fix(cmakev2/kconfig): avoid unnecessary sdkconfig generation

Add a helper function `__should_generate_sdkconfig()` that checks
whether the sdkconfig file should be generated.  The
`__generate_sdkconfig()` function can be called multiple times, such as
when the initial sdkconfig is generated at the start of the build
process and later after additional components are fetched by the
component manager.  There might be no components fetched by the
component manager, for example, in the hello_world example, or the
downloaded components may not contain any configuration files. In such
cases, there is no need to regenerate the sdkconfig. This helper
function stores the list of configuration files in the
`__PREV_KCONFIGS`, `__PREV_KCONFIG_PROJBUILDS`, and
`__PREV_SDKCONFIG_RENAMES` build properties at its end, and at the
beginning, it compares them with the current lists of configuration
files.

Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>

tools/cmakev2/kconfig.cmake

@@ -68,6 +68,69 @@ function(__init_kconfig)
     idf_build_set_property(CONFIG_DIR "${config_dir}")
 endfunction()
 
+#[[
+.. cmakev2:function:: __should_generate_sdkconfig
+
+    .. code-block:: cmake
+
+        __should_generate_sdkconfig(OUTPUT <variable>)
+
+    *OUTPUT[out]*
+
+        The output variable will contain ``YES`` or ``NO`` depending on whether
+        the sdkconfig should be generated.
+
+    Check if any new ``Kconfig``, ``Kconfig.projbuild``, or
+    ``sdkconfig.rename`` files have been added. If so, store ``YES`` in the
+    ``OUTPUT`` variable; otherwise, store ``NO``. The
+    ``__generate_sdkconfig()`` function can be called multiple times, such as
+    when the initial sdkconfig is generated at the start of the build process
+    and later after additional components are fetched by the component manager.
+    There might be no components fetched by the component manager, for example,
+    in the hello_world example, or the downloaded components may not contain
+    any configuration files. In such cases, there is no need to regenerate the
+    sdkconfig. This helper function stores the list of configuration files in
+    the ``__PREV_KCONFIGS``, ``__PREV_KCONFIG_PROJBUILDS``, and
+    ``__PREV_SDKCONFIG_RENAMES`` build properties at its end, and at the
+    beginning, it compares them with the current lists of configuration files.
+#]]
+function(__should_generate_sdkconfig)
+    set(options)
+    set(one_value OUTPUT)
+    set(multi_value)
+    cmake_parse_arguments(ARG "${options}" "${one_value}" "${multi_value}" ${ARGN})
+
+    if(NOT DEFINED ARG_OUTPUT)
+        idf_die("OUTPUT option is required")
+    endif()
+
+    idf_build_get_property(kconfigs __KCONFIGS)
+    idf_build_get_property(projbuilds __KCONFIG_PROJBUILDS)
+    idf_build_get_property(renames __SDKCONFIG_RENAMES)
+    list(SORT kconfigs)
+    list(SORT projbuilds)
+    list(SORT renames)
+
+    idf_build_get_property(prev_kconfigs __PREV_KCONFIGS)
+    idf_build_get_property(prev_projbuilds __PREV_KCONFIG_PROJBUILDS)
+    idf_build_get_property(prev_renames __PREV_SDKCONFIG_RENAMES)
+    list(SORT prev_kconfigs)
+    list(SORT prev_projbuilds)
+    list(SORT prev_renames)
+
+    idf_build_set_property(__PREV_KCONFIGS "${kconfigs}")
+    idf_build_set_property(__PREV_KCONFIG_PROJBUILDS "${projbuilds}")
+    idf_build_set_property(__PREV_SDKCONFIG_RENAMES "${renames}")
+
+    if("${kconfigs}" STREQUAL "${prev_kconfigs}"
+            AND "${projbuilds}" STREQUAL "${prev_projbuilds}"
+            AND "${renames}" STREQUAL "${prev_renames}")
+        set(${ARG_OUTPUT}  NO PARENT_SCOPE)
+    else()
+        set(${ARG_OUTPUT}  YES PARENT_SCOPE)
+    endif()
+endfunction()
+
 #[[
     __generate_sdkconfig()
 
@@ -78,14 +141,21 @@ endfunction()
     4. Generate all output files (sdkconfig.h, sdkconfig.cmake, etc.)
 #]]
 function(__generate_sdkconfig)
-    idf_msg("Generating sdkconfig configuration...")
-
     # Collect Kconfig files from discovered components
     __consolidate_component_kconfig_files()
 
     # Collect Kconfig files from bootloader components
     __collect_kconfig_files_from_bootloader_components()
 
+    # Check if sdkconfig needs to be generated
+    __should_generate_sdkconfig(OUTPUT generate)
+    if(NOT generate)
+        idf_dbg("Configuration files have not changed, skipping sdkconfig generation.")
+        return()
+    endif()
+
+    idf_msg("Generating sdkconfig configuration...")
+
     # Prepare Kconfig environment using collected files
     __setup_kconfig_environment()
 
@@ -622,7 +692,6 @@ endfunction()
 function(__run_kconfgen)
     idf_build_get_property(base_kconfgen_cmd __BASE_KCONFGEN_CMD)
     idf_build_get_property(kconfgen_outputs_cmd __KCONFGEN_OUTPUTS_CMD)
-    idf_build_get_property(sdkconfig SDKCONFIG)
     idf_build_get_property(config_env_path __CONFIG_ENV_PATH)
 
     # Create full command with output file paths