ocaml: re-tune to exp_nodes + depth 2 (Rust config); add --weights flag

A larger LLM-judge sweep on a nonna+deps corpus (nonna, vendor/opengrep,
opam libs; n=93 sonnet-judged, vs the earlier n=37 single-lib pass) flips
the OCaml tuning: exp_nodes at depth 2 is decisive — spearman(jaccard,
overall) 0.592 (base) -> 0.787 (+exp) -> 0.846 (+exp, depth 2). string/field
and per-tag weight tweaks were flat-to-negative on top of exp. exp_nodes
separates OCaml's variant-dispatch twins (big match-mappers) that otherwise
collapse to near-identical blobs. The config now matches Rust (same ML-family
expression/match shape), and is robust: ~0.84 on BOTH corpora, where the old
string+field config scored 0.88 on generic libs but only 0.59 here.

Also adds a --weights name=val runtime flag (signature.ml dfg_weight is now
override-aware) so per-tag weights are sweepable like --with/--iters; the
sweep confirmed defaults win, so no weight change is encoded.

Author: thebabush

nonna/cli/main.ml

@@ -233,6 +233,17 @@ let rec strip_profile acc = function
   | "--iters" :: v :: rest ->
       Dfg.iterations_override := Some (int_of_string v);
       strip_profile acc rest
+  | "--weights" :: v :: rest ->
+      (* per-DFG-tag weight overrides for tuning sweeps, e.g.
+         --weights construct=1.3,control=1.2 (tag names per Dfg.tag_name) *)
+      String.split_on_char ',' v
+      |> List.iter (fun kv ->
+             match String.split_on_char '=' kv with
+             | [ name; w ] -> Signature.set_weight name (float_of_string w)
+             | _ ->
+                 prerr_endline ("bad --weights entry: " ^ kv);
+                 exit 1);
+      strip_profile acc rest
   | "--with" :: v :: rest ->
       (* fold channels into the BASE hashes (ablation studies) *)
       String.split_on_char ',' v

nonna/features/dfg.ml

@@ -72,7 +72,9 @@ let iters_for (lang : Lang.t option) : int =
          Tuned via LLM-judge correlation on a Chrome (net/) corpus, 2026-06-15
          (n=62 sonnet-judged pairs): spearman(jaccard, judge overall)
          0.859 (depth0/no-exp) -> 0.879 (+exp) -> 0.890 (+exp, depth2). *)
-      | Some (Lang.Rust | Lang.Python | Lang.Python2 | Lang.Python3 | Lang.Cpp) ->
+      | Some
+          ( Lang.Rust | Lang.Python | Lang.Python2 | Lang.Python3 | Lang.Cpp
+          | Lang.Ocaml ) ->
           2 (* exp-node features specialize per round *)
       | _ -> 1)
 
@@ -196,17 +198,19 @@ let base_cfg_for (lang : Lang.t) : cfg =
      Chrome net/ corpus (2026-06-15, n=62): +exp_nodes lifted spearman 0.859->0.879
      (0.890 with depth-2 iters). call_names measured flat (0.859) — left off. *)
   | Lang.Cpp -> { b with string_values = true; field_names = true; exp_nodes = true }
-  (* OCaml lands on the C config, NOT the Rust/Python one: record/module field
-     access (Dot offsets) and format/label strings are API identity, while
-     exp_nodes — decomposed expression graphs that win for Rust/Python/Cpp —
-     HURT here. Tuned via LLM-judge correlation on a 5-lib corpus (base,
-     containers, dune, re, yojson; 2026-06-30, n=37 sonnet-judged pairs):
-     spearman(jaccard, overall) 0.873 (base) -> 0.884 (+string/field);
-     +exp_nodes measured 0.844, iters-2 neutral. Corroborated on 732 mined
-     pairs: samefile FPR halved (0.027 -> 0.014), positive recall unchanged.
-     (OCaml IL itself required fixing opengrep's AST_to_IL — without it every
-     OCaml body collapsed to NTodo; see vendor/opengrep patches.) *)
-  | Lang.Ocaml -> { b with string_values = true; field_names = true }
+  (* OCaml takes the Rust config (exp_nodes, depth 2 — see iters_for): it is the
+     same ML-family expression/match-oriented shape, and decomposed expression
+     graphs are what separate OCaml's ubiquitous variant-dispatch twins (big
+     `match`-mapper functions that collapse to near-identical blobs without it).
+     Re-tuned via LLM-judge correlation on a nonna + deps corpus (nonna,
+     vendor/opengrep, opam libs; 2026-06-30, n=93 sonnet-judged pairs):
+     spearman(jaccard, overall) 0.592 (base) -> 0.787 (+exp) -> 0.846 (+exp,
+     depth 2). string/field and per-tag weight tweaks were flat-to-negative on
+     top of exp. (An earlier n=37 single-lib pass had picked the C config; the
+     larger judge corrected it — exp wins decisively at scale.)
+     (OCaml IL itself is recovered by units.ml's normalize_ocaml AST pre-pass;
+     without it every OCaml body collapses to NTodo.) *)
+  | Lang.Ocaml -> { b with exp_nodes = true }
   (* exp-nodes sweeps (2026-06): decomposed expression graphs at depth 2
      win the evolved kind on Rust (MRR 0.723->0.766, r@5 0.812->0.859) AND
      Python (0.929->0.950, r@5 0.964->0.986), everything else flat — an

nonna/features/signature.ml

@@ -10,14 +10,25 @@ type t = {
 
 (* Per-source weights (v1 defaults: dfg 1.0, call surface 0.8, consts 0.5,
    structural 0.3). DFG features are weighted per tag. *)
-let dfg_weight (tag : Dfg.tag) : float =
+let default_dfg_weight (tag : Dfg.tag) : float =
   match tag with
   | Dfg.BinOp | Dfg.UnOp | Dfg.Call | Dfg.Field | Dfg.Index | Dfg.Construct
   | Dfg.Control ->
       1.0
   | Dfg.ConstString | Dfg.ConstOther -> 0.8
   | Dfg.MacroBag -> 0.8
 
+(* Runtime per-tag weight overrides (--weights, for tuning sweeps), keyed by
+   Dfg.tag_name. Empty = the defaults above. *)
+let weight_overrides : (string, float) Hashtbl.t = Hashtbl.create 8
+let set_weight (name : string) (w : float) : unit =
+  Hashtbl.replace weight_overrides name w
+
+let dfg_weight (tag : Dfg.tag) : float =
+  match Hashtbl.find_opt weight_overrides (Dfg.tag_name tag) with
+  | Some w -> w
+  | None -> default_dfg_weight tag
+
 let misc_weight = 0.8
 let structural_weight = 0.3