msbuild does not build precompiled header before building source file if UseMultiToolTask=true and path to the pch.h is relative

[autoantwort]

Issue Description

I have the following project:

pch.h
pch.cpp
test/in-sub-folder.cpp 
Directory.Build.props

The content of the Directory.Build.props is

<Project>
  <PropertyGroup>
    <UseMultiToolTask>true</UseMultiToolTask>            
  </PropertyGroup>
</Project>

and the test/in-sub-folder.cpp file has a #include "../pch.h"

If I try to compile the project I get

03:08:37:193	Rebuild started at 03:08...
03:08:37:252	1>------ Rebuild All started: Project: TestCcache2, Configuration: Debug x64 ------
03:08:37:383	1>in-sub-folder.cpp
03:08:37:433	1>pch.cpp
03:08:37:433	1>F:\git_projects\TestCcache2\test\in-sub-folder.cpp(1,10): error C1083: Cannot open precompiled header file: 'TestCcache2\x64\Debug\TestCcache2.pch': No such file or directory
03:08:38:000	1>Done building project "TestCcache2.vcxproj" -- FAILED.
03:08:38:007	========== Rebuild All: 0 succeeded, 1 failed, 0 skipped ==========
03:08:38:007	========== Rebuild completed at 03:08 and took 00,849 seconds ==========

Steps to Reproduce

You can find an example project here: https://github.com/autoantwort/msbuild-bug-repro

Expected Behavior

The file in the subfolder should be compiled after the precompiled header is compiled

Actual Behavior

The file in the subfolder is compiled before the precompiled header is compiled

Analysis

It seems that msbuild misses the dependency on the precompiled header file.

Versions & Configurations

** Visual Studio 2022 Developer Command Prompt v17.12.4
C:\Program Files\Microsoft Visual Studio\2022\Professional>msbuild -version
MSBuild-Version 17.12.12+1cce77968 für .NET Framework
17.12.12.57101

[autoantwort]

BTW the bug does not occur when I do a #include "pch.h" in test/in-sub-folder.cpp which should be an error because there is no such file in the include search paths (IntelliSence also complains).

[YuliiaKovalova]

Hi @yuehuang010,

Could you please check if it belongs to custom C++ targets/tasks that might cause this issue?
Thanks!

[yuehuang010]

It is designed to use #include "pch.h" in test/in-sub-folder.cpp. The compiler takes the name from the /Yu"pch.h" switch to look for the #include line.

[autoantwort]

But you can also use #include "../pch.h" in test/in-sub-folder.cpp which is theoretically more correct and specify /Yu"../pch.h". When I don't use UseMultiToolTask this also works fine, otherwise I get the described bug.

[yuehuang010]

MTT detect the pch dependency using the /Yu name to associate to the creating <ClCompile> item. I would expect an error like below because the pch.cpp is still being created in parallel with infolder.cpp.

Adding source "ConsoleApplication1.cpp" with dependency on "pch.cpp".
Adding source "Folder\infolder.cpp".
Adding source "pch.cpp".

error C1083: Cannot open precompiled header file: 'ConsoleApplication1.pch': No such file or directory

[yuehuang010]

What is the use case? Is it to address the Intellisense squiggle?

A simple workaround is to add the pch path to the list of Include path. That will satisfy the compiler and intellisense.

[autoantwort]

I would expect an error like below because the pch.cpp is still being created in parallel with infolder.cpp.

No it works fine (UseMultiToolTask=false):

1>------ Rebuild All started: Project: TestCcache2, Configuration: Debug x64 ------
1>pch.cpp
1>TestCcache2.cpp
1>in-sub-folder.cpp
1>TestCcache2.vcxproj -> F:\git_projects\TestCcache2\x64\Debug\TestCcache2.exe
========== Rebuild All: 1 succeeded, 0 failed, 0 skipped ==========
========== Rebuild completed at 21:07 and took 01,240 seconds ==========

[autoantwort]

What is the use case? Is it to address the Intellisense squiggle?

Yes, otherwise everything gets red and code completion does not work.

[yuehuang010]

I would expect an error like below because the pch.cpp is still being created in parallel with infolder.cpp.

No it works fine (UseMultiToolTask=false):

1>------ Rebuild All started: Project: TestCcache2, Configuration: Debug x64 ------
1>pch.cpp
1>TestCcache2.cpp
1>in-sub-folder.cpp
1>TestCcache2.vcxproj -> F:\git_projects\TestCcache2\x64\Debug\TestCcache2.exe
========== Rebuild All: 1 succeeded, 0 failed, 0 skipped ==========
========== Rebuild completed at 21:07 and took 01,240 seconds ==========

MTT will parallelize all work, but it needs information to create a DAG. Help set the edges directly.

<ClCompile>
  <MultiToolTaskDependency>pch.h</MultiToolTaskDependency>
</ClCompile>

[autoantwort]

So normally when UseMultiToolTask=false the tasks don't get parallelized?

Do I have to set MultiToolTaskDependency for every of my ~6600 files?

[yuehuang010]

So normally when UseMultiToolTask=false the tasks don't get parallelized?

By default compile parallelism is off. Your options are 1) to enable the MSVC compiler parallelism via the switch /MP. or 2) Use task level MTT.

Do I have to set MultiToolTaskDependency for every of my ~6600 files?

You can use <ItemDefinitionGroup/> to set the value for all <ClCompile/>. The metadata on an individual <ItemGroup/> will overwrite the <ItemDefinitionGroup/>.

<ItemDefinitionGroup>
  <ClCompile>
    <MultiToolTaskDependency>pch.h</MultiToolTaskDependency>
  </ClCompile>
</ItemDefinitionGroup>