feat(3p/typedGo): Add derivation for the Go alpha with a type system r/1003

The Go language authors have released an experimental version of Go
that has a type system: https://blog.golang.org/generics-next-step

This overrides the existing Go derivation to build the typed Go. The
next step is a buildTypedGo set of functions that wrap buildGo.

Change-Id: Idb8a4868bca003d821ed5cb324af633398faf002
Reviewed-on: https://cl.tvl.fyi/c/depot/+/443
Reviewed-by: lukegb <lukegb@tvl.fyi>

1 files changed, 30 insertions, 0 deletions

diff --git a/third_party/default.nix b/third_party/default.nix
index 8fda06857ef5..0f25b3730e3f 100644
--- a/third_party/default.nix
+++ b/third_party/default.nix
@@ -179,6 +179,36 @@ in exposed.lib.fix(self: exposed // {
   clangStdenv = nixpkgs.llvmPackages_10.stdenv;
   stdenv = nixpkgs.llvmPackages_10.stdenv;
 
+  # The Go authors have released a version of Go (in alpha) that has a
+  # type system. This makes it available, specifically for use with
+  # //nix/buildTypedGo.
+  typedGo = nixpkgs.go.overrideAttrs(old: {
+    version = "dev-go2go";
+    doCheck = false;
+    patches = []; # they all don't apply and are mostly about Darwin crap
+
+    src = nixpkgs.fetchgit {
+      url = "https://go.googlesource.com/go";
+      # You might think these hashes are trivial to update. It's just
+      # a branch in a git repository, right?
+      #
+      # Well, think again. Somehow I managed to get no fewer than 3
+      # (!) different commit hashes for the same branch by cloning
+      # this repository thrice. Only the third one (which you, the
+      # reader, can find below for your reading pleasure) actually
+      # gave me `go tool go2go`.
+      rev = "ad307489d41133f32c779cfa1b0db4a852ace047";
+      leaveDotGit = true;
+      sha256 = "0wxa1zawvmf0hflrb42qi1ggrj28nwr8vjmmygnxny8f00xi8198";
+
+      postFetch = ''
+        cd $out
+        ${nixpkgs.git}/bin/git log -n 1 "--format=format: +%h %cd" HEAD > VERSION
+        rm -rf .git
+      '';
+    };
+  });
+
   # Make NixOS available
   nixos = import "${nixpkgsSrc}/nixos";
 })