From 2f85dfe50c1eb9622a1b409de95629bcced0992f Mon Sep 17 00:00:00 2001
From: Griffin Smith <grfn@gws.fyi>
Date: Fri, 24 Jul 2020 21:30:42 -0400
Subject: fix(3p/nix): Don't include depotPath in the main drv

Including depotPath in the shellHook of the main derivation for tvix
was, unsurprisingly, causing spurious rebuilds. It's still useful when
developing locally, though, so I've extracted it to a `build-shell`
derivation as a passthru attribute and updated the documentation.

Fixes: #20
Change-Id: Ibc686b9f06ec68e79759ca2c989414bd5fbce696
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1426
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI
---
 third_party/nix/README.md   |  2 +-
 third_party/nix/default.nix | 19 +++++++++++--------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/third_party/nix/README.md b/third_party/nix/README.md
index 9e3d7486c87a..36ba7d0c2742 100644
--- a/third_party/nix/README.md
+++ b/third_party/nix/README.md
@@ -144,7 +144,7 @@ nix-shell.
 mkdir ~/build/tvix
 cd ~/build/tvix
 
-nix-shell $DEPOT_PATH -A third_party.nix
+nix-shell $DEPOT_PATH -A third_party.nix.build-shell
 
 # Disable clang-tidy for quicker builds
 cmake $DEPOT_PATH -DCLANG_TIDY_PATH=""
diff --git a/third_party/nix/default.nix b/third_party/nix/default.nix
index c8ed5adc8720..a5f2e5bd7677 100644
--- a/third_party/nix/default.nix
+++ b/third_party/nix/default.nix
@@ -30,7 +30,7 @@ let
       --plugin=protoc-gen-grpc=${pkgs.grpc}/bin/grpc_cpp_plugin --grpc_out=$out/libproto \
       $PROTO_SRCS/*.proto
   '';
-in pkgs.llvmPackages.libcxxStdenv.mkDerivation {
+in lib.fix (self: pkgs.llvmPackages.libcxxStdenv.mkDerivation {
   pname = "tvix";
   version = "2.3.4";
   inherit src;
@@ -133,13 +133,16 @@ in pkgs.llvmPackages.libcxxStdenv.mkDerivation {
     ln -s $out/bin/nix $out/libexec/nix/build-remote
   '';
 
-  shellHook = ''
-    export NIX_DATA_DIR="${toString depotPath}/third_party"
-    export NIX_TEST_VAR=foo
-  '';
-
   # TODO(tazjin): integration test setup?
   # TODO(tazjin): docs generation?
 
-  passthru = { test-vm = import ./test-vm.nix args; };
-}
+  passthru = {
+    build-shell = self.overrideAttrs (_: {
+      shellHook = ''
+        export NIX_DATA_DIR="${toString depotPath}/third_party"
+        export NIX_TEST_VAR=foo
+      '';
+    });
+    test-vm = import ./test-vm.nix args;
+  };
+})
-- 
cgit 1.4.1