Fix Number.isNaN sometimes returning false for NaN

We use Encode(std::isnan(v)) and while std::isnan() is documented to
have bool as a return type, there is the case where cmath pulls ::isnan
into std with a using declaration when ::isnan() will sometimes return
an int.

See also https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69450

This appears to be the only case where we use the overloaded Encode()
constructor in conjunction with a direct std::isXXX call.

[ChangeLog][QtQml] Fix Number.isNaN() returning incorrect values with
some glibc versions.

Task-number: QTBUG-63464
Change-Id: Iaaba3735f7400eac0950aad8f3ac47befaf9dab9
Reviewed-by: Ville Voutilainen <ville.voutilainen@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 3 insertions, 1 deletions

diff --git a/src/qml/jsruntime/qv4numberobject.cpp b/src/qml/jsruntime/qv4numberobject.cpp
index 09644c161d..255d0212c1 100644
--- a/src/qml/jsruntime/qv4numberobject.cpp
+++ b/src/qml/jsruntime/qv4numberobject.cpp
@@ -163,7 +163,9 @@ void NumberPrototype::method_isNaN(const BuiltinFunction *, Scope &scope, CallDa
     }
 
     double v = callData->args[0].toNumber();
-    scope.result = Encode(std::isnan(v));
+    // cast to bool explicitly as std::isnan() may give us ::isnan(), which
+    // sometimes returns an int and we don't want the Encode(int) overload.
+    scope.result = Encode(bool(std::isnan(v)));
 }
 
 void NumberPrototype::method_toString(const BuiltinFunction *, Scope &scope, CallData *callData)