Perhaps I'm reading too much into the standards, but that's how
--with-jpeg etc. behave in GNU Emacs 'configure'.
FWIW, I think you are right, and --with should fail if the specified
package is not installed, per the standards text. Alternatively, it
could configure "as if" the with-package will be installed, even if it's
not now, but as far as I have seen that is usually not possible. (It
also seems pretty undesirable to me.)
The wording for --enable is not as clear-cut, but there I would say that
if the user explicitly asked to enable foo, and foo is not available,
they would prefer to abort over continuing anyway.
If we think different wording/behavior for the standards are desirable,
we can certainly propose a change to rms. I doubt he is hard-and-fast
on this question.
karl
File: standards.info, Node: Configuration
[...]
`--enable-FEATURE[=PARAMETER]'
Configure the package to build and install an optional user-level
facility called FEATURE. This allows users to choose which
optional features to include. Giving an optional PARAMETER of
`no' should omit FEATURE, if it is built by default.
No `--enable' option should *ever* cause one feature to replace
another. No `--enable' option should ever substitute one useful
behavior for another useful behavior. The only proper use for
`--enable' is for questions of whether to build part of the program
or exclude it.
`--with-PACKAGE'
The package PACKAGE will be installed, so configure this package
to work with PACKAGE.
Possible values of PACKAGE include `gnu-as' (or `gas'), `gnu-ld',
`gnu-libc', `gdb', `x', and `x-toolkit'.
Do not use a `--with' option to specify the file name to use to
find certain files. That is outside the scope of what `--with'
options are for.
