QMimeBinaryProvider: cut out the QMap middle-man

In Qt 6, QMap is just a shared pointer to a std::map.

QMimeBinaryProvider::m_mimetypeExtra is never copied, though, so the
implicit sharing that QMap adds on top of std::map is useless.

Use the underlying std::map directly.

Yes, the std::map API is a bit raw around the edges (std::pair
value_type), but we're professionals here.

Saves more than 1.7KiB in TEXT size on optimized AMD64 GCC 11 C++20
Linux builds.

As a drive-by, cut out the insertIt temporary, too, and assign
directly to `it`.

Change-Id: If3fd98a7e7017909d00b8725f8c252b19459d5b6
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: David Faure <david.faure@kdab.com>

src/corelib/mimetypes/qmimeprovider.cpp

@@ -9,7 +9,6 @@
 #include <qstandardpaths.h>
 #include "qmimemagicrulematcher_p.h"
 
-#include <QMap>
 #include <QXmlStreamReader>
 #include <QBuffer>
 #include <QDir>
@@ -488,30 +487,24 @@ void QMimeBinaryProvider::addAllMimeTypes(QList<QMimeType> &result)
 QMimeTypePrivate::LocaleHash QMimeBinaryProvider::localeComments(const QString &name)
 {
     MimeTypeExtraMap::const_iterator it = loadMimeTypeExtra(name);
-    if (it != m_mimetypeExtra.constEnd()) {
-        const MimeTypeExtra &e = it.value();
-        return e.localeComments;
-    }
+    if (it != m_mimetypeExtra.cend())
+        return it->second.localeComments;
     return {};
 }
 
 bool QMimeBinaryProvider::hasGlobDeleteAll(const QString &name)
 {
     MimeTypeExtraMap::const_iterator it = loadMimeTypeExtra(name);
-    if (it != m_mimetypeExtra.constEnd()) {
-        const MimeTypeExtra &e = it.value();
-        return e.hasGlobDeleteAll;
-    }
+    if (it != m_mimetypeExtra.cend())
+        return it->second.hasGlobDeleteAll;
     return {};
 }
 
 QStringList QMimeBinaryProvider::globPatterns(const QString &name)
 {
     MimeTypeExtraMap::const_iterator it = loadMimeTypeExtra(name);
-    if (it != m_mimetypeExtra.constEnd()) {
-        const MimeTypeExtra &e = it.value();
-        return e.globPatterns;
-    }
+    if (it != m_mimetypeExtra.cend())
+        return it->second.globPatterns;
     return {};
 }
 
@@ -519,8 +512,8 @@ QMimeBinaryProvider::MimeTypeExtraMap::const_iterator
 QMimeBinaryProvider::loadMimeTypeExtra(const QString &mimeName)
 {
 #if QT_CONFIG(xmlstreamreader)
-    auto it = m_mimetypeExtra.constFind(mimeName);
-    if (it == m_mimetypeExtra.constEnd()) {
+    auto it = m_mimetypeExtra.find(mimeName);
+    if (it == m_mimetypeExtra.cend()) {
         // load comment and globPatterns
 
         // shared-mime-info since 1.3 lowercases the xml files
@@ -530,21 +523,20 @@ QMimeBinaryProvider::loadMimeTypeExtra(const QString &mimeName)
 
         QFile qfile(mimeFile);
         if (!qfile.open(QFile::ReadOnly))
-            return m_mimetypeExtra.constEnd();
+            return m_mimetypeExtra.cend();
 
-        auto insertIt = m_mimetypeExtra.insert(mimeName, MimeTypeExtra{});
-        it = insertIt;
-        MimeTypeExtra &extra = insertIt.value();
+        it = m_mimetypeExtra.try_emplace(mimeName).first;
+        MimeTypeExtra &extra = it->second;
         QString mainPattern;
 
         QXmlStreamReader xml(&qfile);
         if (xml.readNextStartElement()) {
             if (xml.name() != "mime-type"_L1) {
-                return m_mimetypeExtra.constEnd();
+                return m_mimetypeExtra.cend();
             }
             const auto name = xml.attributes().value("type"_L1);
             if (name.isEmpty())
-                return m_mimetypeExtra.constEnd();
+                return m_mimetypeExtra.cend();
             if (name.compare(mimeName, Qt::CaseInsensitive))
                 qWarning() << "Got name" << name << "in file" << mimeFile << "expected" << mimeName;
 
@@ -585,7 +577,7 @@ QMimeBinaryProvider::loadMimeTypeExtra(const QString &mimeName)
 #else
     Q_UNUSED(mimeName);
     qWarning("Cannot load mime type since QXmlStreamReader is not available.");
-    return m_mimetypeExtra.constEnd();
+    return m_mimetypeExtra.cend();
 #endif // feature xmlstreamreader
 }
 

src/corelib/mimetypes/qmimeprovider_p.h

@@ -23,7 +23,8 @@ QT_REQUIRE_CONFIG(mimetype);
 #include "qmimeglobpattern_p.h"
 #include <QtCore/qdatetime.h>
 #include <QtCore/qset.h>
-#include <QtCore/qmap.h>
+
+#include <map>
 
 QT_BEGIN_NAMESPACE
 
@@ -123,7 +124,7 @@ private:
         QStringList globPatterns;
         bool hasGlobDeleteAll = false;
     };
-    using MimeTypeExtraMap = QMap<QString, MimeTypeExtra>;
+    using MimeTypeExtraMap = std::map<QString, MimeTypeExtra>;
     MimeTypeExtraMap m_mimetypeExtra;
 
     MimeTypeExtraMap::const_iterator loadMimeTypeExtra(const QString &mimeName);