feat(dot): emit Graphviz source for the action graph

Nodes coloured by action kind, with a targets-only mode for graphs too large
to read in full.

lib/dot.ml

@@ -0,0 +1,46 @@
+open Types
+
+let color = function
+  | "cc" | "c++" -> "#4c78a8"
+  | "ar" -> "#b279a2"
+  | "so" -> "#72b7b2"
+  | "ld" -> "#54a24b"
+  | "gen" -> "#eeca3b"
+  | _ -> "#888888"
+
+let render ?(nodes = true) (b : Build.t) =
+  let buf = Buffer.create 4096 in
+  Buffer.add_string buf "digraph meowc {\n";
+  Buffer.add_string buf "  rankdir=LR;\n  bgcolor=\"transparent\";\n";
+  Buffer.add_string buf
+    "  node [shape=box, style=\"rounded,filled\", fontname=\"Inter,Helvetica,sans-serif\", fontsize=10, color=\"#00000000\", fontcolor=\"#ffffff\"];\n";
+  Buffer.add_string buf "  edge [color=\"#999999\", arrowsize=0.6];\n";
+  if nodes then
+    Array.iter
+      (fun (n : Graph.node) ->
+        Buffer.add_string buf
+          (Printf.sprintf "  n%d [label=%s, fillcolor=%s];\n" n.id
+             (Json.str (n.tag ^ "  " ^ Filename.basename n.label))
+             (Json.str (color n.tag))))
+      b.g.Graph.nodes;
+  Array.iter
+    (fun (n : Graph.node) ->
+      List.iter (fun d -> Buffer.add_string buf (Printf.sprintf "  n%d -> n%d;\n" d n.id)) n.deps)
+    b.g.Graph.nodes;
+  Buffer.add_string buf "}\n";
+  Buffer.contents buf
+
+let targets_only (p : project) =
+  let buf = Buffer.create 1024 in
+  Buffer.add_string buf "digraph targets {\n  rankdir=LR;\n";
+  List.iter
+    (fun (t : target) ->
+      Buffer.add_string buf
+        (Printf.sprintf "  %s [label=%s];\n" (Json.str t.name)
+           (Json.str (kind_name t.kind ^ " " ^ t.name)));
+      List.iter
+        (fun u -> Buffer.add_string buf (Printf.sprintf "  %s -> %s;\n" (Json.str t.name) (Json.str u)))
+        t.uses)
+    p.targets;
+  Buffer.add_string buf "}\n";
+  Buffer.contents buf