如何在Makefile中通过MY_TYPE变量切换top目标的依赖项？

这个需求在Makefile里很容易实现，我给你两种实用的方案，你可以根据自己的偏好选择：

方案一：提前定义条件依赖变量（推荐，可读性更高） #

这种方法先把依赖的逻辑抽离出来，通过ifeq判断MY_TYPE的值，定义一个统一的本地依赖变量，再让top目标引用它，代码结构更清晰：

BUILD = build
TARGETS = targets
XLOCALS = xlocals
YLOCALS = ylocals
# 默认值为FOO，可通过命令行覆盖
MY_TYPE ?= FOO

# 根据MY_TYPE选择对应的本地依赖
ifeq ($(MY_TYPE),FOO)
LOCAL_DEP = $(XLOCALS)
else ifeq ($(MY_TYPE),BAR)
LOCAL_DEP = $(YLOCALS)
else
# 处理非法值，提前报错提示
$(error MY_TYPE must be set to FOO or BAR)
endif

$(BUILD):
	printf "\t Doing Build\n"

$(TARGETS):
	printf "\t Doing target\n"

$(XLOCALS):
	printf "\t my local build for X \n"

$(YLOCALS):
	printf "\t my local build for Y \n"

# 统一引用LOCAL_DEP变量，目标定义更简洁
top: $(BUILD) $(TARGETS) $(LOCAL_DEP)
	printf "\t doing top\n"

测试方法： #

• 运行make MY_TYPE=FOO top，会执行BUILD、TARGETS和XLOCALS的规则
• 运行make MY_TYPE=BAR top，会执行BUILD、TARGETS和YLOCALS的规则

方案二：直接在依赖中使用条件函数（紧凑写法） #

如果喜欢更紧凑的代码，可以用Makefile的$(if)和$(filter)函数，直接在top目标的依赖行里完成判断：

BUILD = build
TARGETS = targets
XLOCALS = xlocals
YLOCALS = ylocals
MY_TYPE ?= FOO

$(BUILD):
	printf "\t Doing Build\n"

$(TARGETS):
	printf "\t Doing target\n"

$(XLOCALS):
	printf "\t my local build for X \n"

$(YLOCALS):
	printf "\t my local build for Y \n"

# 直接在依赖中嵌入条件判断逻辑
top: $(BUILD) $(TARGETS) \
	$(if $(filter FOO,$(MY_TYPE)),$(XLOCALS),\
		$(if $(filter BAR,$(MY_TYPE)),$(YLOCALS),\
			$(error MY_TYPE must be FOO or BAR)\
		)\
	)
	printf "\t doing top\n"

这种写法适合简单的二选一场景，但逻辑都集中在依赖行里，复杂场景下可读性会稍差。

内容的提问来源于stack exchange，提问作者user2532296