find_*: Disable the PACKAGE_ROOT search path group for CMake 3.9

Disable the feature added by commit v3.9.0-rc1~71^2~2 (find_*: Add a new
PackageRoot search path group, 2017-05-03) and remove documentation
added by commit v3.9.0-rc1~71^2 (find_*: Add docs for PackageRoot search
path group, 2017-05-03).  Unfortunately the name `<pkg>_ROOT` may
already be set by projects for their own incompatible purposes.  Disable
the behavior change for now to fix the regression for CMake 3.9.  We can
restore it later with a policy.

In order to keep the implementation and tests working, add an
undocumented variable we can use in the tests to enable the behavior
before the policy is introduced.

Fixes: #17144

1 files changed, 6 insertions, 22 deletions

diff --git a/Help/command/FIND_XXX.txt b/Help/command/FIND_XXX.txt
index 8a0fc8d744..7db221cb88 100644
--- a/Help/command/FIND_XXX.txt
+++ b/Help/command/FIND_XXX.txt
@@ -16,7 +16,6 @@ The general signature is:
              [PATH_SUFFIXES suffix1 [suffix2 ...]]
              [DOC "cache documentation string"]
              [NO_DEFAULT_PATH]
-             [NO_PACKAGE_ROOT_PATH]
              [NO_CMAKE_PATH]
              [NO_CMAKE_ENVIRONMENT_PATH]
              [NO_SYSTEM_ENVIRONMENT_PATH]
@@ -61,10 +60,6 @@ If ``NO_DEFAULT_PATH`` is specified, then no additional paths are
 added to the search.
 If ``NO_DEFAULT_PATH`` is not specified, the search process is as follows:
 
-.. |FIND_PACKAGE_ROOT_PREFIX_PATH_XXX_SUBDIR| replace::
-   |prefix_XXX_SUBDIR| for each ``<prefix>`` in ``PackageName_ROOT`` if called
-   from within a find module
-
 .. |CMAKE_PREFIX_PATH_XXX_SUBDIR| replace::
    |prefix_XXX_SUBDIR| for each ``<prefix>`` in :variable:`CMAKE_PREFIX_PATH`
 
@@ -76,18 +71,7 @@ If ``NO_DEFAULT_PATH`` is not specified, the search process is as follows:
    |prefix_XXX_SUBDIR| for each ``<prefix>`` in
    :variable:`CMAKE_SYSTEM_PREFIX_PATH`
 
-1. If called from within a find module, search prefix paths unique to the
-   current package being found.  Specifically look in the ``PackageName_ROOT``
-   CMake and environment variables.  The package root variables are maintained
-   as a stack so if called from nested find modules, root paths from the
-   parent's find module will be searchd after paths from the current module,
-   i.e. ``CurrentPackage_ROOT``, ``ENV{CurrentPackage_ROOT}``,
-   ``ParentPackage_ROOT``, ``ENV{ParentPacakge_ROOT}``, etc.
-   This can be skipped if ``NO_PACKAGE_ROOT_PATH`` is passed.
-
-   * |FIND_PACKAGE_ROOT_PREFIX_PATH_XXX|
-
-2. Search paths specified in cmake-specific cache variables.
+1. Search paths specified in cmake-specific cache variables.
    These are intended to be used on the command line with a ``-DVAR=value``.
    The values are interpreted as :ref:`;-lists <CMake Language Lists>`.
    This can be skipped if ``NO_CMAKE_PATH`` is passed.
@@ -96,7 +80,7 @@ If ``NO_DEFAULT_PATH`` is not specified, the search process is as follows:
    * |CMAKE_XXX_PATH|
    * |CMAKE_XXX_MAC_PATH|
 
-3. Search paths specified in cmake-specific environment variables.
+2. Search paths specified in cmake-specific environment variables.
    These are intended to be set in the user's shell configuration,
    and therefore use the host's native path separator
    (``;`` on Windows and ``:`` on UNIX).
@@ -106,17 +90,17 @@ If ``NO_DEFAULT_PATH`` is not specified, the search process is as follows:
    * |CMAKE_XXX_PATH|
    * |CMAKE_XXX_MAC_PATH|
 
-4. Search the paths specified by the ``HINTS`` option.
+3. Search the paths specified by the ``HINTS`` option.
    These should be paths computed by system introspection, such as a
    hint provided by the location of another item already found.
    Hard-coded guesses should be specified with the ``PATHS`` option.
 
-5. Search the standard system environment variables.
+4. Search the standard system environment variables.
    This can be skipped if ``NO_SYSTEM_ENVIRONMENT_PATH`` is an argument.
 
    * |SYSTEM_ENVIRONMENT_PATH_XXX|
 
-6. Search cmake variables defined in the Platform files
+5. Search cmake variables defined in the Platform files
    for the current system.  This can be skipped if ``NO_CMAKE_SYSTEM_PATH``
    is passed.
 
@@ -124,7 +108,7 @@ If ``NO_DEFAULT_PATH`` is not specified, the search process is as follows:
    * |CMAKE_SYSTEM_XXX_PATH|
    * |CMAKE_SYSTEM_XXX_MAC_PATH|
 
-7. Search the paths specified by the PATHS option
+6. Search the paths specified by the PATHS option
    or in the short-hand version of the command.
    These are typically hard-coded guesses.