Fix the interpretation of

doc/manual.org

@@ -628,7 +628,7 @@ that are expanded by Jbuilder.
 
 Jbuilder supports the following variables:
 
-- =ROOT= is the relative path to the root of the workspace
+- =ROOT= is the relative path to the root of the build context
 - =CC= is the C compiler command line being used in the current build
   context
 - =CXX= is the C++ compiler command line being used in the current

src/gen_rules.ml

@@ -385,7 +385,7 @@ module Gen(P : Params) = struct
 
   let root_var_lookup ~dir var_name =
     match var_name with
-    | "ROOT" -> Some (Path.reach ~from:dir Path.root)
+    | "ROOT" -> Some (Path.reach ~from:dir ctx.build_dir)
     | _ -> String_map.find var_name dollar_var_map
 
   let expand_vars ~dir s =