Propper dependency on .git/HEAD and .git/refs/heads/the_current_branch to regenerate Version.ml. Will not update correctly if a git worktree or its main .git are moved, in these cases use dune clean.

.gitHEAD

@@ -1 +0,0 @@
-.git/HEAD

dune

@@ -40,10 +40,27 @@
   (mode promote-until-clean)
 )
 
+(rule
+  (targets .git_main_dir)
+  (deps)
+  (action (run "sh" "-c" "if test -d ../../.git; then printf %s '../../.git' > .git_main_dir; else cat ../../.git | sed -e 's/^gitdir: //' | sed -e 's|$|/../..|' > .git_main_dir; fi")))
+
+(rule
+  (targets .git_worktree_dir)
+  (deps)
+  (action (run "sh" "-c" "if test -d ../../.git; then printf %s '../../.git' > .git_worktree_dir; else cat ../../.git | sed -e 's/^gitdir: //' > .git_worktree_dir; fi")))
+
+(rule
+  (targets .gitHEAD)
+  (deps .git_main_dir .git_worktree_dir)
+  ;; TODO: re-compute .git_main_dir, just in case (since it does not have a dependency on .git)
+  (action (run "sh" "-c" "ln -s \"$(cat .git_worktree_dir)/HEAD\" .gitHEAD")))
+
 (rule
   (targets Version.gitHEAD)
   (deps .gitHEAD)
-  (action (run "sh" "-c" "if git symbolic-ref HEAD; then ln -s ../../.git/\"$(git symbolic-ref HEAD)\" Version.gitHEAD; else ln -s hd Version.gitHEAD; fi"))
+  ;; TODO: re-compute .git_main_dir, just in case (since it does not have a dependency on .git)
+  (action (run "sh" "-c" "if git symbolic-ref HEAD >/dev/null 2>&1; then ln -s \"$(cat .git_main_dir)/$(git symbolic-ref HEAD)\" Version.gitHEAD; else ln -s \"$(cat .git_worktree_dir)/HEAD\" Version.gitHEAD; fi"))
 )
 
 (rule