Disentangle string-related headers

It's starting to hinder QStringView development
(QString::append(QStringView), e.g.).

- qbytearray.h includes qstring.h, but is included by qstring.h
  -> remove qstring.h include from qbytearray.h

- the QStringLiteral definition is used from both qstring.h and
  qstringview.h
  -> extract into its own header, move QStringViewLiteral definition
     there, too

- the qCompareStrings(), qConvertTo*() functions are used by QString
  and QStringView
  -> also extract into own header, included from qstring.h and
     qstringview.h

- QStringView::toString() depends on QString, which depends on
  QStringView
  -> move QStringView::toString() definition to qstring.h, after the
     definition of QString
  -> move qstringview.h up to all the other includes in qstring.h

This is starting to look like a DAG again, and allows to remove the
unholy

  #ifndef QSTRING_H
  #  include <qstring.h>
  #endif

hack from qstringview.h.

[ChangeLog][Potentially Source-Incompatible Changes][QByteArray]
qbytearray.h no longer includes qstring.h. In particular, this means
that in order to use QStringBuilder with QByteArray, you need to
include both qbytearray.h and qstring.h now (or <QByteArray> and
<QString>, resp.).

Change-Id: I7f8acf9c11bc1731266cd25c6eda9fb36723f364
Reviewed-by: Anton Kudryavtsev <antkudr@mail.ru>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 0 insertions, 4 deletions

diff --git a/src/corelib/tools/qbytearray.h b/src/corelib/tools/qbytearray.h
index 453f28f39f..144216a6ef 100644
--- a/src/corelib/tools/qbytearray.h
+++ b/src/corelib/tools/qbytearray.h
@@ -692,8 +692,4 @@ Q_DECLARE_SHARED(QByteArray)
 
 QT_END_NAMESPACE
 
-#ifdef QT_USE_QSTRINGBUILDER
-#include <QtCore/qstring.h>
-#endif
-
 #endif // QBYTEARRAY_H