fix(frontends/lean/builtin_exprs): bug in 'using' construct

src/frontends/lean/builtin_exprs.cpp

@@ -289,7 +289,7 @@ static expr parse_proof(parser & p, expr const & prop) {
         buffer<expr> new_locals;
         while (!p.curr_is_token(get_comma_tk())) {
             auto id_pos = p.pos();
-            expr l      = p.parse_expr();
+            expr l      = p.parse_id();
             if (!is_local(l))
                 throw parser_error("invalid 'using' declaration for 'have', local expected", id_pos);
             expr new_l = l;

tests/lean/run/using_bug.lean

@@ -0,0 +1,9 @@
+example (p q r : Prop) : p ∧ q ∧ r → q ∧ p :=
+assume Hpqr : p ∧ q ∧ r,
+have   Hp   : p,     from and.elim_left Hpqr,
+have   Hqr  : q ∧ r, from and.elim_right Hpqr,
+have   Hq   : q,     from and.elim_left Hqr,
+show q ∧ p, using Hp Hq, from
+proof
+  and.intro Hq Hp
+qed