[swift-dev] [Suggestion] swift/utils/update-checkout should keep llvm/clang up-to-date

[Jordan Rose]

> On Feb 8, 2016, at 16:34, Michael Gottesman via swift-dev <swift-dev at swift.org> wrote:
> 
>> 
>> On Feb 8, 2016, at 3:54 PM, Kevin Ballard <kevin at sb.org> wrote:
>> 
>> On Mon, Feb 8, 2016, at 03:33 PM, Michael Gottesman wrote:
>>> 
>>>> On Feb 8, 2016, at 3:09 PM, Kevin Ballard via swift-dev <swift-dev at swift.org> wrote:
>>>> 
>>>> I was surprised to discover that swift/utils/update-checkout doesn't update LLVM/clang by default. Looking at the script, it supports a --all flag to update those (and llbuild too), but that led to the second surprise, which is that the script doesn't make any attempt to ensure it's checking out a compatible version of llvm/clang, it just runs `git fetch` and `git rebase FETCH_HEAD`.
>>> 
>>> We ensure that the trunk stable clang/llvm branches are always in sync. So just rebasing head should be sufficient.
>> 
>> Ah right, the llvm/clang checkouts are to copies of llvm/clang instead of to the original.
>> 
>> In that case, why doesn't the update-checkout script update llvm/clang by default? The only reason I can think of to not update it (besides for when you're intentionally targeting a non-stable version of llvm/clang because you're working on migrating it) is to avoid having to recompile llvm/clang if a backwards-compatible change happens to llvm/clang, but I assume the llvm/clang repos aren't updated very often, and when they are updated we all should probably update our checkouts of it even if we don't get compilation errors.
> 
> That is most likely an oversight. Pull request and assign to me?

IIRC Dmitri was concerned about doing more serialized network requests on slow connections.

Jordan
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