extract_settings_attr attrs returns the expression carried by [@@settings expr] if present, else None.

parse_string_list e returns the list of literal strings carried by e when e has the shape [ "..."; "..."; ... ], else raises a located error pointing at the offending sub-expression.

extract_failure_blobs_attr attrs returns the parsed string list if a [@@failure_blobs ...] attribute is present, else None.

extract_function_name pat returns the name bound by pat if pat is a simple variable, else raises.

build_location_record ~loc ~function_name returns an expression of type Hegel.test_location populated from the binding's source location.

build_items ~loc ~function_name ~settings_expr ~body_fn returns the pair of structure items the expander splices in:

  let function_name () =
    Hegel.run_hegel_test [?settings] location body_fn
  ;;

  let () =
    Hegel_test_runtime.register ~name:.. ~file:.. ~line:.. function_name

is_draw_lident lid is true when lid's final component is draw, whether unqualified (draw) or qualified (Hegel.draw, Generators.draw, a module alias G.draw, …). Precision comes from the receiver check in draw_binding_name (the draw must be applied to the test's own tc), so this only needs to recognize the name; draw_silent is a different name and is excluded.

draw_named_lident lid is lid with its final draw component replaced by draw_named, preserving the module prefix the user wrote, so the rewrite targets the same module's internal entry point (e.g. Hegel.draw becomes Hegel.draw_named).

has_label_arg args is true when an application already passes ~label (or ?label) explicitly, in which case the hand-written label wins.

param_name pat is the variable bound by pat, if it is a simple variable (possibly type-annotated), else None.

test_case_name e is the name of the test function's first parameter (its tc), used as the receiver the rewrite keys off. None when the binding is not a function or its parameter is not a simple variable.

tc_arg_is ~tc_name args is true when the first positional argument of an application is exactly the identifier tc_name.

draw_binding_name ~tc_name vb returns Some name when vb is let <name> = draw tc … — a simple-variable binding whose right-hand side is a draw application on the test's own tc — and None otherwise.

collect_repeatable body maps each draw-bound name to whether its draws should be numbered. A name is repeatable if it is drawn more than once, or drawn anywhere at block depth > 0 (inside a function, for, or while body, where it may run repeatedly).

inject_draw ~tc_name flags vb rewrites let x = M.draw tc gen into let x = M.draw_named ~label:"x" ~repeatable:b tc gen, so the drawn value prints as x = value (numbered when x is flagged repeatable in flags — reused name or drawn in a loop). It targets the internal draw_named rather than the public draw (so repeatable stays off the public API), keeping the module prefix M the user wrote. It fires only for a simple-variable binding whose right-hand side is a draw application on tc with no explicit ~label; every other binding is unchanged.

A traversal that applies inject_draw to every let-binding in an expression, threading the precomputed flags, so labels are injected throughout the test body (nested lets, helper functions, match arms, …). Draws nested inside a generation span are still suppressed at runtime by the depth gate, so labeling them is harmless.

Expander for a single let%hegel_test ... structure item.

The hegel_test extension is attached to structure_item (top-level let%hegel_test). It supports only the non-recursive single-binding form. The expander splices in two top-level items: the test function itself and a Hegel_test_runtime.register side effect so that dune runtest (via the ppx_hegel_test inline-tests backend) discovers and runs the test.