find_package: Use PackageName_ROOT variables as search prefixes

This feature was originally added by commit v3.9.0-rc1~71^2~2 (find_*:
Add a new PackageRoot search path group, 2017-05-03) and documented by
commit v3.9.0-rc1~71^2 (find_*: Add docs for PackageRoot search path
group, 2017-05-03).  However, we had to disable the feature and remove
the documentation in commit v3.9.1~2^2 (find_*: Disable the PACKAGE_ROOT
search path group for CMake 3.9, 2017-08-08) due to breaking projects
that used `PackageName_ROOT` variables themselves.

Add policy `CMP0074` to restore the `PackageName_ROOT` variable behavior
in a compatible way.  Also revise the stack of root paths to store the
paths themselves rather than the package names.  This way the policy can
be considered at the `find_package` call site instead of individual
`find_` calls inside a find module.

Co-Author: Chuck Atkins <chuck.atkins@kitware.com>
Issue: #17144

1 files changed, 46 insertions, 0 deletions

diff --git a/Tests/RunCMake/find_package/CMP0074-common.cmake b/Tests/RunCMake/find_package/CMP0074-common.cmake
new file mode 100644
index 0000000..bfacd82
--- /dev/null
+++ b/Tests/RunCMake/find_package/CMP0074-common.cmake
@@ -0,0 +1,46 @@
+# (includer selects CMP0074)
+cmake_policy(SET CMP0057 NEW)
+list(INSERT CMAKE_MODULE_PATH 0 ${CMAKE_CURRENT_SOURCE_DIR}/PackageRoot)
+set(PackageRoot_BASE ${CMAKE_CURRENT_SOURCE_DIR}/PackageRoot)
+
+function(PrintPath label path)
+  string(REPLACE "${PackageRoot_BASE}" "<base>" out "${path}")
+  message("${label}${out}")
+endfunction()
+
+macro(CleanUpPackageRootTest)
+  unset(Foo_ROOT)
+  unset(ENV{Foo_ROOT})
+  unset(FOO_TEST_FILE_FOO)
+  unset(FOO_TEST_FILE_ZOT)
+  unset(FOO_TEST_PATH_FOO)
+  unset(FOO_TEST_PATH_ZOT)
+  unset(FOO_TEST_PROG_FOO)
+  unset(FOO_TEST_FILE_FOO CACHE)
+  unset(FOO_TEST_FILE_ZOT CACHE)
+  unset(FOO_TEST_PATH_FOO CACHE)
+  unset(FOO_TEST_PATH_ZOT CACHE)
+  unset(FOO_TEST_PROG_FOO CACHE)
+endmacro()
+
+macro(RunPackageRootTest)
+  message("----------")
+  PrintPath("Foo_ROOT      :" "${Foo_ROOT}")
+  PrintPath("ENV{Foo_ROOT} :" "$ENV{Foo_ROOT}")
+  message("")
+
+  find_package(Foo)
+  message("find_package(Foo)")
+  PrintPath("FOO_TEST_FILE_FOO :" "${FOO_TEST_FILE_FOO}")
+  PrintPath("FOO_TEST_FILE_ZOT :" "${FOO_TEST_FILE_ZOT}")
+  PrintPath("FOO_TEST_PATH_FOO :" "${FOO_TEST_PATH_FOO}")
+  PrintPath("FOO_TEST_PATH_ZOT :" "${FOO_TEST_PATH_ZOT}")
+  PrintPath("FOO_TEST_PROG_FOO :" "${FOO_TEST_PROG_FOO}")
+  CleanUpPackageRootTest()
+  message("")
+endmacro()
+
+set(Foo_ROOT      ${PackageRoot_BASE}/foo/cmake_root)
+set(ENV{Foo_ROOT} ${PackageRoot_BASE}/foo/env_root)
+RunPackageRootTest()
+message("----------")