cabal update with unreachable http_proxy yields unhelpful cabal: does not exist

[nomeata]

In order to avoid #1602 I upgraded HTTP to version 4000.2.17. But I noticed a new (minor) problem: If the proxy mentioned in http_proxy is down, I get

(sid)root@kirk:~# unset http_proxy
(sid)root@kirk:~#  cabal update
Downloading the latest package list from hackage.haskell.org
(sid)root@kirk:~# export http_proxy=http://localhost:3128/
(sid)root@kirk:~#  cabal update
Downloading the latest package list from hackage.haskell.org
cabal: does not exist
# now starting the proxy
(sid)root@kirk:~#  cabal update
Downloading the latest package list from hackage.haskell.org

Certainly the error message could be more helpful.

[23Skidoo]

Isn't this a problem in HTTP's error reporting? E.g. if I set HTTP_PROXY to foo, I get a decent error message:

$ cabal update
Downloading the latest package list from hackage.haskell.org
cabal: openTCPConnection: host lookup failure for "foo"

[ttuegel]

@23Skidoo Did you intend to re-open this?

[23Skidoo]

Apparently I reverted that commit. IIRC I didn't like how that patch replaced all possible HTTP error messages (which can be quite useful, as in example above) with "Cannot connect to uri. Is http_proxy set?". Should be easy to fix by just re-raising the exception.

[23Skidoo]

Hmm, looks like it only handles DoesNotExistError. Maybe I just wanted to improve the patch a bit and then forgot about it.