Add Path.drop_prefix

src/path.ml

@@ -429,3 +429,13 @@ let change_extension ~ext t =
 let extension = Filename.extension
 
 let pp = Format.pp_print_string
+
+let drop_prefix t ~prefix =
+  let t = to_string t in
+  let prefix =
+    to_string (
+      if String.is_suffix prefix ~suffix:"/" then
+        prefix
+      else
+        prefix ^ "/") in
+  String.drop_prefix t ~prefix

src/path.mli

@@ -114,4 +114,12 @@ val change_extension : ext:string -> t -> t
 
 val extension : t -> string
 
+(** maintains the invariant:
+    {[
+      let suffix = Option.value_exn (Path.drop_prefix t ~prefix) in
+      Path.relative prefix suffix = t
+    ]}
+*)
+val drop_prefix : t -> prefix:t -> string option
+
 val pp : t Fmt.t