RoslynDeterministic.md

## RoslynDeterministic.md

      
        

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              RoslynDeterministic.md
            
          
        
      
    
  
    Deterministic Builds in C#
Status
The C# compiler (Roslyn) supports deterministic builds since Visual Studio 2015.
This means that compiling assemblies under the same conditions (permalink) would produce byte-for-byte equivalent binaries.
However, things get a bit more complicated when Windows (non-portable (permalink)) PDBs are involved. Currently, PDBs themselves are always non-deterministic.
Additionally, the compiler adds the full path of the PDB to the assembly.
This latter limitation might be fully addressed in a future Visual Studio 2017 Update,
but currently (starting with Visual Studio 2015 Update 3), there's a compiler feature flag (pdb-path-determinism) that makes this path relative (temporary workaround).
There's also an option to map paths if you build from different enlistment paths (important if you use [CallerFilePath] or #line directives).
For more information, see this blog post and the umbrella issue.
How To

Deterministic requires Visual Studio 2015 (Roslyn version 1.0).
pdb-path-determinism requires Visual Studio 2015 Update 3 (Roslyn version 1.3).

In MSBuild (.csproj):
<Project>
  <PropertyGroup>
    <Deterministic>true</Deterministic>
    <Features>pdb-path-determinism</Features>
  </PropertyGroup>
</Project>
In the compiler command-line:
> csc /deterministic /features:pdb-path-determinism