Checking if Makefile exists before executing autocmd

Question

I want Vim to execute build the project automatically after I write the buffer to a *.c or *.cpp file. Here is what I've done:

autocmd BufWritePost *.c,*.cpp make

This one works as expected (but the output is noisy; see the bonus question below):

"main.c" 26L, 448C written
:!make  2>&1| tee /var/folders/x0/lrg8j6r535n4lvnfnj6lr2fr0000gn/T/vF0bk92/0
clang -g main.c
               (1 of 1): clang -g main.c
Press ENTER or type command to continue

The problem is, when there is no makefiles in the current directory, an error is thrown:

"test.c" [New] 0L, 0C written
:!make  2>&1| tee /var/folders/x0/lrg8j6r535n4lvnfnj6lr2fr0000gn/T/vtVN9SA/0
make: *** No targets specified and no makefile found.  Stop.
(1 of 1): make: *** No targets specified and no makefile found.  Stop.
Press ENTER or type command to continue

How can I tell autocmd to check if a makefile exists before executing the command?

Bonus question: can I tell autocmd to execute the command quietly? That is, don't show the output of the command, or more preferably, show it in the status line.

Answer 1

Indeed filereadable() is how we could detect whether a file exists. Here, you'd want to check filereadable(expand('<amatch>:p:h').'/Makefile')).

In order to check for a Makefile in a directory above the one where your file is, it's findfile() you're looking for.

But beware if you have a lot of files, you won't want to freeze vim every time you save a file among the hundred if not the thousand a project contains. And if you want to do that in the background, you'll have to make sure to not start make several times in parallel.

Also, I don't know if you're aware of it, but single file projects don't need a Makefile. If you're using gnu-make, and if your version of gnu make is properly configured (Mingw one is the only one I'm aware of to be improperly configured), you can just execute :make %< to compile the current file into an executable.