Summary

Fixes #15132.

When running ipython -c "import sys;sys.exit(2)", IPython returned exit code 1 instead of 2. Regular Python correctly returns 2.

Root cause: TerminalIPythonApp.start() in ipapp.py hardcoded sys.exit(1) for all failed executions, regardless of the actual exit code passed to sys.exit().

Changes

• IPython/terminal/ipapp.py -- Extract the original exit code from last_execution_result.error_in_exec when the error is a SystemExit. Falls back to exit code 1 for non-SystemExit failures.
• IPython/core/shellapp.py -- Add a separate except SystemExit clause in the file execution path of _run_cmd_line_code() to preserve exit codes when running script files.
• tests/test_shellapp.py -- Add 8 tests covering exit code preservation for -c execution and script file execution (codes 0, 1, 2, 42, no-arg, normal execution).

How it works

When sys.exit(N) is called inside user code, InteractiveShell.run_code() catches the SystemExit and stores it in result.error_in_exec. The fix reads error_in_exec.code to extract the original exit code instead of discarding it.

Edge cases handled:

• sys.exit(0) and sys.exit() -- exit code 0
• sys.exit(N) for any integer N -- preserves N
• sys.exit("message") -- exit code 1 (matches Python behavior)
• Non-SystemExit failures -- exit code 1 (unchanged)

Test plan

• ipython -c "import sys; sys.exit(2)" returns code 2 (was 1)
• ipython -c "import sys; sys.exit(42)" returns code 42 (was 1)
• ipython -c "import sys; sys.exit(0)" returns code 0
• ipython -c "print('hello')" returns code 0 (unchanged)
• Script file with sys.exit(2) returns code 2
• All 3 modified files pass syntax check