1 files changed, 101 insertions, 37 deletions
diff --git a/Help/command/macro.rst b/Help/command/macro.rst
index 6bee69c73..05e5d79ac 100644
--- a/Help/command/macro.rst
+++ b/Help/command/macro.rst
@@ -1,27 +1,66 @@
 macro
 -----
 
-Start recording a macro for later invocation as a command::
-
-  macro(<name> [arg1 [arg2 [arg3 ...]]])
-    COMMAND1(ARGS ...)
-    COMMAND2(ARGS ...)
-    ...
-  endmacro(<name>)
-
-Define a macro named ``<name>`` that takes arguments named ``arg1``,
-``arg2``, ``arg3``, (...).
-Commands listed after macro, but before the matching
-:command:`endmacro()`, are not invoked until the macro is invoked.
-When it is invoked, the commands recorded in the macro are first
-modified by replacing formal parameters (``${arg1}``) with the arguments
-passed, and then invoked as normal commands.
+Start recording a macro for later invocation as a command
+
+.. code-block:: cmake
+
+  macro(<name> [<arg1> ...])
+    <commands>
+  endmacro()
+
+Defines a macro named ``<name>`` that takes arguments named
+``<arg1>``, ... Commands listed after macro, but before the
+matching :command:`endmacro()`, are not executed until the macro
+is invoked.
+
+Per legacy, the :command:`endmacro` command admits an optional
+``<name>`` argument. If used, it must be a verbatim repeat of the
+argument of the opening ``macro`` command.
+
+See the :command:`cmake_policy()` command documentation for the behavior
+of policies inside macros.
+
+See the :ref:`Macro vs Function` section below for differences
+between CMake macros and :command:`functions <function>`.
+
+Invocation
+^^^^^^^^^^
+
+The macro invocation is case-insensitive. A macro defined as
+
+.. code-block:: cmake
+
+  macro(foo)
+    <commands>
+  endmacro()
+
+can be invoked through any of
+
+.. code-block:: cmake
+
+  foo()
+  Foo()
+  FOO()
+
+and so on. However, it is strongly recommended to stay with the
+case chosen in the macro definition.  Typically macros use
+all-lowercase names.
+
+Arguments
+^^^^^^^^^
+
+When a macro is invoked, the commands recorded in the macro are
+first modified by replacing formal parameters (``${arg1}``, ...)
+with the arguments passed, and then invoked as normal commands.
+
 In addition to referencing the formal parameters you can reference the
 values ``${ARGC}`` which will be set to the number of arguments passed
 into the function as well as ``${ARGV0}``, ``${ARGV1}``, ``${ARGV2}``,
 ...  which will have the actual values of the arguments passed in.
 This facilitates creating macros with optional arguments.
-Additionally ``${ARGV}`` holds the list of all arguments given to the
+
+Furthermore, ``${ARGV}`` holds the list of all arguments given to the
 macro and ``${ARGN}`` holds the list of arguments past the last expected
 argument.
 Referencing to ``${ARGV#}`` arguments beyond ``${ARGC}`` have undefined
@@ -29,48 +68,73 @@ behavior. Checking that ``${ARGC}`` is greater than ``#`` is the only
 way to ensure that ``${ARGV#}`` was passed to the function as an extra
 argument.
 
-See the :command:`cmake_policy()` command documentation for the behavior
-of policies inside macros.
+.. _`Macro vs Function`:
+
+Macro vs Function
+^^^^^^^^^^^^^^^^^
 
-Macro Argument Caveats
-^^^^^^^^^^^^^^^^^^^^^^
+The ``macro`` command is very similar to the :command:`function` command.
+Nonetheless, there are a few important differences.
 
-Note that the parameters to a macro and values such as ``ARGN`` are
-not variables in the usual CMake sense.  They are string
-replacements much like the C preprocessor would do with a macro.
-Therefore you will NOT be able to use commands like::
+In a function, ``ARGN``, ``ARGC``, ``ARGV`` and ``ARGV0``, ``ARGV1``, ...
+are true variables in the usual CMake sense.  In a macro, they are not,
+they are string replacements much like the C preprocessor would do
+with a macro.  This has a number of consequences, as explained in
+the :ref:`Argument Caveats` section below.
+
+Another difference between macros and functions is the control flow.
+A function is executed by transferring control from the calling
+statement to the function body.  A macro is executed as if the macro
+body were pasted in place of the calling statement.  This has the
+consequence that a :command:`return()` in a macro body does not
+just terminate execution of the macro; rather, control is returned
+from the scope of the macro call.  To avoid confusion, it is recommended
+to avoid :command:`return()` in macros altogether.
+
+.. _`Argument Caveats`:
+
+Argument Caveats
+^^^^^^^^^^^^^^^^
+
+Since ``ARGN``, ``ARGC``, ``ARGV``, ``ARGV0`` etc. are not variables,
+you will NOT be able to use commands like
+
+.. code-block:: cmake
 
  if(ARGV1) # ARGV1 is not a variable
  if(DEFINED ARGV2) # ARGV2 is not a variable
  if(ARGC GREATER 2) # ARGC is not a variable
  foreach(loop_var IN LISTS ARGN) # ARGN is not a variable
 
-In the first case, you can use ``if(${ARGV1})``.
-In the second and third case, the proper way to check if an optional
-variable was passed to the macro is to use ``if(${ARGC} GREATER 2)``.
-In the last case, you can use ``foreach(loop_var ${ARGN})`` but this
-will skip empty arguments.
-If you need to include them, you can use::
+In the first case, you can use ``if(${ARGV1})``.  In the second and
+third case, the proper way to check if an optional variable was
+passed to the macro is to use ``if(${ARGC} GREATER 2)``.  In the
+last case, you can use ``foreach(loop_var ${ARGN})`` but this will
+skip empty arguments.  If you need to include them, you can use
+
+.. code-block:: cmake
 
  set(list_var "${ARGN}")
  foreach(loop_var IN LISTS list_var)
 
 Note that if you have a variable with the same name in the scope from
 which the macro is called, using unreferenced names will use the
-existing variable instead of the arguments. For example::
+existing variable instead of the arguments. For example:
+
+.. code-block:: cmake
 
- macro(_BAR)
+ macro(bar)
    foreach(arg IN LISTS ARGN)
-     [...]
+     <commands>
    endforeach()
  endmacro()
 
- function(_FOO)
-   _bar(x y z)
+ function(foo)
+   bar(x y z)
  endfunction()
 
- _foo(a b c)
+ foo(a b c)
 
-Will loop over ``a;b;c`` and not over ``x;y;z`` as one might be expecting.
+Will loop over ``a;b;c`` and not over ``x;y;z`` as one might have expected.
 If you want true CMake variables and/or better CMake scope control you
 should look at the function command.