build: add ppx_inline_test and inline test for external deps

Co-authored-by: aider (openai//workspace/models/openai-mirror/gpt-oss-120b/) <aider@aider.chat>

Author: zenfey

lib/dune

@@ -1,3 +1,3 @@
 (library
  (name dune_ai_context)
- (libraries str unix compiler-libs.common sexplib))
+ (libraries str unix compiler-libs.common sexplib ppx_inline_test))

lib/dune_ai_context.ml

@@ -119,3 +119,13 @@ let print_vendor_dependencies () =
                   Format.printf "%a\n" Printtyp.signature cmi.cmi_sign)
                cmi_paths)
         deps
+
+(* Inline test for [extract_external_deps] *)
+let%test "extract_external_deps parses external_deps correctly" =
+  let s =
+    "(default\n ((library\n   ((names (inst))\n    (extensions ())\n    (package (inst))\n    (source_dir lib)\n    (external_deps\n     ((core required)\n      (str required)\n      (ppx_jane required)\n      (ppx_deriving_yojson required)))\n    (internal_deps ())))))"
+  in
+  let sexp = Sexplib.Sexp.of_string s in
+  let deps = extract_external_deps sexp in
+  let expected = ["core"; "str"; "ppx_jane"; "ppx_deriving_yojson"] in
+  List.sort String.compare deps = List.sort String.compare expected