Rework the way curl's custom Find modules advertise their properties.
Before this patch, Find modules returned detected dependency properties
(header dirs, libs, libdirs, C flags, etc.) via global variables. curl's
main `CMakeLists.txt` copied their values into global lists, which it
later applied to targets. This solution worked internally, but it was
unsuited for the public, distributed `CURLConfig.cmake` and publishing
curl's Find modules with it, due to polluting the namespace of consumer
projects. It's also impractical to apply the many individual variables
to every targets depending on libcurl.
To allow using Find modules in consumer projects, this patch makes them
define as imported interface targets, named `CURL::<dependency>`. Then
store dependency information as target properties. It avoids namespace
pollution and makes the dependency information apply automatically
to all targets using `CURL::libcurl_static`.
Find modules continue to return `*_FOUND` and `*_VERSION` variables.
For dependencies detected via `pkg-config`, CMake 3.16+ is recommended.
Older CMake versions have a varying degree of support for
propagating/handling library directories. This may cause issues in envs
where dependencies reside in non-system locations and detected via
`pkg-config` (e.g. macOS + Homebrew). Use `CURL_USE_PKGCONFIG=OFF`
to fix these issues. Or upgrade to newer CMake, or link libcurl
dynamically.
Also:
- re-enable `pkg-config` for old cmake `find_library()` integration
tests.
- make `curlinfo` build after these changes.
- distribute local Find modules.
- export the raw list of lib dependencies via `CURL_LIBRARIES_PRIVATE`.
- `CURLconfig.cmake`: use curl's Find modules to detect dependencies in
the consumer env.
- add custom property to target property debug function.
- the curl build process no longer modifies `CMAKE_C_FLAGS`.
Follow-up to e86542038d#17047
Ref: #14930
Ref: https://github.com/libssh2/libssh2/pull/1535
Ref: https://github.com/libssh2/libssh2/pull/1571
Ref: https://github.com/libssh2/libssh2/pull/1581
Ref: https://github.com/libssh2/libssh2/pull/1623Closes#16973
To not have to guess. Also to sync with autotools, which already uses
this wording.
Also:
- replace the stray term 'folder' with 'directory' for consistency.
- store help text in a temp variable to avoid overly long strings
(mandatory in CMake <4.2.0 and can't be trivially split), also
to avoid repeating this string 4 times.
Ref: https://cmake.org/cmake/help/v4.2/command/set.htmlCloses#19169
Replacing a combination of custom logic in the main script and relying
on CMake's built-in Find module, with code and behavior used for
the rest of dependencies.
Also to:
- add version detection in the non-pkg-config path.
- make `GNUTLS_INCLUDE_DIR` and `GNUTLS_LIBRARY` take precedence over
pkg-config. As with other dependencies.
- document the above two configuration options.
- prepare for #16973, which originally introduced this local Find
module.
The local module is doing largely the same as CMake's built-in
FindGnuTLS. Differences:
- honors `CURL_USE_PKGCONFIG`.
- returns GnuTLS version for non-pkg-config detection.
- consistently returns `GNUTLS_VERSION`.
(CMake's built-in uses s different name in <3.16.)
- CMake 3.16+ returns an imported target. curl supports 3.7,
therefore we may only use it conditionally, which isn't worth it.
Cherry-picked from #16973Closes#19163
