cmake: dt: Reconfigure when DTS dependencies change

When DT sources change CMake must be run again. CMake is currently
detecting changes to DT source files that we manually specify, but not
sources that are included through use of the preprocessor.

This patch makes the preprocessor output the includes used and adds
them to the 'CMAKE_CONFIGURE_DEPENDS' property.

This fixes #16791.

Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>

cmake/dts.cmake

@@ -65,12 +65,6 @@ if(SUPPORTS_DTS)
       message(STATUS "Overlaying ${dts_file}")
     endif()
 
-    # Ensure that changes to 'dts_file's cause CMake to be re-run
-    set_property(DIRECTORY APPEND PROPERTY
-      CMAKE_CONFIGURE_DEPENDS
-      ${dts_file}
-      )
-
     math(EXPR i "${i}+1")
   endforeach()
 
@@ -109,7 +103,8 @@ if(SUPPORTS_DTS)
 
   # Run the C preprocessor on an empty C source file that has one or
   # more DTS source files -include'd into it to create the
-  # intermediary file *.dts.pre.tmp
+  # intermediary file *.dts.pre.tmp. Also, generate a dependency file
+  # so that changes to DT sources are detected.
   execute_process(
     COMMAND ${CMAKE_C_COMPILER}
     -x assembler-with-cpp
@@ -119,8 +114,10 @@ if(SUPPORTS_DTS)
     ${NOSYSDEF_CFLAG}
     -D__DTS__
     -P
-    -E ${ZEPHYR_BASE}/misc/empty_file.c
+    -E   # Stop after preprocessing
+    -MD  # Generate a dependency file as a side-effect
     -o ${BOARD}.dts.pre.tmp
+    ${ZEPHYR_BASE}/misc/empty_file.c
     WORKING_DIRECTORY ${PROJECT_BINARY_DIR}
     RESULT_VARIABLE ret
     )
@@ -128,6 +125,19 @@ if(SUPPORTS_DTS)
     message(FATAL_ERROR "command failed with return code: ${ret}")
   endif()
 
+  # Parse the generated dependency file to find the DT sources that
+  # were included and then add them to the list of files that trigger
+  # a re-run of CMake.
+  toolchain_parse_make_rule(
+    ${PROJECT_BINARY_DIR}/${BOARD}.dts.pre.d
+    include_files # Output parameter
+    )
+
+  set_property(DIRECTORY APPEND PROPERTY
+    CMAKE_CONFIGURE_DEPENDS
+    ${include_files}
+    )
+
   # Run the DTC on *.dts.pre.tmp to create the intermediary file *.dts_compiled
 
   set(DTC_WARN_UNIT_ADDR_IF_ENABLED "")