From 6779902b32a208f39ab5d073714a12a7ac72bcf1 Mon Sep 17 00:00:00 2001
From: Tom McLaughlin <tom@codedown.io>
Date: Mon, 23 Nov 2020 11:08:07 -0700
Subject: [PATCH] fetchgit: support passing tree hashes as "rev"

---
 pkgs/build-support/fetchgit/nix-prefetch-git | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/pkgs/build-support/fetchgit/nix-prefetch-git b/pkgs/build-support/fetchgit/nix-prefetch-git
index 3cb115c5e6e6..fc633506fbe7 100755
--- a/pkgs/build-support/fetchgit/nix-prefetch-git
+++ b/pkgs/build-support/fetchgit/nix-prefetch-git
@@ -149,7 +149,19 @@ checkout_hash(){
     fi
 
     clean_git fetch -t ${builder:+--progress} origin || return 1
-    clean_git checkout -b "$branchName" "$hash" || return 1
+
+    local object_type=$(git cat-file -t "$hash")
+    if [[ "$object_type" == "commit" ]]; then
+        clean_git checkout -b "$branchName" "$hash" || return 1
+    elif [[ "$object_type" == "tree" ]]; then
+        clean_git config user.email "nix-prefetch-git@localhost"
+        clean_git config user.name "nix-prefetch-git"
+        local commit_id=$(git commit-tree "$hash" -m "Commit created from tree hash $hash")
+        clean_git checkout -b "$branchName" "$commit_id" || return 1
+    else
+        echo "Unrecognized git object type: $object_type"
+        return 1
+    fi
 }
 
 # Fetch only a branch/tag and checkout it.