From b3edce58e5aea76d1d84c868f76171c2b40520a4 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Wed, 5 Jun 2024 20:55:22 +0200
Subject: [PATCH] QStringConverter: port encodingForName() to QAnyStringView

These kinds of lookup functions are no-brainers for QAnyStringView.

This is required to replace the QStringEncoder/Decoder constructors
from QString, newly added for 6.8, and found in API review to be
better written using QAnyStringView.

Because this is API-Review-relevant, keep the QStringView case
pessimized. It's not worse than the code that it replaces (toLatin1()
on an unshared QString performs in-place conversion), and can be
improved later.

[ChangeLog][QtCore][QStringConverter] The encodingForName() function
now takes QAnyStringView (was: const char*).

Pick-to: 6.8
Task-number: QTBUG-126108
Change-Id: I02cc53bfbc8f1eebe539816487a10b39e96fac2d
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/compat/removed_api.cpp       |  7 ++++++
 src/corelib/text/qstringconverter.cpp    | 30 +++++++++++++++++++-----
 src/corelib/text/qstringconverter_base.h |  4 ++++
 3 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/src/corelib/compat/removed_api.cpp b/src/corelib/compat/removed_api.cpp
index babdc74f42c..8826716bde8 100644
--- a/src/corelib/compat/removed_api.cpp
+++ b/src/corelib/compat/removed_api.cpp
@@ -1138,6 +1138,13 @@ bool QtPrivate::ResultIteratorBase::operator!=(const QtPrivate::ResultIteratorBa
 
 #include "qstring.h" // inlined API
 
+#include "qstringconverter.h"
+
+auto QStringConverter::encodingForName(const char *name) noexcept -> std::optional<Encoding>
+{
+    return encodingForName(QAnyStringView{name});
+}
+
 #if QT_CONFIG(thread)
 #  include "qthreadpool.h" // inlined API
 #endif
diff --git a/src/corelib/text/qstringconverter.cpp b/src/corelib/text/qstringconverter.cpp
index a960899e59d..745261cd559 100644
--- a/src/corelib/text/qstringconverter.cpp
+++ b/src/corelib/text/qstringconverter.cpp
@@ -1910,20 +1910,37 @@ const QStringConverter::Interface QStringConverter::encodingInterfaces[QStringCo
 };
 
 // match names case insensitive and skipping '-' and '_'
-static bool nameMatch(const char *a, const char *b)
+static bool nameMatch_impl(const char *a, QLatin1StringView rhs)
 {
+    const char *b = rhs.data();
+    const char *b_end = rhs.end();
     do {
         while (*a == '-' || *a == '_')
             ++a;
-        while (*b == '-' || *b == '_')
+        while (b != b_end && (*b == '-' || *b == '_'))
             ++b;
-        if (!*a && !*b) // end of both strings
+        if (!*a && b == b_end) // end of both strings
             return true;
     } while (QtMiscUtils::toAsciiLower(*a++) == QtMiscUtils::toAsciiLower(*b++));
 
     return false;
 }
 
+static bool nameMatch_impl(const char *a, QUtf8StringView b)
+{
+    return nameMatch_impl(a, QLatin1StringView{QByteArrayView{b}});
+}
+
+static bool nameMatch_impl(const char *a, QStringView b)
+{
+    return nameMatch_impl(a, QLatin1StringView{b.toString().toLatin1()}); // ### optimize
+}
+
+static bool nameMatch(const char *a, QAnyStringView b)
+{
+    return b.visit([a](auto b) { return nameMatch_impl(a, b); });
+}
+
 
 /*!
     \fn constexpr QStringConverter::QStringConverter()
@@ -2237,11 +2254,12 @@ const char *QStringConverter::name() const noexcept
     the QStringConverter constructor when Qt is built with ICU, if ICU provides a
     converter with the given name.
 
-    \a name is expected to be UTF-8 encoded.
+    \note In Qt versions prior to 6.8, this function took only a \c{const char *},
+    which was expected to be UTF-8-encoded.
 */
-std::optional<QStringConverter::Encoding> QStringConverter::encodingForName(const char *name) noexcept
+std::optional<QStringConverter::Encoding> QStringConverter::encodingForName(QAnyStringView name) noexcept
 {
-    if (!name)
+    if (name.isEmpty())
         return std::nullopt;
     for (qsizetype i = 0; i < LastEncoding + 1; ++i) {
         if (nameMatch(encodingInterfaces[i].name, name))
diff --git a/src/corelib/text/qstringconverter_base.h b/src/corelib/text/qstringconverter_base.h
index d6b6fcb484b..0c4a19cbe7b 100644
--- a/src/corelib/text/qstringconverter_base.h
+++ b/src/corelib/text/qstringconverter_base.h
@@ -14,6 +14,7 @@
 #include <QtCore/qglobal.h> // QT_{BEGIN,END}_NAMESPACE
 #include <QtCore/qflags.h> // Q_DECLARE_FLAGS
 #include <QtCore/qcontainerfwd.h>
+#include <QtCore/qstringfwd.h>
 
 #include <cstring>
 
@@ -156,7 +157,10 @@ public:
 
     Q_CORE_EXPORT const char *name() const noexcept;
 
+#if QT_CORE_REMOVED_SINCE(6, 8)
     Q_CORE_EXPORT static std::optional<Encoding> encodingForName(const char *name) noexcept;
+#endif
+    Q_CORE_EXPORT static std::optional<Encoding> encodingForName(QAnyStringView name) noexcept;
     Q_CORE_EXPORT static const char *nameForEncoding(Encoding e);
     Q_CORE_EXPORT static std::optional<Encoding>
     encodingForData(QByteArrayView data, char16_t expectedFirstCharacter = 0) noexcept;