[llvm-dev] MSBuild incremental builds are broken with LLVM 6 (and beyond)

[Scott Funkenhauser via llvm-dev]

I was using the VS integration from the Marketplace.

I initially discovered this issue while using my own tool set (based on
LLVM) with it's own VS integration. I only mentioned the LLVM VS
integration as I thought it would be easier for somebody else to reproduce,
instead of trying to explain my custom setup. You can also reproduce by
just calling tracker.exe and invoking Clang directly, completely removing
VS integration from the equation.

On Fri, Jan 25, 2019 at 11:49 PM Zachary Turner <zturner at google.com> wrote:

> You mention that you disabled features clang doesn’t support, so I take
> this to mean you’re using the LLVM VS integration.
>
> If so, what version of the VS integration is being used? Is it the version
> that’s on the Marketplace and installs from a vsix, or the version that you
> run a batch file to install?
> On Fri, Jan 25, 2019 at 10:23 AM Reid Kleckner via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> I had no idea they were broken, that seems like a major regression. Come
>> to think of it, I think someone may have reported this behavior, but it was
>> never root caused, so thanks for that.
>>
>> However, we spent a lot of time coming up with this particular code
>> pattern to:
>> 1. (mostly) atomically write the whole output file or nothing at all on
>> failure
>> 2. not leak temporary files when the compiler crashes
>>
>> Before our use of SetInformationByFileHandle we leaked temporary object
>> files in build directories like crazy. All you had to do was basically
>> interrupt a build and clang would leave behind files. The linker suffered
>> from similar problems.
>>
>> So, I would be very careful about going back to our old code patterns. I
>> wonder if Microsoft would accept this as a bug in FileTracker.dll instead.
>>
>> On Fri, Jan 25, 2019 at 7:00 AM Scott Funkenhauser via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> Hi,
>>>
>>> Starting with LLVM 6, MSBuild incremental builds stopped working. I've
>>> tracked this down to a CL that modified how file renaming was done on
>>> Windows. It appears that FileTracker does not recognize renaming a file
>>> with SetFileInformationByHandle.
>>>
>>>
>>> https://github.com/llvm-mirror/llvm/commit/1b6a51a1425cc0180359ecd64733edb965f65d7c#diff-70db51c38d748dc9debf5f309643fcd8
>>>
>>> You can repro this fairly easily by:
>>> 1) Downloading the prebuilt binaries of LLVM 6 or 7 for Windows.
>>> 2) Creating a new C++ project (I just chose the default console
>>> application) in VS 2017.
>>> 3) Mess with the project settings to disable all the features clang
>>> doesn't support (Conformance mode, Just my code, etc...)
>>> 4) Build
>>>
>>> Every time you build it will rebuild everything.
>>>
>>> I'm curious if this is a known issue? (I couldn't find any open bugs
>>> relating to this)
>>> Is MSBuild incremental builds something that is officially supported? Or
>>> did it just work in the past by chance?
>>>
>>> Thanks,
>>> Scott
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>> _______________________________________________
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>
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