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CMP0053
-------
Simplify variable reference and escape sequence evaluation.
CMake 3.1 introduced a much faster implementation of evaluation of the
:ref:`Variable References` and :ref:`Escape Sequences` documented in the
:manual:`cmake-language(7)` manual. While the behavior is identical
to the legacy implementation in most cases, some corner cases were
cleaned up to simplify the behavior. Specifically:
* Expansion of ``@VAR@`` reference syntax defined by the
:command:`configure_file` and :command:`string(CONFIGURE)`
commands is no longer performed in other contexts.
* Literal ``${VAR}`` reference syntax may contain only
alphanumeric characters (``A-Z``, ``a-z``, ``0-9``) and
the characters ``_``, ``.``, ``/``, ``-``, and ``+``.
Variables with other characters in their name may still
be referenced indirectly, e.g.
.. code-block:: cmake
set(varname "otherwise & disallowed $ characters")
message("${${varname}}")
* The setting of policy :policy:`CMP0010` is not considered,
so improper variable reference syntax is always an error.
* More characters are allowed to be escaped in variable names.
Previously, only ``()#" \@^`` were valid characters to
escape. Now any non-alphanumeric, non-semicolon, non-NUL
character may be escaped following the ``escape_identity``
production in the :ref:`Escape Sequences` section of the
:manual:`cmake-language(7)` manual.
The ``OLD`` behavior for this policy is to honor the legacy behavior for
variable references and escape sequences. The ``NEW`` behavior is to
use the simpler variable expansion and escape sequence evaluation rules.
This policy was introduced in CMake version 3.1.
CMake version |release| warns when the policy is not set and uses
``OLD`` behavior. Use the :command:`cmake_policy` command to set
it to ``OLD`` or ``NEW`` explicitly.
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