[llvm-dev] CMake executable dependency woes

[Chris Bieneman via llvm-dev]

Ultimately we do need to migrate to the new interface for `target_link_libarires` because some day CMake could (and probably should) deprecate the old syntax. If you're willing to take that task on that seems like the right solution and the best way to move forward.

-Chris

> On Dec 1, 2017, at 1:41 PM, Shoaib Meenai via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> I discovered that I can hack around my particular problem by placing
> 
> set_property(TARGET clang PROPERTY INTERFACE_LINK_LIBRARIES)
> 
> at the end of tools/driver/CMakeLists.txt. I'd prefer to fix this properly though,
> of course.
> 
> On 12/1/17, 4:18 PM, "llvm-dev on behalf of Shoaib Meenai via llvm-dev" <llvm-dev-bounces at lists.llvm.org on behalf of llvm-dev at lists.llvm.org> wrote:
>    (accidentally sent the previous one to llvm-commits instead of llvm-dev, sigh)
> 
>    Hi all (CC beanz for CMake advice),
> 
>    I stumbled into an issue with LLVM_DISTRIBUTION_COMPONENTS. The simplest way
>    to reproduce is to run a configure with `-DLLVM_DISTRIBUTION_COMPONENTS=clang`.
>    This should show lots of errors of the following form:
> 
>    CMake Error: install(EXPORT "ClangTargets" ...) includes target "clang" which requires target "LLVMAArch64CodeGen" that is not in the export set.
> 
>    The issue is that we add dependencies to executables using the legacy
>    target_link_libraries signature, which marks the dependencies as public (i.e.
>    they apply to both the target and any other targets linking against it, or in
>    other words they're interface dependencies). CMake requires install(EXPORT) to
>    also export all interface dependencies, which seems like a reasonable
>    requirement.
> 
>    I wasn't running into this previously since I was using LLVM_INSTALL_TOOLCHAIN_ONLY,
>    but I need to install some non-tools. I definitely don't want to install all
>    of them, however, and I'm building with the default (static library)
>    configuration, which makes installing most libraries pretty unnecessary
>    for my use case.
> 
>    My preferred solution would be to mark all dependencies of an executable
>    target as PRIVATE, since I don't think interface dependencies make much sense
>    for an executable. I hacked this in locally for clang and confirmed that it
>    made the install(EXPORT) CMake errors go away. Unfortunately, cmake also
>    requires all instances of target_link_libraries for a particular target to use
>    either the legacy or the non-legacy signature, and it turns out all our uses
>    of target_link_library for executables are using the legacy signature right
>    now, so this would have to be a substantial cross-repository change in order
>    to avoid breaking the world. I'm fine with taking the work on, but I wanted to
>    confirm my approach before putting that work in.
> 
>    Thanks,
>    Shoaib
> 
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