Help: Fix find_package search order w.r.t. globs

Add documentation to clarify that `find_package` searches paths in the
specified order and stops at the first match.  Clarify documentation of
`CMAKE_FIND_PACKAGE_SORT_*` to match the actual behavior.

Note that no behavior is actually changed, this merely improves the
documentation to reflect actual behavior rather than seeming to imply
something else.

Also, update the test to verify that what we claim in the updated
documentation is what's actually happening.

Help/command/find_package.rst

@@ -503,6 +503,42 @@ The :variable:`CMAKE_IGNORE_PATH`, :variable:`CMAKE_IGNORE_PREFIX_PATH`,
 :variable:`CMAKE_SYSTEM_IGNORE_PREFIX_PATH` variables can also cause some
 of the above locations to be ignored.
 
+Paths are searched in the order described above.  The first viable package
+configuration file found is used, even if a newer version of the package
+resides later in the list of search paths.
+
+For search paths which contain ``<name>*``, the order among matching paths
+is unspecified unless the :variable:`CMAKE_FIND_PACKAGE_SORT_ORDER` variable
+is set.  This variable, along with the
+:variable:`CMAKE_FIND_PACKAGE_SORT_DIRECTION` variable, determines the order
+in which CMake considers paths that match a single search path containing
+``<name>*``.  For example, if the file system contains the package
+configuration files
+
+::
+
+  <prefix>/example-1.2/example-config.cmake
+  <prefix>/example-1.10/example-config.cmake
+  <prefix>/share/example-2.0/example-config.cmake
+
+it is unspecified (when the aforementioned variables are unset) whether
+``find_package(example)`` will find ``example-1.2`` or ``example-1.10``
+(assuming that both are viable), but ``find_package`` will *not* find
+``example-2.0``, because one of the other two will be found first.
+
+To control the order in which ``find_package`` searches directories that match
+a glob expression, use :variable:`CMAKE_FIND_PACKAGE_SORT_ORDER` and
+:variable:`CMAKE_FIND_PACKAGE_SORT_DIRECTION`.
+For instance, to cause the above example to select ``example-1.10``,
+one can set
+
+.. code-block:: cmake
+
+  SET(CMAKE_FIND_PACKAGE_SORT_ORDER NATURAL)
+  SET(CMAKE_FIND_PACKAGE_SORT_DIRECTION DEC)
+
+before calling ``find_package``.
+
 .. versionadded:: 3.16
    Added the ``CMAKE_FIND_USE_<CATEGORY>`` variables to globally disable
    various search locations.
@@ -648,22 +684,6 @@ is acceptable the following variables are set:
   Number of version components, 0 to 4
 
 and the corresponding package configuration file is loaded.
-When multiple package configuration files are available whose version files
-claim compatibility with the version requested it is unspecified which
-one is chosen: unless the variable :variable:`CMAKE_FIND_PACKAGE_SORT_ORDER`
-is set no attempt is made to choose a highest or closest version number.
-
-To control the order in which ``find_package`` checks for compatibility use
-the two variables :variable:`CMAKE_FIND_PACKAGE_SORT_ORDER` and
-:variable:`CMAKE_FIND_PACKAGE_SORT_DIRECTION`.
-For instance in order to select the highest version one can set
-
-.. code-block:: cmake
-
-  SET(CMAKE_FIND_PACKAGE_SORT_ORDER NATURAL)
-  SET(CMAKE_FIND_PACKAGE_SORT_DIRECTION DEC)
-
-before calling ``find_package``.
 
 Package File Interface Variables
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Help/variable/CMAKE_FIND_PACKAGE_SORT_ORDER.rst

@@ -3,23 +3,26 @@ CMAKE_FIND_PACKAGE_SORT_ORDER
 
 .. versionadded:: 3.7
 
-The default order for sorting packages found using :command:`find_package`.
-It can assume one of the following values:
+The default order for sorting directories which match a search path containing
+a glob expression found using :command:`find_package`.  It can assume one of
+the following values:
 
 ``NONE``
-  Default.  No attempt is done to sort packages.
+  Default.  No attempt is done to sort directories.
   The first valid package found will be selected.
 
 ``NAME``
-  Sort packages lexicographically before selecting one.
+  Sort directories lexicographically before searching.
 
 ``NATURAL``
-  Sort packages using natural order (see ``strverscmp(3)`` manual),
+  Sort directories using natural order (see ``strverscmp(3)`` manual),
   i.e. such that contiguous digits are compared as whole numbers.
 
 Natural sorting can be employed to return the highest version when multiple
-versions of the same library are found by :command:`find_package`.  For
-example suppose that the following libraries have been found:
+versions of the same library are available to be found by
+:command:`find_package`.  For example suppose that the following libraries
+have package configuration files on disk, in a directory of the same name,
+with all such directories residing in the same parent directory:
 
 * libX-1.1.0
 * libX-1.2.9
@@ -35,4 +38,4 @@ version number ``libX-1.2.10``.
 
 The sort direction can be controlled using the
 :variable:`CMAKE_FIND_PACKAGE_SORT_DIRECTION` variable
-(by default decrescent, e.g. lib-B will be tested before lib-A).
+(by default descending, e.g. lib-B will be tested before lib-A).

Tests/FindPackageTest/CMakeLists.txt

@@ -571,6 +571,14 @@ endif()
 set(SortLib_DIR "" CACHE FILEPATH "Wipe out find results for testing." FORCE)
 unset(SortLib_VERSION)
 
+
+set(SortLib_DIR "" CACHE FILEPATH "Wipe out find results for testing." FORCE)
+FIND_PACKAGE(SortLib 4.0 CONFIG)
+IF (NOT "${SortLib_VERSION}" STREQUAL "4.0.0")
+  message(SEND_ERROR "FIND_PACKAGE_SORT_ORDER gave up too soon! ${SortLib_VERSION}")
+endif()
+unset(SortLib_VERSION)
+
 unset(CMAKE_FIND_PACKAGE_SORT_ORDER)
 unset(CMAKE_FIND_PACKAGE_SORT_DIRECTION)
 set(CMAKE_PREFIX_PATH )

Tests/FindPackageTest/lib/SortLib-4.0.0/SortLibConfig.cmake

@@ -0,0 +1,2 @@
+set(SORT_LIB_VERSION 4.0.0)
+message("SortLib 4.0.0 config reached")

Tests/FindPackageTest/lib/SortLib-4.0.0/SortLibConfigVersion.cmake

@@ -0,0 +1,9 @@
+set(PACKAGE_VERSION 4.0.0)
+if(PACKAGE_FIND_VERSION_MAJOR EQUAL 4)
+  if(PACKAGE_FIND_VERSION_MINOR EQUAL 0)
+    set(PACKAGE_VERSION_COMPATIBLE 1)
+    if(PACKAGE_FIND_VERSION_PATCH EQUAL 0)
+      set(PACKAGE_VERSION_EXACT 1)
+    endif()
+  endif()
+endif()