[cfe-users] MSVC always trying to rebuild project while using clang-cl (LLVM-vs2014 toolset)

[Hans Wennborg via cfe-users]

This is the problem described in https://bugs.llvm.org/show_bug.cgi?id=36140

Have you tried using the new VS extension?
https://marketplace.visualstudio.com/items?itemName=LLVMExtensions.llvm-toolchain
It should not have this problem.

 - Hans

On Mon, Sep 3, 2018 at 12:34 PM, Aleksei via cfe-users
<cfe-users at lists.llvm.org> wrote:
> Hello everyone,
>
>
>
> I don’t know if I’ve found a bug in clang-cl using Visual Studio 2015, or
> it’s a quite normal behavior… It would be nice if someone clarify it and
> (better) fix something in clang-cl, because the current behavior is IMHO
> very confusing.
>
>
>
> Background: Visual Studio 2015, version 14.0.25431.01 Update 3, LLVM version
> 6.0.1 for win64
>
>
>
> So, the problem is MSVC (under some condition) would always require to
> rebuild a project that has to be built with LLVM-vs2014 toolset, even if
> it’d just finished last rebuild.
>
>
>
> The root cause of it in the absence of a file, that is specified under
> “Configuration Properties / C/C++ / Output Files / Program Database File
> Name” (typically, it’s filled with macro
> “$(IntDir)vc$(PlatformToolsetVersion).pdb” that expands to something similar
> to “x64\Debug\vc140.pdb”). I might be wrong in general case, but in my case
> this file is not generated by clang-cl at all during build process, it’s
> generated only by VC’s native compiler. So, should one delete it
> intentionally during manual cleanup or by an accident, MSVC would start to
> always require a full project rebuild before each run/debug.
>
>
>
> It’s very easy to reproduce the problem: create a new Win32 console project
> in MSVC, then immediately change the toolset used to build the project to
> LLVM-vs2015 and then build the project (don’t build the project with native
> compiler before this step). Then run it and notice that MSVC would require
> the project to be rebuild.
>
> Now, if one to switch back the toolset to VC’s native, build the project (to
> produce corresponding .pdb file), then switch the toolset to LLVM again and
> then build it and after that run it – MSVC would start the program
> immediately.
>
>
>
> If the .pdb file is not required to run/debug a project, I guess it would be
> much better if clang-cl to emit some kind of warning/information during
> compilation about that fact. I’ve just wasted about 3-4 hours to find out
> why VC requires project rebuilding all the time…
>
>
>
> Thanks.
>
>
>
> Sincerely,
>
> Aleksei
>
>
>
>
>
>
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