Re: Strange behaviour of AC_ARG_ENABLE with ./configure --help

First of all, thanks for your help.

> M4 macros are fine but as documented, AS_HELP_STRING does not expand its
> second argument, so you need to be careful about quoting when you use it.
> [...]
> If the defaults can be determined by m4 then you can use m4 to generate
> the help string.
> [...]
> All the help text is generated statically at m4 time and is included
> into the configure script as a quoted here-document.  So the shell will
> not expand anything found within the help text at configure time.


I think that is the root of the problem. The default comes from variable ${host_cpu}, which cannot be determined by m4 alone when generating the configure script.

To illustrate it, this is a piece of code I tried, which did not work either:

AS_CASE(["${host_cpu}"],
   [arm*], [
     m4_define([host_arm_bitbang_adapters_default], [auto])
     m4_define([host_arm_or_aarch64_bitbang_adapters_default], [auto])
   ],
   [aarch64], [
     m4_define([host_arm_or_aarch64_bitbang_adapters_default], [auto])
   ],
   [
     m4_define([host_arm_bitbang_adapters_default], [TODO])
     m4_define([host_arm_or_aarch64_bitbang_adapters_default], [TODO])
   ]
)

I am guessing there is no way around this, is there?


> Otherwise, just write some text which is vague about the default.
> Something like "default: auto" is usually fine.

The trouble is, OpenOCD uses "auto" with the following meaning: if the right libraries etc. are installed, enable the option. That is, enable the option if compilation should succeed. I would have to rewrite a chunk of configure.ac to provide a different "vague" help text for these options alone, and to implement the meaning of "auto" differently for those options.

Furthermore, I don't like the idea of being vague. It is then hard to predict whether a particular option would be automatically enabled, and that opens a window for head scratching, or perhaps I should write yet more custom configure.ac code for these options.

But I guess I am out of options. I'll speak to the OpenOCD guys about this.

Thanks again,
   rdiez