Fix ArgvToCommandLine SFINAE

include/wil/win32_helpers.h

@@ -971,17 +971,40 @@ bool init_once(_Inout_ INIT_ONCE& initOnce, T func)
 /// @cond
 namespace details
 {
+    // NOTE: We can't have a 'using std::begin' at class scope, hence the workaround for handling both 'begin' with ADL
+    // and 'std::begin' separately. We want to handle both because there's no guarantee the type has a 'begin' method
     template <typename RangeT>
+    struct deduce_char_type_from_string_range_traits
+    {
+        template <typename U>
+        static std::true_type deduce_has_adl_begin(U&& range, std::void_t<decltype((*begin(range))[0])>*);
+        template <typename U>
+        static std::false_type deduce_has_adl_begin(U&&, ...);
+
+        template <typename U>
+        static std::true_type deduce_has_std_begin(U&& range, std::void_t<decltype((*std::begin(range))[0])>*);
+        template <typename U>
+        static std::false_type deduce_has_std_begin(U&&, ...);
+
+        static constexpr bool has_adl_begin = decltype(deduce_has_adl_begin(std::declval<RangeT>(), nullptr))::value;
+        static constexpr bool has_std_begin = decltype(deduce_has_std_begin(std::declval<RangeT>(), nullptr))::value;
+    };
+
+    template <typename RangeT, bool hasAdlBegin = deduce_char_type_from_string_range_traits<RangeT>::has_adl_begin, bool hasStdBegin = deduce_char_type_from_string_range_traits<RangeT>::has_std_begin>
     struct deduce_char_type_from_string_range
     {
-        template <typename T = RangeT>
-        static auto deduce(T& range)
-        {
-            using std::begin;
-            return (*begin(range))[0];
-        }
+    };
 
-        using type = decltype(deduce(wistd::declval<RangeT&>()));
+    template <typename RangeT, bool hasStdBegin>
+    struct deduce_char_type_from_string_range<RangeT, true, hasStdBegin>
+    {
+        using type = std::decay_t<decltype((*begin(std::declval<RangeT>()))[0])>;
+    };
+
+    template <typename RangeT>
+    struct deduce_char_type_from_string_range<RangeT, false, true>
+    {
+        using type = std::decay_t<decltype((*std::begin(std::declval<RangeT>()))[0])>;
     };
 
     template <typename RangeT>

tests/wiTest.cpp

@@ -4225,6 +4225,11 @@ TEST_CASE("WindowsInternalTests::ArgvToCommandLine", "[win32_helpers]")
         {L"test", L"This\u00A0string\u180Ehas\u2000no\u2001space\u2002characters\u2003even\u2004though\u2005it\u2006contains\u2007characters\u2008that\u2009look\u200Athe\u200Bsame\u200Cor\u200Dare\u202Fsometimes\u205Ftreated\u2060the\u2800same\u3000as\u3164whitespace"},
         L"test This\u00A0string\u180Ehas\u2000no\u2001space\u2002characters\u2003even\u2004though\u2005it\u2006contains\u2007characters\u2008that\u2009look\u200Athe\u200Bsame\u200Cor\u200Dare\u202Fsometimes\u205Ftreated\u2060the\u2800same\u3000as\u3164whitespace",
         L"\"test\" \"This\u00A0string\u180Ehas\u2000no\u2001space\u2002characters\u2003even\u2004though\u2005it\u2006contains\u2007characters\u2008that\u2009look\u200Athe\u200Bsame\u200Cor\u200Dare\u202Fsometimes\u205Ftreated\u2060the\u2800same\u3000as\u3164whitespace\"");
+
+    // Finally, ensure that we can call the argc+argv version using the default flags
+    const char* const argvArray[] = {"test.exe", "foo", "bar"}; // Simple... this is just to verify we can call it
+    auto cmdLine = wil::ArgvToCommandLine(3, argvArray);
+    REQUIRE(cmdLine == "test.exe foo bar");
 }
 #endif