I pressed enter too early and made this command line:
darcs cha --last=

The error is not so great:
darcs: Prelude.read: no parse

I expected something like "The --last flag requires a value".

On Wed, Jan 28, 2009 at 06:18:36PM +0000, Drew Perttula wrote:
> I pressed enter too early and made this command line:
> darcs cha --last=
> 
> The error is not so great:
> darcs: Prelude.read: no parse
> 
> I expected something like "The --last flag requires a value".

Curiously:

    $ darcs cha --last

    darcs failed:  option `--last' requires an argument NUMBER

    $ darcs cha --last=
    darcs: Prelude.read: no parse
    $

I guess this means the problem is in the piece of code that normalizes
--foo=bar to --foo bar.

I suspect that GNU getopt happily sends an empty string to the Haskell code, and
the Haskell code then fails to parse that.

I'll bet this is the problem (Darcs/Arguments.lhs):

number_string :: String -> Int
number_string s = if and (map isDigit s) then read s else (-1)

Looks like we need add

number_string "" = -1

Marking need-implementation (instead of going ahead and just doing it) because
I'd like the implementor to make sure this gives a good result UI-wise and also
consider if we need a special error message for this case. Tests would be nice
too.  Definitely an easy job, even for a Haskell newbie.

The following patch updated the status of issue1336 to be resolved:

* Resolve issue1336: poor error message on --last "" (empty string to numbers parser) 
Ignore-this: 93b2708bc87ea0a8aefc49732455b14e