QString: add char8_t overload of fromUtf8()

Use the overload-with-template trick from P1423 to avoid ambiguities
when existing callers pass 0 or nullptr.

Add a qdoc-ignored macro to hide the fact that the overload is a
template.

[ChangeLog][QtCore][QString] Added char8_t overload of fromUtf8().

Change-Id: Iaa2d365bfa161ef36cc73fa3bad50aabf34d01db
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

3 files changed, 19 insertions, 0 deletions

diff --git a/src/corelib/global/qcompilerdetection.h b/src/corelib/global/qcompilerdetection.h
index 7b86279670..6341d060f1 100644
--- a/src/corelib/global/qcompilerdetection.h
+++ b/src/corelib/global/qcompilerdetection.h
@@ -1233,6 +1233,12 @@
 #endif
 
 /*
+ * "Weak overloads" - makes an otherwise confliciting overload weaker
+ * (by making it a template)
+ */
+#define Q_WEAK_OVERLOAD template <typename = void>
+
+/*
  * Warning/diagnostic handling
  */
 
diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index 16e9f1d63b..dff0dbce7f 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -5098,6 +5098,14 @@ QString QString::fromLocal8Bit_helper(const char *str, int size)
 */
 
 /*!
+    \fn QString QString::fromUtf8(const char8_t *str, qsizetype size)
+    \overload
+    \since 6.0
+
+    This overload is only available when compiling in C++20 mode.
+*/
+
+/*!
     \fn QString QString::fromUtf8(const QByteArray &str)
     \overload
     \since 5.0
diff --git a/src/corelib/text/qstring.h b/src/corelib/text/qstring.h
index f14644d956..b77c6134d5 100644
--- a/src/corelib/text/qstring.h
+++ b/src/corelib/text/qstring.h
@@ -658,6 +658,11 @@ public:
     {
         return fromUtf8_helper(str, (str && size == -1) ? int(strlen(str)) : size);
     }
+#ifdef __cpp_char8_t
+    Q_WEAK_OVERLOAD
+    static inline QString fromUtf8(const char8_t *str, qsizetype size = -1)
+    { return fromUtf8(reinterpret_cast<const char *>(str), int(size)); }
+#endif
     static inline QString fromLocal8Bit(const char *str, int size = -1)
     {
         return fromLocal8Bit_helper(str, (str && size == -1) ? int(strlen(str)) : size);