fix(library/elaborator): bug in simple_ho_match

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/library/elaborator/elaborator.cpp

@@ -747,6 +747,14 @@ class elaborator::imp {
             (is_eq(c) || (is_lhs && !is_actual_upper(b)) || (!is_lhs && !is_actual_lower(b)));
     }
 
+    optional<expr> try_get_type(context const & ctx, expr const & e) {
+        try {
+            return some_expr(m_type_inferer(e, ctx));
+        } catch (...) {
+            return none_expr();
+        }
+    }
+
     /**
         \brief Return true iff ctx |- a == b is a "simple" higher-order matching constraint. By simple, we mean
         a constraint of the form
@@ -761,7 +769,7 @@ class elaborator::imp {
             expr m = arg(a, 0);
             buffer<expr> types;
             for (unsigned i = 1; i < num_args(a); i++) {
-                optional<expr> d = lookup(ctx, var_idx(arg(a, i))).get_domain();
+                optional<expr> d = try_get_type(ctx, arg(a, i));
                 if (d)
                     types.push_back(*d);
                 else

tests/lean/elab6.lean

@@ -0,0 +1,2 @@
+Theorem ForallIntro2 (A : Type U) (P : A -> Bool) (H : Pi x, P x) : forall x, P x :=
+        Abst (fun x, EqTIntro (H x))

tests/lean/elab6.lean.expected.out

@@ -0,0 +1,3 @@
+  Set: pp::colors
+  Set: pp::unicode
+  Proved: ForallIntro2