[3.11] gh-85267: Improvements to inspect.signature __text_signature__ handling (GH-98796) (#100392)

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 GH-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 GH-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 GH-85267), I
add constant folding of a couple binary operations to RewriteSymbolics.

(There's some discussion of making signature expression evaluation
arbitrary powerful in GH-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 GH-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`..
(cherry picked from commit 79311cbfe7)

Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>

Lib/inspect.py

@@ -2116,7 +2116,7 @@ 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)
 
@@ -2192,7 +2192,6 @@ def _signature_fromstr(cls, obj, s, skip_bound_arg=True):
 
     parameters = []
     empty = Parameter.empty
-    invalid = object()
 
     module = None
     module_dict = {}
@@ -2216,11 +2215,11 @@ def _signature_fromstr(cls, obj, s, skip_bound_arg=True):
             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):
@@ -2230,7 +2229,7 @@ def _signature_fromstr(cls, obj, s, skip_bound_arg=True):
                 a.append(n.attr)
                 n = n.value
             if not isinstance(n, ast.Name):
-                raise RuntimeError()
+                raise ValueError
             a.append(n.id)
             value = ".".join(reversed(a))
             return wrap_value(value)
@@ -2240,19 +2239,29 @@ def _signature_fromstr(cls, obj, s, skip_bound_arg=True):
                 raise ValueError()
             return wrap_value(node.id)
 
+        def visit_BinOp(self, node):
+            # Support constant folding of a couple simple binary operations
+            # commonly used to define default values in text signatures
+            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