Why is --include-dir option effective only in sub make ?

[Masahiro Yamada]

Hello,


I wonder why --include-dir does not become
effective in the current Makefile.

Here is the test case.



[ Not working sample ]


-------------(Makefile)--------------
MAKEFLAGS += --include-dir=foo

include inc.mk

all:
        @echo hello
-------------(Makefile END)------------


$ mkdir foo
$ touch foo/inc.mk
$ make
Makefile:3: inc.mk: No such file or directory
make: *** No rule to make target 'inc.mk'.  Stop.






[ Working sample ]

-------------(Makefile)--------------
MAKEFLAGS += --include-dir=foo

ifneq ($(IN_SUBMAKE),1)
all:
        @$(MAKE) IN_SUBMAKE=1

else

include inc.mk

all:
        @echo hello

endif
-------------(Makefile END)------------


$ mkdir foo
$ touch foo/inc.mk
$ make
make[1]: Entering directory '/home/masahiro/workspace'
hello
make[1]: Leaving directory '/home/masahiro/workspace'





>From the example above, --include-dir is effective
only after diving into sub make.

Is this an intentional behavior?


Is there a way to make it effective in the current make?


-- 
Best Regards
Masahiro Yamada