environment variable from preset during build

Usage
1

I have an issue where the environment setting in a config preset is not used when running ninja.

$ cmake --preset default && touch CMakeLists.txt && (cd build/default; ninja)
Preset environment variables:

  MY_ENVIRONMENT_VARIABLE="Test"

-- MY_ENVIRONMENT_VARIABLE: Test
-- Configuring done (0.0s)
-- Generating done (0.0s)
-- Build files have been written to: /home/kuka/cmake_env/build/default
[0/1] Re-running CMake...
-- MY_ENVIRONMENT_VARIABLE: 
-- Configuring done (0.0s)
-- Generating done (0.0s)
-- Build files have been written to: /home/kuka/cmake_env/build/default
ninja: no work to do.

I expected that the environment variable is set during the configuration triggered by ninja.
Is this a bug or expected behavior?

See my simple project:
cmake_env.zip (691 Bytes)

Note:

  • Setting the variable again in the build preset does not help
  • running cmake --build --preset default instead of ninja works, but I still think the generated build.ninja should know this.
2

Expected behavior. Environment variables that are set by CMake at configure time don’t persist to build time. This has been the case since long before CMakePresets.json existed.

1 Like
3

Seems fair. Did not think about it this way. Thanks.

4

Just realized I misread your question. The answer is still “expected behavior”, but not for the reason I stated above.

When you cd build/default; ninja, you’re running CMake a second time without the preset active, which means the environment variable is not set. The second time MY_ENVIRONMENT_VARIABLE: is printed, it’s being printed at configure time, not build time.