Make errno/strerror/filename available on IOError

An error reporting flaw was that most raised IOErrors got their
errno/strerror/filename fields stripped, due to wanting to show a custom
messages. The problem was that adding back 'errno' and 'strerror' made
IOError.__str__() always return a fixed string
("[Errno <errno>] <strerror>"), ignoring any custom message.

This is friendly to users, but unfriendly to scripts (the menuconfig had
a workaround). Make things friendly to both by raising an internal
subclass of IOError instead, that preserves errno/strerror/filename but
prints a custom message. The exception can then still be caught as
IOError/OSError by scripts.

1 files changed, 2 insertions, 12 deletions

diff --git a/menuconfig.py b/menuconfig.py
index 081496f..4aa21c3 100755
--- a/menuconfig.py
+++ b/menuconfig.py
@@ -1646,22 +1646,12 @@ def _try_load(filename):
     # filename:
     #   Configuration file to load
 
-    # Hack: strerror and errno are lost after we raise the custom IOError with
-    # troubleshooting help in Kconfig.load_config(). Adding them back to the
-    # exception loses the custom message. As a workaround, try opening the file
-    # separately first and report any errors.
-    try:
-        open(filename).close()
-    except OSError as e:
-        _error("Error loading {}\n\n{} (errno: {})"
-               .format(filename, e.strerror, errno.errorcode[e.errno]))
-        return False
-
     try:
         _kconf.load_config(filename)
         return True
     except OSError as e:
-        _error("Error loading {}\n\nUnknown error".format(filename))
+        _error("Error loading {}\n\n{} (errno: {})"
+               .format(filename, e.strerror, errno.errorcode[e.errno]))
         return False
 
 def _save_dialog(save_fn, default_filename, description):