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Modernizes the Windows native-extension loader from legacy LoadLibraryW to LoadLibraryExW with LOAD_WITH_ALTERED_SEARCH_PATH. The .so's own directory is searched first for its transitive DLL imports — gems that bundle DLLs alongside the .so are found without walking PATH. Wall-clock impact in this setup is noise (deps for gtk3 live in ucrt64/bin via PATH, not next to the .so). Kept anyway as the recommended form on Win10+.
Adds a RUBY_DLL_PATH environment variable that, when set, switches the process from legacy PATH-walking DLL search to the Win10+ AddDllDirectory + LOAD_LIBRARY_SEARCH_DEFAULT_DIRS mechanism. The named directory is registered as a user dir, ruby.exe's own dir is also registered, and dln.c's LoadLibraryExW uses LOAD_LIBRARY_SEARCH_DEFAULT_DIRS | LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR to skip PATH walking entirely. Without RUBY_DLL_PATH the legacy behavior is unchanged (dln.c uses LOAD_WITH_ALTERED_SEARCH_PATH, the modern equivalent of LoadLibraryW that searches the .so's own directory first for transitive imports). Measured wall-clock impact on gtk3/tzinfo/sqlite3 require is noise (~0 ms either way). The cost in modern Windows LoadLibrary is not in the path search — it's in PE relocation and DllMain execution. Kept the change as the recommended form on Win10+; turn on per-installation if desired.
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Adds an opt-in
RUBY_DLL_PATHenvironment variable. When set, the process switches from legacyPATH-walking DLL search to the Win10+AddDllDirectory+LOAD_LIBRARY_SEARCH_DEFAULT_DIRSmechanism: the named directory is registered as a user dir,ruby.exe's own directory is registered too, anddln.cusesLOAD_LIBRARY_SEARCH_DEFAULT_DIRS | LOAD_LIBRARY_SEARCH_DLL_LOAD_DIRto skipPATHwalking entirely.Without
RUBY_DLL_PATHbehavior is unchanged.Measured wall-clock impact on gtk3/tzinfo/sqlite3 requires is ~0 ms either way; the cost in modern Windows
LoadLibraryis not in the search. The value is determinism — a Ruby install can point at its own DLL directory instead of depending onPATHorder.Depends on the
dln-loadlibraryexbranch, whoseLoadLibraryExWcall this builds on; that commit is included here as the first of the two.Windows-only. Not built or tested on Windows CI — measured in a local MSYS2/UCRT64 VM.