builtins.fetchgit: Support specifying commit hashes

This adds an argument "rev" specififying the Git commit hash. The
existing argument "rev" is renamed to "ref". The default value for
"ref" is "master". When specifying a hash, it's necessary to specify a
ref since we're not cloning the entire repository but only fetching a
specific ref.

Example usage:

  builtins.fetchgit {
    url = https://github.com/NixOS/nixpkgs.git;
    ref = "release-16.03";
    rev = "c1c0484041ab6f9c6858c8ade80a8477c9ae4442";
  };

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libexpr/primops/fetchgit.hh b/src/libexpr/primops/fetchgit.hh
index 6ffb21a96daa..ff228f3b3c6a 100644
--- a/src/libexpr/primops/fetchgit.hh
+++ b/src/libexpr/primops/fetchgit.hh
@@ -8,7 +8,7 @@ namespace nix {
 
 class Store;
 
-Path exportGit(ref<Store> store,
-    const std::string & uri, const std::string & rev);
+Path exportGit(ref<Store> store, const std::string & uri,
+    const std::string & ref, const std::string & rev = "");
 
 }