[llvm-core] bring package up to date. Support for Conan 2.

[planetmarshall]

Specify library name and version: llvm-core/*

Attempt to bring the llvm-core recipe up to date. Includes contributions from @jusito and #17509. Fixes #20339

Note that I have opted not to add the latest version (18.1.3) as part of this PR, as the existing recipe needed updating and is already quite complex. I (or someone else) will add the latest version as a followup.

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• I've read the contributing guidelines.
• I've used a recent Conan client version close to the currently deployed.
• I've tried at least one configuration locally with the conan-center hook activated.

[github-actions]

🤖 Beep Boop! This pull request is making changes to 'recipes/llvm-core//'.

👋 @Hopobcn @paulharris you might be interested. 😉

[planetmarshall]

@jcar87 Most recent CI build failed but i'm unable to view any logs.

[cynix]

I think this needs to be kept. Without something like this, I’m seeing shared libraries (libRemarks.so and libLTO.so) in the produced package even when shared=False.

[cynix]

Might also want to delete *.so and *.so.* from the package.

[planetmarshall]

libRemarks and libLTO are part of the LLVM infrastructure and not available as static libraries.

libLTO specifically is used by some out of tree linkers but not by LLVM itself - See https://discourse.llvm.org/t/how-to-use-dynamic-library-liblto-so/74541 for example.

[cynix]

I understand these are not available statically. However I don’t think it’s correct to include shared libs in a static package. For example, if my intention of using a static package is to produce an executable that doesn’t depend on any shared libs for ease of deployment, now I’m forced to link to these 2 shared libs when I link to llvm-core::llvm::core, and the executable will not run in the target environment as intended.

I think we should delete them, and the users of the static package should simply be aware that these 2 components are not available.

[planetmarshall]

llvm-core::llvm-core is a conan-generated target and would not ordinarily be available to consumers of LLVM, and I would expect users of the package to use the targets in the official docs, as the test package does.

One issue with deleting the libraries for static builds is that a shared library build is not supported (by LLVM) for Windows, so a static build is the only way to build those libraries. Deleting the libraries for all platforms apart from Windows seems to me inconsistent behaviour.

It's not a perfect solution - but currently the package works exactly as described in the official LLVM documentation. I'm sure further contributions to the recipe to improve the linking behaviour will be welcome.

[cynix]

llvm-core::llvm-core is a conan-generated target and would not ordinarily be available to consumers of LLVM

By “not available” do you just mean “not recommended”? Because I certainly have code using it, and it works fine (except for linking to the 2 shared libs).

[planetmarshall]

I mean it is a target provided by conan, not by LLVM. So if you are linking to llvm-core::llvm-core, your application will work with the conan package but it would not work against a package built directly from the LLVM sources just using cmake.

The test_package in the repository should still work whether LLVM is provided by conan or not.

[planetmarshall]

I do think that LTO and Remarks should probably be made separate components for the shared build, but IMHO this is something that can be added as a future improvement and shouldn't block this PR.

[conan-center-bot]

Conan v1 pipeline ✔️

All green in build 43 (bd3f92f10901ca9fe5487ffaca59e3ed312454a9):

• llvm-core/11.1.0:
  All packages built successfully! (All logs)

• llvm-core/13.0.0:
  All packages built successfully! (All logs)

• llvm-core/12.0.0:
  All packages built successfully! (All logs)

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Conan v2 pipeline ✔️

Note: Conan v2 builds are now mandatory. Please read our discussion about it.

All green in build 44 (bd3f92f10901ca9fe5487ffaca59e3ed312454a9):

• llvm-core/13.0.0:
  All packages built successfully! (All logs)

• llvm-core/12.0.0:
  All packages built successfully! (All logs)

• llvm-core/11.1.0:
  All packages built successfully! (All logs)

[jcar87]

Thanks @planetmarshall and everyone involved - this was not an easy recipe to port, and hopefully this can unblock some of the usages that are required by the community.

There's still a few things to look into further down the line - the issue with libiconv in macOS, and the parsing of CMake files (it is obvious from the recipe code that this can be fragile) - however, I dont think these are an impediment to merge the recipe as proposed in this PR.

Thanks so much!