Compiler: do not convert the absense of sourceRoot to empty sourceRoot

compiler/lib/source_map.ml

@@ -373,25 +373,31 @@ module Standard = struct
   let json t =
     let stringlit s = `Stringlit (Yojson.Safe.to_string (`String s)) in
     `Assoc
-      [ "version", `Intlit (string_of_int t.version)
-      ; "file", stringlit (rewrite_path t.file)
-      ; ( "sourceRoot"
-        , stringlit
-            (match t.sourceroot with
-            | None -> ""
-            | Some s -> rewrite_path s) )
-      ; "names", `List (List.map t.names ~f:(fun s -> stringlit s))
-      ; "sources", `List (List.map t.sources ~f:(fun s -> stringlit (rewrite_path s)))
-      ; "mappings", stringlit (Mappings.to_string t.mappings)
-      ; ( "sourcesContent"
-        , `List
-            (match t.sources_content with
-            | None -> []
-            | Some l ->
-                List.map l ~f:(function
-                    | None -> `Null
-                    | Some x -> Source_content.to_json x)) )
-      ]
+      (List.filter_map
+         ~f:(fun (name, v) ->
+           match v with
+           | None -> None
+           | Some v -> Some (name, v))
+         [ "version", Some (`Intlit (string_of_int t.version))
+         ; "file", Some (stringlit (rewrite_path t.file))
+         ; ( "sourceRoot"
+           , match t.sourceroot with
+             | None -> None
+             | Some s -> Some (stringlit (rewrite_path s)) )
+         ; "names", Some (`List (List.map t.names ~f:(fun s -> stringlit s)))
+         ; ( "sources"
+           , Some (`List (List.map t.sources ~f:(fun s -> stringlit (rewrite_path s)))) )
+         ; "mappings", Some (stringlit (Mappings.to_string t.mappings))
+         ; ( "sourcesContent"
+           , match t.sources_content with
+             | None -> None
+             | Some l ->
+                 Some
+                   (`List
+                     (List.map l ~f:(function
+                         | None -> `Null
+                         | Some x -> Source_content.to_json x))) )
+         ])
 
   let of_json (json : Yojson.Raw.t) =
     match json with

compiler/tests-compiler/build_path_prefix_map.ml

@@ -41,8 +41,8 @@ let%expect_test _ =
       | None -> failwith "no sourcemap generated!");
   [%expect
     {|
-      file: test.js
-      sourceRoot:
-      sources:
-      - /dune-root/test.ml
+    file: test.js
+    sourceRoot: <none>
+    sources:
+    - /dune-root/test.ml
     |}]

compiler/tests-sourcemap/dump.reference

@@ -1,7 +1,7 @@
 sourcemap for test.bc.js
-b.ml:1:4 -> 12:   function <>f(x){return x - 1 | 0;}
-b.ml:1:6 -> 14:   function f(<>x){return x - 1 | 0;}
-b.ml:1:10 -> 17:   function f(x){<>return x - 1 | 0;}
-b.ml:1:6 -> 24:   function f(x){return <>x - 1 | 0;}
-b.ml:1:15 -> 34:   function f(x){return x - 1 | 0;<>}
-b.ml:1:4 -> 23:   var Testlib_B = [0, <>f];
+/my/sourceRoot#b.ml:1:4 -> 12:   function <>f(x){return x - 1 | 0;}
+/my/sourceRoot#b.ml:1:6 -> 14:   function f(<>x){return x - 1 | 0;}
+/my/sourceRoot#b.ml:1:10 -> 17:   function f(x){<>return x - 1 | 0;}
+/my/sourceRoot#b.ml:1:6 -> 24:   function f(x){return <>x - 1 | 0;}
+/my/sourceRoot#b.ml:1:15 -> 34:   function f(x){return x - 1 | 0;<>}
+/my/sourceRoot#b.ml:1:4 -> 23:   var Testlib_B = [0, <>f];

compiler/tests-sourcemap/dump_sourcemap.ml

@@ -62,8 +62,14 @@ let print_mapping lines ?(line_offset = 0) (sm : Source_map.Standard.t) =
         -> (
           match file ori_source with
           | "a.ml" | "b.ml" | "c.ml" | "d.ml" ->
+              let root =
+                match sm.sourceroot with
+                | None -> ""
+                | Some root -> root ^ "#"
+              in
               Printf.printf
-                "%s:%d:%d -> %d:%s\n"
+                "%s%s:%d:%d -> %d:%s\n"
+                root
                 (file ori_source)
                 ori_line
                 ori_col

compiler/tests-sourcemap/dune

@@ -7,6 +7,7 @@
  (name test)
  (modules test)
  (modes js)
+ (js_of_ocaml (link_flags (:standard --source-map-root /my/sourceRoot)))
  (libraries testlib))
 
 (library