makefile library dependencies - resolve circular dependency

Question

I am trying to build a feature into my makefile which allows me to specify a list of libraries a particular library depends on

This will allow dependants of a library to automatically be rebuilt if that library's dependencies are rebuilt, and also have the dependencies added to the link line.

I asked a related question on SO here , and working through a given answer, I came up with the following test

uniq = $(if $1,$(firstword $1) $(call uniq,$(filter-out $(firstword $1),$1)))
expand-deps = $1 $(foreach _,$1, $(call expand-deps,$($__deps)))
make-dep-list = $(call uniq,$(call expand-deps,$1))

define make-lib
    $(warning $1_deps: $2)
    # capture the list of libraries this library depends on
    $1_deps = $2
endef

define make-bin
    # show the fully expanded list of libraries this binary depends on
    $(warning $1 dep-list: [$(call make-dep-list,$2)])
endef

#$(eval $(call make-lib, thread, log utils)) circular-dependency log->thread; thread->log
$(eval $(call make-lib, thread, utils))
$(eval $(call make-lib, log, thread))
$(eval $(call make-lib, order, log))
$(eval $(call make-lib, price, log))
$(eval $(call make-bin, test, order price))

running the above makefile yields the following results:

$ make
makefile:15:  thread_deps:  utils
makefile:16:  log_deps:  thread
makefile:17:  order_deps:  log
makefile:18:  price_deps:  log
makefile:19:  test dep-list: [order price log thread utils ]
make: *** No targets.  Stop.

It is possible for libraries to have circular dependencies.

As an example: The logging library is multi-threaded, so requires the thread library. The thread library can issue log statements, so requires the log library.

If I uncomment out the line which has a circular dependency

$(eval $(call make-lib, thread, log utils))
$(eval $(call make-lib, log, thread))

The makefile will get stuck in an infinite loop.

How can I allow users to specify circular dependencies, and break out of the infinite loop?

Answer 1

So, your problem is that you are recursively expanding lib_deps (say). While doing that you start expanding lib_deps again. Infinite loop (er, stack crash). To stop yourself you need to keep a list of things that you have already expanded. Falling out of functional style and keeping the answer in the global expansion (ugh!), something like:

expand-deps = \
  $(foreach _,$1, \
    $(if $(filter $_,${expansion}),, \
      $(eval expansion += $_)$(call expand-deps,${$__deps})))

make-dep-list = $(eval expansion :=)$(call expand-deps,$1)${expansion}

define make-lib
  $(warning $1_deps: $2)
  # capture the list of libraries this library depends on
  $1_deps := $2
endef

define make-bin
  # show the fully expanded list of libraries this binary depends on
  $(warning $1 dep-list: [$(call make-dep-list,$2)])
endef

$(eval $(call make-lib,thread,log utils))#circular-dependency log->thread; thread->log
#$(eval $(call make-lib,thread,utils))
$(eval $(call make-lib,log,thread))
$(eval $(call make-lib,order,log))
$(eval $(call make-lib,price,log))
$(eval $(call make-bin,test,order price))

(As an exercise you might like to rewrite this in functional style, ie, get rid of the global $expansion replacing it with a parameter that gets passed around.)