Re: [BUG] --warn-undefined-variable is not triggered in prerequisites

[Alejandro Colomar (man-pages)]

Hi Paul,

On 1/28/22 23:49, Paul Smith wrote:
> On Fri, 2022-01-28 at 01:09 +0100, Alejandro Colomar (man-pages) wrote:
>> I'd like make to warn about this.  It took me a while to debug 
>> a Makefile bug, which I thought was not happening, since make should
>> have warned me.  Isn't this supposed to trigger the warning?
> 
> In previous versions of GNU make, the value of MAKEFLAGS set inside a
> makefile is only re-parsed once before all makefiles are read (from the
> environment) and again after all makefiles are read.
> 
> So, changes to this variable within the makefile don't take effect
> until after all makefiles are parsed.  In your situation the variable
> in question is part of a prerequisite list and that's expanded while
> parsing the makefile, so the option is not set yet and you don't get
> warnings.  Undefined variables used in a recipe WOULD be warned about
> since recipes are expanded after all makefiles are parsed.
> 
> To make this option do what you want you must pass it in either via the
> command line:
> 
>    $ make --warn-undefined-variables
> 
> or the environment:
> 
>    $ MAKEFLAGS=--warn-undefined-variables make
> 
> or:
> 
>    $ GNUMAKEFLAG=--warn-undefined-variables make
> 
> In the next release of GNU make, this has been changed; from the NEWS
> file:
> 
> * If the MAKEFLAGS variable is modified in a makefile, it will be re-parsed
>   immediately rather than after all makefiles have been read.  Note that
>   although all options are parsed immediately, some special effects won't
>   appear until after all makefiles are read.

Sounds like good news :)

I'll be waiting for that release!

Cheers,

Alex


-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/