iterate over a directory, dealing with permission errors

[Adrian Matoga via Digitalmars-d]

On Friday, 18 September 2015 at 11:35:45 UTC, John Colvin wrote:
> Posting here instead of learn because I think it uncovers a 
> design flaw
>
> void main(string[] args)
> {
>     import std.file : dirEntries, SpanMode;
>     import std.stdio : writeln;
>     foreach(file; dirEntries(args[1], SpanMode.depth))
>         writeln(file.name);
> }
>
> Modify this program such that it will print "<file.name> access 
> denied" instead of crashing with an exception whenever it hits 
> a permissions problem. Remember that you might not even have 
> permission to read the directory given in args[1]. Remember 
> that access permissions can change at any time.
>
> It can be done, but it is seriously ugly.

https://github.com/D-Programming-Language/phobos/pull/931

I had to move to some urgent stuff instead of improving the PR 
and later I forgot about it. The discussion points out what not 
to do when solving this issue. :)