'typename' disambiguates a qualified dependent name, telling the
compiler that something like T::iterator names a type rather than a
value. Before a plain identifier there is nothing to disambiguate: P1
is already a type, and so is PopupIndex.
The grammar wants a qualified name after the keyword, so clang reports
"expected a qualified name after 'typename'", drops the keyword and
carries on -- 15175 times, since the offending declarations sit in
widely included headers. MSVC accepts them without a word.
Semantics do not change. Both compilers already ignored the keyword,
so the partial specialisations matched before this and match after it.
The diagnostic belongs to no -W group and therefore cannot be switched
off with -Wno-, which makes deleting the tokens the only way to quiet
it.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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