Only show stack trace in debug mode (#1860)

* Only show stack trace in dev mode

* Update custom exception handler to handle KeyboardInterrupts

capa/main.py

@@ -18,6 +18,7 @@
 import datetime
 import textwrap
 import contextlib
+from types import TracebackType
 from typing import Any, Set, Dict, List, Callable, Optional
 from pathlib import Path
 
@@ -977,6 +978,27 @@ def handle_common_args(args):
         args.signatures = sigs_path
 
 
+def simple_message_exception_handler(exctype, value: BaseException, traceback: TracebackType):
+    """
+    prints friendly message on unexpected exceptions to regular users (debug mode shows regular stack trace)
+
+    args:
+      # TODO(aaronatp): Once capa drops support for Python 3.8, move the exctype type annotation to
+      # the function parameters and remove the "# type: ignore[assignment]" from the relevant place
+      # in the main function, see (https://github.com/mandiant/capa/issues/1896)
+      exctype (type[BaseException]): exception class
+    """
+
+    if exctype is KeyboardInterrupt:
+        print("KeyboardInterrupt detected, program terminated")
+    else:
+        print(
+            f"Unexpected exception raised: {exctype}. Please run capa in debug mode (-d/--debug) "
+            + "to see the stack trace. Please also report your issue on the capa GitHub page so we "
+            + "can improve the code! (https://github.com/mandiant/capa/issues)"
+        )
+
+
 def main(argv: Optional[List[str]] = None):
     if sys.version_info < (3, 8):
         raise UnsupportedRuntimeError("This version of capa can only be used with Python 3.8+")
@@ -1019,6 +1041,8 @@ def main(argv: Optional[List[str]] = None):
     install_common_args(parser, {"sample", "format", "backend", "os", "signatures", "rules", "tag"})
     parser.add_argument("-j", "--json", action="store_true", help="emit JSON instead of text")
     args = parser.parse_args(args=argv)
+    if not args.debug:
+        sys.excepthook = simple_message_exception_handler  # type: ignore[assignment]
     ret = handle_common_args(args)
     if ret is not None and ret != 0:
         return ret