Rework how --debug is handled in main

Move the `run` call into a wrapper function and inline the exception
handling while moving the try-finally around `run` into the
nested function.

This reduces the amount of code at a deeper nesting level and moves the
self-version-check logic into the "around the run" exception catching so
that a consistent message is presented in cases of failures.

src/pip/_internal/cli/base_command.py

@@ -1,14 +1,13 @@
 """Base Command class, and related routines"""
 
-import functools
 import logging
 import logging.config
 import optparse
 import os
 import sys
 import traceback
 from optparse import Values
-from typing import Any, Callable, List, Optional, Tuple
+from typing import List, Optional, Tuple
 
 from pip._vendor.rich import reconfigure
 from pip._vendor.rich import traceback as rich_traceback
@@ -91,6 +90,63 @@ def handle_pip_version_check(self, options: Values) -> None:
     def run(self, options: Values, args: List[str]) -> int:
         raise NotImplementedError
 
+    def _run_wrapper(self, level_number: int, options: Values, args: List[str]) -> int:
+        def _inner_run() -> int:
+            try:
+                return self.run(options, args)
+            finally:
+                self.handle_pip_version_check(options)
+
+        if options.debug_mode:
+            rich_traceback.install(show_locals=True)
+            return _inner_run()
+
+        try:
+            status = _inner_run()
+            assert isinstance(status, int)
+            return status
+        except DiagnosticPipError as exc:
+            logger.error("%s", exc, extra={"rich": True})
+            logger.debug("Exception information:", exc_info=True)
+
+            return ERROR
+        except PreviousBuildDirError as exc:
+            logger.critical(str(exc))
+            logger.debug("Exception information:", exc_info=True)
+
+            return PREVIOUS_BUILD_DIR_ERROR
+        except (
+            InstallationError,
+            BadCommand,
+            NetworkConnectionError,
+        ) as exc:
+            logger.critical(str(exc))
+            logger.debug("Exception information:", exc_info=True)
+
+            return ERROR
+        except CommandError as exc:
+            logger.critical("%s", exc)
+            logger.debug("Exception information:", exc_info=True)
+
+            return ERROR
+        except BrokenStdoutLoggingError:
+            # Bypass our logger and write any remaining messages to
+            # stderr because stdout no longer works.
+            print("ERROR: Pipe to stdout was broken", file=sys.stderr)
+            if level_number <= logging.DEBUG:
+                traceback.print_exc(file=sys.stderr)
+
+            return ERROR
+        except KeyboardInterrupt:
+            logger.critical("Operation cancelled by user")
+            logger.debug("Exception information:", exc_info=True)
+
+            return ERROR
+        except BaseException:
+            logger.critical("Exception:", exc_info=True)
+
+            return UNKNOWN_ERROR
+
     def parse_args(self, args: List[str]) -> Tuple[Values, List[str]]:
         # factored out for testability
         return self.parser.parse_args(args)
@@ -172,65 +228,4 @@ def _main(self, args: List[str]) -> int:
                 )
                 options.cache_dir = None
 
-        def intercepts_unhandled_exc(
-            run_func: Callable[..., int]
-        ) -> Callable[..., int]:
-            @functools.wraps(run_func)
-            def exc_logging_wrapper(*args: Any) -> int:
-                try:
-                    status = run_func(*args)
-                    assert isinstance(status, int)
-                    return status
-                except DiagnosticPipError as exc:
-                    logger.error("%s", exc, extra={"rich": True})
-                    logger.debug("Exception information:", exc_info=True)
-
-                    return ERROR
-                except PreviousBuildDirError as exc:
-                    logger.critical(str(exc))
-                    logger.debug("Exception information:", exc_info=True)
-
-                    return PREVIOUS_BUILD_DIR_ERROR
-                except (
-                    InstallationError,
-                    BadCommand,
-                    NetworkConnectionError,
-                ) as exc:
-                    logger.critical(str(exc))
-                    logger.debug("Exception information:", exc_info=True)
-
-                    return ERROR
-                except CommandError as exc:
-                    logger.critical("%s", exc)
-                    logger.debug("Exception information:", exc_info=True)
-
-                    return ERROR
-                except BrokenStdoutLoggingError:
-                    # Bypass our logger and write any remaining messages to
-                    # stderr because stdout no longer works.
-                    print("ERROR: Pipe to stdout was broken", file=sys.stderr)
-                    if level_number <= logging.DEBUG:
-                        traceback.print_exc(file=sys.stderr)
-
-                    return ERROR
-                except KeyboardInterrupt:
-                    logger.critical("Operation cancelled by user")
-                    logger.debug("Exception information:", exc_info=True)
-
-                    return ERROR
-                except BaseException:
-                    logger.critical("Exception:", exc_info=True)
-
-                    return UNKNOWN_ERROR
-
-            return exc_logging_wrapper
-
-        try:
-            if not options.debug_mode:
-                run = intercepts_unhandled_exc(self.run)
-            else:
-                run = self.run
-                rich_traceback.install(show_locals=True)
-            return run(options, args)
-        finally:
-            self.handle_pip_version_check(options)
+        return self._run_wrapper(level_number, options, args)