maintainer-feedback requested: [Bug 281431] www/qt5-webengine: fix build with clang and libc++ 19

[bugzilla-noreply at freebsd.org]

Bugzilla Automation <bugzilla at FreeBSD.org> has asked freebsd-kde (group)
<kde at FreeBSD.org> for maintainer-feedback:
Bug 281431: www/qt5-webengine: fix build with clang and libc++ 19
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=281431



--- Description ---
As noted in the libc++ 19 release notes [1], std::char_traits<> is now
only provided for char, char8_t, char16_t, char32_t and wchar_t, and any
instantiation for other types will fail.

This causes www/qt5-webengine to fail to compile with clang 19 and
libc++ 19, resulting in errors similar to:

  /usr/include/c++/v1/string:820:42: error: implicit instantiation of undefined
template 'std::char_traits<unsigned short>'
    820 |   static_assert(is_same<_CharT, typename
traits_type::char_type>::value,
	|					   ^
 
../../../../kde-qtwebengine-5.15.17p3/src/3rdparty/chromium/v8/src/inspector/v8
-string-conversions.cc:390:26:
note: in instantiation of template class 'std::basic_string<unsigned short>'
requested here
    390 | std::basic_string<UChar> UTF8ToUTF16(const char* stringStart, size_t
length) {
	|			   ^
  /usr/include/c++/v1/__fwd/string.h:23:29: note: template is declared here
     23 | struct _LIBCPP_TEMPLATE_VIS char_traits;
	|			      ^

Upstream v8 has fixed this in commit 182d9c05e78 [2], so add it as a
backported patch, until the next version of qt5-webengine is released.

Also, clang 19 now implements CWG 96 [1], which requires a template
argument list after a 'template' keyword, resulting in errors similar
to:

 
../../../../kde-qtwebengine-5.15.17p3/src/3rdparty/chromium/third_party/blink/r
enderer/platform/wtf/hash_table.h:1789:23:
error: a template argument list is expected after a name prefixed by the
template keyword [-Wmissing-template-arg-list-after-template-kw]
   1789 |   Allocator::template BackingWriteBarrier(&table_);
	|			^
 
../../../../kde-qtwebengine-5.15.17p3/src/3rdparty/chromium/third_party/blink/r
enderer/platform/wtf/hash_table.h:1847:23:
error: a template argument list is expected after a name prefixed by the
template keyword [-Wmissing-template-arg-list-after-template-kw]
   1847 |   Allocator::template BackingWriteBarrier(&table_);
	|			^
 
../../../../kde-qtwebengine-5.15.17p3/src/3rdparty/chromium/third_party/blink/r
enderer/platform/wtf/hash_table.h:2015:23:
error: a template argument list is expected after a name prefixed by the
template keyword [-Wmissing-template-arg-list-after-template-kw]
   2015 |   Allocator::template BackingWriteBarrier(&table_);
	|			^
 
../../../../kde-qtwebengine-5.15.17p3/src/3rdparty/chromium/third_party/blink/r
enderer/platform/wtf/hash_table.h:2016:23:
error: a template argument list is expected after a name prefixed by the
template keyword [-Wmissing-template-arg-list-after-template-kw]
   2016 |   Allocator::template BackingWriteBarrier(&other.table_);
	|			^

and:

 
../../../../kde-qtwebengine-5.15.17p3/src/3rdparty/chromium/third_party/perfett
o/include/perfetto/tracing/internal/track_event_data_source.h:110:20:
error: a template argument list is expected after a name prefixed by the
template keyword [-Wmissing-template-arg-list-after-template-kw]
    110 |     Base::template Trace([](typename Base::TraceContext ctx) {
ctx.Flush(); });
	|		     ^
 
../../../../kde-qtwebengine-5.15.17p3/src/3rdparty/chromium/third_party/perfett
o/include/perfetto/tracing/internal/track_event_data_source.h:124:20:
error: a template argument list is expected after a name prefixed by the
template keyword [-Wmissing-template-arg-list-after-template-kw]
    124 |     Base::template Trace([&](typename Base::TraceContext ctx) {
	|		     ^
 
../../../../kde-qtwebengine-5.15.17p3/src/3rdparty/chromium/third_party/perfett
o/include/perfetto/tracing/internal/track_event_data_source.h:431:20:
error: a template argument list is expected after a name prefixed by the
template keyword [-Wmissing-template-arg-list-after-template-kw]
    431 |     Base::template Trace([&](typename Base::TraceContext ctx) {
	|		     ^
 
../../../../kde-qtwebengine-5.15.17p3/src/3rdparty/chromium/third_party/perfett
o/include/perfetto/tracing/internal/track_event_data_source.h:548:22:
error: a template argument list is expected after a name prefixed by the
template keyword [-Wmissing-template-arg-list-after-template-kw]
    548 |	Base::template TraceWithInstances(instances,
std::move(lambda));
	|		       ^
 
../../../../kde-qtwebengine-5.15.17p3/src/3rdparty/chromium/third_party/perfett
o/include/perfetto/tracing/internal/track_event_data_source.h:563:20:
error: a template argument list is expected after a name prefixed by the
template keyword [-Wmissing-template-arg-list-after-template-kw]
    563 |     Base::template Trace([&](typename Base::TraceContext ctx) {
	|		     ^

In case of wtf, appending "<>" is enough to satisfy the constraint. For
perfetto, this was fixed by upstream commit e2f661907a [3].

[1] https://libcxx.llvm.org/ReleaseNotes/19.html#deprecations-and-removals
[2] https://chromium.googlesource.com/v8/v8.git/+/182d9c05e78
[3] https://android.googlesource.com/platform/external/perfetto/+/e2f661907a