gdb-stubs fixes (#9439)

* fix: Union subprinters with `None`

See https://github.com/bminor/binutils-gdb/blob/a4418a9c6f99fd31c51698b1f6a6f8dbc1b81b6f/gdb/python/lib/gdb/printing.py#L52-L55

* fix: Allow callables as argument to `printer`

See https://github.com/bminor/binutils-gdb/blob/a4418a9c6f99fd31c51698b1f6a6f8dbc1b81b6f/gdb/python/lib/gdb/printing.py#L77 and the description of "function / old way" in the body of `register_pretty_printer`.

The new union's signature is equivalent to `gdb.printing.PrettyPrinter(...).__call__`.

* fix: make `gdb.Block` iterable over `gdb.Symbol`

See https://sourceware.org/gdb/onlinedocs/gdb/Blocks-In-Python.html#Blocks-In-Python:

> A gdb.Block is iterable. The iterator returns the symbols (see [Symbols In Python](https://sourceware.org/gdb/onlinedocs/gdb/Symbols-In-Python.html#Symbols-In-Python)) local to the block.

Implementation of `gdb.BlockIterator` is given in https://github.com/bminor/binutils-gdb/blob/gdb-12-branch/gdb/python/py-block.c. As with many of the other classes, `BlockIterator` is actually imported from the built-in `_gdb` module (https://github.com/bminor/binutils-gdb/blob/a4418a9c6f99fd31c51698b1f6a6f8dbc1b81b6f/gdb/python/lib/gdb/__init__.py#L28).

Co-authored-by: Alex Waygood <[email protected]>

Author: bzoracler

stubs/gdb/gdb/__init__.pyi

@@ -492,6 +492,12 @@ class Block:
     is_static: bool
 
     def is_valid(self) -> bool: ...
+    def __iter__(self) -> BlockIterator: ...
+
+class BlockIterator:
+    def is_valid(self) -> bool: ...
+    def __iter__(self: _typeshed.Self) -> _typeshed.Self: ...
+    def __next__(self) -> Symbol: ...
 
 # Symbols
 

stubs/gdb/gdb/printing.pyi

@@ -1,12 +1,12 @@
-from collections.abc import Iterable
+from collections.abc import Callable, Iterable
 
 import gdb
 from gdb import _PrettyPrinterLookupFunction
 
 class PrettyPrinter:
 
     name: str
-    subprinters: list[SubPrettyPrinter]
+    subprinters: list[SubPrettyPrinter] | None
     enabled: bool
 
     def __init__(self, name: str, subprinters: Iterable[SubPrettyPrinter] | None = ...) -> None: ...
@@ -26,4 +26,8 @@ class RegexpCollectionPrettyPrinter(PrettyPrinter):
 class FlagEnumerationPrinter(PrettyPrinter):
     def __init__(self, enum_type: str) -> None: ...
 
-def register_pretty_printer(obj: gdb.Objfile | gdb.Progspace | None, printer: PrettyPrinter, replace: bool = ...) -> None: ...
+def register_pretty_printer(
+    obj: gdb.Objfile | gdb.Progspace | None,
+    printer: PrettyPrinter | Callable[[gdb.Value], gdb._PrettyPrinter | None],
+    replace: bool = ...,
+) -> None: ...