Use the use-site location for errors from pps

src/lib.ml

@@ -790,7 +790,12 @@ and resolve_user_deps db deps ~allow_private_deps ~pps ~stack =
   let deps, pps =
     match pps with
     | [] -> (deps, Ok [])
-    | pps ->
+    | first :: others as pps ->
+      (* Location of the list of ppx rewriters *)
+      let loc =
+        let last = Option.value (List.last others) ~default:first in
+        { (fst first) with stop = (fst last).stop }
+      in
       let pps =
         let pps = (pps : (Loc.t * Jbuild.Pp.t) list :> (Loc.t * string) list) in
         resolve_simple_deps db pps ~allow_private_deps:true ~stack
@@ -798,16 +803,16 @@ and resolve_user_deps db deps ~allow_private_deps ~pps ~stack =
         closure_with_overlap_checks None pps ~stack
       in
       let deps =
-        let rec check_runtime_deps acc pps ~loc = function
+        let rec check_runtime_deps acc pps = function
           | [] -> loop acc pps
           | lib :: ppx_rts ->
             check_private_deps ~lib ~loc ~allow_private_deps >>= fun rt ->
-            check_runtime_deps (rt :: acc) pps ~loc ppx_rts
+            check_runtime_deps (rt :: acc) pps ppx_rts
         and loop acc = function
           | [] -> Ok acc
           | pp :: pps ->
             pp.ppx_runtime_deps >>= fun rt_deps ->
-            check_runtime_deps acc pps ~loc:pp.loc rt_deps
+            check_runtime_deps acc pps rt_deps
         in
         deps >>= fun deps ->
         pps  >>= fun pps  ->

test/blackbox-tests/test-cases/private-public-overlap/run.t

@@ -22,7 +22,7 @@ On the other hand, public libraries may have private preprocessors
 
 Unless they introduce private runtime dependencies:
   $ $JBUILDER build -j1 --display short --root private-runtime-deps 2>&1 | grep -v Entering
-  File "jbuild", line 8, characters 1-143:
+  File "jbuild", line 1, characters 0-327:
   Error: Library "private_runtime_dep" is private, it cannot be a dependency of a public library.
   You need to give "private_runtime_dep" a public name.
         ocamlc .private_ppx.objs/private_ppx.{cmi,cmo,cmt}