feat(frontends/lean): change the name resolution rules: when in a namespace N that defines C, then C always refers to N.C (i.e., it overrides any alias)

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

src/frontends/lean/parser.cpp

@@ -941,26 +941,28 @@ expr parser::id_to_expr(name const & id, pos_info const & p) {
             save_identifier_info(p, id);
             return r;
         }
-    } else {
-        lean_assert(!id.is_atomic());
-        name new_id = remove_root_prefix(id);
+    }
+
+    for (name const & ns : get_namespaces(m_env)) {
+        auto new_id = ns + id;
+        if (!ns.is_anonymous() && m_env.find(new_id)) {
+            auto r = save_pos(mk_constant(new_id, ls), p);
+            save_type_info(r);
+            add_ref_index(new_id, p);
+            save_identifier_info(p, new_id);
+            return r;
+        }
+    }
+
+    if (!id.is_atomic()) {
+        name new_id = id;
+        new_id = remove_root_prefix(new_id);
         if (m_env.find(new_id)) {
             auto r = save_pos(mk_constant(new_id, ls), p);
             save_type_info(r);
             add_ref_index(new_id, p);
             save_identifier_info(p, new_id);
             return r;
-        } else {
-            for (name const & ns : get_namespaces(m_env)) {
-                auto new_id = ns + id;
-                if (m_env.find(new_id)) {
-                    auto r = save_pos(mk_constant(new_id, ls), p);
-                    save_type_info(r);
-                    add_ref_index(new_id, p);
-                    save_identifier_info(p, new_id);
-                    return r;
-                }
-            }
         }
     }
 

tests/lean/run/ns.lean

@@ -0,0 +1,19 @@
+
+
+variable nat : Type.{1}
+variable f : nat → nat
+
+namespace foo
+  variable int : Type.{1}
+  variable f   : int → int
+  variable a   : nat
+  variable i   : int
+  check _root_.f a
+  check f i
+end foo
+
+using foo
+variables a : nat
+variables i : int
+check f a
+check f i

tests/lean/t4.lean.expected.out

@@ -11,7 +11,7 @@ C : Type
 t4.lean:25:6: error: unknown identifier 'A'
 R : Type → Prop
 λ (x y : N), x : N → N → N
-[choice N N]
+N
 N
 N
 M