sysbuild: add a hook to tie an app snippet to its MCUboot counterpart

Simplify the usage of Matter FOTA external flash snippet by allowing
a single `SNIPPET=matter_fota_ext_flash` argument for building.

Signed-off-by: Eduardo Montoya <eduardo.montoya@nordicsemi.no>

Author: edmont

docs/includes/matter_extension_activation.txt

@@ -8,29 +8,21 @@ This selects the :file:`prj_matter_fota.conf` configuration, which enables Matte
 
 The same configuration is supported on ``nrf54lm20dk/nrf54lm20a/cpuapp`` and ``nrf54lm20dk/nrf54lm20b/cpuapp``.
 
-To place the MCUboot secondary slot on external SPI NOR flash instead, apply the ``matter_fota_ext_flash`` and ``matter_fota_mcuboot_ext_flash`` snippets to the application and MCUboot images respectively.
 On the nRF54L15 DK, the combined Matter and Zigbee image requires this variant due to the available internal slot size.
+To place the MCUboot secondary slot on external SPI NOR flash instead, pass the ``matter_fota_ext_flash`` snippet.
 
 .. parsed-literal::
    :class: highlight
 
-   west build |sample dir| -b nrf54l15dk/nrf54l15/cpuapp --sysbuild -- \\
-     -DFILE_SUFFIX=matter_fota \\
-     -D|sample|_SNIPPET=matter_fota_ext_flash \\
-     -Dmcuboot_SNIPPET=matter_fota_mcuboot_ext_flash
-
-Replace ``|sample|`` with ``light_bulb`` or ``light_switch``.
+   west build |sample dir| -b nrf54l15dk/nrf54l15/cpuapp -S matter_fota_ext_flash -- -DFILE_SUFFIX=matter_fota
+   west build |sample dir| -b nrf54lm20dk/nrf54lm20a/cpuapp -S matter_fota_ext_flash -- -DFILE_SUFFIX=matter_fota
 
 To produce a size-optimized release build (no logging, console or shell), add :file:`matter_fota_release.conf` as an extra overlay:
 
 .. parsed-literal::
    :class: highlight
 
-   west build |sample dir| -b nrf54l15dk/nrf54l15/cpuapp --sysbuild -- \\
-     -DFILE_SUFFIX=matter_fota \\
-     -D|sample|_SNIPPET=matter_fota_ext_flash \\
-     -Dmcuboot_SNIPPET=matter_fota_mcuboot_ext_flash \\
-     -DEXTRA_CONF_FILE='matter_fota_release.conf'
+   west build |sample dir| -b nrf54l15dk/nrf54l15/cpuapp -S matter_fota_ext_flash -- -DFILE_SUFFIX=matter_fota -DEXTRA_CONF_FILE='matter_fota_release.conf'
 
 Use ``nrf54lm20dk/nrf54lm20b/cpuapp`` as the board target for the nRF54LM20B SoC variant.
 

docs/memory.rst

@@ -74,7 +74,7 @@ The following table lists the available files, which targets they cover, and whe
      - | nRF54L15 DK (DK only)
        | nRF54LM20 DK (DK only)
      - Same as the Matter and Zigbee layout, but places ``slot1_partition`` on external flash and enlarges ``slot0_partition``.
-       Build with ``FILE_SUFFIX=matter_fota``, the ``matter_fota_ext_flash`` snippet on the application image, and the ``matter_fota_mcuboot_ext_flash`` snippet on the MCUboot image.
+       Build with ``FILE_SUFFIX=matter_fota`` and ``SNIPPET=matter_fota_ext_flash``.
 
    * - External flash (FOTA)
      - :file:`dts/ext_flash/<board>_partitions.dtsi`

samples/light_bulb/sample.yaml

@@ -7,8 +7,7 @@ tests:
     build_only: true
     extra_args:
       - FILE_SUFFIX=matter_fota
-      - light_bulb_SNIPPET=matter_fota_ext_flash
-      - mcuboot_SNIPPET=matter_fota_mcuboot_ext_flash
+      - SNIPPET=matter_fota_ext_flash
     integration_platforms:
       - nrf54l15dk/nrf54l15/cpuapp
       - nrf54lm20dk/nrf54lm20a/cpuapp
@@ -41,8 +40,7 @@ tests:
     build_only: true
     extra_args:
       - FILE_SUFFIX=matter_fota
-      - light_bulb_SNIPPET=matter_fota_ext_flash
-      - mcuboot_SNIPPET=matter_fota_mcuboot_ext_flash
+      - SNIPPET=matter_fota_ext_flash
       - EXTRA_CONF_FILE=matter_fota_release.conf
     integration_platforms:
       - nrf54l15dk/nrf54l15/cpuapp

samples/light_switch/sample.yaml

@@ -7,8 +7,7 @@ tests:
     build_only: true
     extra_args:
       - FILE_SUFFIX=matter_fota
-      - light_switch_SNIPPET=matter_fota_ext_flash
-      - mcuboot_SNIPPET=matter_fota_mcuboot_ext_flash
+      - SNIPPET=matter_fota_ext_flash
     integration_platforms:
       - nrf54l15dk/nrf54l15/cpuapp
       - nrf54lm20dk/nrf54lm20a/cpuapp
@@ -41,8 +40,7 @@ tests:
     build_only: true
     extra_args:
       - FILE_SUFFIX=matter_fota
-      - light_switch_SNIPPET=matter_fota_ext_flash
-      - mcuboot_SNIPPET=matter_fota_mcuboot_ext_flash
+      - SNIPPET=matter_fota_ext_flash
       - EXTRA_CONF_FILE=matter_fota_release.conf
     integration_platforms:
       - nrf54l15dk/nrf54l15/cpuapp

sysbuild/CMakeLists.txt

@@ -4,6 +4,51 @@
 # SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
 #
 
+# Global SNIPPET/SB_SNIPPET is applied to every sysbuild image. Some addon
+# snippets target the application only and need a different MCUboot counterpart.
+# This hook remaps those pairs on the mcuboot image so builds can pass a single
+# -DSNIPPET=<app_snippet>. Extend the list below as <app_snippet> <mcuboot_snippet>.
+function(${SYSBUILD_CURRENT_MODULE_NAME}_pre_cmake)
+  if(NOT SB_CONFIG_BOOTLOADER_MCUBOOT)
+    return()
+  endif()
+
+  zephyr_get(SB_SNIPPET)
+  if(SB_SNIPPET)
+    set(global_snippets ${SB_SNIPPET})
+  else()
+    zephyr_get(SNIPPET)
+    set(global_snippets ${SNIPPET})
+  endif()
+
+  # Extend this list as needed.
+  set(app_mcuboot_snippet_pairs
+    matter_fota_ext_flash matter_fota_mcuboot_ext_flash
+  )
+
+  set(mcuboot_snippets ${global_snippets})
+  set(remapped FALSE)
+  list(LENGTH app_mcuboot_snippet_pairs pair_count)
+  math(EXPR last_pair_idx "${pair_count} - 2")
+  foreach(idx RANGE 0 ${last_pair_idx} 2)
+    list(GET app_mcuboot_snippet_pairs ${idx} app_snippet)
+    math(EXPR mcuboot_idx "${idx} + 1")
+    list(GET app_mcuboot_snippet_pairs ${mcuboot_idx} mcuboot_snippet)
+
+    if(app_snippet IN_LIST global_snippets)
+      set(remapped TRUE)
+      list(REMOVE_ITEM mcuboot_snippets ${app_snippet})
+      if(NOT mcuboot_snippet IN_LIST mcuboot_snippets)
+        list(APPEND mcuboot_snippets ${mcuboot_snippet})
+      endif()
+    endif()
+  endforeach()
+
+  if(remapped)
+    set(mcuboot_SNIPPET ${mcuboot_snippets} CACHE STRING "" FORCE)
+  endif()
+endfunction()
+
 function(${SYSBUILD_CURRENT_MODULE_NAME}_post_cmake)
   sysbuild_get(CONFIG_ZIGBEE_ADD_ON IMAGE ${DEFAULT_IMAGE} VAR CONFIG_ZIGBEE_ADD_ON KCONFIG)
   sysbuild_get(CONFIG_ZIGBEE_FOTA IMAGE ${DEFAULT_IMAGE} VAR CONFIG_ZIGBEE_FOTA KCONFIG)