golang: Adjust @func to wrap functions with standalone wrapper with recognizable name

Since 5146eb0b (Add support for defer & recover) we have func, which for

    @func
    def f():
        ...

will turn f to be run with additional frame where defer can register calls.

This works ok, but so far the worker of the wrapper was defined inside
func itself - each time func was used, and also the worker had "no
speaking" name _. The latter was making tracebacks a bit harder to read.

-> Move the wrapper to be standalone function with _goframe name. This
removes a bit of import-time overhead when @func is called, and makes
tracebacks a bit more readable.

But my original motivation here is to be able to detect double
func(func(·)) calls and make it idempotent - see next patch for that.

/reviewed-by @levin.zimmermann
/reviewed-on nexedi/pygolang!31

golang/__init__.py

@@ -117,14 +117,9 @@ def _func(f):
         fclass = type(f)
         f = f.__func__
 
-    def _(f, *argv, **kw):
-        # run f under separate frame, where defer will register calls.
-        __goframe__ = _GoFrame()
-        with __goframe__:
-            return f(*argv, **kw)
-
-    # keep all f attributes, like __name__, __doc__, etc on _
-    _ = decorator.decorate(f, _)
+    # prepare function that runs f under separate frame, where defer will register calls
+    # keep all f attributes, like __name__, __doc__, etc on the wrapper
+    _ = decorator.decorate(f, _goframe)
 
     # repack _ into e.g. @staticmethod if that was used on f.
     if fclass is not None:
@@ -132,7 +127,13 @@ def _func(f):
 
     return _
 
-# _GoFrame serves __goframe__ that is setup by @func.
+# _goframe is used by @func to run f under separate frame.
+def _goframe(f, *argv, **kw):
+    __goframe__ = _GoFrame()
+    with __goframe__:
+        return f(*argv, **kw)
+
+# _GoFrame serves __goframe__ that is setup by _goframe.
 class _GoFrame:
     def __init__(self):
         self.deferv    = []     # defer registers funcs here

golang/golang_test.py

@@ -1568,7 +1568,7 @@ RuntimeError: gamma
 
     assertDoc("""\
 Traceback (most recent call last):
-  File "PYGOLANG/golang/__init__.py", line ..., in _
+  File "PYGOLANG/golang/__init__.py", line ..., in _goframe
     return f(*argv, **kw)
            ^^^^^^^^^^^^^^                                       +PY311
   File "PYGOLANG/golang/golang_test.py", line ..., in caller
@@ -1590,7 +1590,7 @@ Traceback (most recent call last):
   File "PYGOLANG/golang/golang_test.py", line ..., in test_defer_excchain_traceback
     caller()
   ...
-  File "PYGOLANG/golang/__init__.py", line ..., in _
+  File "PYGOLANG/golang/__init__.py", line ..., in _goframe
     return f(*argv, **kw)                                       -PY310
     with __goframe__:                                           +PY310
   File "PYGOLANG/golang/__init__.py", line ..., in __exit__
@@ -1609,7 +1609,7 @@ Traceback (most recent call last):
   File "PYGOLANG/golang/golang_test.py", line ..., in test_defer_excchain_traceback
     caller()
   ...
-  File "PYGOLANG/golang/__init__.py", line ..., in _
+  File "PYGOLANG/golang/__init__.py", line ..., in _goframe
     return f(*argv, **kw)                                       -PY310
     with __goframe__:                                           +PY310
   File "PYGOLANG/golang/__init__.py", line ..., in __exit__
@@ -1625,7 +1625,7 @@ RuntimeError: aaa
     e.__cause__ = e.__context__
     assertDoc("""\
 Traceback (most recent call last):
-  File "PYGOLANG/golang/__init__.py", line ..., in _
+  File "PYGOLANG/golang/__init__.py", line ..., in _goframe
     return f(*argv, **kw)
            ^^^^^^^^^^^^^^                                       +PY311
   File "PYGOLANG/golang/golang_test.py", line ..., in caller
@@ -1647,7 +1647,7 @@ Traceback (most recent call last):
   File "PYGOLANG/golang/golang_test.py", line ..., in test_defer_excchain_traceback
     caller()
   ...
-  File "PYGOLANG/golang/__init__.py", line ..., in _
+  File "PYGOLANG/golang/__init__.py", line ..., in _goframe
     return f(*argv, **kw)                                       -PY310
     with __goframe__:                                           +PY310
   File "PYGOLANG/golang/__init__.py", line ..., in __exit__

golang/testprog/golang_test_defer_excchain.txt

 Traceback (most recent call last):
-  File "PYGOLANG/golang/__init__.py", line ..., in _
+  File "PYGOLANG/golang/__init__.py", line ..., in _goframe
     return f(*argv, **kw)
            ^^^^^^^^^^^^^^                                       +PY311
   File "PY39(PYGOLANG/golang/testprog/)golang_test_defer_excchain.py", line 42, in main
@@ -31,7 +31,7 @@ Traceback (most recent call last):
   ... "PY39(PYGOLANG/golang/testprog/)golang_test_defer_excchain.py", line 45, in <module>
     main()
   ...
-  File "PYGOLANG/golang/__init__.py", line ..., in _
+  File "PYGOLANG/golang/__init__.py", line ..., in _goframe
     return f(*argv, **kw)                                       -PY310
     with __goframe__:                                           +PY310
   File "PYGOLANG/golang/__init__.py", line ..., in __exit__

golang/testprog/golang_test_defer_excchain.txt-ipython

 ...
 RuntimeError                              Traceback (most recent call last)
-PYGOLANG/golang/__init__.py in _(f, *argv, **kw)
+PYGOLANG/golang/__init__.py in _goframe(f, *argv, **kw)
 ...
 --> ...         return f(*argv, **kw)
 ...
@@ -50,7 +50,7 @@ PYGOLANG/golang/testprog/golang_test_defer_excchain.py in ...
 
 ...
 
-PYGOLANG/golang/__init__.py in _(f, *argv, **kw)
+PYGOLANG/golang/__init__.py in _goframe(f, *argv, **kw)
 ...
 --> ...         return f(*argv, **kw)
 ...

golang/testprog/golang_test_defer_excchain.txt-pytest

 ...
 ...________________ main ________________...
-../__init__.py:...: in _
+../__init__.py:...: in _goframe
     return f(*argv, **kw)
 golang_test_defer_excchain.py:42: in main
     raise RuntimeError("err")