Makefiles can actually be quite dynamic, so a program merely trying to figure out the list of target has to execute code. For example put this in a Makefile and do `make <TAB>`, the file will be created (no need to press enter):

    VALUE := $(shell touch /tmp/something)

FWIW, while both bash and fish completion execute "make -n" for tab completion that isn't the case for zsh. zsh uses an internal parser for makefiles¹, and as such won't execute the shell function or recipes that use the + prefix.

¹ https://github.com/zsh-users/zsh/blob/master/Completion/Unix...

You're not just viewing it. You're opening it in an IDE which compiles it behind the scenes for you.

Many IDEs also do this for other languages (e.g. by running make), and the same problem applies.