[nrf fromtree] cmake: support snippets scope for zephyr_get()

Fixes: #57139

Snippets provides the possibility of defining EXTRA_DTC_OVERLAY_FILE and
EXTRA_CONF_FILE in snippets.
Snippets must co-exist with existing infrastructure of
EXTRA_DTC_OVERLAY_FILE and EXTRA_CONF_FILE, and a user specifying a
snippet must be able to specify extra files for adjusting the snippet.

This means that if the following is specified:
`-DSNIPPET=some_snippet -DEXTRA_CONF_FILE=extra.conf`
then `extra.conf` may contain adjustments to the snippet.
Similar to sysbuild. Imagine a sysbuild controlled image uses a default
snippet for building, by ensuring that any extra
`-D<image>_EXTRA_CONF_FILE=extra.conf` arguments takes precedence over
the snippet we allow users to make adjustments if they need.

This commit introduces a snippets scope where snippet scoped variables
can be set with `zephyr_set()` and then `zephyr_get()` will take the
snippet scoped variables into consideration before returning.

Adjust calls to `zephyr_get(EXTRA_DTC_OVERLAY_FILE)` and
`zephyr_get(EXTRA_CONF_FILE)` to use `MERGE` to ensure all scopes are
considered.

Signed-off-by: Torsten Rasmussen <[email protected]>
(cherry picked from commit ba48dd8)

Author: tejlmand

cmake/modules/configuration_files.cmake

@@ -116,5 +116,5 @@ DTC_OVERLAY_FILE=\"dts1.overlay dts2.overlay\"")
 # The DTC_OVERLAY_FILE variable is now set to its final value.
 zephyr_boilerplate_watch(DTC_OVERLAY_FILE)
 
-zephyr_get(EXTRA_CONF_FILE SYSBUILD LOCAL VAR EXTRA_CONF_FILE OVERLAY_CONFIG)
-zephyr_get(EXTRA_DTC_OVERLAY_FILE SYSBUILD LOCAL)
+zephyr_get(EXTRA_CONF_FILE SYSBUILD LOCAL VAR EXTRA_CONF_FILE OVERLAY_CONFIG MERGE REVERSE)
+zephyr_get(EXTRA_DTC_OVERLAY_FILE SYSBUILD LOCAL MERGE REVERSE)

cmake/modules/extensions.cmake

@@ -2568,9 +2568,13 @@ function(zephyr_get variable)
     else()
       set(sysbuild_${var})
     endif()
+
+    if(TARGET snippets_scope)
+      get_property(snippets_${var} TARGET snippets_scope PROPERTY ${var})
+    endif()
   endforeach()
 
-  set(scopes "sysbuild;CACHE;ENV;current")
+  set(scopes "sysbuild;CACHE;snippets;ENV;current")
   if(GET_VAR_REVERSE)
     list(REVERSE scopes)
   endif()

cmake/modules/snippets.cmake

@@ -93,10 +93,6 @@ function(zephyr_process_snippets)
   endif()
   include(${snippets_generated})
 
-  # Propagate include()d build system settings to the caller.
-  set(DTC_OVERLAY_FILE ${DTC_OVERLAY_FILE} PARENT_SCOPE)
-  set(OVERLAY_CONFIG ${OVERLAY_CONFIG} PARENT_SCOPE)
-
   # Create the 'snippets' target. Each snippet is printed in a
   # separate command because build system files are not fond of
   # newlines.

scripts/snippets.py

@@ -133,6 +133,9 @@ def print_cmake(self):
 # The paths to all the snippet.yml files. One snippet
 # can have multiple snippet.yml files.
 set(SNIPPET_PATHS {snippet_path_list})
+
+# Create variable scope for snippets build variables
+zephyr_create_scope(snippets)
 ''')
 
         for snippet_name in snippet_names:
@@ -168,7 +171,7 @@ def print_appends(self, appends: Appends, indent: int):
         space = '  ' * indent
         for name, values in appends.items():
             for value in values:
-                self.print(f'{space}list(APPEND {name} {value})')
+                self.print(f'{space}zephyr_set({name} {value} SCOPE snippets APPEND)')
 
     def print(self, *args, **kwargs):
         kwargs['file'] = self.out_file