Msbuild ignores continueonerror? - tfs

Question

I am trying to invoke MSbuild for a couple of projects twice. First time without any clean, but if this fails I will invoke a clean followed by a new build. (The reasoning is that I want my build to be fast but if that fails fall back to clean, restore nuget packages build etcetera). This works but the build will still fail if the first call failed (it has continueonerror set to true so I dont want it to fail...). Here are the relevant parts of the build file:
<ItemGroup>
<ProjectsToPublish Include="X.sln" />
</ItemGroup>
<Target Name="RestoreAllPackages">
<Message Text="#(ProjectsToPublish)" />
<Exec Command='"$(MSBuildProjectDirectory)\.nuget\nuget.exe" restore "$(MSBuildProjectDirectory)\%(ProjectsToPublish.Identity)"'
/>
</Target>
<Target Name="Build" >
<MSBuild Projects="#(ProjectsToPublish)" Properties="SkipRestore=True;RunCodeAnalysis=False;Retries=10;RetryDelayMilliseconds=50"
BuildInParallel="true" ContinueOnError="WarnAndContinue" />
<!-- MSBuildLastTaskResult outcome of previous task-->
<PropertyGroup>
<FastBuildFailed>false</FastBuildFailed>
<FastBuildFailed Condition="'$(MSBuildLastTaskResult)' == 'false'" >true</FastBuildFailed>
</PropertyGroup>
<Message Importance="high" Text="Initial build failed? $(FastBuildFailed)" />
<Message Importance="high" Text="Initial build failed will retry" Condition="'$(FastBuildFailed)'" />
<CallTarget Targets="FullBuild" Condition="'$(FastBuildFailed)'" />
</Target>
<Target Name="FullBuild" DependsOnTargets="RestoreAllPackages">
<!--Fake property below to reexecute build exact same properties prevents the build lform re-->
<MSBuild Projects="#(ProjectsToPublish)" Properties="SkipRestore=True;RunCodeAnalysis=False;FakeProperty=one" BuildInParallel="true" />
</Target>
<Target Name="RestoreAllPackages">
<Message Text="#(ProjectsToPublish)" />
<Exec Command='"$(MSBuildProjectDirectory)\.nuget\nuget.exe" restore "$(MSBuildProjectDirectory)\%(ProjectsToPublish.Identity)"'
/>
</Target>

Answer 1

For anyone with this rather exotic error. It seems that when a build is run inside of a TFS build server, the build server parses log output and will fail a build even with a ContinueOnError setting. My workaround ended up being <Exec Command="$(MSBuildBinPath)\msbuild.exe #(ProjectsToPublish) /noconlog " ContinueOnError="true" />
Basically spawning a new MSBuild using Exec and making sure that it did not output anything using /noconlog

Answer 2

Rather than using <OnError..., you can assign ContinueOnError the value 'WarnAndContinue', and then use a condition to check the $(MSBuildLastTaskResult) property.
Generic example:
<Error ContinueOnError="WarnAndContinue" />
<Message Importance="High" Text ="$(MSBuildLastTaskResult)" />
<!-- (Returns false) -->
(I believe both "WarnAndContinue" and $(MSBuildLastTaskResult) were introduced in MSBuild 4.0; they should be available on your TFS 2012 build server.)