Fix warning in QStringView::compare(QChar) on qsizetype->int

size() - 1 is converted to int as the result, but size() is a qsizetype
and could be bigger than INT_MAX. So rewrite to not depend on the cast.
This was introduced on b2f79cceb11dfd15ac9eea631bc18ad6b036eb91.

I could have replaced size() - 1 with int(size() > 1) - 1, but that's
even more complex. To simplify, I split the function in two while
retaining the C++11 constexpr requirements.

Bonus: removes the use of the ambiguously-named "empty()" function that
looks like a verb.

Fixes: QTBUG-85665
Pick-to: 5.15
Change-Id: Ieffc3453b88c4517a1dbfffd162338fdb084a376
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 4 insertions, 1 deletions

diff --git a/src/corelib/text/qstringview.h b/src/corelib/text/qstringview.h
index 58412974bc..24cea33e7f 100644
--- a/src/corelib/text/qstringview.h
+++ b/src/corelib/text/qstringview.h
@@ -304,7 +304,7 @@ public:
     { return QtPrivate::compareStrings(*this, other, cs); }
     Q_REQUIRED_RESULT inline int compare(QLatin1String other, Qt::CaseSensitivity cs = Qt::CaseSensitive) const noexcept;
     Q_REQUIRED_RESULT Q_DECL_CONSTEXPR int compare(QChar c) const noexcept
-    { return empty() || front() == c ? size() - 1 : *utf16() - c.unicode() ; }
+    { return size() >= 1 ? compare_single_char_helper(*utf16() - c.unicode()) : -1; }
     Q_REQUIRED_RESULT int compare(QChar c, Qt::CaseSensitivity cs) const noexcept
     { return QtPrivate::compareStrings(*this, QStringView(&c, 1), cs); }
 
@@ -408,6 +408,9 @@ public:
 private:
     qsizetype m_size;
     const storage_type *m_data;
+
+    Q_DECL_CONSTEXPR int compare_single_char_helper(int diff) const noexcept
+    { return diff ? diff : size() > 1 ? 1 : 0; }
 };
 Q_DECLARE_TYPEINFO(QStringView, Q_PRIMITIVE_TYPE);