Exec EchoOff="true" does not work

[ctaggart]

Steps to reproduce

Either include a project sample, attach a zipped project, or provide IDE / CLI steps to create the project and repro the behaviour. Example of a project sample:

Project file

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net461</TargetFramework>
  </PropertyGroup>
  <Target Name="DebugEchoOff" BeforeTargets="Build">
    <Exec Command="git rev-parse HEAD" ConsoleToMsBuild="true" EchoOff="true">
      <Output TaskParameter="ConsoleOutput" PropertyName="SourceLinkCommit" />
    </Exec>
    <Message Importance="high" Text="SourceLinkCommit: $(SourceLinkCommit)" />
  </Target>
</Project>

Directory contents:
https://github.com/ctaggart/sourcelink-test/tree/EchoOff/VS2017CSharpLibraryCore

Command line

dotnet build

Expected behavior

C:\Users\camer\cs\sourcelink-test\VS2017CSharpLibraryCore [EchoOff +0 ~2 -0 !]> dotnet build
Microsoft (R) Build Engine version 15.5.179.9764 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Restoring packages for C:\Users\camer\cs\sourcelink-test\VS2017CSharpLibraryCore\VS2017CSharpLibraryCore.csproj...
  Restore completed in 87.18 ms for C:\Users\camer\cs\sourcelink-test\VS2017CSharpLibraryCore\VS2017CSharpLibraryCore.csproj.
  VS2017CSharpLibraryCore -> C:\Users\camer\cs\sourcelink-test\VS2017CSharpLibraryCore\bin\Debug\net461\VS2017CSharpLibraryCore.dll
  SourceLinkCommit: 3a8feea438d3f097fbada82c37dc35206c9775fe

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:01.95

Actual behavior

C:\Users\camer\cs\sourcelink-test\VS2017CSharpLibraryCore [EchoOff +0 ~2 -0 !]> dotnet build
Microsoft (R) Build Engine version 15.5.179.9764 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Restoring packages for C:\Users\camer\cs\sourcelink-test\VS2017CSharpLibraryCore\VS2017CSharpLibraryCore.csproj...
  Restore completed in 87.18 ms for C:\Users\camer\cs\sourcelink-test\VS2017CSharpLibraryCore\VS2017CSharpLibraryCore.csproj.
  VS2017CSharpLibraryCore -> C:\Users\camer\cs\sourcelink-test\VS2017CSharpLibraryCore\bin\Debug\net461\VS2017CSharpLibraryCore.dll
  3a8feea438d3f097fbada82c37dc35206c9775fe
  SourceLinkCommit: 3a8feea438d3f097fbada82c37dc35206c9775fe

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:01.95

Environment data

C:\Users\camer\cs\sourcelink-test\VS2017CSharpLibraryCore [2.7 ≡ +1 ~1 -0 !]> dotnet --info
.NET Command Line Tools (2.1.2)

Product Information:
 Version:            2.1.2
 Commit SHA-1 hash:  5695315371

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.16299
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\2.1.2\

Microsoft .NET Core Shared Framework Host

  Version  : 2.0.3
  Build    : a9190d4a75f4a982ae4b4fa8d1a24526566c69df

C:\Users\camer\cs\sourcelink-test\VS2017CSharpLibraryCore [2.7 ≡ +1 ~1 -0 !]> dotnet msbuild /version
Microsoft (R) Build Engine version 15.5.179.9764 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

15.5.179.9764

[rainersigwald]

Thanks for filing this!

I had to look through the source to figure out what was going on, which is no good. I'm changing this bug to be "update the docs so it's possible to understand this without looking in the code".

What EchoOff="true" does is avoid logging the command: https://github.com/Microsoft/msbuild/blob/f2754cdbf8f50b99101a001c29f19211368e3009/src/Tasks/Exec.cs#L391-L395

That's the difference between (at /verbosity:normal):

       DebugEchoOff:
         git rev-parse HEAD
         603aaaf589669dd9bf7a457ce70d3506eb69fc8f
         SourceLinkCommit: 603aaaf589669dd9bf7a457ce70d3506eb69fc8f

and

       DebugEchoOff:
         603aaaf589669dd9bf7a457ce70d3506eb69fc8f
         SourceLinkCommit: 603aaaf589669dd9bf7a457ce70d3506eb69fc8f

The extra output you're seeing in the build isn't from echoing the command, but from Exec logging the standard output of the command. It does that because Exec sets its default StandardOutputImportance to High.

You can override that default by explicitly specifying StandardOutputImportance="Low" in the Exec invocation. Then only detailed-and-higher logging will print it. I tested this in your example project.

It's especially confusing because the command line is not logged at dotnet's default verbosity (which is minimal), so if you usually build using dotnet build it looks like EchoOff does nothing!

[rainersigwald]

Please let us know if there's anything else we can do to further clarify this.

[ctaggart]

Thank you!