GNU Make 4.3: Makefile rule spooky action at a distance

[Danny Milosavljevic]

Hi,

I just got a build failure in lz4.  I've isolated it and made a minimal test 
case, see below.

This is on GNU Guix on a x86_64 machine.

The reason is that apparently one Makefile rule can unwittingly change how 
another unrelated rule functions, IF a submake is involved.

To reproduce:

$ cat Makefile 

all:
        $(MAKE) -C foo all

dummy: CFLAGS ?= bar
dummy:

$ cat foo/Makefile 

CFLAGS ?= internal

all:
        echo $(CFLAGS)

Expected behavior:

$ CFLAGS=ok make
make -C foo all
make[1]: Entering directory 'foo'
echo ok
ok
make[1]: Leaving directory 'foo'

Actual behavior:

$ CFLAGS=ok make
make -C foo all
make[1]: Entering directory 'foo'
echo internal
internal
make[1]: Leaving directory 'foo'

BR,
   Danny Milosavljevic

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