Merges a forest of paths into one directory tree with symlinks.
Conflicts are not handled and will always error out.
We use one symlink for every node that is unique to a given store path.

Performance likely becomes bad when joining lots of derivations, but I
have not investigated. The should algorithm do no unnecessary work
though.

Akin to nixpkgs' symlinkJoin.

@@ -0,0 +15,4 @@
+          description = "Derivations to join under a single store path";
+          type =
+            let
+              initial = lib.types.attrs.of lib.types.derivation;

@@ -0,0 +108,4 @@
+                passAsFile = [ "content" ];
+              });
+          in
+          # FIXME: surely we have an assertion system to use instead of this ? right ?

@@ -0,0 +42,4 @@
+                Path of the program used to execute this file as a script.
+                If set, a shebang is prepended to the file.
+              '';
+            type = lib.types.nullish lib.types.path;

@@ -0,0 +16,4 @@
+    echo -n "$1$sep" >&2
+  done
+  echo "${1:-}" >&2
+}

@@ -0,0 +22,4 @@
+  echo "[PANIC] $1" >&2
+  while shift && [ -n "${1:+x}" ]
+  do echo -e "$1" >&2
+  done

@@ -0,0 +34,4 @@
+    echo -n "$1, " >&2
+  done
+  echo "${1:-}" >&2
+}

@@ -0,0 +38,4 @@
+
+function debug { true; }
+if ((NIX_DEBUG > 0 ))
+then {

@@ -0,0 +46,4 @@
+      echo -n "$1, " >&2
+    done
+    echo "${1:-}" >&2
+  }

@@ -0,0 +96,4 @@
+  local path="${3:-}"
+  entry="${entry:+"${entry%%/}/"}$path"
+  entry="${entry:-/}"
+  # entry="$(normalize_path "$entry")"

@@ -0,0 +143,4 @@
+      while read -d $'\n' -r path
+      do
+        push_entry "$origin" "$entry" "$path"
+      done < <( \

@@ -0,0 +173,4 @@
+# # shellcheck disable=2154 # $out is an input
+# if ! mkdir "$out" 2>/dev/null
+# then panic "output directory $out already exists"
+# fi