Merge topic 'doc_varreq'

9e1b30121f Help:toolchain: refer to CheckSourceCompiles
cf48022dc5 Help:Check*: include CMAKE_REQUIRED_* vars to dedupe

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !8300

1 files changed, 23 insertions, 11 deletions

diff --git a/Modules/CheckCCompilerFlag.cmake b/Modules/CheckCCompilerFlag.cmake
index 696096d8bb..cd89a55a92 100644
--- a/Modules/CheckCCompilerFlag.cmake
+++ b/Modules/CheckCCompilerFlag.cmake
@@ -11,25 +11,37 @@ Check whether the C compiler supports a given flag.
 
   .. code-block:: cmake
 
-    check_c_compiler_flag(<flag> <var>)
+    check_c_compiler_flag(<flag> <resultVar>)
 
   Check that the ``<flag>`` is accepted by the compiler without
   a diagnostic.  Stores the result in an internal cache entry
-  named ``<var>``.
-
-This command temporarily sets the ``CMAKE_REQUIRED_DEFINITIONS`` variable
-and calls the ``check_c_source_compiles`` macro from the
-:module:`CheckCSourceCompiles` module.  See documentation of that
-module for a listing of variables that can otherwise modify the build.
+  named ``<resultVar>``.
 
 A positive result from this check indicates only that the compiler did not
 issue a diagnostic message when given the flag.  Whether the flag has any
 effect or even a specific one is beyond the scope of this module.
 
-.. note::
-  Since the :command:`try_compile` command forwards flags from variables
-  like :variable:`CMAKE_C_FLAGS <CMAKE_<LANG>_FLAGS>`, unknown flags
-  in such variables may cause a false negative for this check.
+The check is only performed once, with the result cached in the variable named
+by ``<resultVar>``. Every subsequent CMake run will re-use this cached value
+rather than performing the check again, even if the ``<code>`` changes. In
+order to force the check to be re-evaluated, the variable named by
+``<resultVar>`` must be manually removed from the cache.
+
+The compile and link commands can be influenced by setting any of the
+following variables prior to calling ``check_c_compiler_flag()``
+
+.. include:: /module/CMAKE_REQUIRED_FLAGS.txt
+
+.. include:: /module/CMAKE_REQUIRED_DEFINITIONS.txt
+
+.. include:: /module/CMAKE_REQUIRED_INCLUDES.txt
+
+.. include:: /module/CMAKE_REQUIRED_LINK_OPTIONS.txt
+
+.. include:: /module/CMAKE_REQUIRED_LIBRARIES.txt
+
+.. include:: /module/CMAKE_REQUIRED_QUIET.txt
+
 #]=======================================================================]
 
 include_guard(GLOBAL)