Unexpected interaction between command line variables and override

[J.T. Conklin]

I discovered an unexpected interaction between environment variables
and the override directive earlier this week (I tried gmake-3.81 and
gmake-3.82 on NetBSD and Linux).

Normally, when a variable is set on the command line, it is exported
to the environment:

    'Except by explicit request, `make' exports a variable only if 
    it is either defined in the environment initially or set on the
    command line,...'


So for the following Makefile:

    CFLAGS = -O2

    all: ; @echo $$CFLAGS

There is no output if gmake is invoked without arguments, and "-O2 -g"
if gmake is invoked as "gmake CFLAGS='-O2 -g'".

But if the Makefile is changed to use the override directive, like this:

    override CFLAGS += -g

    all: ; @echo $$CFLAGS

CFLAGS is not exported to the environment when gmake is invoked as
"gmake CFLAGS=-O2".

In my use case, it was easy enough to change it to the equivalent to 

    export override CFLAGS += -g

    all: ; @echo $$CFLAGS

Perhaps it's implied, but I thought I'd mention it, as neither the
'override directive' nor the 'communicating variables to a sub-make' 
sections explicitly say that the variables specified on the command
line will not be exported to the environment if used with the over-
ride directive.

    --jtc

-- 
J.T. Conklin