esp-idf/components/app_update/component.mk

#
# Component Makefile
#
# (Uses default behaviour of compiling all source files in directory, adding 'include' to include path.)

# esp_app_desc structure is added as an undefined symbol because otherwise the
# linker will ignore this structure as it has no other files depending on it.
COMPONENT_ADD_LDFLAGS += -u esp_app_desc

ifndef IS_BOOTLOADER_BUILD
    # If ``CONFIG_APP_PROJECT_VER_FROM_CONFIG`` option is set, the value of ``CONFIG_APP_PROJECT_VER`` will be used
    # Else, if ``PROJECT_VER`` variable set in project Makefile file, its value will be used.
    # Else, if the ``$PROJECT_PATH/version.txt`` exists, its contents will be used as ``PROJECT_VER``.
    # Else, if the project is located inside a Git repository, the output of git describe will be used.
    # Otherwise, ``PROJECT_VER`` will be "1".
    ifdef CONFIG_APP_PROJECT_VER_FROM_CONFIG
        PROJECT_VER:= $(CONFIG_APP_PROJECT_VER)
    else
        ifneq ("${PROJECT_VER}", "")
            PROJECT_VER:= $(PROJECT_VER)
        else
            ifneq ("$(wildcard ${PROJECT_PATH}/version.txt)","")
                PROJECT_VER := $(shell cat ${PROJECT_PATH}/version.txt)
            else
                GIT_PROJECT_VER := $(shell cd ${PROJECT_PATH} && git describe --always --tags --dirty 2> /dev/null)
                ifeq ("${GIT_PROJECT_VER}", "")
                    PROJECT_VER := "1"
                    $(info Project is not inside a git repository, or git repository has no commits)
                    $(info will not use 'git describe' to determine PROJECT_VER.)
                else
                    PROJECT_VER:= $(GIT_PROJECT_VER)
                endif # a git repository
            endif # version.txt
        endif # PROJECT_VER
    endif # CONFIG_APP_PROJECT_VER_FROM_CONFIG

    # cut PROJECT_VER and PROJECT_NAME to required 32 characters.
    PROJECT_VER_CUT  := $(shell echo "$(PROJECT_VER)"  | cut -c 1-31)
    PROJECT_NAME_CUT := $(shell echo "$(PROJECT_NAME)" | cut -c 1-31)

    $(info App "$(PROJECT_NAME_CUT)" version: $(PROJECT_VER_CUT))

    NEW_DEFINES:= "$(PROJECT_VER_CUT) $(PROJECT_NAME_CUT) $(IDF_VER)"
    ifeq ("$(wildcard ${TMP_DEFINES})","")
        OLD_DEFINES:= ""
    else
        OLD_DEFINES:= "$(shell cat $(TMP_DEFINES))"
    endif

    # If NEW_DEFINES (PROJECT_VER, PROJECT_NAME) were changed then rebuild only esp_app_desc.
    ifneq (${NEW_DEFINES}, ${OLD_DEFINES})
        $(shell echo $(NEW_DEFINES) > $(TMP_DEFINES); rm -f esp_app_desc.o;)
    endif

    esp_app_desc.o: CPPFLAGS += -D PROJECT_VER=\""$(PROJECT_VER_CUT)"\" -D PROJECT_NAME=\""$(PROJECT_NAME_CUT)"\"
endif # IS_BOOTLOADER_BUILD