Don't create non-existent namespaces in Var.find (#211)

* Don't create non-existent namespace in Var.find

* Add a test

Author: chrisrink10

src/basilisp/lang/runtime.py

@@ -175,8 +175,10 @@ def intern_unbound(ns: sym.Symbol,
     def find_in_ns(ns_sym: sym.Symbol, name_sym: sym.Symbol) -> "Optional[Var]":
         """Return the value current bound to the name `name_sym` in the namespace
         specified by `ns_sym`."""
-        ns = Namespace.get_or_create(ns_sym)
-        return ns.find(name_sym)
+        ns = Namespace.get(ns_sym)
+        if ns:
+            return ns.find(name_sym)
+        return None
 
     @staticmethod
     def find(ns_qualified_sym: sym.Symbol) -> "Optional[Var]":
@@ -419,6 +421,12 @@ def get_or_create(cls, name: sym.Symbol, module: types.ModuleType = None) -> "Na
         Return the namespace."""
         return cls._NAMESPACES.swap(Namespace.__get_or_create, name, module=module)[name]
 
+    @classmethod
+    def get(cls, name: sym.Symbol) -> "Optional[Namespace]":
+        """Get the namespace bound to the symbol `name` in the global namespace
+        cache. Return the namespace if it exists or None otherwise.."""
+        return cls._NAMESPACES.deref().entry(name, None)
+
     @classmethod
     def remove(cls, name: sym.Symbol) -> Optional["Namespace"]:
         """Remove the namespace bound to the symbol `name` in the global

tests/basilisp/namespace_test.py

@@ -46,7 +46,8 @@ def test_create_ns(ns_sym: sym.Symbol, ns_cache: patch):
 
 
 @pytest.fixture
-def ns_cache_with_existing_ns(ns_sym: sym.Symbol, core_ns_sym: sym.Symbol,
+def ns_cache_with_existing_ns(ns_sym: sym.Symbol,
+                              core_ns_sym: sym.Symbol,
                               core_ns: Namespace) -> patch:
     """Patch the Namespace cache with a test fixture with an existing namespace."""
     return patch('basilisp.lang.runtime.Namespace._NAMESPACES',
@@ -67,6 +68,26 @@ def test_get_existing_ns(ns_sym: sym.Symbol,
         assert len(cache.deref().keys()) == 2
 
 
+def test_get_existing_ns_with_get(ns_sym: sym.Symbol,
+                                  ns_cache_with_existing_ns: patch):
+    with ns_cache_with_existing_ns as cache:
+        assert len(cache.deref().keys()) == 2
+        ns = Namespace.get(ns_sym)
+        assert isinstance(ns, Namespace)
+        assert ns.name == ns_sym.name
+        assert len(cache.deref().keys()) == 2
+
+
+def test_get_nil_for_non_existent_ns(ns_sym: sym.Symbol):
+    with patch('basilisp.lang.runtime.Namespace._NAMESPACES',
+               atom.Atom(
+                   lmap.map({}))) as cache:
+        assert len(cache.deref().keys()) == 0
+        ns = Namespace.get(ns_sym)
+        assert ns is None
+        assert len(cache.deref().keys()) == 0
+
+
 def test_remove_ns(ns_sym: sym.Symbol, ns_cache_with_existing_ns: patch):
     with ns_cache_with_existing_ns as cache:
         assert len(cache.deref().keys()) == 2