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

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

src/frontends/lean/parser_cmds.cpp

@@ -803,12 +803,12 @@ void parser_imp::parse_using() {
         new_prefix = curr_name();
         next();
     }
-    buffer<std::pair<name, expr>> to_add;
+    buffer<std::pair<name, name>> to_add;
     for (auto it = m_env->begin_objects(); it != m_env->end_objects(); ++it) {
         if (it->has_type() && it->has_name() && !is_hidden_object(*it) && is_prefix_of(prefix, it->get_name())) {
             auto n = replace_prefix(it->get_name(), prefix, new_prefix);
             if (!n.is_anonymous())
-                to_add.emplace_back(n, mk_constant(it->get_name()));
+                to_add.emplace_back(n, it->get_name());
         }
     }
     for (auto p : to_add) {

src/frontends/lean/parser_expr.cpp

@@ -247,7 +247,7 @@ expr parser_imp::parse_mixfixc(operator_info const & op) {
 expr parser_imp::get_name_ref(name const & id, pos_info const & p, bool implicit_args) {
     auto it = m_using_decls.find(id);
     if (it != m_using_decls.end()) {
-        return it->second;
+        return get_name_ref(it->second, p, implicit_args);
     } else {
         lean_assert(!m_namespace_prefixes.empty());
         auto it    = m_namespace_prefixes.end();

src/frontends/lean/parser_imp.h

@@ -56,7 +56,7 @@ class parser_imp {
     typedef name_map<expr> builtins;
     typedef expr_map<pos_info> expr_pos_info;
     typedef expr_map<tactic>   tactic_hints; // a mapping from placeholder to tactic
-    typedef scoped_map<name, expr, name_hash, name_eq>      using_decls;
+    typedef scoped_map<name, name, name_hash, name_eq>      using_decls;
     enum class scope_kind { Scope, Namespace };
 
     std::weak_ptr<parser_imp>          m_this;

tests/lean/using_bug1.lean

@@ -0,0 +1,12 @@
+variables a b c d : Nat
+axiom H : a + (b + c) = a + (b + d)
+using Nat
+check add_succr a
+
+theorem mul_zerol2 (a : Nat) : 0 * a = 0
+:= induction_on a
+    (have 0 * 0 = 0 : trivial)
+    (λ (n : Nat) (iH : 0 * n = 0),
+        calc  0 * (n + 1)  =  (0 * n) + 0 : mul_succr 0 n
+                      ...  =  0 + 0       : { iH }
+                      ...  =  0           : trivial)

tests/lean/using_bug1.lean.expected.out

@@ -0,0 +1,10 @@
+  Set: pp::colors
+  Set: pp::unicode
+  Assumed: a
+  Assumed: b
+  Assumed: c
+  Assumed: d
+  Assumed: H
+  Using: Nat
+Nat::add_succr a : ∀ b : ℕ, a + (b + 1) = a + b + 1
+  Proved: mul_zerol2