The idea of linking dependencies found to `libcurl.pc` turns out not
to work in practice in some cases.
Specifically: gss, ldap, mbedtls, libmsh3, rustls
A `.pc` may not work or be missing for a couple of reasons:
- not all build methods generate it: mbedTLS, Rustls
- generated file is broken: msh3
Ref: https://github.com/nibanks/msh3/pull/225
- installed package flavour isn't shipping with one:
FreeBSD GSS, OmniOS LDAP, macOS LDAP
The effect of such issues shall be subtle in theory, because
`libcurl.pc` normally lists these dependencies in the `Requires.private`
section meant for static linking. But, e.g. `pkg-config --exists`
requires these to be present, and builds sometimes use this check
regardless of build type. This bug is not present in `pkgconf`; it only
checks for them when `--static` is also passed.
Fix these by adding affected `.pc` references to `libcurl.pc` only when
we detected the dependency via `pkg-config`.
There are a few side-effects of this solution:
- references are never added for dependencies where curl doesn't
implement `pkg-config` detection. These are:
- autotools: ldap, mbedtls, msh3
- cmake: ldap (pending #15273)
- generated `libcurl.pc` depends on the build-time environment.
- generated `libcurl.pc` depends on curl build tool (cmake, autotools).
- generated `libcurl.pc` depends on curl build implementation details.
Make an exception for GNU GSS, where I blindly guess that `gss.pc` is
always available, as no issues were reported.
Other, not mentioned, dependencies continue to be added regardless
of the detection method.
Reported-by: Harmen Stoppels, Thomas, Daniel Engberg, Andy Fiddaman
Fixes#15469Fixes#15507Fixes#15535
Fixes https://github.com/curl/curl/pull/15163#issuecomment-2473358444Closes#15573
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