pythongh-134466: Don't run when termios is inaccessible (pythonGH-138911)

Without the ability to set required capabilities, the REPL cannot
function properly (syntax highlighting and multiline editing can't
work).

We refuse to work in this degraded state.
(cherry picked from commit 2fc7004)

Co-authored-by: Łukasz Langa <[email protected]>

Author: ambv

Lib/_pyrepl/fancy_termios.py

@@ -20,19 +20,25 @@
 import termios
 
 
+TYPE_CHECKING = False
+
+if TYPE_CHECKING:
+    from typing import cast
+else:
+    cast = lambda typ, val: val
+
+
 class TermState:
-    def __init__(self, tuples):
-        (
-            self.iflag,
-            self.oflag,
-            self.cflag,
-            self.lflag,
-            self.ispeed,
-            self.ospeed,
-            self.cc,
-        ) = tuples
+    def __init__(self, attrs: list[int | list[bytes]]) -> None:
+        self.iflag = cast(int, attrs[0])
+        self.oflag = cast(int, attrs[1])
+        self.cflag = cast(int, attrs[2])
+        self.lflag = cast(int, attrs[3])
+        self.ispeed = cast(int, attrs[4])
+        self.ospeed = cast(int, attrs[5])
+        self.cc = cast(list[bytes], attrs[6])
 
-    def as_list(self):
+    def as_list(self) -> list[int | list[bytes]]:
         return [
             self.iflag,
             self.oflag,
@@ -45,32 +51,32 @@ def as_list(self):
             self.cc[:],
         ]
 
-    def copy(self):
+    def copy(self) -> "TermState":
         return self.__class__(self.as_list())
 
 
-def tcgetattr(fd):
+def tcgetattr(fd: int) -> TermState:
     return TermState(termios.tcgetattr(fd))
 
 
-def tcsetattr(fd, when, attrs):
+def tcsetattr(fd: int, when: int, attrs: TermState) -> None:
     termios.tcsetattr(fd, when, attrs.as_list())
 
 
 class Term(TermState):
     TS__init__ = TermState.__init__
 
-    def __init__(self, fd=0):
+    def __init__(self, fd: int = 0) -> None:
         self.TS__init__(termios.tcgetattr(fd))
         self.fd = fd
-        self.stack = []
+        self.stack: list[list[int | list[bytes]]] = []
 
-    def save(self):
+    def save(self) -> None:
         self.stack.append(self.as_list())
 
-    def set(self, when=termios.TCSANOW):
+    def set(self, when: int = termios.TCSANOW) -> None:
         termios.tcsetattr(self.fd, when, self.as_list())
 
-    def restore(self):
+    def restore(self) -> None:
         self.TS__init__(self.stack.pop())
         self.set()

Lib/_pyrepl/unix_console.py

@@ -35,7 +35,7 @@
 
 from . import terminfo
 from .console import Console, Event
-from .fancy_termios import tcgetattr, tcsetattr
+from .fancy_termios import tcgetattr, tcsetattr, TermState
 from .trace import trace
 from .unix_eventqueue import EventQueue
 from .utils import wlen
@@ -51,16 +51,19 @@
 
 # types
 if TYPE_CHECKING:
-    from typing import IO, Literal, overload
+    from typing import AbstractSet, IO, Literal, overload, cast
 else:
     overload = lambda func: None
+    cast = lambda typ, val: val
 
 
 class InvalidTerminal(RuntimeError):
-    pass
+    def __init__(self, message: str) -> None:
+        super().__init__(errno.EIO, message)
 
 
 _error = (termios.error, InvalidTerminal)
+_error_codes_to_ignore = frozenset([errno.EIO, errno.ENXIO, errno.EPERM])
 
 SIGWINCH_EVENT = "repaint"
 
@@ -125,12 +128,13 @@ def __init__(self):
 
         def register(self, fd, flag):
             self.fd = fd
+
         # note: The 'timeout' argument is received as *milliseconds*
         def poll(self, timeout: float | None = None) -> list[int]:
             if timeout is None:
                 r, w, e = select.select([self.fd], [], [])
             else:
-                r, w, e = select.select([self.fd], [], [], timeout/1000)
+                r, w, e = select.select([self.fd], [], [], timeout / 1000)
             return r
 
     poll = MinimalPoll  # type: ignore[assignment]
@@ -164,8 +168,15 @@ def __init__(
             and os.getenv("TERM_PROGRAM") == "Apple_Terminal"
         )
 
+        try:
+            self.__input_fd_set(tcgetattr(self.input_fd), ignore=frozenset())
+        except _error as e:
+            raise RuntimeError(f"termios failure ({e.args[1]})")
+
         @overload
-        def _my_getstr(cap: str, optional: Literal[False] = False) -> bytes: ...
+        def _my_getstr(
+            cap: str, optional: Literal[False] = False
+        ) -> bytes: ...
 
         @overload
         def _my_getstr(cap: str, optional: bool) -> bytes | None: ...
@@ -205,7 +216,9 @@ def _my_getstr(cap: str, optional: bool = False) -> bytes | None:
 
         self.__setup_movement()
 
-        self.event_queue = EventQueue(self.input_fd, self.encoding, self.terminfo)
+        self.event_queue = EventQueue(
+            self.input_fd, self.encoding, self.terminfo
+        )
         self.cursor_visible = 1
 
         signal.signal(signal.SIGCONT, self._sigcont_handler)
@@ -217,7 +230,6 @@ def _sigcont_handler(self, signum, frame):
     def __read(self, n: int) -> bytes:
         return os.read(self.input_fd, n)
 
-
     def change_encoding(self, encoding: str) -> None:
         """
         Change the encoding used for I/O operations.
@@ -329,6 +341,8 @@ def prepare(self):
         """
         Prepare the console for input/output operations.
         """
+        self.__buffer = []
+
         self.__svtermstate = tcgetattr(self.input_fd)
         raw = self.__svtermstate.copy()
         raw.iflag &= ~(termios.INPCK | termios.ISTRIP | termios.IXON)
@@ -340,14 +354,7 @@ def prepare(self):
         raw.lflag |= termios.ISIG
         raw.cc[termios.VMIN] = 1
         raw.cc[termios.VTIME] = 0
-        try:
-            tcsetattr(self.input_fd, termios.TCSADRAIN, raw)
-        except termios.error as e:
-            if e.args[0] != errno.EIO:
-                # gh-135329: when running under external programs (like strace),
-                # tcsetattr may fail with EIO. We can safely ignore this
-                # and continue with default terminal settings.
-                raise
+        self.__input_fd_set(raw)
 
         # In macOS terminal we need to deactivate line wrap via ANSI escape code
         if self.is_apple_terminal:
@@ -356,8 +363,6 @@ def prepare(self):
         self.screen = []
         self.height, self.width = self.getheightwidth()
 
-        self.__buffer = []
-
         self.posxy = 0, 0
         self.__gone_tall = 0
         self.__move = self.__move_short
@@ -379,11 +384,7 @@ def restore(self):
         self.__disable_bracketed_paste()
         self.__maybe_write_code(self._rmkx)
         self.flushoutput()
-        try:
-            tcsetattr(self.input_fd, termios.TCSADRAIN, self.__svtermstate)
-        except termios.error as e:
-            if e.args[0] != errno.EIO:
-                raise
+        self.__input_fd_set(self.__svtermstate)
 
         if self.is_apple_terminal:
             os.write(self.output_fd, b"\033[?7h")
@@ -820,3 +821,17 @@ def __tputs(self, fmt, prog=delayprog):
                 os.write(self.output_fd, self._pad * nchars)
             else:
                 time.sleep(float(delay) / 1000.0)
+
+    def __input_fd_set(
+        self,
+        state: TermState,
+        ignore: AbstractSet[int] = _error_codes_to_ignore,
+    ) -> bool:
+        try:
+            tcsetattr(self.input_fd, termios.TCSADRAIN, state)
+        except termios.error as te:
+            if te.args[0] not in ignore:
+                raise
+            return False
+        else:
+            return True

Misc/NEWS.d/next/Core_and_Builtins/2025-09-15-14-04-56.gh-issue-134466.yR4fYW.rst

@@ -0,0 +1,2 @@
+Don't run PyREPL in a degraded environment where setting termios attributes
+is not allowed.