qmk_firmware is an open source firmware that supports a number of programmable keyboards. Popular keyboards supported by this firmware are planck, ergodox, etc. Documentation and more information can be found at https://qmk.fm/. To clone and build this source for the first time, the documentation will guide you as follows.

$ make <my_keyboard>:<my_keymap>

However, if you follow along, you’ll see the error below.

$ make ergodo_infinity:default

tmk_core/chibios.mk:38: lib/chibios-contrib/os/common/startup/ARMCMx/compilers/GCC/mk/startup_k20x7.mk: No such file or directory
tmk_core/chibios.mk:40: lib/chibios/os/hal/hal.mk: No such file or directory
tmk_core/chibios.mk:46: lib/chibios-contrib/os/hal/ports/KINETIS/K20x/platform.mk: No such file or directory
tmk_core/chibios.mk:78: lib/chibios-contrib/os/hal/boards/PJRC_TEENSY_3_1/board.mk: No such file or directory
tmk_core/chibios.mk:79: lib/chibios/os/hal/osal/rt/osal.mk: No such file or directory
tmk_core/chibios.mk:81: lib/chibios/os/rt/rt.mk: No such file or directory
tmk_core/chibios.mk:87: lib/chibios/os/common/ports/ARMCMx/compilers/GCC/mk/port_v7m.mk: No such file or directory
tmk_core/chibios.mk:89: lib/chibios/os/hal/lib/streams/streams.mk: No such file or directory
quantum/visualizer/visualizer.mk:77: lib/ugfx/gfx.mk: No such file or directory
make[1]: *** No rule to make target `lib/ugfx/gfx.mk'.  Stop.
make: *** [ergodox_infinity:default] Error 1

This is caused by the submodule not being updated properly, so update the submodule with the command below and you should be able to rebuild normally.

$ make git-submodule

Alternatively, the following two commands do the same thing

$ git submodule sync --recursive
$ git submodule update --init --recursive --progress