Merge topic 'mark_as_advanced-without-cache'

3ec82b713e cmMarkAsAdvancedCommand: ignore variables which don't exist in the cache
701a5c60e0 cmake: avoid marking local or unused variables as advanced
af158149e7 FindOpenSSL: do not mark a local variable as advanced
74f659f1f2 FindCurses: only mark CURSES_EXTRA_LIBRARY when it is used
7e2ae4e96d FindOpenGL: only mark declared cache variables as advanced
7cc02a0c29 FindLua: only mark LUA_MATH_LIBRARY as advanced if required
85cd26b8a6 FindBoost: only mark Boost_DIR as advanced if defined
338c7916ba CTest: avoid marking undeclared cache variables as advanced
...

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !4150

4 files changed, 34 insertions, 0 deletions

diff --git a/Help/command/mark_as_advanced.rst b/Help/command/mark_as_advanced.rst
index 5712fb4..e52e623 100644
--- a/Help/command/mark_as_advanced.rst
+++ b/Help/command/mark_as_advanced.rst
@@ -22,3 +22,9 @@ If neither ``FORCE`` nor ``CLEAR`` is specified,
 new values will be marked as advanced, but if a
 variable already has an advanced/non-advanced state,
 it will not be changed.
+
+.. note::
+
+  Policy :policy:`CMP0102` affects the behavior of the ``mark_as_advanced``
+  call. When set to ``NEW``, variables passed to this command which are not
+  already in the cache are ignored. See policy :policy:`CMP0102`.
diff --git a/Help/manual/cmake-policies.7.rst b/Help/manual/cmake-policies.7.rst
index 53cf264..c256250 100644
--- a/Help/manual/cmake-policies.7.rst
+++ b/Help/manual/cmake-policies.7.rst
@@ -57,6 +57,7 @@ Policies Introduced by CMake 3.17
 .. toctree::
    :maxdepth: 1
 
+   CMP0102: mark_as_advanced() does nothing if a cache entry does not exist. </policy/CMP0102>
    CMP0101: target_compile_options honors BEFORE keyword in all scopes. </policy/CMP0101>
    CMP0100: Let AUTOMOC and AUTOUIC process .hh header files. </policy/CMP0100>
    CMP0099: Link properties are transitive over private dependency on static libraries. </policy/CMP0099>
diff --git a/Help/policy/CMP0102.rst b/Help/policy/CMP0102.rst
new file mode 100644
index 0000000..9859006
--- /dev/null
+++ b/Help/policy/CMP0102.rst
@@ -0,0 +1,25 @@
+CMP0102
+-------
+
+The :command:`mark_as_advanced` command no longer creates a cache entry if one
+does not already exist.
+
+In CMake 3.16 and below, if a variable was not defined at all or just defined
+locally, the :command:`mark_as_advanced` command would create a new cache
+entry with an ``UNINITIALIZED`` type and no value. When a :command:`find_path`
+(or other similar ``find_`` command) would next run, it would find this
+undefined cache entry and set it up with an empty string value. This process
+would end up deleting the local variable in the process (due to the way the
+cache works), effectively clearing any stored ``find_`` results that were only
+available in the local scope.
+
+The ``OLD`` behavior for this policy is to create the empty cache definition.
+The ``NEW`` behavior of this policy is to ignore variables which do not
+already exist in the cache.
+
+This policy was introduced in CMake version 3.17.  Use the
+:command:`cmake_policy` command to set it to ``OLD`` or ``NEW`` explicitly.
+Unlike many policies, CMake version |release| does *not* warn
+when this policy is not set and simply uses ``OLD`` behavior.
+
+.. include:: DEPRECATED.txt
diff --git a/Help/variable/CMAKE_POLICY_WARNING_CMPNNNN.rst b/Help/variable/CMAKE_POLICY_WARNING_CMPNNNN.rst
index fc52e7b..de71d0e 100644
--- a/Help/variable/CMAKE_POLICY_WARNING_CMPNNNN.rst
+++ b/Help/variable/CMAKE_POLICY_WARNING_CMPNNNN.rst
@@ -23,6 +23,8 @@ warn by default:
   policy :policy:`CMP0082`.
 * ``CMAKE_POLICY_WARNING_CMP0089`` controls the warning for
   policy :policy:`CMP0089`.
+* ``CMAKE_POLICY_WARNING_CMP0102`` controls the warning for
+  policy :policy:`CMP0102`.
 
 This variable should not be set by a project in CMake code.  Project
 developers running CMake may set this variable in their cache to