FindPython: misc. fixes

Help: Fix errors regardings HINTS.
Code: Optimize Python signature cache variable to avoid unecessary searchs.

Modules/FindPython.cmake

@@ -191,8 +191,7 @@ Hints
 
 ``Python_FIND_STRATEGY``
   This variable defines how lookup will be done.
-  The ``Python_FIND_STRATEGY`` variable can be set to empty or one of the
-  following:
+  The ``Python_FIND_STRATEGY`` variable can be set to one of the following:
 
   * ``VERSION``: Try to find the most recent version in all specified
     locations.
@@ -205,8 +204,7 @@ Hints
 ``Python_FIND_REGISTRY``
   On Windows the ``Python_FIND_REGISTRY`` variable determine the order
   of preference between registry and environment variables.
-  the ``Python_FIND_REGISTRY`` variable can be set to empty or one of the
-  following:
+  the ``Python_FIND_REGISTRY`` variable can be set to one of the following:
 
   * ``FIRST``: Try to use registry before environment variables.
     This is the default.
@@ -216,8 +214,8 @@ Hints
 ``Python_FIND_FRAMEWORK``
   On macOS the ``Python_FIND_FRAMEWORK`` variable determine the order of
   preference between Apple-style and unix-style package components.
-  This variable can be set to empty or take same values as
-  :variable:`CMAKE_FIND_FRAMEWORK` variable.
+  This variable can take same values as :variable:`CMAKE_FIND_FRAMEWORK`
+  variable.
 
   .. note::
 
@@ -231,8 +229,8 @@ Hints
   ``virtualenv`` or ``conda``. It is meaningful only when a virtual environment
   is active (i.e. the ``activate`` script has been evaluated). In this case, it
   takes precedence over ``Python_FIND_REGISTRY`` and ``CMAKE_FIND_FRAMEWORK``
-  variables.  The ``Python_FIND_VIRTUALENV`` variable can be set to empty or
-  one of the following:
+  variables.  The ``Python_FIND_VIRTUALENV`` variable can be set to one of the
+  following:
 
   * ``FIRST``: The virtual environment is used before any other standard
     paths to look-up for the interpreter. This is the default.

Modules/FindPython/Support.cmake

@@ -941,15 +941,15 @@ endif()
 
 # Compute search signature
 # This signature will be used to check validity of cached variables on new search
-set (_${_PYTHON_PREFIX}_SIGNATURE "${${_PYTHON_PREFIX}_ROOT_DIR}:${${_PYTHON_PREFIX}_FIND_STRATEGY}:${${_PYTHON_PREFIX}_FIND_VIRTUALENV}")
+set (_${_PYTHON_PREFIX}_SIGNATURE "${${_PYTHON_PREFIX}_ROOT_DIR}:${_${_PYTHON_PREFIX}_FIND_STRATEGY}:${${_PYTHON_PREFIX}_FIND_VIRTUALENV}")
 if (NOT WIN32)
   string (APPEND _${_PYTHON_PREFIX}_SIGNATURE ":${${_PYTHON_PREFIX}_USE_STATIC_LIBS}:")
 endif()
 if (CMAKE_HOST_APPLE)
-  string (APPEND _${_PYTHON_PREFIX}_SIGNATURE ":${${_PYTHON_PREFIX}_FIND_FRAMEWORK}")
+  string (APPEND _${_PYTHON_PREFIX}_SIGNATURE ":${_${_PYTHON_PREFIX}_FIND_FRAMEWORK}")
 endif()
 if (CMAKE_HOST_WIN32)
-  string (APPEND _${_PYTHON_PREFIX}_SIGNATURE ":${${_PYTHON_PREFIX}_FIND_REGISTRY}")
+  string (APPEND _${_PYTHON_PREFIX}_SIGNATURE ":${_${_PYTHON_PREFIX}_FIND_REGISTRY}")
 endif()
 
 

Modules/FindPython2.cmake

@@ -140,8 +140,7 @@ Hints
 
 ``Python2_FIND_STRATEGY``
   This variable defines how lookup will be done.
-  The ``Python2_FIND_STRATEGY`` variable can be set to empty or one of the
-  following:
+  The ``Python2_FIND_STRATEGY`` variable can be set to one of the following:
 
   * ``VERSION``: Try to find the most recent version in all specified
     locations.
@@ -154,8 +153,7 @@ Hints
 ``Python2_FIND_REGISTRY``
   On Windows the ``Python2_FIND_REGISTRY`` variable determine the order
   of preference between registry and environment variables.
-  the ``Python2_FIND_REGISTRY`` variable can be set to empty or one of the
-  following:
+  the ``Python2_FIND_REGISTRY`` variable can be set to one of the following:
 
   * ``FIRST``: Try to use registry before environment variables.
     This is the default.
@@ -165,8 +163,8 @@ Hints
 ``Python2_FIND_FRAMEWORK``
   On macOS the ``Python2_FIND_FRAMEWORK`` variable determine the order of
   preference between Apple-style and unix-style package components.
-  This variable can be set to empty or take same values as
-  :variable:`CMAKE_FIND_FRAMEWORK` variable.
+  This variable can take same values as :variable:`CMAKE_FIND_FRAMEWORK`
+  variable.
 
   .. note::
 
@@ -180,8 +178,8 @@ Hints
   ``virtualenv`` or ``conda``. It is meaningful only when a virtual environment
   is active (i.e. the ``activate`` script has been evaluated). In this case, it
   takes precedence over ``Python2_FIND_REGISTRY`` and ``CMAKE_FIND_FRAMEWORK``
-  variables.  The ``Python2_FIND_VIRTUALENV`` variable can be set to empty or
-  one of the following:
+  variables.  The ``Python2_FIND_VIRTUALENV`` variable can be set to one of the
+  following:
 
   * ``FIRST``: The virtual environment is used before any other standard
     paths to look-up for the interpreter. This is the default.

Modules/FindPython3.cmake

@@ -188,8 +188,7 @@ Hints
 
 ``Python3_FIND_STRATEGY``
   This variable defines how lookup will be done.
-  The ``Python3_FIND_STRATEGY`` variable can be set to empty or one of the
-  following:
+  The ``Python3_FIND_STRATEGY`` variable can be set to one of the following:
 
   * ``VERSION``: Try to find the most recent version in all specified
     locations.
@@ -202,8 +201,7 @@ Hints
 ``Python3_FIND_REGISTRY``
   On Windows the ``Python3_FIND_REGISTRY`` variable determine the order
   of preference between registry and environment variables.
-  The ``Python3_FIND_REGISTRY`` variable can be set to empty or one of the
-  following:
+  The ``Python3_FIND_REGISTRY`` variable can be set to one of the following:
 
   * ``FIRST``: Try to use registry before environment variables.
     This is the default.
@@ -213,8 +211,8 @@ Hints
 ``Python3_FIND_FRAMEWORK``
   On macOS the ``Python3_FIND_FRAMEWORK`` variable determine the order of
   preference between Apple-style and unix-style package components.
-  This variable can be set to empty or take same values as
-  :variable:`CMAKE_FIND_FRAMEWORK` variable.
+  This variable can take same values as :variable:`CMAKE_FIND_FRAMEWORK`
+  variable.
 
   .. note::
 
@@ -228,8 +226,8 @@ Hints
   ``virtualenv`` or ``conda``. It is meaningful only when a virtual environment
   is active (i.e. the ``activate`` script has been evaluated). In this case, it
   takes precedence over ``Python3_FIND_REGISTRY`` and ``CMAKE_FIND_FRAMEWORK``
-  variables.  The ``Python3_FIND_VIRTUALENV`` variable can be set to empty or
-  one of the following:
+  variables.  The ``Python3_FIND_VIRTUALENV`` variable can be set to one of the
+  following:
 
   * ``FIRST``: The virtual environment is used before any other standard
     paths to look-up for the interpreter. This is the default.