[nrf fromlist] west: update build extension command to use APP_DIR

`west build` can be invoked without specifying the source directory when
being invoked from the source directory itself.
When using `west build` for incremental builds, then the build command
will examine the CMake cache to determine the application dir by using
the value of CMAKE_HOME_DIRECTORY.

With sysbuild, this leads to the wrong assumption that the sysbuild
itself is the application to build.

Instead, have west build look for APP_DIR which points to the correct
source dir when sysbuild is used. Use APPLICATION_SOURCE_DIR when
APP_DIR is not set, as this indicates a no-sysbuild build.

Keep CMAKE_HOME_DIRECTORY behavior as last fallback mechanism.

Upstream PR: zephyrproject-rtos/zephyr#74230

Signed-off-by: Torsten Rasmussen <[email protected]>

Author: tejlmand

scripts/west_commands/build.py

@@ -429,7 +429,14 @@ def _find_source_dir(self):
         if self.args.source_dir:
             source_dir = self.args.source_dir
         elif self.cmake_cache:
-            source_dir = self.cmake_cache.get('CMAKE_HOME_DIRECTORY')
+            source_dir = self.cmake_cache.get('APP_DIR')
+
+            if not source_dir:
+                source_dir = self.cmake_cache.get('APPLICATION_SOURCE_DIR')
+
+            if not source_dir:
+                source_dir = self.cmake_cache.get('CMAKE_HOME_DIRECTORY')
+
             if not source_dir:
                 # This really ought to be there. The build directory
                 # must be corrupted somehow. Let's see what we can do.