1. Summarise the issue (what were doing, what went wrong?)

I created a file foo with no trailing \n, and recorded its addition.
Upon removing foo, the output was strange (there is a spurious line
addition symbol):

hunk ./foo 1
-foo
+
rmfile ./foo

Indeed, when first adding foo, if I had diffed the file addition, I
would have seem the same problem, but inverted:

addfile ./foo
hunk ./foo 1
-
+foo

The same problem occurs for files with any number of (\n-terminated)
lines, but with no \n on the final line.

2. What behaviour were you expecting instead?

The spurious '+' should not be present for the removal case and the '-'
not present for the addition case.

There is a question about what darcs should do in the presence of such
"text files" (Text files should be a list of newline-terminated strings)
Git for example warns when handling such files.

Might be related to http://bugs.darcs.net/issue1717

verified behaviour on darcs 2.11.0 :
$ darcs record foo
Recording changes in "foo":

hunk ./foo 1
+foo

$vim foo #removed foo line
$ darcs record foo
Recording changes in "foo":

hunk ./foo 1
-foo

#working now as expected, without any spurious line.
#checked issue1717 too, and couldn't reproduce that, should I mark that 
resolved too?

I can reproduce this with 2.11:

> darcs --version
2.11.0 (unknown)
> darcs init
Repository initialized.
> echo -n foo >foo
> darcs record -lm'added foo'
addfile ./foo
Shall I record this change? (1/2)  [ynW...], or ? for more options: y
hunk ./foo 1
-
+foo
Shall I record this change? (2/2)  [ynW...], or ? for more options: y
Do you want to record these changes? [Yglqk...], or ? for more options: y
Do you want to add a long comment? [yn]n
Finished recording patch 'added foo'
> rm foo                     
> darcs record -lm'removed foo'
hunk ./foo 1
-foo
+
Shall I record this change? (1/2)  [ynW...], or ? for more options: y
rmfile ./foo
Shall I record this change? (2/2)  [ynW...], or ? for more options: y
Do you want to record these changes? [Yglqk...], or ? for more options: y
Do you want to add a long comment? [yn]n
Finished recording patch 'removed foo'

Should we mark this (and issue1717 which is a duplicate) as wont-fix?
Ganesh explained the reasons for this in a comment to issue1717, but I
don't understand the explanation. Perhaps some elaboration would help?

The model of how darcs handles this case is described in long comments 
in Darcs.Repository.Diff and in Darcs.Patch.Prim.V1.Apply.

A warning (a la diff or git) may be appropriate.