When the branch can not be corrected selected by ifeq?

[Peng Yu]

Hi,

I have the following Makefile. The execution result is shown below.

CXX_SOURCE_FILES is an empty string. I think that the top branch
should be taken.  But in fact, the bottom one is taken.

Would you please let me know what I'm wrong?

Thanks,
Peng

$ cat Makefile
.PHONY: all

CXX_SOURCE_FILES =

ifeq ($CXX_SOURCE_FILES, )

all:
        @echo x$(CXX_SOURCE_FILES)y

else

all:
        @echo X$(CXX_SOURCE_FILES)Y

endif

$ make
XY