Properly thread let-bindings in Funind principle construction.

Fixes #11846: Funind fails to generate principles for terms with let bindings.

2 files changed, 18 insertions, 2 deletions

diff --git a/plugins/funind/functional_principles_types.ml b/plugins/funind/functional_principles_types.ml
index 797d421c56..436d36f029 100644
--- a/plugins/funind/functional_principles_types.ml
+++ b/plugins/funind/functional_principles_types.ml
@@ -63,14 +63,14 @@ let compute_new_princ_type_from_rel rel_to_fun sorts princ_type =
 (*   observe (str "princ_infos : " ++ pr_elim_scheme princ_type_info); *)
   let change_predicate_sort i decl =
     let new_sort = sorts.(i) in
-    let args,_ = decompose_prod (EConstr.Unsafe.to_constr (RelDecl.get_type decl)) in
+    let args,_ = decompose_prod_assum (EConstr.Unsafe.to_constr (RelDecl.get_type decl)) in
     let real_args =
       if princ_type_info.indarg_in_concl
       then List.tl args
       else args
     in
     Context.Named.Declaration.LocalAssum (map_annot Nameops.Name.get_id (Context.Rel.Declaration.get_annot decl),
-                                          Term.compose_prod real_args (mkSort new_sort))
+                                          Term.it_mkProd_or_LetIn (mkSort new_sort) real_args)
   in
   let new_predicates =
     List.map_i
diff --git a/test-suite/bugs/closed/bug_11846.v b/test-suite/bugs/closed/bug_11846.v
new file mode 100644
index 0000000000..53517e7703
--- /dev/null
+++ b/test-suite/bugs/closed/bug_11846.v
@@ -0,0 +1,16 @@
+Require Import FunInd.
+
+Inductive tree : Type :=
+| Node : unit -> tree.
+
+Definition height (s : tree) : unit :=
+match s with
+| Node h => h
+end.
+
+Definition bal : forall l, let h := height l in tree := fun l =>
+  let h := height l in
+  Node h.
+
+Set Warnings "+all".
+Functional Scheme bal_ind := Induction for bal Sort Prop.