cmake: Use NUTTX(_DIR/_BIN_DIR) instead CMAKE(_SRC_DIR/_BIN_DIR)

[acassis]

Summary

This change fixes NuttX’s CMake support when NuttX is embedded in another project via add_subdirectory(). CMake’s CMAKE_SOURCE_DIR and CMAKE_BINARY_DIR refer to the outermost project, causing NuttX to access its .config, generated files, host tools, and build artifacts in the parent project’s directories. The fix introduces NUTTX_DIR and NUTTX_BINARY_DIR, based on CMAKE_CURRENT_SOURCE_DIR and CMAKE_CURRENT_BINARY_DIR, and consistently uses them for NuttX self-references while preserving existing standalone builds. It fixes the Kconfig initialization failure reported in #19697 and allows an embedded sim:nsh build to configure, build, and boot successfully. The change affects only the CMake build system (not Make or Kconfig defaults), requires the corresponding nuttx-apps change, and does not extend add_subdirectory() support to cross-compiled non-sim boards due to CMake’s toolchain-file limitation.

Depends-on: apache/nuttx-apps#3711

Impact

Fixes #19697

Testing

  Test performed

  Reproduced the reported scenario end-to-end: a parent project pulling NuttX in
  as a git submodule/third-party dependency via add_subdirectory(), configured
  from the top level.

  Setup (parent_proj/CMakeLists.txt):
  cmake_minimum_required(VERSION 3.20)
  project(ParentProj)
  add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/third_party/nuttx nuttx_build)
  with third_party/nuttx and third_party/nuttx-apps as the vendored trees
  (analogous to the reporter's ~/dev/proj/third_party/nuttx).

  Steps
  $ cd parent_proj
  $ cmake -B build
  $ cmake --build build -j$(nproc)
  nuttx_build/CMakeFiles/nuttx.dir/arch/sim/src/sim/posix/sim_hostsmp.c.o
  [100%] Linking C executable nuttx
  [100%] Built target nuttx
  [100%] Generating System.map
  [100%] Built target systemmap
  [100%] Built target nuttx_post
  [100%] Pac SIM with dynamic libs in nuttx.tgz
  [100%] Built target nuttx_post_build
  [100%] Built target post_build

Complete log: apache/nuttx-apps#3711

[github-actions]

MemBrowse Memory Report

No memory changes detected for:

• arduino-mega2560
• esp32-devkitc
• hifive1-revb
• mirtoo
• qemu-armv8a
• qemu-intel64
• rx65n-rsk2mb
• s698pm-dkit
• stm32-nucleo-f103rb

[acassis]

Please ignore Check issue, "siz" is the file extension:

# instruct the gsize to generate a "*.siz" file that contains the detailed

[acassis]

@simbit18 I think if the Check fails because typos we need to continue the next steps, because it is producing false positives. The only way to make it passing it modifying a legit text to make it wrong just to satisfy the CI

[github-actions]

🔗 Cross-repo PR dependencies

The read-only Build run reported the following dependent PR(s) and fetched head SHA(s):

• cmake: Use NUTTX(_DIR/_BIN_DIR) instead of CMAKE(_SOURCE_DIR/BIN_DIR) nuttx-apps#3711 @ 65fc90c96a

CI run: https://github.com/apache/nuttx/actions/runs/31277642253

[raiden00pl]

What problem exactly does this PR solve? support for add_subdirectory is not possible with current cmake support in nuttx and supporting this may require a complete rebuild of cmake build

[acassis]

What problem exactly does this PR solve? support for add_subdirectory is not possible with current cmake support in nuttx and supporting this may require a complete rebuild of cmake build

@raiden00pl with this simple modification we can run the NuttX sim as external project:

$ cat CMakeLists.txt 
cmake_minimum_required(VERSION 3.20)
project(NuttXExternal)
add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/../nuttx nuttx_build)

This is just the initial step, more modifications will be necessary to support cross-compiling too. As you said it will be a redesign of CMake build system. So I want to do it in baby steps

[acassis]

Hi @simbit18 what is necessary to make the Depends-on Check to reflect here in the official CI Check list?

[raiden00pl]

@acassis add_subdirectory works for host compiler just by coincidence. Cmake design in nuttx is not ready for this. But either way, this change makes sense for other reasons.

[cederom]

Thank you @acassis :-)