Remove tuple unpacking in lambda lists

NEWS.rst

@@ -9,6 +9,8 @@ Removals
   These were redundant with Python's built-in data structures and Hy's most
   common model types (`HyExpression`, `HyList`, etc.).
 * `&key` is no longer special in lambda lists. Use `&optional` instead.
+* Tuple unpacking is no longer built into special forms for function
+  definition (`fn` etc.)
 
 Other Breaking Changes
 ------------------------------

hy/compiler.py

@@ -553,6 +553,8 @@ class HyASTCompiler(object):
                 continue
 
             if lambda_keyword is None:
+                if not isinstance(expr, HySymbol):
+                    raise HyTypeError(expr, "Parameters must be symbols")
                 args.append(expr)
             elif lambda_keyword == "&rest":
                 if varargs:
@@ -1893,19 +1895,6 @@ class HyASTCompiler(object):
 
         (ret, args, defaults, stararg,
          kwonlyargs, kwonlydefaults, kwargs) = self._parse_lambda_list(arglist)
-        for i, arg in enumerate(args):
-            if isinstance(arg, HyList):
-                # Destructuring argument
-                if not arg:
-                    raise HyTypeError(arglist,
-                                      "Cannot destruct empty list")
-                args[i] = var = HySymbol(self.get_anon_var())
-                expression = HyExpression([
-                    HyExpression([
-                        HySymbol("setv"), arg, var
-                    ])]
-                ) + expression
-                expression = expression.replace(arg[0])
 
         # Before Python 3.7, docstrings must come at the start, so ensure that
         # happens even if we generate anonymous variables.

tests/compilers/test_ast.py

@@ -414,12 +414,6 @@ def test_ast_tuple():
     assert type(code) == ast.Tuple
 
 
-def test_argument_destructuring():
-    """ Ensure argument destructuring compilers. """
-    can_compile("(fn [[a b]] (print a b))")
-    cant_compile("(fn [[]] 0)")
-
-
 def test_lambda_list_keywords_rest():
     """ Ensure we can compile functions with lambda list keywords."""
     can_compile("(fn [x &rest xs] (print xs))")

tests/native_tests/language.hy

@@ -1761,11 +1761,6 @@ macros()
    (= (identify-keywords 1 "bloo" :foo)
       ["other" "other" "keyword"])))
 
-(defn test-argument-destr []
-  "Make sure argument destructuring works"
-  (defn f [[a b] [c]] (, a b c))
-  (assert (= (f [1 2] [3]) (, 1 2 3))))
-
 #@(pytest.mark.xfail
 (defn test-assert-multistatements []
   ; https://github.com/hylang/hy/issues/1390
@@ -1789,21 +1784,11 @@ macros()
   (defn f [] "docstring" 5)
   (assert (= (. f __doc__) "docstring"))
 
-  ; destructuring and the implicit variables it creates
-  ; shouldn't interfere with docstrings
-  ; (https://github.com/hylang/hy/issues/1409)
-  (defn f2 [[a b]] "docstring" 5)
-  (assert (= (. f2 __doc__) "docstring"))
-
   ; a single string is the return value, not a docstring
   ; (https://github.com/hylang/hy/issues/1402)
   (defn f3 [] "not a docstring")
   (assert (none? (. f3 __doc__)))
-  (assert (= (f3) "not a docstring"))
-
-  (defn f4 [[a b]] "not a docstring")
-  (assert (none? (. f4 __doc__)))
-  (assert (= (f4 [1 2]) "not a docstring")))
+  (assert (= (f3) "not a docstring")))
 
 (defn test-module-docstring []
   (import [tests.resources.module-docstring-example :as m])