find_package: Save/restore PACKAGE_PREFIX_DIR

Package configuration files generated by `configure_package_config_file`
set this variable in `@PACKAGE_INIT@` and then use it later.  There may
be intervening calls to `find_package`, e.g., via `find_dependency`.
If the loaded package also used `configure_package_config_file`, it
may change the value of `PACKAGE_PREFIX_DIR`.  Explicitly save and
restore the value to avoid this.

Fixes: #25827

3 files changed, 51 insertions, 0 deletions

diff --git a/Tests/RunCMake/CMakePackage/NestedConfigFile-stdout.txt b/Tests/RunCMake/CMakePackage/NestedConfigFile-stdout.txt
new file mode 100644
index 0000000..cdb3384
--- /dev/null
+++ b/Tests/RunCMake/CMakePackage/NestedConfigFile-stdout.txt
@@ -0,0 +1,6 @@
+(-- )?Before find_dependency: PACKAGE_PREFIX_DIR = .*/Tests/RunCMake/CMakePackage/NestedConfigFile-build/install_pkg_b
+(-- )?Hello from pkg_a
+(-- )?Leaving pkg_a-config\.cmake with PACKAGE_PREFIX_DIR = .*/Tests/RunCMake/CMakePackage/NestedConfigFile-build/install_pkg_a
+(-- )?After find_dependency:  PACKAGE_PREFIX_DIR = .*/Tests/RunCMake/CMakePackage/NestedConfigFile-build/install_pkg_b
+(-- )?Hello from pkg_b
+(-- )?Leaving pkg_b-config\.cmake with PACKAGE_PREFIX_DIR = .*/Tests/RunCMake/CMakePackage/NestedConfigFile-build/install_pkg_b
diff --git a/Tests/RunCMake/CMakePackage/NestedConfigFile.cmake b/Tests/RunCMake/CMakePackage/NestedConfigFile.cmake
new file mode 100644
index 0000000..2eeaebb
--- /dev/null
+++ b/Tests/RunCMake/CMakePackage/NestedConfigFile.cmake
@@ -0,0 +1,43 @@
+set(CMAKE_INSTALL_DATADIR share)
+
+include(CMakePackageConfigHelpers)
+
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/pkg_a-config.cmake.in [[
+@PACKAGE_INIT@
+include("@PACKAGE_CMAKE_INSTALL_DATADIR@/pkg_a_included.cmake")
+message(STATUS "Leaving pkg_a-config.cmake with PACKAGE_PREFIX_DIR = ${PACKAGE_PREFIX_DIR}")
+]])
+configure_package_config_file(
+  ${CMAKE_CURRENT_BINARY_DIR}/pkg_a-config.cmake.in
+  ${CMAKE_CURRENT_BINARY_DIR}/install_pkg_a/pkg_a-config.cmake
+  INSTALL_DESTINATION .
+  PATH_VARS CMAKE_INSTALL_DATADIR
+)
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/install_pkg_a/share/pkg_a_included.cmake
+  [[message(STATUS "Hello from pkg_a")]]
+)
+
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/pkg_b-config.cmake.in [[
+@PACKAGE_INIT@
+include(CMakeFindDependencyMacro)
+message(STATUS "Before find_dependency: PACKAGE_PREFIX_DIR = ${PACKAGE_PREFIX_DIR}")
+find_dependency(pkg_a NO_DEFAULT_PATH
+    PATHS "@CMAKE_CURRENT_BINARY_DIR@/install_pkg_a"
+)
+message(STATUS "After find_dependency:  PACKAGE_PREFIX_DIR = ${PACKAGE_PREFIX_DIR}")
+include("@PACKAGE_CMAKE_INSTALL_DATADIR@/pkg_b_included.cmake")
+message(STATUS "Leaving pkg_b-config.cmake with PACKAGE_PREFIX_DIR = ${PACKAGE_PREFIX_DIR}")
+]])
+configure_package_config_file(
+  ${CMAKE_CURRENT_BINARY_DIR}/pkg_b-config.cmake.in
+  ${CMAKE_CURRENT_BINARY_DIR}/install_pkg_b/pkg_b-config.cmake
+  INSTALL_DESTINATION .
+  PATH_VARS CMAKE_INSTALL_DATADIR
+)
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/install_pkg_b/share/pkg_b_included.cmake
+  [[message(STATUS "Hello from pkg_b")]]
+)
+
+find_package(pkg_b REQUIRED NO_DEFAULT_PATH
+  PATHS ${CMAKE_CURRENT_BINARY_DIR}/install_pkg_b
+)
diff --git a/Tests/RunCMake/CMakePackage/RunCMakeTest.cmake b/Tests/RunCMake/CMakePackage/RunCMakeTest.cmake
index 3b4bef5..c4a05e3 100644
--- a/Tests/RunCMake/CMakePackage/RunCMakeTest.cmake
+++ b/Tests/RunCMake/CMakePackage/RunCMakeTest.cmake
@@ -4,6 +4,8 @@ if(NOT RunCMake_GENERATOR_IS_MULTI_CONFIG)
   set(maybe_CMAKE_BUILD_TYPE -DCMAKE_BUILD_TYPE=Release)
 endif()
 
+run_cmake_with_options(NestedConfigFile ${maybe_CMAKE_BUILD_TYPE})
+
 function(apple_export platform system_name archs sysroot)
   set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/apple-export-${platform}-build)
   string(REPLACE ";" "\\;" archs "${archs}")