Wait, I accidentally reverted the update.

Does it impossible to build it from source?

It uses a custom build process which automatically downloads pre-compiled Mono binaries.

I bit back I was looking at your original pr and applied some of @samueldr feedback.
Almost died in a stash but here it is 😄

diff --git a/pkgs/development/tools/build-managers/msbuild/default.nix b/pkgs/development/tools/build-managers/msbuild/default.nix
index 781f5b1c524..93d19fb047c 100644
--- a/pkgs/development/tools/build-managers/msbuild/default.nix
+++ b/pkgs/development/tools/build-managers/msbuild/default.nix
@@ -14,15 +14,21 @@ stdenv.mkDerivation rec {
   dontConfigure = true;
   dontBuild = true;
 
-  unpackPhase = "dpkg-deb -x $src .";
-  installPhase = ''
-    substituteInPlace usr/bin/msbuild --replace /usr/bin/mono ${mono}/bin/mono --replace /usr/lib/mono/msbuild/15.0/bin/MSBuild.dll '$(dirname $0)/../usr/lib/mono/msbuild/15.0/bin/MSBuild.dll'
+  unpackPhase = "dpkg-deb -x $src build";
+  installPhase = "
+    (
+    cd build
     mv usr/bin .
-    mkdir -p $out
-    cp -r ./bin ./usr $out
-    cp -rs ${mono}/lib/mono/msbuild/15.0/bin/Roslyn $out/usr/lib/mono/msbuild/15.0/bin/Roslyn
-    cp -rs ${mono}/lib/mono/4.5 $out/usr/lib/mono/4.5
-  '';
+    mv usr/lib .
+    rm -rf usr
+    )
+    cp -r build/ $out
+
+    substituteInPlace $out/bin/msbuild --replace /usr/bin/mono ${mono}/bin/mono --replace /usr/lib/mono/msbuild/15.0/bin/MSBuild.dll $out/lib/mono/msbuild/15.0/bin/MSBuild.dll
+
+    ln -s ${mono}/lib/mono/msbuild/15.0/bin/Roslyn $out/lib/mono/msbuild/15.0/bin/Roslyn
+    ln -s ${mono}/lib/mono/4.5 $out/lib/mono/4.5
+  ";
 
   meta = with stdenv.lib; {
     description = "The Microsoft Build Engine (MSBuild) is the build platform for .NET and Visual Studio";

Main things addressed if I recall correctly were:

• Symlink instead of copying stuff from mono
• No usr in $out
• Bring in the env-vars file

Also didn't include anything from share/doc/ because it didn't look useful.

Nice GitHub bug 😛 I'll create a new PR again, I guess.

@leo60228 #50842 (comment)

I don't have a good build machine. Could you see if it still runs without it?

I was actually able to reproduce what @jdanekrh mentioned in the older pr without this change.

I think I've encountered the same error also. When compiling a project, the compilation would fail with

  Microsoft.Common.CurrentVersion.targets(3446, 5): [MSB3491] Could not write lines to file "/Debug/ClientLib.csproj.CoreCompileInputs.cache". Could not find a part of the path "/Debug/ClientLib.csproj.CoreCompileInputs.cache".
  Microsoft.Common.CurrentVersion.targets(5101, 5): [MSB3191] Unable to create directory "/Debug/". Access to the path "/Debug/" is denied.

(it attempts to write to the filesystem root, because a prefix is not set correctly).

I resolved the same thing by 1) downloading msbuild and unpacking msbuild, 2) setting it in jetbrains.rider in GUI in Use custom MSBuild version to

/home/jdanek/Downloads/msbuild/MSBuild.dll

and 3) adding to my .bashrc the following

export MSBuildExtensionsPath=/home/jdanek/Downloads/msbuild/Extensions

It went away when I applied it IIRC.
I'll test your new pr, with the latest msbuild, and see if I can reproduce it again.

@leo60228 Have you opened your new PR already? If not, can you link to https://github.com/NixOS/nixpkgs/issues/29817 from it when you do it (preferably with some keyword like Closes #29817), so that it can close the issue automatically once it's merged? :)

😕 I am a bit confused, what is the state of msbuild? I can't find anything in master.

I'm not sure, @leo60228 do you still have the expression?
If you don't have enough time for it, it could still be there for someone to pick up.

It would improve the situation for getting source builds for applications that need msbuild dramatically, because we'd actually have it.

I still have it, but I don't have time for it. I'll try and push it later.

@leo60228 any progress or any chance of sharing that expressions so someone else can pick it up.
i too have the requirement for msbuild ;)

@leo60228 I would love to get msbuild in too. That way I can use NixOS for work projects.

@billksun Just BTW, there is MSBuild 16 available in dotnet core. I have it at /nix/store/klwr9h00b25ws7g7wj2iasnvl3b63xa3-dotnet-sdk-2.2.203/sdk/2.2.203/MSBuild.dll and the Rider IDE is able to detect it and use it, My only issue regarding C# on NixOS is #55435, and that has a reasonable workaround.