fix(preamble): add the preamble before the // Generated comment (#574)

* fix(preamble): add the preamble before the `// Generated` comment

* add missing unstaged test

Changes.md

@@ -61,7 +61,8 @@ Unreleased
   ([#554](https://github.com/melange-re/melange/pull/554))
 - melange: add `--preamble` flag to add a preamble to emitted JS. An example is
   `"use client";` in React Server Components, which needs to appear before
-  imports ([#545](https://github.com/melange-re/melange/pull/545))
+  imports ([#545](https://github.com/melange-re/melange/pull/545),
+  [#574](https://github.com/melange-re/melange/pull/574))
 
 0.3.2 2022-11-19
 ---------------

jscomp/core/js_dump_program.ml

@@ -103,14 +103,14 @@ let es6_program ~package_info ~output_info ~output_dir f (x : J.deps_program) =
 
 let pp_deps_program ~package_info ~(output_info : Js_packages_info.output_info)
     ~(output_prefix : string) (f : Ext_pp.t) (program : J.deps_program) =
-  if not !Js_config.no_version_header then (
-    P.string f Melange_version.header;
-    P.newline f);
   Option.iter
     (fun preamble ->
       P.string f preamble;
       P.newline f)
     program.preamble;
+  if not !Js_config.no_version_header then (
+    P.string f Melange_version.header;
+    P.newline f);
   if deps_program_is_empty program then P.string f empty_explanation
     (* This is empty module, it won't be referred anywhere *)
   else

jscomp/test/dist/jscomp/test/preamble_test.js

@@ -1,5 +1,5 @@
-// Generated by Melange
 "use client";
+// Generated by Melange
 'use strict';
 
 

nix/shell.nix

@@ -27,7 +27,7 @@ in
 with ocamlPackages;
 
 mkShell {
-  inputsFrom = lib.attrValues derivations ++ [ melange-compiler-libs ];
+  inputsFrom = lib.attrValues derivations;
   nativeBuildInputs = [
     ocamlformat
     utop

test/preamble.t

@@ -0,0 +1,34 @@
+Demonstrate usage of `--preamble`
+
+  $ . ./setup.sh
+  $ cat > x.ml <<EOF
+  > let x = 1
+  > EOF
+
+  $ melc x.ml --preamble '"use client";'
+  "use client";
+  // Generated by Melange
+  'use strict';
+  
+  
+  var x = 1;
+  
+  exports.x = x;
+  /* No side effect */
+
+  $ cat > x.ml <<EOF
+  > [@@@bs.config { flags = [| "--preamble"; "\"use client\";" |] }]
+  > let x = 1
+  > EOF
+  $ melc x.ml
+  "use client";
+  // Generated by Melange
+  'use strict';
+  
+  
+  var x = 1;
+  
+  exports.x = x;
+  /* No side effect */
+
+