Add option for "warning as errors except ..."

[natemcmaster]

Follow up to #68

I would like to have the ability to make all warnings by errors, but with some exclusions.

msbuild.exe -warnAsError -warnNotAsError MSB3277

This is not the same as -nowarn which would make the warning a low-importance message and hide the warning. I still want the warnings to appear as warnings so show the user there may be a problem, but I want to be able to specify which problems are non-fatal.

My scenario:
We would like to enable -warnAsError by default in the build system that produces ASP.NET Core, but we can't because there are a handful of warning that we can't always do anything about. We would like the warnings to appear, but to be non-fatal to a build passing.

For comparison, C# supports a WarningsNotAsErrors properties which allows users to set TreatWarningsAsErrors=true which exclusions defined as WarningsNotAsErrors.

[ghost]

Just sent a PR for inclusion in F# project system request as well dotnet/fsharp#3395 😄

[MarkKharitonov]

I need that too.
We do not even need a new flag. There is already the /nowarn flag, just assign it higher priority than /err.

[rainersigwald]

@MarkKharitonov That is already the case. This is a request to make some warnings produced as warnings even when -warnAsError is set.

$ type warnaserror.proj
<Project>
 <Target Name="Warn">
  <Warning Code="Code1" Text="Warning 1" />
  <Warning Code="Code2" Text="Warning 2" />
 </Target>
</Project>

$ msbuild warnaserror.proj -warnAsError
Microsoft (R) Build Engine version 15.9.20+g88f5fadfbe for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 11/19/2018 10:02:37 AM.
Project "s:\warnaserror.proj" on node 1 (default targets).
s:\warnaserror.proj(3,3): error Code1: Warning 1
s:\warnaserror.proj(4,3): error Code2: Warning 2
Done Building Project "s:\warnaserror.proj" (default targets).


Build FAILED.

"s:\warnaserror.proj" (default target) (1) ->
(Warn target) ->
  s:\warnaserror.proj(3,3): error Code1: Warning 1


"s:\warnaserror.proj" (default target) (1) ->
  s:\warnaserror.proj(4,3): error Code2: Warning 2

    0 Warning(s)
    2 Error(s)

Time Elapsed 00:00:00.10

$ msbuild warnaserror.proj -warnAsError -nowarn:Code1
Microsoft (R) Build Engine version 15.9.20+g88f5fadfbe for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 11/19/2018 10:02:47 AM.
Project "s:\warnaserror.proj" on node 1 (default targets).
s:\warnaserror.proj(4,3): error Code2: Warning 2
Done Building Project "s:\warnaserror.proj" (default targets).


Build FAILED.

"s:\warnaserror.proj" (default target) (1) ->
(Warn target) ->
  s:\warnaserror.proj(4,3): error Code2: Warning 2

    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:00.12

$ msbuild warnaserror.proj -warnAsError -nowarn:Code1 -verbosity:detailed
Microsoft (R) Build Engine version 15.9.20+g88f5fadfbe for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 11/19/2018 10:03:03 AM.
Project "s:\warnaserror.proj" on node 1 (default targets).
Building with tools version "15.0".
Target "Warn" in project "s:\warnaserror.proj" (entry point):
Using "Warning" task from assembly "Microsoft.Build.Tasks.Core, Version=15.1.0.0, Culture=neutral, PublicKeyToken=b03f5
f7f11d50a3a".
Task "Warning"
s:\warnaserror.proj(3,3): message Code1: Warning 1
Done executing task "Warning".
Task "Warning"
s:\warnaserror.proj(4,3): error Code2: Warning 2
Done executing task "Warning".
Done building target "Warn" in project "warnaserror.proj".
Done Building Project "s:\warnaserror.proj" (default targets).


Build FAILED.

"s:\warnaserror.proj" (default target) (1) ->
(Warn target) ->
  s:\warnaserror.proj(4,3): error Code2: Warning 2

    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:00.18

[MarkKharitonov]

Excellent, then we do not have a problem. So, I can pass /err /nowarn:MSB3026 to treat all the warnings as errors except for MSB3026

I do not know if this is your thing, but could you answer to https://stackoverflow.com/questions/53375076/does-the-new-msbuild-15-warnaserror-switch-allow-to-fail-on-all-the-warnings-ex?noredirect=1#comment93638635_53375076 so that I could credit you?

[sandyarmstrong]

This would be very useful, so that build output still shows the warnings, but simply doesn't treat them as errors.

[benvillalobos]

Is there still demand for a feature like this despite the workaround @rainersigwald suggested further up in this thread? msbuild warnaserror.proj -warnAsError -nowarn:Code1

[benvillalobos]

Linking some relevant pull requests:

#6174

#6308

#5774

[leshy84]

We also bumped into the problem in C# projects:

<PropertyGroup>
  <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
  <WarningsNotAsErrors>NU1701</WarningsNotAsErrors>
</PropertyGroup>

We expected the warning to be displayed as warning, but it's displayed as error.
So had to replace WarningsNotAsErrors with NoWarn property to hide the warning completely.

[rseanhall]

Yes, I would still like this feature. So would the people commenting on #5053.

[benvillalobos]

Will make sure we at least discuss this during our next planning meeting.

[rseanhall]

Thanks!

[baronfel]

Added the Documentation label to signal that we need a Docs addition for this feature.

[Forgind]

MicrosoftDocs/visualstudio-docs#7585
MicrosoftDocs/visualstudio-docs#7586