Fix build failure on mswin due to empty UNREACHABLE_RETURN() - #398
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byroot merged 1 commit intoJul 10, 2026
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On MSVC, ruby.h expands UNREACHABLE_RETURN(val) to
`return (__assume(0), (val))`, so calling it without an argument
produces an empty parenthesized expression and fails to compile:
packer.h(421): error C2059: syntax error: ')'
GCC and Clang happen to accept the empty argument, which is why this
only surfaced on mswin. rb_raise is declared NORETURN so the hint is
redundant; drop it along with the Ruby 2.5 fallback definition.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Pull request overview
This PR fixes a Windows (MSVC) build failure caused by calling Ruby’s UNREACHABLE_RETURN() macro with no argument in ext/msgpack/packer.h. Since the error path already uses rb_raise (declared NORETURN), the explicit “unreachable” return hint is unnecessary and is removed along with the now-unused Ruby 2.5 fallback macro.
Changes:
- Removed the Ruby 2.5-only fallback UNREACHABLE_RETURN() macro definition from packer.h.
- Removed the UNREACHABLE_RETURN(); invocation after rb_raise in the oversized-string error path.
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byroot
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Jul 10, 2026
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Installing msgpack 1.8.3 on the x64-mswin64_140 platform fails to compile with the following error.
On MSVC, ruby.h expands UNREACHABLE_RETURN(val) to return (__assume(0), (val)), so calling it without an argument produces an empty parenthesized expression that fails to parse. GCC and Clang happen to accept the empty argument, which is why this only surfaces on mswin. rb_raise is declared NORETURN so the unreachability hint is redundant. This removes the call along with the Ruby 2.5 fallback definition that existed only for it.
With this change the extension builds with MSVC 14.51 and the test suite passes on Windows with 455 examples and 0 failures.