Make sure there is a location at the start of functions

If the first block of the function starts with an event, we use the
event's location. This is useful in case of tail-calls, where some code
is generated before this first block. If we don't have an event, we set
the initial location to unkown to prevent previous locations to bleed
into the function body.

Author: vouillon

compiler/lib/generate.ml

@@ -1101,19 +1101,6 @@ let rec translate_expr ctx queue loc x e level : _ * J.statement_list =
       let loc = source_location ctx After pc in
       let fv = Addr.Map.find pc ctx.freevars in
       let clo = compile_closure ctx cont in
-      let clo =
-        match clo with
-        | (st, x) :: rem ->
-            let loc =
-              match x, source_location ctx Before pc with
-              | (J.U | J.N), (J.U | J.N) -> J.U
-              | x, (J.U | J.N) -> x
-              | (J.U | J.N), x -> x
-              | _, x -> x
-            in
-            (st, loc) :: rem
-        | _ -> clo
-      in
       let clo =
         J.EFun
           ( None
@@ -1925,8 +1912,14 @@ and compile_closure ctx (pc, args) =
   let current_blocks = Structure.get_nodes st.structure in
   if debug () then Format.eprintf "@[<hv 2>closure {@;";
   let scope_stack = [] in
+  let start_loc =
+    let block = Addr.Map.find pc ctx.Ctx.blocks in
+    match block.body with
+    | (Event loc, _) :: _ -> J.Pi loc
+    | _ -> J.U
+  in
   let _never, res =
-    compile_branch st J.N [] (pc, args) scope_stack ~fall_through:Return
+    compile_branch st start_loc [] (pc, args) scope_stack ~fall_through:Return
   in
   if Addr.Set.cardinal !(st.visited_blocks) <> Addr.Set.cardinal current_blocks
   then (

compiler/tests-compiler/gh747.ml

@@ -265,7 +265,7 @@ end
      45:       [248,
      46:        caml_string_of_jsbytes("Test.Unhandled"),
      47:        runtime.caml_fresh_oo_id(0)],
-     48:     cst_Raised_at = caml_string_of_jsbytes("Raised at"),
+     48:     cst_Raised_at =  /*<<?>>*/ caml_string_of_jsbytes("Raised at"),
      49:     cst_Re_raised_at = caml_string_of_jsbytes("Re-raised at"),
      50:     cst_Raised_by_primitive_operat =
      51:       caml_string_of_jsbytes("Raised by primitive operation at"),

compiler/tests-compiler/sourcemap.ml

@@ -90,8 +90,7 @@ let%expect_test _ =
       /dune-root/test.ml:1:11 -> 6:18
       /dune-root/test.ml:1:12 -> 6:28
       /dune-root/test.ml:1:12 -> 7:7
-      /dune-root/test.ml:1:12 -> 7:14
-      null -> 10:2
+      null -> 7:14
     |}]
 
 let%expect_test _ =