pythongh-85267: Improvements to inspect.signature __text_signature__ handling

This makes a couple related changes to inspect.signature's behaviour
when parsing a signature from `__text_signature__`.

First, `inspect.signature` is documented as only raising ValueError or
TypeError. However, in some cases, we could raise RuntimeError.  This PR
changes that, thereby fixing python#83685.

(Note that the new ValueErrors in RewriteSymbolics are caught and then
reraised with a message)

Second, `inspect.signature` could randomly drop parameters that it
didn't understand (corresponding to `return None` in the `p` function).
This is the core issue in python#85267. I think this is very surprising
behaviour and it seems better to fail outright.

Third, adding this new failure broke a couple tests. To fix them (and to
e.g. allow `inspect.signature(select.epoll.register)` as in python#85267), I
add constant folding of a couple binary operations to RewriteSymbolics.

(There's some discussion of making signature expression evaluation
arbitrary powerful in python#68155. I think that's out of scope. The
additional constant folding here is pretty straightforward, useful, and
not much of a slippery slope)

Fourth, while python#85267 is incorrect about the cause of the issue, it turns
out if you had consecutive newlines in __text_signature__, you'd get
`tokenize.TokenError`.

Finally, the `if name is invalid:` code path was dead, since
`parse_name` never returned `invalid`.

Author: hauntsaninja

Lib/inspect.py

@@ -2109,7 +2109,7 @@ def _signature_strip_non_python_syntax(signature):
     self_parameter = None
     last_positional_only = None
 
-    lines = [l.encode('ascii') for l in signature.split('\n')]
+    lines = [l.encode('ascii') for l in signature.split('\n') if l]
     generator = iter(lines).__next__
     token_stream = tokenize.tokenize(generator)
 
@@ -2185,7 +2185,6 @@ def _signature_fromstr(cls, obj, s, skip_bound_arg=True):
 
     parameters = []
     empty = Parameter.empty
-    invalid = object()
 
     module = None
     module_dict = {}
@@ -2209,11 +2208,11 @@ def wrap_value(s):
             try:
                 value = eval(s, sys_module_dict)
             except NameError:
-                raise RuntimeError()
+                raise ValueError
 
         if isinstance(value, (str, int, float, bytes, bool, type(None))):
             return ast.Constant(value)
-        raise RuntimeError()
+        raise ValueError
 
     class RewriteSymbolics(ast.NodeTransformer):
         def visit_Attribute(self, node):
@@ -2233,19 +2232,27 @@ def visit_Name(self, node):
                 raise ValueError()
             return wrap_value(node.id)
 
+        def visit_BinOp(self, node):
+            left = self.visit(node.left)
+            right = self.visit(node.right)
+            if not isinstance(left, ast.Constant) or not isinstance(right, ast.Constant):
+                raise ValueError
+            if isinstance(node.op, ast.Add):
+                return ast.Constant(left.value + right.value)
+            elif isinstance(node.op, ast.Sub):
+                return ast.Constant(left.value - right.value)
+            elif isinstance(node.op, ast.BitOr):
+                return ast.Constant(left.value | right.value)
+            raise ValueError
+
     def p(name_node, default_node, default=empty):
         name = parse_name(name_node)
-        if name is invalid:
-            return None
         if default_node and default_node is not _empty:
             try:
                 default_node = RewriteSymbolics().visit(default_node)
-                o = ast.literal_eval(default_node)
+                default = ast.literal_eval(default_node)
             except ValueError:
-                o = invalid
-            if o is invalid:
-                return None
-            default = o if o is not invalid else default
+                raise ValueError("{!r} builtin has invalid signature".format(obj)) from None
         parameters.append(Parameter(name, kind, default=default, annotation=empty))
 
     # non-keyword-only parameters

Lib/test/test_inspect.py

@@ -2474,7 +2474,7 @@ def p(name): return signature.parameters[name].default
         self.assertEqual(p('f'), False)
         self.assertEqual(p('local'), 3)
         self.assertEqual(p('sys'), sys.maxsize)
-        self.assertNotIn('exp', signature.parameters)
+        self.assertEqual(p('exp'), sys.maxsize - 1)
 
         test_callable(object)
 
@@ -4235,10 +4235,30 @@ def func(*args, **kwargs):
         sig = inspect.signature(func)
         self.assertIsNotNone(sig)
         self.assertEqual(str(sig), '(self, /, a, b=1, *args, c, d=2, **kwargs)')
+
         func.__text_signature__ = '($self, a, b=1, /, *args, c, d=2, **kwargs)'
         sig = inspect.signature(func)
         self.assertEqual(str(sig), '(self, a, b=1, /, *args, c, d=2, **kwargs)')
 
+        func.__text_signature__ = '(self, a=1+2, b=4-3, c=1 | 4 | 16)'
+        sig = inspect.signature(func)
+        self.assertEqual(str(sig), '(self, a=3, b=1, c=21)')
+
+        func.__text_signature__ = '(self, a=1,\nb=2,\n\n\n   c=3)'
+        sig = inspect.signature(func)
+        self.assertEqual(str(sig), '(self, a=1, b=2, c=3)')
+
+        func.__text_signature__ = '(self, x=does_not_exist)'
+        with self.assertRaises(ValueError):
+            inspect.signature(func)
+        func.__text_signature__ = '(self, x=sys, y=inspect)'
+        with self.assertRaises(ValueError):
+            inspect.signature(func)
+        func.__text_signature__ = '(self, 123)'
+        with self.assertRaises(ValueError):
+            inspect.signature(func)
+
+
     def test_base_class_have_text_signature(self):
         # see issue 43118
         from test.ann_module7 import BufferedReader