bug#16782: Insensitive behavior in date when given invalid fomatting string

[fuz]

Consider the following set of date invocations:

    $ date --version
    date (GNU coreutils) 8.20
    Copyright (C) 2012 Free Software Foundation, Inc.
    License GPLv3+: GNU GPL version 3 or later 
<http://gnu.org/licenses/gpl.html>.
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.

    Written by David MacKenzie.
    $ date +%05
    00%05
    $ date +%Y%#05
    20140%#05
    $ date +x%7
    x     %7
    $ date "+%7 xyz"
        %7 xyz
    $ date "+%7q xyz"
        %7q xyz

GNU date behaves strangely when given an invalid formatting string. GNU date
does not inform the user about the invalid formatting string; instead it outputs
padding as if the flags and field-width, flags and E/O modifier were the whole
formatting string, then the unchanged formatting string. This behavior is not
incorrect as of POSIX.1-2008, as the standard does not specify the behavior of
date in case of an invalid format string, yet it is highly unexpected and weird.

I suggest changing GNU date to output incorrect parts of a formatting string
as-is (as done by the date shipped with Solaris) and possibly exiting with a
non-zero exit status.

Yours sincerely,
Robert Clausecker

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