如何使用宏在foreach中生成多个Makefile目标/规则?神秘行为 [英] How can I use macros to generate multiple Makefile targets/rules inside foreach? Mysterious behaviour

问题描述

我正在使用GNU make 3.81.这是一个演示该问题的测试文件:

I am using GNU make 3.81. Here is a test makefile that demonstrates the problem:

define BOZO

a$(1): b c
    touch a$(1)

endef

$(foreach i,1 2 3,$(call BOZO,$(i)))

这里的想法是使用宏模板(BOZO)生成遵循可预测模式的规则.

The idea here is to use a macro template (BOZO) to generate rules that follow a predictable pattern.

问题:当我在此makefile上运行make时，出现错误消息:

Problem: when I run make on this makefile I get an error saying:

Makefile.fake:10: *** multiple target patterns.  Stop.

(其中第10行是带有foreach的行).

(where line 10 is the line with the foreach).

现在，我知道该错误通常表示什么.让我们看看通过使用info函数将扩展发送到标准输出行会扩展到什么.我将第10行更改为:

Now, I know what that error normally indicates. Let's see what that line expands to by using the info function to send the expansion to standard out. I change line 10 to be:

$(info $(foreach i,1 2 3,$(call BOZO,$(i))))

然后我跑:

$ make -n

a1: b c
    touch a1

a2: b c
    touch a2

a3: b c
    touch a3

make: *** No targets.  Stop.

请注意，由于$ {info ...)函数的值为空，但会导致make对所生成的规则进行 print 打印.

Note that the "no targets" message is expected, since the $(info ...) function evaluates to empty but causes make to print the generated rules.

那我们去执行那些规则吧?

Let's run those rules then shall we?

$make -n > out.txt
make: *** No targets.  Stop.
$make -f out.txt a1 a2 a3
touch a1
touch a2
touch a3
$

AAARGH！规则工作正常.那么...是制造还是我的理解中的错误?

AAARGH! The rules work fine. So... is the bug in make, or in my understanding?

最后一条可能有助于诊断的线索:如果我将foreach行更改为:

One final clue that might help diagnose: if I change the foreach line to:

$(foreach i,1,$(call BOZO,$(i)))

(这样foreach只有一个迭代)

(so that foreach has only one iteration)

然后做

$make a1

我收到另一个错误:

make: *** No rule to make target `a1'.  Stop.

我不知道有什么办法可以看到" $(foreach )的扩展，除了$(info )以外，sees的输出是合法的，所以我很困惑.

I don't know of any way to "see" the expansion of $(foreach ) that make sees except for $(info ), and its output is legal, so I'm quite stumped.

推荐答案

$(foreach i,1 2 3,$(eval $(call BOZO,$(i))))

eval函数告诉Make将结构解析为makefile语法， 颁布"他们.我不确定为什么Make会以这种特殊的方式反对不合规则的规则，但这是一种学术性的方法.

The eval function tells Make to parse the structures as makefile syntax, to "enact" them. I'm not sure why Make objected to the un-eval'd rules this particular way, but that's kind of academic.

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