仅在列出的第一个依赖项中运行

Question

我正在编写一个makefile，它接受三个目标：

make build-consul
make build-envoy

make build # (builds both)

build-consul/build-envoy任务可以按照预期自行工作。但是，build任务仅运行第一个依赖项。考虑下面的Makefile：

%consul: APP=consul
%envoy: APP=envoy

build-consul: _build
build-envoy: _build

build: build-consul build-envoy
_build:
  echo building $(APP)

运行build目标的输出为：

$ make build
echo working on consul
working on consul

为什么只运行第一个依赖项build-consul，而忽略第二个build-envoy依赖项？看起来，首先为build任务列出的任何依赖项都将始终运行(如果我交换它们，则输出为envoy。

Answer 1

这是因为build-consul和build-envoy都不能单独执行任何操作。它们都依赖于一个单独的目标_build，这个目标总是只执行一次。当make访问build-consul时，它会重新生成_build目标(因为该文件可能不存在)，而当稍后访问build-envoy时，它不会重新生成_build目标，因为这已经生成了。你自己看一下：

$ make build -dr
Considering target file 'build'.
 File 'build' does not exist.
 Looking for an implicit rule for 'build'.
 No implicit rule found for 'build'.
  Considering target file 'build-consul'.
   File 'build-consul' does not exist.
   Looking for an implicit rule for 'build-consul'.
   No implicit rule found for 'build-consul'.
    Considering target file '_build'.
     File '_build' does not exist.
     Finished prerequisites of target file '_build'.
    Must remake target '_build'.
echo building consul
Putting child 0x55931292b870 (_build) PID 8627 on the chain.
Live child 0x55931292b870 (_build) PID 8627
building consul
Reaping winning child 0x55931292b870 PID 8627
Removing child 0x55931292b870 PID 8627 from chain.
    Successfully remade target file '_build'.
   Finished prerequisites of target file 'build-consul'.
  Must remake target 'build-consul'.
  Successfully remade target file 'build-consul'.
  Considering target file 'build-envoy'.
   File 'build-envoy' does not exist.
   Looking for an implicit rule for 'build-envoy'.
   No implicit rule found for 'build-envoy'.
    Pruning file '_build'.                            <--- Already built, not making again
   Finished prerequisites of target file 'build-envoy'.
  Must remake target 'build-envoy'.
  Successfully remade target file 'build-envoy'.
 Finished prerequisites of target file 'build'.
Must remake target 'build'.
Successfully remade target file 'build'.

您可以在没有额外目标的情况下使其工作，如下所示：

$ cat Makefile
%consul: APP=consul
%envoy: APP=envoy

.PHONY: build
build: build-consul build-envoy

.PHONY: build-consul build-envoy
build-consul build-envoy:
        echo building $(APP)

.PHONY是确保即使存在相同名称的文件也能构建目标(这是一个很好的实践)。

输出：

$ make build
echo building consul
building consul
echo building envoy
building envoy

Answer 2

我没有注意到您指定make build作为命令行。

在这种情况下，请参阅以下答案：makefile: second dependency not execute