Support Clojure's object instantiation syntax (#152)

* Support Clojure's object instantiation syntax

* Add an extra test case

* Disable linter :shame:

Author: chrisrink10

basilisp/compiler.py

@@ -1459,12 +1459,23 @@ def _resolve_sym_var(ctx: CompilerContext, v: Var) -> Optional[str]:
     return None
 
 
-def _resolve_sym(ctx: CompilerContext, form: sym.Symbol) -> Optional[str]:
+def _resolve_sym(ctx: CompilerContext, form: sym.Symbol) -> Optional[str]:  # noqa: C901
     """Resolve a Basilisp symbol down to a Python Name (or Attribute).
 
     If the symbol cannot be resolved or is specifically marked to prefer Var
     indirection, then this function will return None. _sym_ast will generate a
     Var.find call for runtime resolution."""
+    # Support special class-name syntax to instantiate new classes
+    #   (Classname. *args)
+    #   (aliased.Classname. *args)
+    #   (fully.qualified.Classname. *args)
+    if form.ns is None and form.name.endswith('.'):
+        try:
+            ns, name = form.name[:-1].rsplit('.', maxsplit=1)
+            form = sym.symbol(name, ns=ns)
+        except ValueError:
+            form = sym.symbol(form.name[:-1])
+
     # Attempt to resolve any symbol with a namespace to a direct Python call
     if form.ns is not None:
         if form.ns == _BUILTINS_NS:

basilisp/core/__init__.lpy

@@ -684,6 +684,39 @@
   ([m k default]
    (basilisp.lang.runtime/get m k default)))
 
+(defmacro new
+  "Create a new instance of class with args.
+
+  New objects may be created as any of:
+    (new builtins/str *args)
+    (new builtins.str *args)
+    (new builtins.str. *args)
+
+  This is compatibility syntax for Clojure, since Python (and therefore
+  Basilisp) do not require the new keyword for object instantiation."
+  [class & args]
+  (cond
+    (not (symbol? class))
+    (throw
+     (ex-info "Expected a class name as a symbol"
+              {:class-name class}))
+
+    (namespace class)
+    (let [n  (name class)
+          ns (namespace class)
+          s  (symbol (str ns "."
+                          (if (.endswith n ".")
+                            n
+                            (str n "."))))]
+      `(~s ~@args))
+
+    :else
+    (let [n (name class)
+          s (symbol (if (.endswith n ".")
+                      n
+                      (str n ".")))]
+      `(~s ~@args))))
+
 (defn range
   "Return a range of integers from start. If end is specified, the
   sequence will terminate at end."

tests/compiler_test.py

@@ -350,6 +350,15 @@ def test_truthiness(ns_var: Var):
     assert kw.keyword("a") == lcompile("(if #{true} :a :b)")
 
 
+def test_interop_new(ns_var: Var):
+    assert "hi" == lcompile('(builtins.str. "hi")')
+    assert "1" == lcompile('(builtins.str. 1)')
+    assert sym.symbol('hi') == lcompile('(basilisp.lang.symbol.Symbol. "hi")')
+
+    with pytest.raises(AttributeError):
+        lcompile('(builtins.str "hi")')
+
+
 def test_interop_call(ns_var: Var):
     assert lcompile('(. "ALL-UPPER" lower)') == "all-upper"
     assert lcompile('(.upper "lower-string")') == "LOWER-STRING"