Program logic bugs vs input/environmental errors

[Steven Schveighoffer via Digitalmars-d]

On 9/29/14 7:53 AM, Walter Bright wrote:
> On 9/29/2014 4:47 AM, Steven Schveighoffer wrote:
>> On 9/27/14 9:52 PM, Walter Bright wrote:
>>> If the app is concerned about invalid filenames as bugs, you should
>>> scrub the filenames first. I.e. the interface is defined improperly if
>>> the code confuses a programming bug with input errors.
>>
>> OK, so if you want to avoid improperly having errors/exceptions, don't
>> put bugs
>> into your code.
>>
>> A simple plan!
>
> Validating user input is not the same thing as removing all the logic
> bugs from the program.
>

What if it's not user input?

-Steve