Allow Path.is_descendant to work on external paths.

otherlibs/stdune/src/path.ml

@@ -570,6 +570,7 @@ let is_descendant t ~of_ =
   match t, of_ with
   | In_source_tree t, In_source_tree of_ -> Source0.is_descendant t ~of_
   | In_build_dir t, In_build_dir of_ -> Build.is_descendant t ~of_
+  | External t, External of_ -> External.is_descendant t ~of_
   | _ -> false
 ;;
 

otherlibs/stdune/src/path_external.ml

@@ -75,7 +75,7 @@ include (
 let to_string_maybe_quoted t = String.maybe_quoted (to_string t)
 
 let is_descendant b ~of_:a =
-  is_root a || String.starts_with ~prefix:(to_string a ^ "/") (to_string b)
+  is_root a || equal a b || String.starts_with ~prefix:(to_string a ^ "/") (to_string b)
 ;;
 
 module Map = String.Map

otherlibs/stdune/test/path_tests.ml

@@ -129,18 +129,12 @@ true
 
 let%expect_test _ =
   is_descendant (e "/foo/bar") ~of_:(e "/foo");
-  [%expect
-    {|
-false
-|}]
+  [%expect {| true |}]
 ;;
 
 let%expect_test _ =
   is_descendant (e "/foo/bar") ~of_:(e "/foo/bar");
-  [%expect
-    {|
-false
-|}]
+  [%expect {| true |}]
 ;;
 
 let%expect_test _ =
@@ -153,18 +147,12 @@ false
 
 let%expect_test _ =
   is_descendant (e "/foo/bar/") ~of_:(e "/foo/bar");
-  [%expect
-    {|
-false
-|}]
+  [%expect {| true |}]
 ;;
 
 let%expect_test _ =
   is_descendant (e "/foo/bar") ~of_:(e "/");
-  [%expect
-    {|
-false
-|}]
+  [%expect {| true |}]
 ;;
 
 let%expect_test _ =