Return a useful error message if a Var isn't found (#201)

Author: chrisrink10

src/basilisp/compiler.py

@@ -400,7 +400,7 @@ def _expressionize(body: MixedNodeStream,
 _NEW_UUID_FN_NAME = _load_attr(f'{_UTIL_ALIAS}.uuid_from_str')
 _NEW_VEC_FN_NAME = _load_attr(f'{_VEC_ALIAS}.vector')
 _INTERN_VAR_FN_NAME = _load_attr(f'{_VAR_ALIAS}.intern')
-_FIND_VAR_FN_NAME = _load_attr(f'{_VAR_ALIAS}.find')
+_FIND_VAR_FN_NAME = _load_attr(f'{_VAR_ALIAS}.find_safe')
 _COLLECT_ARGS_FN_NAME = _load_attr(f'{_RUNTIME_ALIAS}._collect_args')
 _COERCE_SEQ_FN_NAME = _load_attr(f'{_RUNTIME_ALIAS}.to_seq')
 _TRAMPOLINE_FN_NAME = _load_attr(f'{_RUNTIME_ALIAS}._trampoline')
@@ -570,7 +570,7 @@ def _is_sym_macro(ctx: CompilerContext, form: sym.Symbol) -> bool:
         ns_sym = sym.symbol(form.ns)
         if ns_sym in ctx.current_ns.aliases:
             aliased_ns = ctx.current_ns.aliases[ns_sym]
-            v = Var.find(sym.symbol(form.name, ns=aliased_ns))
+            v = Var.find(sym.symbol(form.name, ns=aliased_ns.name))
             if v is not None:
                 return _is_macro(v)
 

src/basilisp/lang/runtime.py

@@ -189,6 +189,18 @@ def find(ns_qualified_sym: sym.Symbol) -> "Optional[Var]":
         name_sym = sym.symbol(ns_qualified_sym.name)
         return Var.find_in_ns(ns_sym, name_sym)
 
+    @staticmethod
+    def find_safe(ns_qualified_sym: sym.Symbol) -> "Var":
+        """Return the Var currently bound to the name in the namespace specified
+        by `ns_qualified_sym`. If no Var is bound to that name, raise an exception.
+
+        This is a utility method to return useful debugging information when code
+        refers to an invalid symbol at runtime."""
+        v = Var.find(ns_qualified_sym)
+        if v is None:
+            raise RuntimeException(f"Unable to resolve symbol {ns_qualified_sym} in this context")
+        return v
+
 
 class Namespace:
     """Namespaces serve as organizational units in Basilisp code, just as

tests/basilisp/compiler_test.py

@@ -371,7 +371,7 @@ def test_interop_new(ns_var: Var):
     assert "1" == lcompile('(builtins.str. 1)')
     assert sym.symbol('hi') == lcompile('(basilisp.lang.symbol.Symbol. "hi")')
 
-    with pytest.raises(AttributeError):
+    with pytest.raises(runtime.RuntimeException):
         lcompile('(builtins.str "hi")')
 
 
@@ -399,7 +399,7 @@ def test_let(ns_var: Var):
     assert lcompile("(let* [a 1 b :length c {b a} a 4] a)") == 4
     assert lcompile("(let* [a \"lower\"] (.upper a))") == "LOWER"
 
-    with pytest.raises(AttributeError):
+    with pytest.raises(runtime.RuntimeException):
         lcompile("(let* [a 'sym] c)")
 
     with pytest.raises(compiler.CompilerException):
@@ -672,17 +672,17 @@ def test_try_catch(capsys, ns_var):
 
 
 def test_unquote(ns_var: Var):
-    with pytest.raises(AttributeError):
+    with pytest.raises(runtime.RuntimeException):
         lcompile("~s")
 
     assert llist.l(sym.symbol('s')) == lcompile('`(s)')
 
-    with pytest.raises(AttributeError):
+    with pytest.raises(runtime.RuntimeException):
         lcompile("`(~s)")
 
 
 def test_unquote_splicing(ns_var: Var, resolver: reader.Resolver):
-    with pytest.raises(AttributeError):
+    with pytest.raises(runtime.RuntimeException):
         lcompile("~@[1 2 3]")
 
     assert llist.l(1, 2, 3) == lcompile("`(~@[1 2 3])")