Not quite: it does declare "foo" as the default target. Without the Makefile, it would be necessary to type `make foo` instead of just `make`.

The built in rule to copy 'build.sh' to 'build' and make it executable is also interesting.. confused the hell out of me

That doesn't work for me. Tried with empty Makefile, no Makefile, with make (PMake) and gmake (GNU Make).

Don't know why that would be. I'm using GNU Make 4.1, but this has worked for years and years as far as I knew. Not a particularly useful feature, so I it doesn't really matter, but you messed up my fun fact.

  dima@fatty:/tmp$ mkdir dir

  dima@fatty:/tmp$ cd dir

  dima@fatty:/tmp/dir$ touch foo.c

  dima@fatty:/tmp/dir$ make -n foo
  cc     foo.c   -o foo

  dima@fatty:/tmp/dir$ make --version
  GNU Make 4.1
  Built for x86_64-pc-linux-gnu
  Copyright (C) 1988-2014 Free Software Foundation, Inc.
  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
  This is free software: you are free to change and redistribute it.
  There is NO WARRANTY, to the extent permitted by law.

I had fun learning about that.

Try "make foo" instead of "make"

Ah, that works!

Then you did something wrong — it definitely works with GNU make (can’t speak for PMake):

https://asciinema.org/a/zVu7sYyh7lQZTNAgAsbKUmocr

Yeah

   make foo.c

Should just work. No makefile needed.

No, `make foo`. You need to state the target, not the input.

You're correct.

   make foo

or

   make foo.o