CMake ignore custom toolchain file. (Cache is cleaned)

Question

Windows 10, CMake 3.19.1

Im trying to compile test project with XC8 compiler, CMake and custom toolchain (third party). Link: Toolchain repository

Toolchains quick guide says to only add two strings at top of my CMakeLists.txt. So ive got the next CMakeLists.txt:

   project(Test)

   # set up the Microchip cross toolchain
   set(CMAKE_TOOLCHAIN_FILE ./external/cmake-microchip/toolchain.cmake)

   # set the default MCU model
   set(MICROCHIP_MCU PIC18F97J60)

   add_executable(main main.c)

But occasionaly, every time CMake generation output starts with:

-- Building for: Visual Studio 16 2019
-- The C compiler identification is MSVC 19.28.29333.0
-- The CXX compiler identification is MSVC 19.28.29333.0
..... more

And i havent any Makefile in the output folder. Also im try to run CMake with -G "Unix makefiles". And makefile been generated, with wrong output and any trace of custom toolchain use. Output been:

-- The C compiler identification is GNU 9.2.0
-- The CXX compiler identification is GNU 9.2.0
-- Detecting C compiler ABI info

Every CMake generation try, im cleanup the output folder. Why custom toolchain doesnt starts?

Answer 1

The variable CMAKE_TOOLCHAIN_FILE should be set before the first project() call:

cmake_minimum_required(VERSION <..>)

# set up the Microchip cross toolchain
set(CMAKE_TOOLCHAIN_FILE ./external/cmake-microchip/toolchain.cmake)

project(Test)

# set the default MCU model
set(MICROCHIP_MCU PIC18F97J60)

add_executable(main main.c)

When first project() call is processed, CMake automatically calls the script specified in CMAKE_TOOLCHAIN_FILE.

Note, that preferred way is to not hardcode path to the toolchain in the CMakeLists.txt but pass -DCMAKE_TOOLCHAIN_FILE=/path/to/toolchain option to the cmake.