Look for zstd before Clang The story is more or less the following: - LLVM ships its own Findzstd cmake find module from 16; this module defines 2 targets: zstd::libzstd_shared and zstd::libzstd_static - libzstd ships a cmake config module that defines 3 targets: zstd::libzstd_shared, zstd::libzstd_static, and zstd::libzstd - the libzstd config module assumes that if one target is defined, all of them are, as if the config module itself was already run (i.e. multiple "find_package(zstd)" in a cmake project) - in qttools, Clang is searched first, which in turns requires LLVM, and then libzstd . More details here: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1073480#47 . As workaround, look for libzstd before Clang: this way the proper zstd cmake targets are defined, and the Findzstd cmake find module shipped with LLVM will use them just fine without redefining them. . This should most likely be fixed on LLVM side.
