Re: buggy interaction between MAKEFLAGS += rR and CC ?= my_gcc

[Britton Kerin]

On Fri, Aug 26, 2016 at 7:37 AM, Paul Smith <address@hidden> wrote:
> Please be sure to keep the mailing list in the loop, thanks!
>
> On Thu, 2016-08-25 at 11:55 -0800, Britton Kerin wrote:
>> It should explicitly mention that setting it in a makefile won't set
>> flags for that instance.
>
> It does set them for that instance, just not until after all the
> makefiles have been parsed.  So the new flags take effect after the
> makefiles have been parsed and before make starts trying to build
> targets.

Yes, but for options like -rR that isn't good enough, since they have an
effect during the parse pass.  This means setting MAKEFLAGS in the
environment vs in the Makefile has a significantly different effect.
Perhaps this paragraph:

     The flags given to make. You can set this in the environment or a
     makefile to set flags.  See Communicating Options to a Sub-make.

could be rewritten:

     The flags given to make.You can set this in the environment or a
     makefile.  Be aware that in the latter case, the option setting won't
     take effect until the end of parse pass.  See ...

> As far as I know it should be possible to do any combination of things
> that you want with the current behavior.  It will be more ugly than
> using a simple ?= (for example) but it will be less ugly than testing
> for command line flags and failing if they're not provided.
>
> For example this:
>
>   MAKEFLAGS += -rR
>
>   CC ?= my_gcc
>
> says, as far as I can tell, "use the user's version of CC from either
> the command line or the environment, or if that's not set then use

That's not what it ends up doing though (I guess from what you
write below that you know that).

> my_gcc", which can be written like this:
>
>   # In case you wanted it for other reasons...
>   MAKEFLAGS += -rR
>
>   ifneq (,$(filter default undefined,$(origin CC)))
>   CC = my_gcc
>   endif
>
> You can turn this into a macro and use call or eval if you have a lot
> of these.

True.  It would be nice if there were some way to get the behavior of
-rR without those more complicated techniques, however.

The root of the problem is that the functionality of -rR *should* be a
per-Makefile thing, not a per-make-invocation thing.  A given
make file is either written to want the built-in rules, or not.  I suspect
that it's on command line because directives don't modify parsing
behavior in time either.  I took a quick look at the directive list and
didn't notice any that seemed like they would.

Britton