[bug] CMakeToolchain user_toolchain invalid escape character on Windows

Environment Details (include every applicable attribute)

• Operating System+version: Windows servercore 2019
• Compiler+version: MSVC 192
• Conan version: 1.45.0
• Python version: 3.10.2

Steps to reproduce (Include if Applicable)

Create a package for providing a CMake toolchain file via tool_requires and enable short_paths on Windows. When building a test package on Windows the following error occurs, which looks like it could be fixed by using forward slashes in the CMake toolchain instead of backslashes when including the user_toolchain.

Logs (Executed commands with output) (Include/Attach if Applicable)

my-conan-toolchain/c8783856@my-conan-remote/testing (test package): Calling build()
my-conan-toolchain/c8783856@my-conan-remote/testing (test package): CMake command: cmake -G "Ninja" -DCMAKE_TOOLCHAIN_FILE="C:/builds/components/conan-toolchain/test_package/build/79d6417e7f7125abb0ee5e356ea18ea032664329/conan_toolchain.cmake" -DCMAKE_INSTALL_PREFIX="C:/builds/components/conan-toolchain/test_package/build/79d6417e7f7125abb0ee5e356ea18ea032664329/package" "C:\builds\components\conan-toolchain\test_package"
**********************************************************************
** Visual Studio 2019 Developer Command Prompt v16.11.9
** Copyright (c) 2021 Microsoft Corporation
**********************************************************************
[vcvarsall.bat] Environment initialized for: 'x64'
Using Conan toolchain: C:/builds/components/conan-toolchain/test_package/build/79d6417e7f7125abb0ee5e356ea18ea032664329/conan_toolchain.cmake.
CMake Error at build/79d6417e7f7125abb0ee5e356ea18ea032664329/conan_toolchain.cmake:19 (include):
  Syntax error in cmake code at
    C:/builds/components/conan-toolchain/test_package/build/79d6417e7f7125abb0ee5e356ea18ea032664329/conan_toolchain.cmake:19
  when parsing string
    C:\.conan\193a6c\1\conan_toolchain.cmake
  Invalid character escape '\1'.
Call Stack (most recent call first):
  C:/Program Files/CMake/share/cmake-3.22/Modules/CMakeDetermineSystem.cmake:124 (include)
  CMakeLists.txt:3 (project)
CMake Error: CMake was unable to find a build program corresponding to "Ninja".  CMAKE_MAKE_PROGRAM is not set.  You probably need to select a different build tool.
CMake Error: CMAKE_CXX_COMPILER not set, after EnableLanguage
-- Configuring incomplete, errors occurred!

[memsharded]

Oh, that makes sense indeed, if you are directly providing unsanitized paths, then there is little that Conan can do (the template could try to do it too, but the template can also be overriden, so probably not worth the effort). As the solution is straightforward and is reasonable, I think we can close this, thanks for the feedback!

[SpaceIm]

@ericLemanissier In all CCI recipes migrated to conan v2, I add .replace("\\", "/") to all paths injected into variables of CMakeToolchain, not sure it’s worth to expose a conan helper for this.