CMP0053ΒΆ
Warning
The OLD behavior of this policy was removed
in CMake version 4.0.
This policy must be set to NEW by a call to
cmake_minimum_required() or cmake_policy().
Added in version 3.1.
Simplify variable reference and escape sequence evaluation.
CMake 3.1 introduced a much faster implementation of evaluation of the
Variable References and Escape Sequences documented in the
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- configure_file()and- 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- +. Note that- $is technically allowed in the- NEWbehavior, but is invalid for- OLDbehavior. This is due to an oversight during the implementation of- CMP0053and its use as a literal variable reference is discouraged for this reason. Variables with other characters in their name may still be referenced indirectly, e.g.- set(varname "otherwise & disallowed $ characters") message("${${varname}}") 
- The setting of policy - CMP0010is 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_identityproduction in the Escape Sequences section of the- 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.
Prior to removal in CMake version 4.0, it could be
set by cmake_policy() or cmake_minimum_required().
If it was not set, CMake warned, and used OLD behavior.
