Change strategy to avoid ambiguity after a return statement

When pretty-printing, there is no ambiguity since we always have a space
after the return statement. In compact mode, use a newline instead.

compiler/lib/js_output.ml

@@ -1407,8 +1407,14 @@ struct
     let last_semi ?(ret = false) () =
       if can_omit_semi
       then ()
-      else if ret && source_map_enabled
-      then PP.string f "; "
+      else if ret && source_map_enabled && PP.compact f
+      then
+        (* In Chrome, the debugger will stop right after a return
+           statement. We want a whitespace between this statement and
+           the next one to avoid confusing this location and the
+           location of the next statement. When pretty-printing, this
+           is already the case. In compact mode, we add a newline. *)
+        PP.string f ";\n"
       else PP.string f ";"
     in
     if stop_on_statement s then output_debug_info f loc;

compiler/tests-compiler/sourcemap.ml

@@ -75,7 +75,7 @@ let%expect_test _ =
         3: (function(globalThis){
         4:    "use strict";
         5:    var runtime = globalThis.jsoo_runtime;
-        6:    function id(x){return x; }
+        6:    function id(x){return x;}
         7:    var Test = [0, id];
         8:    runtime.caml_register_global(0, Test, "Test");
         9:    return;
@@ -89,7 +89,7 @@ let%expect_test _ =
       /dune-root/test.ml:1:4 -> 6:12
       /dune-root/test.ml:1:7 -> 6:15
       /dune-root/test.ml:1:11 -> 6:18
-      /dune-root/test.ml:1:12 -> 6:28
+      /dune-root/test.ml:1:12 -> 6:27
       /dune-root/test.ml:1:12 -> 7:0
       /dune-root/test.ml:1:12 -> 7:7
       /builtin/blackbox.ml:1:0 -> 7:14

compiler/tests-sourcemap/dump.reference

@@ -1,7 +1,7 @@
 sourcemap for test.bc.js
-/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:1:15 -> 35:   function f(x){return x - 1 | 0; <>}
+/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:1:15 -> 34:   function f(x){return x - 1 | 0;<>}
 /my/sourceRoot#b.ml:1:15 -> 0:<>   var Testlib_B = [0, f];
 /my/sourceRoot#b.ml:1:15 -> 7:   var <>Testlib_B = [0, f];