Merge topic 'function-var-current'

24fdd51f45 Refactor: Replace CMAKE_CURRENT_LIST_DIR with CMAKE_CURRENT_FUNCTION_LIST_DIR
90e3e2a777 cmFunctionCommand: Introduce `CMAKE_CURRENT_FUNCTION*` variables
dd54290dab Refactor: Modernize `function` command

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Ben Boeckel <ben.boeckel@kitware.com>
Merge-request: !4000

Help/variable/CMAKE_CURRENT_FUNCTION.rst

@@ -0,0 +1,6 @@
+CMAKE_CURRENT_FUNCTION
+----------------------
+
+When executing code inside a :command:`function`, this variable
+contains the name of the current function.  It can be used for
+diagnostic or debug messages.

Help/variable/CMAKE_CURRENT_FUNCTION_LIST_DIR.rst

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+CMAKE_CURRENT_FUNCTION_LIST_DIR
+-------------------------------
+
+When executing code inside a :command:`function`, this variable
+contains the full directory of the listfile defining the current function.
+
+It is quite common practice in CMake that modules use some additional files
+(e.g., templates to render).  And the code typically did the following:
+
+.. code-block:: cmake
+    :caption: Bad
+
+    set(_THIS_MODULE_BASE_DIR "${CMAKE_CURRENT_LIST_DIR}")
+
+    function(foo)
+      configure_file(
+        "${_THIS_MODULE_BASE_DIR}/some.template.in"
+        some.output
+      )
+    endfunction()
+
+Using this variable inside a function eliminates the neccessity of the
+additional one with "global" scope:
+
+.. code-block:: cmake
+    :caption: Good
+
+    function(foo)
+      configure_file(
+        "${CMAKE_CURRENT_FUNCTION_LIST_DIR}/some.template.in"
+        some.output
+      )
+    endfunction()

Help/variable/CMAKE_CURRENT_FUNCTION_LIST_FILE.rst

@@ -0,0 +1,5 @@
+CMAKE_CURRENT_FUNCTION_LIST_FILE
+--------------------------------
+
+When executing code inside a :command:`function`, this variable
+contains the full path to the listfile declaring a current function.

Help/variable/CMAKE_CURRENT_FUNCTION_LIST_LINE.rst

@@ -0,0 +1,5 @@
+CMAKE_CURRENT_FUNCTION_LIST_LINE
+--------------------------------
+
+When executing code inside a :command:`function`, this variable
+contains the line number in the listfile where a current function has defined.