Incorrect install paths

[jansol]

When given an absolute path for e.g. CMAKE_INSTALL_LIBDIR, cmake does NOT prepend CMAKE_INSTALL_PREFIX, that is only done for relative paths (see the CMake manual)

However path wrangling in draco_install.cmake always unconditionally prepends the prefix, leading to broken installs e.g. on NixOS. Nix always passes absolute paths to cmake for the specific install directories, as they may have different prefixes in order to split large packages into smaller ones (such as having a separate package for documentation or data files).

[tomfinegan]

When given an absolute path for e.g. CMAKE_INSTALL_LIBDIR, cmake does NOT prepend CMAKE_INSTALL_PREFIX, that > is only done for relative paths (see the CMake manual)

Can you cite the section of the manual that you're referring to? I took a quick look over the script, and just reread the CMAKE_INSTALL_PREFIX documentation. There is no mention of behavioral changes relating to absolute paths. The GNUInstallDirs documentation is pretty clear that CMAKE_INSTALL_LIBDIR is not absolute and is built using CMAKE_INSTALL_PREFIX. CMAKE_INSTALL_FULL_LIBDIR is absolute, but the CMAKE_INSTALL_LIBDIR is not. Specifying an absolute path as the value of that variable appears incorrect by my reading.

The CMake install() code in Draco is ancient, and I see from looking at the documentation that things have changed, but the problem you're having downstream is clearly related to the behavior of Nix, which is not typical:

Nix always passes absolute paths to cmake for the specific install directories.

CMAKE_INSTALL_LIBDIR, according to CMake docs, is a relative path (GNUInstallDirs doc):

CMAKE_INSTALL_<dir>

Destination for files of a given type. This value may be passed to the DESTINATION options of install() commands for the
corresponding file type. It should typically be a path relative to the installation prefix so that it can be converted to an
absolute path in a relocatable way (see CMAKE_INSTALL_FULL_<dir>). However, an absolute path is also allowed.

Edit to add:

Looking at this a bit more it does seem that the install for Draco could use some updates-- I would be happy to look at a PR that makes this work a little better for your use case. The Draco install rules were not written with a fully custom install path structure in mind.

[jansol]

My bad, the part I was thinking of is about the destination parameter to install() and it is described right in the intro section of the page I linked:

If a relative path is given it is interpreted relative to the value of the CMAKE_INSTALL_PREFIX variable. The prefix can be relocated at install time using the DESTDIR mechanism explained in the CMAKE_INSTALL_PREFIX variable documentation.

If an absolute path (with a leading slash or drive letter) is given it is used verbatim.

Draco is explicitly prepending the prefix to all of the paths, i.e.:

install(TARGETS draco_decoder DESTINATION "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_BINDIR}")

Whereas the same result would be obtained with simply:

install(TARGETS draco_decoder DESTINATION "${CMAKE_INSTALL_BINDIR}")

...except in the case where CMAKE_INSTALL_BINDIR is an absolute path, like with Nix, where the latter would also work the way it is intended. Not sure what the best way to generate the paths for the pkg-config and cmake config files is, though.

[tomfinegan]

@jansol Thank you for the PR. I haven't had a chance to look it over yet, but we'll try to get this pulled in for the next release.