Man pages matching name al_attach_shader_source_file in section 3alleg5:

al_attach_shader_source_file.3alleg5.en	debian 10 / allegro5-doc
al_attach_shader_source_file.3alleg5.en	debian 11 / allegro5-doc
al_attach_shader_source_file.3alleg5.en	debian 12 / allegro5-doc