VisualStudio projects always out of date using clang-cl toolset integration

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Bugzilla Link	PR37187
Status	CONFIRMED
Importance	P normal
Reported by	Benn Herrera (bherrera@reification.io)
Reported on	2018-04-20 09:01:22 -0700
Last modified on	2019-02-21 13:31:22 -0800
Version	6.0
Hardware	PC Windows NT
CC	hans@chromium.org, llvm-bugs@lists.llvm.org, rnk@google.com, zturner@google.com
Fixed by commit(s)
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Issue observed using LLVM 6.0 x64 toolchain (<llvm_insall_dir>/msbuild-
bin/cl.exe) with Visual Studio 14 (and Visual Studio 15 using a manual toolset
integration),

MSVS default compiler options include flag for specifying location of .pdb file
for libraries. clang-cl silently ignores this switch and embeds intermediate
debug data in obj files instead of producing a single separate pdb for the
entire library. (not an issue - debugging works fine)

Projects always appear out of date due to msbuild expecting a pdb file and not
finding one.

This can be remedied by modifying the toolset-vs20XX.props file used for
MSVS/MSBuild integration:

Under the compile options add a tag to clear the pdb filename option
<ItemDefinitionGroup>
  <ClCompile>
    ...
    <!-- clang-cl embeds debug data in obj files. does not generate pdb per lib. if option not cleared projects will always appear out of date to MSVS. -->
    <ProgramDataBaseFileName/>
  </ClCompile>
</ItemDefinitionGroup>

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Does the new VS integration (did we land it yet?) fix this?

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(In reply to Reid Kleckner from comment #1)
> Does the new VS integration (did we land it yet?) fix this?

Latest 7.0 snapshot does not appear to have 2017 integration

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This is the same problem discussed in https://bugs.llvm.org/show_bug.cgi?id=36140#c6

The workaround of setting an empty ProgramDataBaseFileName is new though.

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Re-discovered and posted about here:
http://lists.llvm.org/pipermail/llvm-dev/2019-January/129589.html