In what scenario is the --srcdir config option valid?

Question

I am working on a configuration program - it isn't autoconf, but I'm trying (as much as possible) to get it so that ./configure files that use it can be interfaced in a similar manner to those that are made with autoconf -- and that means (as much as possible) supporting the same variable options.

Only there's one option that makes no sense to me. I mean, yes, I am fully clear on what the option means, I just can't conceive of a single scenario in which someone would be well-advised to use that option - except for one scenario in which I'm equally curious why ./configure scripts can't auto-detect the information it would provide.

The option I am referring to is the "--srcdir" option. The reason it so befuddles me is that the only scenario I can imagine in which the source-code files won't be in your present-working-directory (or relative to your present-working-directory as the configure script is programmed to expect) is if the "configure" script itself isn't in your present-working-directory ---- and in that one scenario, I really am unable to imagine why the "configure" script can't extrapolate the source-directory from the name it is invoked by - and instead has to have that --srcdir option to give it that information.

For example, let's say your program's source-code is located in the "awesome/software" directory. That means that, from where you are, the "configure" script would be "awesome/software/configure". Why can't the "configure" script deduce that the source-directory is "awesome/software" just from the fact that it is invoked by the name "awesome/software/configure", and instead require me to add a separate command-line option of:
    --srcdir=awesome/software

And if this is not the kind of scenario where one would need to specify the --srcdir option (or if it is not the only kind of such scenario) can someone describe to me any other kind of scenario where the person installing a program would be well-advised to alter the "srcdir" variable from it's default?

Answer 1

The option I am referring to is the "--srcdir" option. ... the only scenario I can imagine in which the source-code files won't be in your present-working-directory (or relative to your present-working-directory as the configure script is programmed to expect) is if the "configure" script itself isn't in your present-working-directory

Right.

and in that one scenario, I really am unable to imagine why the "configure" script can't extrapolate the source-directory from the name it is invoked by - and instead has to have that --srcdir option to give it that information.

I'm not sure it's required. The configure script will attempt to guess the location of srcdir:

# Find the source files, if location was not specified.
if test -z "$srcdir"; then
  ac_srcdir_defaulted=yes
# Try the directory containing this script, then the parent directory.
...

So if it's in neither of those places, this will fail, hence the need for --srcdir. Maybe this is (was?) needed where there's some kind of performance differential where the sources are stored on a "slow" drive and the build happens on a "fast" drive, and configure seems to run faster on the "fast" drive so it needs to be there as well...

At any rate, --srcdir is just a variable assignment, so it's not hard to do.

Why can't the "configure" script deduce that the source-directory is "awesome/software" just from the fact that it is invoked by the name "awesome/software/configure"

The configure source seems to do that without specifying --srcdir, but I have not tried it.