Fix the interpretation of except [[]]

NEWS.rst

@@ -12,6 +12,9 @@ New Features
 Bug Fixes
 ------------------------------
 * Fixed a crash from using an empty string in a `(. …)` expression.
+* `(except [[]] …)` now catches no exceptions, rather than being treated like
+  `(except [] …)`, which catches all exceptions.
+* `(except [e []] …)` is now translated to Python correctly by `hy2py`.
 
 1.0.0 ("Afternoon Review", released 2024-09-22)
 ======================================================================

docs/api.rst

@@ -912,6 +912,8 @@ Exception-handling
      ``except ETYPE as VAR:``
    - ``[VAR [ETYPE1 ETYPE2 …]]`` to catch any of the named types and bind it to
      ``VAR``, like Python's ``except ETYPE1, ETYPE2, … as VAR:``
+   - ``[[]]`` or ``[VAR []]`` to catch no exceptions, like Python's
+     ``except ():``.
 
    The return value of ``try`` is the last form evaluated among the main body,
    ``except`` forms, ``except*`` forms, and ``else``.

hy/core/result_macros.py

@@ -1449,20 +1449,24 @@ def compile_try_expression(compiler, expr, root, body, catchers, orelse, finalbo
             )
 
         name = None
-        if len(exceptions) == 2:
-            name = mangle(compiler._nonconst(exceptions[0]))
-
-        exceptions_list = exceptions[-1] if exceptions else List()
-        if isinstance(exceptions_list, List):
-            if len(exceptions_list):
-                # [FooBar BarFoo] → catch Foobar and BarFoo exceptions
-                elts, types, _ = compiler._compile_collect(exceptions_list)
-                types += asty.Tuple(exceptions_list, elts=elts, ctx=ast.Load())
-            else:
-                # [] → all exceptions caught
-                types = Result()
+        if len(exceptions) == 0:
+            exceptions = "ALL"
+        elif len(exceptions) == 1:
+            [exceptions] = exceptions
+        else:
+            [name, exceptions] = exceptions
+            name = mangle(compiler._nonconst(name))
+
+        if exceptions == "ALL":
+            # Catch all exceptions.
+            types = Result()
+        elif isinstance(exceptions, List):
+            # [FooBar BarFoo] → Catch Foobar and BarFoo exceptions.
+            elts, types, _ = compiler._compile_collect(exceptions)
+            types += asty.Tuple(exceptions, elts=elts, ctx=ast.Load())
         else:
-            types = compiler.compile(exceptions_list)
+            # A single exception type.
+            types = compiler.compile(exceptions)
 
         # Create a "fake" scope for the exception variable.
         # See: https://docs.python.org/3/reference/compound_stmts.html#the-try-statement

tests/native_tests/try.hy

@@ -70,6 +70,10 @@
         (setv out ["ccc" (type e)]))
       (except [e [KeyError AttributeError]]
         (setv out ["ddd" (type e)]))
+      (except [[]]
+        (assert False))
+      (except [e []]
+        (assert False))
       (except []
         (setv out ["eee" None]))
       (else

tests/native_tests/with.hy

@@ -2,7 +2,8 @@
   asyncio
   unittest.mock [Mock]
   pytest
-  tests.resources [async-test AsyncWithTest async-exits])
+  tests.resources [async-test]
+  tests.resources.pydemo [AsyncWithTest async-exits])
 
 (defn test-context []
   (with [fd (open "tests/resources/text.txt" "r")] (assert fd))
@@ -39,7 +40,7 @@
   (assert (= exits [4 3 2 1])))
 
 (defn [async-test] test-single-with-async []
-  (setv (cut async-exits) [])
+  (.clear async-exits)
   (setv out [])
   (asyncio.run
     ((fn :async []
@@ -49,7 +50,7 @@
   (assert (= async-exits [1])))
 
 (defn [async-test] test-quince-with-async []
-  (setv (cut async-exits) [])
+  (.clear async-exits)
   (setv out [])
   (asyncio.run
     ((fn :async []

tests/resources/__init__.py

@@ -17,23 +17,3 @@ def function_with_a_dash():
 async_test = pytest.mark.skipif(
     not can_test_async, reason="`asyncio.run` not implemented"
 )
-
-
-async_exits = []
-class AsyncWithTest:
-    def __init__(self, val):
-        self.val = val
-
-    async def __aenter__(self):
-        return self.val
-
-    async def __aexit__(self, exc_type, exc, traceback):
-        async_exits.append(self.val)
-
-
-async def async_loop(items):
-    import asyncio
-
-    for x in items:
-        yield x
-        await asyncio.sleep(0)

tests/resources/pydemo.hy

@@ -1,7 +1,7 @@
 ;; This Hy module is intended to concisely demonstrate all of
 ;; Python's major syntactic features for the purpose of testing hy2py.
 ;; It also tries out macros and reader macros to ensure they work with
-;; hy2py.
+;; hy2py. It's used as part of Hy's test suite as well as py2hy's.
 "This is a module docstring."
 
 (setv mystring (* "foo" 3))
@@ -102,25 +102,6 @@ Call me Ishmael. Some years ago—never mind how long precisely—having little
 (for [x ["fo" "fi" "fu"]]
   (setv for-block (+ x for-block)))
 
-(try
-  (assert (= 1 0))
-  (except [_ AssertionError]
-    (setv caught-assertion True))
-  (finally
-    (setv ran-finally True)))
-
-(try
-  (raise (ValueError "payload"))
-  (except [e ValueError]
-    (setv myraise (str e))))
-
-(try
-  1
-  (except [e ValueError]
-    (raise))
-  (else
-    (setv ran-try-else True)))
-
 (defn fun [a b [c 9] [from 10] #* args #** kwargs]
   "function docstring"
   [a b c from args (sorted (.items kwargs))])
@@ -147,6 +128,26 @@ Call me Ishmael. Some years ago—never mind how long precisely—having little
   (+= myglobal 1))
 (set-global)
 
+(setv finally-values [])
+(defn mytry [error-type]
+  (try
+    (when error-type
+      (raise (error-type "payload")))
+    (except [ZeroDivisionError]
+      "zero-div")
+    (except [e [ValueError TypeError]]
+      ["vt" (type e) e.args])
+    (except [[]]
+      "never")
+    (except [e []]
+      "never2")
+    (except []
+      "other")
+    (else
+      "else")
+    (finally
+      (.append finally-values 1))))
+
 (defclass C1 [])   ; Force the creation of a `pass` statement.
 
 (defclass C2 [C1]
@@ -174,8 +175,7 @@ Call me Ishmael. Some years ago—never mind how long precisely—having little
 (setv py-accum (py "''.join(map(str, pys_accum))"))
 
 (defn :async coro []
-  (import asyncio
-          tests.resources [AsyncWithTest async-loop])
+  (import asyncio)
   (await (asyncio.sleep 0))
   (setv values ["a"])
   (with [:async t (AsyncWithTest "b")]
@@ -186,6 +186,19 @@ Call me Ishmael. Some years ago—never mind how long precisely—having little
     :async item (async-loop ["e" "f"])
     item))
   values)
+(defclass AsyncWithTest []
+  (defn __init__ [self val]
+    (setv self.val val))
+  (defn :async __aenter__ [self]
+    self.val)
+  (defn :async __aexit__ [self exc-type exc traceback]
+    (.append async-exits self.val)))
+(setv async-exits [])
+(defn :async async-loop [items]
+  (import asyncio)
+  (for [x items]
+    (yield x)
+    (await (asyncio.sleep 0))))
 
 (defmacro macaroni [expr]
   `[~expr ~expr])

tests/test_hy2py.py

@@ -1,3 +1,5 @@
+# This file is also used by py2hy.
+
 import asyncio
 import itertools
 import math
@@ -7,20 +9,20 @@
 import hy.importer
 from hy import mangle
 from hy.compat import PYODIDE
-from tests.resources import can_test_async
 
 
 def test_direct_import():
     import tests.resources.pydemo
-
-    assert_stuff(tests.resources.pydemo)
+    from tests.resources import can_test_async
+    assert_stuff(tests.resources.pydemo, can_test_async)
 
 
 @pytest.mark.skipif(PYODIDE, reason="subprocess.check_call not implemented on Pyodide")
 def test_hy2py_import():
     import contextlib
     import os
     import subprocess
+    from tests.resources import can_test_async
 
     path = "tests/resources/pydemo_as_py.py"
     env = dict(os.environ)
@@ -36,10 +38,10 @@ def test_hy2py_import():
     finally:
         with contextlib.suppress(FileNotFoundError):
             os.remove(path)
-    assert_stuff(m)
+    assert_stuff(m, can_test_async)
 
 
-def assert_stuff(m):
+def assert_stuff(m, can_test_async):
 
     # This makes sure that automatically imported builtins go after docstrings.
     assert m.__doc__ == "This is a module docstring."
@@ -121,10 +123,6 @@ def assert_stuff(m):
     assert m.while_block == "xxxxe"
     assert m.cont_and_break == "xyzxyzxxyzxy"
     assert m.for_block == "fufifo"
-    assert m.caught_assertion is True
-    assert m.ran_finally is True
-    assert m.myraise == "payload"
-    assert m.ran_try_else is True
 
     assert type(m.fun) is type(lambda x: x)
     assert m.fun.__doc__ == "function docstring"
@@ -137,6 +135,13 @@ def assert_stuff(m):
     assert m.mydecorated.newattr == "hello"
     assert m.myglobal == 103
 
+    assert m.mytry(ZeroDivisionError) == "zero-div"
+    assert m.mytry(ValueError) == ["vt", ValueError, ("payload",)]
+    assert m.mytry(TypeError) == ["vt", TypeError, ("payload",)]
+    assert m.mytry(OSError) == "other"
+    assert m.mytry(None) == "else"
+    assert len(m.finally_values) == 5
+
     class C:
         pass
 
@@ -155,7 +160,9 @@ class C:
     assert m.py_accum == "01234"
 
     if can_test_async:
+        m.async_exits.clear()
         assert asyncio.run(m.coro()) == list("abcdef")
+        assert m.async_exits == ["b"]
 
     assert m.cheese == [1, 1]
     assert m.mac_results == ["x", "x"]