Impose an order for the prerequisites of a target

问题

I have a makefile snippet:

all: $(objects)
fresh: clean all
clean: ;rm $(objects)

Here, I want to ensure that when I do make fresh - clean should precede all.

But how can I make sure this, given that when I do make all, clean should not be made?

I can imagine that one way could be like this

fresh: clean
    make all

Is it the right (or the only) way to solve this issue?

回答1:

If you use GNU make:

all:
    @echo $@
    @sleep 1
    @echo end $@

clean:
    @echo $@
    @sleep 1
    @echo end $@

fresh:: clean
fresh:: all

.PHONY: clean fresh all

Please note the double colon after targets fresh! See the documentation:

The double-colon rules for a target are executed in the order they appear in the makefile.

If you run make -j2 fresh it shows it works as expect:

clean
end clean
all
end all

But with fresh:: clean all doesn't work properly parallel (maybe unexpected).

With BSD make:

 all:
    @echo $@
    @sleep 1
    @echo end $@

clean:
    @echo $@
    @sleep 1
    @echo end $@

fresh:  clean all
    @echo $@

.ORDER: clean all
.PHONY: clean all fresh

Note the line begin with .ORDER. It works well in parallelization too (see man make). Without parallelization the order of dependencies in line fresh: counts.

回答2:

As you already suggest in your question, calling make recursively on the same makefile for the target all in a recipe whose prerequisite is clean:

# At the very beginning of the makefile
CURRENT_MAKEFILE :=  $(lastword $(MAKEFILE_LIST))
# ...

.PHONY: fresh
fresh: clean
    $(MAKE) -f $(CURRENT_MAKEFILE) all

This imposes an order, since the target fresh depends on the prerequisite clean, clean's recipe will be executed before fresh's recipe, which in turn will execute all's recipe.

Note that I'm using here $(MAKE) instead of make for the recursion.

来源：https://stackoverflow.com/questions/52036534/impose-an-order-for-the-prerequisites-of-a-target

标签

makefile

dependencies

gnu-make

target

prerequisites