,18 @@ static char *q_mkdtemp(char *templateName)
                     qWarning() << "Unable to remove unused directory" << templateNameStr;
                 continue;
             }
-            return templateName;
+            return qMakePair(QFile::decodeName(templateName), true);
         }
     }
-    return 0;
+    return qMakePair(qt_error_string(), false);
 }
 
 #else // defined(Q_OS_QNX ) || defined(Q_OS_WIN) || defined(Q_OS_ANDROID)
 
-static char *q_mkdtemp(char *templateName)
+QPair<QString, bool> q_mkdtemp(char *templateName)
 {
-   return mkdtemp(templateName);
+    bool ok = (mkdtemp(templateName) != 0);
+    return qMakePair(ok ? QFile::decodeName(templateName) : qt_error_string(), ok);
 }
 
 #endif
@@ -153,10 +154,9 @@ void QTemporaryDirPrivate::create(const QString &templateName)
     QByteArray buffer = QFile::encodeName(templateName);
     if (!buffer.endsWith("XXXXXX"))
         buffer += "XXXXXX";
-    if (q_mkdtemp(buffer.data())) { // modifies buffer
-        success = true;
-        path = QFile::decodeName(buffer.constData());
-    }
+    QPair<QString, bool> result = q_mkdtemp(buffer.data()); // modifies buffer
+    pathOrError = result.first;
+    success = result.second;
 }
 
 //************* QTemporaryDir
@@ -255,13 +255,25 @@ bool QTemporaryDir::isValid() const
     return d_ptr->success;
 }
 
+/*!
+   \since 5.6
+
+   If isValid() returns \c false, this function returns the error string that
+   explains why the creation of the temporary directory failed. Otherwise, this
+   function return an empty string.
+*/
+QString QTemporaryDir::errorString() const
+{
+    return d_ptr->success ? QString() : d_ptr->pathOrError;
+}
+
 /*!
    Returns the path to the temporary directory.
    Empty if the QTemporaryDir could not be created.
 */
 QString QTemporaryDir::path() const
 {
-    return d_ptr->path;
+    return d_ptr->success ? d_ptr->pathOrError : QString();
 }
 
 /*!

src/corelib/io/qtemporarydir.h

@@ -52,6 +52,7 @@ public:
     ~QTemporaryDir();
 
     bool isValid() const;
+    QString errorString() const;
 
     bool autoRemove() const;
     void setAutoRemove(bool b);

tests/auto/corelib/io/qfileinfo/tst_qfileinfo.cpp

@@ -281,7 +281,8 @@ void tst_QFileInfo::initTestCase()
     m_resourcesDir = dataPath + QLatin1String("/resources");
     m_proFile = dataPath + QLatin1String("/tst_qfileinfo.pro");
 
-    QVERIFY(m_dir.isValid());
+    QVERIFY2(m_dir.isValid(),
+             ("Failed to create temporary dir: " + m_dir.errorString()).toUtf8());
     QVERIFY(QDir::setCurrent(m_dir.path()));
 }
 

tests/auto/corelib/io/qtemporarydir/tst_qtemporarydir.cpp

@@ -93,6 +93,7 @@ void tst_QTemporaryDir::construction()
     QCOMPARE(dir.path().left(tmp.size()), tmp);
     QVERIFY(dir.path().contains("tst_qtemporarydir"));
     QVERIFY(QFileInfo(dir.path()).isDir());
+    QCOMPARE(dir.errorString(), QString());
 }
 
 // Testing get/set functions
@@ -251,6 +252,7 @@ void tst_QTemporaryDir::nonWritableCurrentDir()
     QTemporaryDir dir("tempXXXXXX");
     dir.setAutoRemove(true);
     QVERIFY(!dir.isValid());
+    QVERIFY(!dir.errorString().isEmpty());
     QVERIFY(dir.path().isEmpty());
 #endif
 }
@@ -287,7 +289,11 @@ void tst_QTemporaryDir::stressTest()
     for (int i = 0; i < iterations; ++i) {
         QTemporaryDir dir(pattern);
         dir.setAutoRemove(false);
-        QVERIFY2(dir.isValid(), qPrintable(QString::fromLatin1("Failed to create #%1 under %2.").arg(i).arg(QDir::toNativeSeparators(pattern))));
+        QVERIFY2(dir.isValid(),
+                 qPrintable(QString::fromLatin1("Failed to create #%1 under %2: %3.")
+                            .arg(i)
+                            .arg(QDir::toNativeSeparators(pattern))
+                            .arg(dir.errorString())));
         QVERIFY(!names.contains(dir.path()));
         names.insert(dir.path());
     }

tests/auto/corelib/mimetypes/qmimedatabase/tst_qmimedatabase.cpp

@@ -82,7 +82,8 @@ tst_QMimeDatabase::tst_QMimeDatabase()
 
 void tst_QMimeDatabase::initTestCase()
 {
-    QVERIFY(m_temporaryDir.isValid());
+    QVERIFY2(m_temporaryDir.isValid(),
+             ("Could not create temporary subdir: " + m_temporaryDir.errorString()).toUtf8());
 
     // Create a "global" and a "local" XDG data dir, right here.
     // The local dir will be empty initially, while the global dir will contain a copy of freedesktop.org.xml