From 522eb86907b41ad460d1fb437c851a4b0007d82b Mon Sep 17 00:00:00 2001
From: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>
Date: Fri, 26 Sep 2025 12:55:07 +0200
Subject: [PATCH] sysbuild: support application CMakePresets.json files with
 sysbuild

This commit provides a CMakePresets.json which includes the sample's
CMakePresets.json file.

`west build` is extended to set `APP_DIR` in environment when sysbuild
is used. This allows sysbuild's CMakePresets.json to include the
sample's presets file.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>
---
 doc/build/sysbuild/index.rst     | 58 ++++++++++++++++++++++++++++++--
 scripts/west_commands/build.py   |  9 +++--
 share/sysbuild/CMakeLists.txt    |  5 +++
 share/sysbuild/CMakePresets.json | 11 ++++++
 4 files changed, 78 insertions(+), 5 deletions(-)
 create mode 100644 share/sysbuild/CMakePresets.json

diff --git a/doc/build/sysbuild/index.rst b/doc/build/sysbuild/index.rst
index 51675569e0853..42d100c554ea1 100644
--- a/doc/build/sysbuild/index.rst
+++ b/doc/build/sysbuild/index.rst
@@ -140,8 +140,8 @@ As mentioned above, you can run sysbuild via ``west build`` or ``cmake``.
 
       To use sysbuild directly with CMake, you must specify the sysbuild
       project as the source folder, and give ``-DAPP_DIR=<path-to-sample>`` as
-      an extra CMake argument. ``APP_DIR`` is the path to the main Zephyr
-      application managed by sysbuild.
+      an extra CMake argument or set APP_DIR as environment variable.
+      ``APP_DIR`` is the path to the main Zephyr application managed by sysbuild.
 
       .. tip::
 
@@ -880,3 +880,57 @@ can be added.
     :maxdepth: 1
 
     images.rst
+
+Sysbuild and CMake presets
+**************************
+
+`CMake presets <https://cmake.org/cmake/help/latest/manual/cmake-presets.7.html>`_ can be used with
+Sysbuild but not all preset macros will work as expected.
+
+.. note::
+
+   Using CMake presets with sysbuild requires CMake version 3.27 or higher.
+
+As described in :ref:`sysbuild` then sysbuild is a higher-level build system which means that when
+CMake presets are used together with sysbuild, then the preset is consumed and processed by sysbuild
+itself and result is passed to the application.
+
+Running sysbuild with preset.
+
+.. tabs::
+
+   .. group-tab:: ``west build``
+
+      Here is an example where preset ``release`` should be used.
+      For details, see :ref:`west-multi-domain-builds` in the ``west build documentation``.
+
+      .. zephyr-app-commands::
+         :tool: west
+         :zephyr-app: samples/hello_world
+         :board: reel_board
+         :goals: build
+         :west-args: --sysbuild -- --preset=release
+         :compact:
+
+   .. group-tab:: ``cmake``
+
+      Here is an example using CMake and Ninja.
+
+      .. code-block:: shell
+
+         APP_DIR=samples/hello_world cmake -Bbuild -GNinja -DBOARD=reel_board share/sysbuild
+         ninja -Cbuild
+
+      When using CMake presets with sysbuild then ``APP_DIR`` must be set in environment in order
+      for Sysbuild CMake to be able to include the ``CMakePresets.json`` from the main Zephyr
+      application's source directory.
+
+.. note::
+
+   As sysbuild changes the top-level cmake project to its own directory, the cmake presets are
+   parsed from there, the application's presets are included from this file verbatim.
+   Therefore relative paths, and macros resolving relative to the source directory will not work as
+   expected, but as relative to share/sysbuild, for example ``${sourceDir}``.
+
+   The ``${fileDir}`` macro can be used to create portable paths relative to the application's
+   directory.
diff --git a/scripts/west_commands/build.py b/scripts/west_commands/build.py
index 8a8b3a23ebeef..0b2b1965cf394 100644
--- a/scripts/west_commands/build.py
+++ b/scripts/west_commands/build.py
@@ -618,6 +618,8 @@ def _run_cmake(self, board, origin, cmake_opts):
         if not self.run_cmake:
             return
 
+        cmake_env = None
+
         self._banner('generating a build system')
 
         if board is not None and origin != 'CMakeCache.txt':
@@ -644,8 +646,9 @@ def _run_cmake(self, board, origin, cmake_opts):
 
         config_sysbuild = config_getboolean('sysbuild', False)
         if self.args.sysbuild or (config_sysbuild and not self.args.no_sysbuild):
-            cmake_opts.extend([f'-S{SYSBUILD_PROJ_DIR}',
-                               f'-DAPP_DIR:PATH={self.source_dir}'])
+            cmake_opts.extend([f'-S{SYSBUILD_PROJ_DIR}'])
+            cmake_env = os.environ.copy()
+            cmake_env["APP_DIR"] = str(self.source_dir)
         else:
             # self.args.no_sysbuild == True or config sysbuild False
             cmake_opts.extend([f'-S{self.source_dir}'])
@@ -661,7 +664,7 @@ def _run_cmake(self, board, origin, cmake_opts):
                             f'-G{config_get("generator", DEFAULT_CMAKE_GENERATOR)}']
         if cmake_opts:
             final_cmake_args.extend(cmake_opts)
-        run_cmake(final_cmake_args, dry_run=self.args.dry_run)
+        run_cmake(final_cmake_args, dry_run=self.args.dry_run, env=cmake_env)
 
     def _run_pristine(self):
         self._banner(f'making build dir {self.build_dir} pristine')
diff --git a/share/sysbuild/CMakeLists.txt b/share/sysbuild/CMakeLists.txt
index f2fbb4b271841..d0180757488a0 100644
--- a/share/sysbuild/CMakeLists.txt
+++ b/share/sysbuild/CMakeLists.txt
@@ -4,6 +4,11 @@
 
 cmake_minimum_required(VERSION 3.20)
 
+
+if(NOT DEFINED APP_DIR AND DEFINED ENV{APP_DIR})
+  set(APP_DIR $ENV{APP_DIR})
+endif()
+
 if(NOT DEFINED APP_DIR)
   message(FATAL_ERROR "No main application specified")
 endif()
diff --git a/share/sysbuild/CMakePresets.json b/share/sysbuild/CMakePresets.json
new file mode 100644
index 0000000000000..437f3b68a9447
--- /dev/null
+++ b/share/sysbuild/CMakePresets.json
@@ -0,0 +1,11 @@
+{
+  "version": 7,
+  "cmakeMinimumRequired": {
+    "major": 3,
+    "minor": 27,
+    "patch": 0
+  },
+  "include": [
+    "$penv{APP_DIR}/CMakePresets.json"
+  ]
+}