CMake Presets vs CLion CMake Profiles: which governs toolchain selection when both target the same configure step?

Direct Answer

When a CMake preset and a CLion CMake Profile both specify a toolchain for the same configure step, CLion’s profile wins. The IDE reads the preset, then injects the profile’s -DCMAKE_TOOLCHAIN_FILE, generator, and cache variables into the final cmake command line. Those profile values appear after the preset-derived ones, so they override them in the generated CMakeCache.txt.

Effect of Switching Profiles Without a Cache Reset

Because CMake sets certain variables (e.g., CMAKE_C_COMPILER, CMAKE_CXX_COMPILER, and the generator) only during the initial configuration of a build directory, changing profiles while the cache remains will leave stale entries. The new profile may partially apply, but the cache still contains the old toolchain path, leading to a mixed state that can cause build failures or inconsistent binaries.

Locking the Preset as Authoritative

JetBrains does not provide a documented way to make a preset the sole source of truth for toolchain selection inside the IDE. The profile is intentionally the local, per‑developer override layer. To enforce CI/CD parity you should:

1. Define the Docker‑based toolchain only in CMakePresets.json (or CMakeUserPresets.json for machine‑specific paths).
2. Create CLion profiles that reference the preset by name but leave toolchain, generator, and cache variables blank.
3. Require a full cache reset (delete the cmake-build-* directory or use File → Invalidate Caches) whenever the preset changes.

Verification Steps

1. Open the CMake tool window, switch to the Output tab, and copy the full cmake command line shown at the start of a configure run.
2. Inspect CMAKE_C_COMPILER and CMAKE_CXX_COMPILER in the generated CMakeCache.txt and confirm they match the profile’s toolchain, not the preset’s.
3. Delete the build directory, reload the project, and verify the cache now reflects only the preset when the profile has no overrides.

Diagnostic Detail Needed

Which CLion version are you using? The merge logic between CMakeUserPresets.json and IDE profiles changed between 2023.1 and 2024.2, and knowing the exact version can confirm whether the profile override is guaranteed or version‑dependent.