Can a Makefile execute code ONLY when an error has occurred?

Question

In my Makefile, I have some code that checks for network connectivity. This code takes a decent amount of time to run and I would only like to run it if another target fails to build.

Current Makefile

all: files network
    # compile files

files:
    # get files from network resources

network:
    # check for network connectivity
    # echo and return an error if it's not available

Execution Order:

if not network:
    # exit with error
if not files:
    # exit with error
if not all:
    # exit with error

Desired Makefile

In the above example, I would like the network target to be "made", only if the files target fails to get "made".

Execution Order:

if not files:
    if not network:
        # exit with error
if not all:
    # exit with error

Answer 1

Recursive make is your friend here I'm afraid.

.PHONY: all
all:
    ${MAKE} files || ${MAKE} network

If make files succeeds, your work is done and the exit code is success. On failure, the exit code is that for make network.