Add declare, defn-, and defonce macros (#480)

* Add `declare`, `defn-`, and `defonce` macros

* Tests for no-op def

Author: chrisrink10

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  * Added multiline REPL support using `prompt-toolkit` (#467)
  * Added node syntactic location (statement or expression) to Basilisp AST nodes emitted by the analyzer (#463)
  * Added `letfn` special form (#473)
+ * Added `defn-`, `declare`, and `defonce` macros (#480)
 
 ### Changed
  * Change the default user namespace to `basilisp.user` (#466)

src/basilisp/core.lpy

@@ -467,28 +467,18 @@
          ~@body))))
 
 (defmacro defasync
-  "Define a new asynchronous function with an optional docstring."
+  "Define a new asynchronous function as by `defn`.
+
+  Asynchronous functions are compiled as Python `async def`s."
+  [name & body]
+  `(defn ~(vary-meta name assoc :async true)
+     ~@body))
+
+(defmacro defn-
+  "Define a new private function as by `defn`."
   [name & body]
-  (let [body   (concat body)
-        doc    (if (string? (first body))
-                 (first body)
-                 nil)
-        body   (if doc
-                 (rest body)
-                 body)
-        fmeta (if (map? (first body))
-                (assoc (first body))
-                nil)
-        body   (if fmeta
-                 (rest body)
-                 body)
-        fmeta (apply assoc fmeta (concat [:async true]
-                                         (if doc
-                                           [:doc doc]
-                                           nil)))]
-    `(defn ~name
-       ~fmeta
-       ~@body)))
+  `(defn ~(vary-meta name assoc :private true)
+     ~@body))
 
 (defn macroexpand-1
   "Macroexpand form one time. Returns the macroexpanded form. The return
@@ -2528,6 +2518,23 @@
                                      {:test test-expr}))))
         test-expr))))
 
+(defmacro declare
+  "Declare the given names as Vars with no bindings, as a forward declaration."
+  [& names]
+  `(do
+     ~@(map (fn [nm]
+              `(def ~(vary-meta nm assoc :redef true)))
+            names)))
+
+(defmacro defonce
+  "Define the Var named by `name` with root binding set to `expr` if and only if
+  a `name` is not already defined as a Var in this namespace. `expr` will not be
+  evaluated if the Var already exists."
+  [name expr]
+  `(let [v (def ~name)]
+     (when-not (.-is-bound v)
+       (def ~name ~expr))))
+
 (defmacro for
   "Produce a list comprehension from 1 or more input sequences, subject to
   optional modifiers.

src/basilisp/lang/compiler/generator.py

@@ -496,6 +496,7 @@ def _noop_node() -> ast.AST:
 _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")
+_INTERN_UNBOUND_VAR_FN_NAME = _load_attr(f"{_VAR_ALIAS}.intern_unbound")
 _FIND_VAR_FN_NAME = _load_attr(f"{_VAR_ALIAS}.find_safe")
 _ATTR_CLASS_DECORATOR_NAME = _load_attr(f"attr.s")
 _ATTRIB_FIELD_FN_NAME = _load_attr(f"attr.ib")
@@ -610,20 +611,16 @@ def __should_warn_on_redef(
         return False
 
     current_ns = ctx.current_ns
-    if safe_name in current_ns.module.__dict__:
-        return True
-    elif defsym in current_ns.interns:
+    if defsym in current_ns.interns:
         var = current_ns.find(defsym)
         assert var is not None, f"Var {defsym} cannot be none here"
 
         if var.meta is not None and var.meta.val_at(SYM_REDEF_META_KEY):
             return False
-        elif var.is_bound:
-            return True
         else:
-            return False
+            return bool(var.is_bound)
     else:
-        return False
+        return safe_name in current_ns.module.__dict__
 
 
 @_with_ast_loc
@@ -635,6 +632,8 @@ def _def_to_py_ast(  # pylint: disable=too-many-branches
 
     defsym = node.name
     is_defn = False
+    is_var_bound = node.var.is_bound
+    is_noop_redef_of_bound_var = is_var_bound and node.init is None
 
     if node.init is not None:
         # Since Python function definitions always take the form `def name(...):`,
@@ -656,6 +655,8 @@ def _def_to_py_ast(  # pylint: disable=too-many-branches
             is_defn = True
         else:
             def_ast = gen_py_ast(ctx, node.init)
+    elif is_noop_redef_of_bound_var:
+        def_ast = None
     else:
         def_ast = GeneratedPyAST(node=ast.Constant(None))
 
@@ -678,8 +679,9 @@ def _def_to_py_ast(  # pylint: disable=too-many-branches
         else []
     )
 
-    # Warn if this symbol is potentially being redefined
-    if __should_warn_on_redef(ctx, defsym, safe_name, def_meta):
+    # Warn if this symbol is potentially being redefined (if the Var was
+    # previously bound)
+    if is_var_bound and __should_warn_on_redef(ctx, defsym, safe_name, def_meta):
         logger.warning(
             f"redefining local Python name '{safe_name}' in module "
             f"'{ctx.current_ns.module.__name__}' ({node.env.ns}:{node.env.line})"
@@ -699,6 +701,16 @@ def _def_to_py_ast(  # pylint: disable=too-many-branches
                 [] if meta_ast is None else meta_ast.dependencies,
             )
         )
+    elif is_noop_redef_of_bound_var:
+        # Re-def-ing previously bound Vars without providing a value is
+        # essentially a no-op, which should not modify the Var root.
+        assert def_ast is None, "def_ast is not defined at this point"
+        def_dependencies = list(
+            chain(
+                [] if node.top_level else [ast.Global(names=[safe_name])],
+                [] if meta_ast is None else meta_ast.dependencies,
+            )
+        )
     else:
         def_dependencies = list(
             chain(
@@ -714,6 +726,23 @@ def _def_to_py_ast(  # pylint: disable=too-many-branches
             )
         )
 
+    if is_noop_redef_of_bound_var:
+        return GeneratedPyAST(
+            node=ast.Call(
+                func=_INTERN_UNBOUND_VAR_FN_NAME,
+                args=[ns_name, def_name],
+                keywords=list(
+                    chain(
+                        dynamic_kwarg,
+                        []
+                        if meta_ast is None
+                        else [ast.keyword(arg="meta", value=meta_ast.node)],
+                    )
+                ),
+            ),
+            dependencies=def_dependencies,
+        )
+
     return GeneratedPyAST(
         node=ast.Call(
             func=_INTERN_VAR_FN_NAME,

tests/basilisp/compiler_test.py

@@ -377,6 +377,25 @@ def test_def_fn_with_meta(self, ns: runtime.Namespace):
         assert lmap.map({kw.keyword("meta-kw"): True}) == v.value.meta
         assert kw.keyword("fn-with-meta-node") == v.value()
 
+    def test_redef_unbound_var(self, ns: runtime.Namespace):
+        v1: Var = lcompile("(def unbound-var)")
+        assert None is v1.root
+
+        v2: Var = lcompile("(def unbound-var :a)")
+        assert kw.keyword("a") == v2.root
+        assert v2.is_bound
+
+    def test_def_unbound_does_not_clear_var_root(self, ns: runtime.Namespace):
+        v1: Var = lcompile("(def bound-var :a)")
+        assert kw.keyword("a") == v1.root
+        assert v1.is_bound
+
+        v2: Var = lcompile("(def bound-var)")
+        assert kw.keyword("a") == v2.root
+        assert v2.is_bound
+
+        assert v1 == v2
+
 
 class TestDefType:
     @pytest.mark.parametrize("code", ["(deftype*)", "(deftype* Point)"])

tests/basilisp/core_macros_test.lpy

@@ -173,6 +173,91 @@
         (is (= "0.1" (:added vmeta)))
         (is (= "another multi-arity docstring" (:doc vmeta)))))))
 
+(deftest defn-private-test
+  (testing "single arity defn-"
+    (testing "simple"
+      (let [fvar  (defn- pf1 [] :kw)
+            vmeta (meta fvar)]
+        (is (= 'pf1 (:name vmeta)))
+        (is (= '([]) (:arglists vmeta)))
+        (is (= true (:private vmeta)))
+        (is (not (contains? vmeta :doc)))))
+
+    (testing "with docstring"
+      (let [fvar  (defn- pf2 "a docstring" [] :kw)
+            vmeta (meta fvar)]
+        (is (= 'pf2 (:name vmeta)))
+        (is (= '([]) (:arglists vmeta)))
+        (is (= true (:private vmeta)))
+        (is (= "a docstring" (:doc vmeta)))))
+
+    (testing "with attr-map"
+      (let [fvar  (defn- pf3 {:added "0.1"} [] :kw)
+            vmeta (meta fvar)]
+        (is (= 'pf3 (:name vmeta)))
+        (is (= '([]) (:arglists vmeta)))
+        (is (= true (:private vmeta)))
+        (is (= "0.1" (:added vmeta)))
+        (is (not (contains? vmeta :doc)))))
+
+    (testing "attr-map and docstring"
+      (let [fvar  (defn- pf4
+                    "another docstring"
+                    {:added "0.1"}
+                    []
+                    :kw)
+            vmeta (meta fvar)]
+        (is (= 'pf4 (:name vmeta)))
+        (is (= '([]) (:arglists vmeta)))
+        (is (= true (:private vmeta)))
+        (is (= "0.1" (:added vmeta)))
+        (is (= "another docstring" (:doc vmeta))))))
+
+  (testing "multi arity defn"
+    (testing "simple"
+      (let [fvar  (defn- pf5 ([] :kw) ([a] a))
+            vmeta (meta fvar)]
+        (is (= 'pf5 (:name vmeta)))
+        (is (= '([] [a]) (:arglists vmeta)))
+        (is (= true (:private vmeta)))
+        (is (not (contains? vmeta :doc)))))
+
+    (testing "with docstring"
+      (let [fvar  (defn- pf6
+                    "multi-arity docstring"
+                    ([] :kw)
+                    ([a] a))
+            vmeta (meta fvar)]
+        (is (= 'pf6 (:name vmeta)))
+        (is (= '([] [a]) (:arglists vmeta)))
+        (is (= true (:private vmeta)))
+        (is (= "multi-arity docstring" (:doc vmeta)))))
+
+    (testing "with attr-map"
+      (let [fvar  (defn- pf7
+                    {:added "0.1"}
+                    ([] :kw)
+                    ([a] a))
+            vmeta (meta fvar)]
+        (is (= 'pf7 (:name vmeta)))
+        (is (= '([] [a]) (:arglists vmeta)))
+        (is (= true (:private vmeta)))
+        (is (= "0.1" (:added vmeta)))
+        (is (not (contains? vmeta :doc)))))
+
+    (testing "attr-map and docstring"
+      (let [fvar  (defn- pf8
+                    "another multi-arity docstring"
+                    {:added "0.1"}
+                    ([] :kw)
+                    ([a] a))
+            vmeta (meta fvar)]
+        (is (= 'pf8 (:name vmeta)))
+        (is (= '([] [a]) (:arglists vmeta)))
+        (is (= true (:private vmeta)))
+        (is (= "0.1" (:added vmeta)))
+        (is (= "another multi-arity docstring" (:doc vmeta)))))))
+
 (deftest fn-meta-test
   (testing "fn has no meta to start"
     (is (nil? (meta (fn* []))))