[m-rev.] for post-commit review: classify oc_link options by target language

[Peter Wang]

On Thu, 12 Jun 2025 23:05:34 +1000 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> For review by anyone.
> 
> The diff to handle_options.m points out what may be a bug, but I cannot tell,
> because the only effect is on the value of an option whose meaning I don't understand:
> default_runtime_library_directory. Does anyone else know?

--no-default-runtime-library-directory prevents the compiler adding any
directories to the runtime search path automatically. You can see the
RUNPATH/RPATH that gets embedded into a binary with (on Linux):
    objdump -x $binary | grep 'R.*PATH'

If you are distributing dynamically linked binaries to the world,
you probably don't want the binary to be searching for shared libraries
in locations specific to YOUR machine.

> The obvious fix is
> to switch the order of the two calls involved, but my guess iis that if that happens
> to be wrong, we don't have an automatic test catch it. Can anyone confirm or
> deny that?

If I understood properly, the bug you mention could occur in this situation:

In handle_directory_options, if mercury_linkage = "static",
then standard library directories are NOT added to
runtime_link_library_directories, and default_runtime_library_directory
is also forced to 'no'.

In handle_target_compile_link_symlink_options,
if shared_lib_not_executable = yes, then linkage and mercury_linkage
will be set to "shared". But no libraries will be have been added to
runtime_link_library_directories, even if
default_runtime_library_directory was originally 'yes'.

--compile-to-shared-lib (shared_lib_not_executable) is an undocumented
option only used to implement interactive queries in the debugger.
The debugger doesn't pass --mercury-linkage static at the same time
(obviously, since it is trying to build a shared library),
so the bug should never arise in practice.

As for a fix, I think we just need to move the shared_lib_not_executable
implications before handle_directory_options?

Peter