Fix Windows configure: point find_package at OBS's exported w32-pthreads

The libobs_DIR fix in 79de5e8f worked -- libobsConfig.cmake now loads on the
Windows runner -- and immediately exposed the next link in the same chain.
obs-studio's libobsConfig.cmake.in carries, under if(MSVC), a hard

    find_dependency(w32-pthreads REQUIRED)

because libobs/cmake/os-windows.cmake links PUBLIC OBS::w32-pthreads. That
lookup failed and aborted the whole configure.

The cause is not a missing export, which was the first hypothesis:
deps/w32-pthreads/CMakeLists.txt ends in target_export(w32-pthreads), the
same helper libobs itself uses, so the install(TARGETS ... EXPORT),
install(EXPORT ... NAMESPACE OBS::) and generated w32-pthreadsConfig.cmake
all exist and all run -- CMake would have hard-errored at generate time if
w32-pthreads were in no export set, and our own patch adds it under the
libobs subtree, which installs before the tolerated obs-frontend-api install
error stops the rest.

It is the same search-path mismatch libobs itself had: target_export installs
to <prefix>/${OBS_CMAKE_DESTINATION}/<target>/, which on Windows is
<prefix>/cmake/w32-pthreads/ -- a shape find_package's Config-mode suffixes
never search. So apply the same remedy CMake's own error message suggests,
and apply it before the find_package(libobs) call that transitively triggers
the find_dependency.

Also adds a fallback Findw32-pthreads.cmake, reached only when that export is
genuinely absent, which reconstructs OBS::w32-pthreads from the bootstrap's
artifacts, and a repair for a locationless imported target mirroring the
existing OBS::libobs one. The fallback deliberately lives in
cmake/windows/find-fallback/ rather than cmake/windows/, which osconfig.cmake
already puts on CMAKE_MODULE_PATH: a find module there would shadow OBS's
real exported package on every build, since MODULE mode is tried first.

Verified on Linux (this is a Linux sandbox) by reconstructing the exact
failure -- a stub libobsConfig.cmake with the same find_dependency, reached
through libobs_DIR -- and confirming it fails without this block and passes
with it, and separately that deleting the package routes find_package through
the fallback module instead. A full Linux configure of the repo is unchanged;
both new blocks are inside if(OS_WINDOWS) and the upstream find_dependency is
inside if(MSVC), so macOS and Linux are no-ops.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RL8abRmgFXkVASHkkqiJbE

CMakeLists.txt

@@ -184,8 +184,119 @@ if(OS_WINDOWS AND NOT libobs_DIR)
     endif()
 endif()
 
+# ...and the exact same problem, one level down, for w32-pthreads.
+#
+# libobs/cmake/os-windows.cmake links `PUBLIC OBS::w32-pthreads`, so
+# obs-studio's libobsConfig.cmake.in carries, verbatim:
+#
+#   if(MSVC)
+#     find_dependency(w32-pthreads REQUIRED)
+#   endif()
+#
+# That call is REQUIRED, it runs from inside libobsConfig.cmake, and until
+# this block existed it aborted the whole configure the moment the libobs_DIR
+# fix above finally succeeded in loading that config file:
+#
+#   By not providing "Findw32-pthreads.cmake" in CMAKE_MODULE_PATH this
+#   project has asked CMake to find a package configuration file provided by
+#   "w32-pthreads", but CMake did not find one.
+#     .deps/cmake/libobs/libobsConfig.cmake:30 (find_dependency)
+#
+# This is NOT a missing export. deps/w32-pthreads/CMakeLists.txt ends with
+# `target_export(w32-pthreads)`, which is the same helper libobs itself uses
+# (cmake/common/helpers_common.cmake): it emits install(TARGETS ... EXPORT
+# w32-pthreadsTargets), install(EXPORT ... NAMESPACE OBS::), a generated
+# w32-pthreadsConfig.cmake and its version file, all COMPONENT Development.
+# Those rules *must* exist and *must* have run, for two independent reasons:
+#
+#  1. CMake hard-errors at generate time if a target in one export set links
+#     to a target that is in no export set at all ("install(EXPORT
+#     "libobsTargets") includes target "libobs" which requires target
+#     "w32-pthreads" that is not in any export set"). obs-studio's generate
+#     step succeeded, so w32-pthreads was exported.
+#  2. The install rules land under the libobs *directory* (this repo's
+#     _patch_obs_studio_w32_pthreads adds deps/w32-pthreads from
+#     libobs/CMakeLists.txt), and libobs is the first subdirectory the modern
+#     top-level CMakeLists.txt adds -- so its whole subtree installs before
+#     the tolerated UI/obs-frontend-api install error aborts the rest.
+#
+# The failure is purely the search path, identical to libobs's: target_export
+# installs the package to "${OBS_CMAKE_DESTINATION}/${target}", which on
+# Windows is <prefix>/cmake/w32-pthreads/ -- a shape find_package never
+# searches. So apply the same remedy CMake's own error message suggests, and
+# do it BEFORE find_package(libobs) below, because that is the call that
+# transitively triggers find_dependency(w32-pthreads).
+#
+# macOS and Linux never reach this: the find_dependency is inside `if(MSVC)`,
+# and OS_WINDOWS gates the block regardless -- a pure no-op off Windows.
+if(OS_WINDOWS AND NOT w32-pthreads_DIR)
+    set(_stplugin_win_pthreads_dir "${CMAKE_CURRENT_SOURCE_DIR}/.deps/cmake/w32-pthreads")
+    if(EXISTS "${_stplugin_win_pthreads_dir}/w32-pthreadsConfig.cmake")
+        set(w32-pthreads_DIR "${_stplugin_win_pthreads_dir}" CACHE PATH
+            "Directory containing w32-pthreadsConfig.cmake" FORCE)
+        message(STATUS
+            "w32-pthreads_DIR not set; libobsConfig.cmake's "
+            "find_dependency(w32-pthreads REQUIRED) hits the same "
+            "OBS_CMAKE_DESTINATION=cmake search-suffix problem as libobs "
+            "itself, so pointing it directly at the from-source install: "
+            "${_stplugin_win_pthreads_dir}")
+    else()
+        # Fall back to a hand-written find module rather than letting the
+        # REQUIRED find_dependency kill the configure. cmake/windows is
+        # already on CMAKE_MODULE_PATH (see cmake/common/osconfig.cmake), so
+        # the fallback module deliberately lives in a subdirectory that is
+        # NOT -- a Findw32-pthreads.cmake sitting on the default module path
+        # would shadow OBS's own exported package on every build, and its
+        # real export is the better answer whenever it is present.
+        #
+        # Reaching here means the bootstrap install did not produce the
+        # export, so say exactly what IS in .deps/cmake/ -- the next CI log
+        # then answers the question directly instead of costing another run.
+        file(GLOB _stplugin_deps_cmake_dirs "${CMAKE_CURRENT_SOURCE_DIR}/.deps/cmake/*")
+        message(STATUS
+            "No w32-pthreadsConfig.cmake at ${_stplugin_win_pthreads_dir}; "
+            "OBS CMake packages actually installed under .deps/cmake: "
+            "'${_stplugin_deps_cmake_dirs}'. Falling back to this repo's own "
+            "Findw32-pthreads.cmake, which builds OBS::w32-pthreads straight "
+            "from the bootstrap's build artifacts.")
+        list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/windows/find-fallback")
+    endif()
+endif()
+
 find_package(libobs QUIET)
 
+# OBS::w32-pthreads can come back locationless for exactly the same reason
+# OBS::libobs can (see the block below this one): the package config loads,
+# but the per-configuration w32-pthreadsTargets-release.cmake that carries
+# IMPORTED_IMPLIB/IMPORTED_LOCATION may not have been installed. libobs links
+# it PUBLIC, so it is on this plugin's own link line and an empty location is
+# a generate-time error, not a warning. Repair it from the known install
+# destinations (obs-studio/cmake/windows/defaults.cmake:
+# OBS_EXECUTABLE_DESTINATION=bin/64bit for the DLL, OBS_LIBRARY_DESTINATION=lib
+# for the import library) -- the same repair, and the same reasoning, as the
+# OBS::libobs one.
+if(OS_WINDOWS AND TARGET OBS::w32-pthreads)
+    get_target_property(_stplugin_pthreads_implib OBS::w32-pthreads IMPORTED_IMPLIB)
+    get_target_property(_stplugin_pthreads_implib_release OBS::w32-pthreads IMPORTED_IMPLIB_RELEASE)
+    if(NOT _stplugin_pthreads_implib AND NOT _stplugin_pthreads_implib_release)
+        find_file(_stplugin_pthreads_implib_found w32-pthreads.lib
+            PATHS "${CMAKE_CURRENT_SOURCE_DIR}/.deps/lib" NO_DEFAULT_PATH)
+        find_file(_stplugin_pthreads_dll_found w32-pthreads.dll
+            PATHS "${CMAKE_CURRENT_SOURCE_DIR}/.deps/bin/64bit" NO_DEFAULT_PATH)
+        if(_stplugin_pthreads_implib_found)
+            set_target_properties(OBS::w32-pthreads PROPERTIES
+                IMPORTED_IMPLIB "${_stplugin_pthreads_implib_found}")
+            if(_stplugin_pthreads_dll_found)
+                set_target_properties(OBS::w32-pthreads PROPERTIES
+                    IMPORTED_LOCATION "${_stplugin_pthreads_dll_found}")
+            endif()
+            message(STATUS
+                "OBS::w32-pthreads had no imported location; pointed it at "
+                "${_stplugin_pthreads_implib_found}")
+        endif()
+    endif()
+endif()
+
 # The imported OBS::libobs target can come back without a location. OBS 30.0.2
 # installs libobsTargets.cmake but not the per-configuration
 # libobsTargets-<config>.cmake alongside it when libobs is built on its own,