[llvm-dev] RFC: Updating to CMake 3.15.0

[Chris Bieneman via llvm-dev]

> On Nov 8, 2019, at 7:53 AM, David Greene via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> James Y Knight via llvm-dev <llvm-dev at lists.llvm.org> writes:
> 
>> Another important point here is that the version of cmake you use to build
>> llvm doesn't impact users of the llvm libraries or binaries that were built
>> with the new cmake.
> 
> Are we sure that's true for the CMake config files installed with LLVM?

The CMake files installed with LLVM can really be broken up into two categories.

(1) The files required for CMake's `findPackage` function
(2) The LLVM CMake modules shared for other projects use

The later will almost certainly require whatever CMake version LLVM is requiring. The former should not.

There are only two files that are required for the `findPackage` function. One is generated by CMake and sticks pretty tightly to old CMake language features. The other is `LLVM-Config.cmake` which we own. That file changes relatively infrequently, and it can go away if we kill off LLVMBuild. It also largely uses very old and stable CMake features and there is little reason to change that.

Does that answer your question?

> 
> I lean toward the newest CMake but want to make sure we don't
> accidentally set up a CMake version bump requirement for users of LLVM
> libraries.
> 
>                        -David
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