git-preview: use worktrees

1 files changed, 13 insertions, 12 deletions

diff --git a/krebs/5pkgs/simple/git-preview/default.nix b/krebs/5pkgs/simple/git-preview/default.nix
index f20f2a63..77826f34 100644
--- a/krebs/5pkgs/simple/git-preview/default.nix
+++ b/krebs/5pkgs/simple/git-preview/default.nix
@@ -1,15 +1,16 @@
-{ coreutils, git, stdenv, writeDashBin }:
+{ coreutils, git, writeDashBin }:
 
 writeDashBin "git-preview" ''
-  PATH=${stdenv.lib.makeBinPath [
-    coreutils
-    git
-  ]}''${PATH+:$PATH}
-  hashes=$(git log --format=%h "..$1")
-  end=$(echo "$hashes" | head -1)
-  start=$(echo "$hashes" | tail -1)
-  # exit if no diff was found
-  test -z "$start" && exit 0
-  shift
-  git diff "$start^..$end" "$@"
+  set -efu
+  head_commit=$(${git}/bin/git log -1 --format=%H)
+  merge_commit=$1; shift
+  merge_message='Merge for git-preview'
+  preview_dir=$(${coreutils}/bin/mktemp --tmpdir -d git-preview.XXXXXXXX)
+  preview_name=$(${coreutils}/bin/basename "$preview_dir")
+  ${git}/bin/git worktree add --detach -f "$preview_dir" 2>/dev/null
+  ${git}/bin/git -C "$preview_dir" checkout -q "$head_commit"
+  ${git}/bin/git -C "$preview_dir" merge -qm "$merge_message" "$merge_commit"
+  ${git}/bin/git -C "$preview_dir" diff "$head_commit.." "$@"
+  ${coreutils}/bin/rm -fR "$preview_dir"
+  ${coreutils}/bin/rm -R .git/worktrees/"$preview_name"
 ''