cabal install is producing rather useless error messages

[wereHamster]

Consider this example, and now go figure out what the actual problem is:

$ cabal install websockets
Resolving dependencies...
Notice: installing into a sandbox located at /project/.cabal-sandbox
Downloading websockets-0.8.2.3...
Failed to install websockets-0.8.2.3
Last 10 lines of the build log ( /project/.cabal-sandbox/logs/websockets-0.8.2.3.log ):
cabal:
/project/.cabal-sandbox/logs/websockets-0.8.2.3.log:
does not exist

[23Skidoo]

I tried to reproduce this, but websockets install fine on my machine. More info needed.

[23Skidoo]

Maybe the download failed, so the log file was never created.

[wereHamster]

Indeed. Disable or disconnect the network before running the command.

Compare cabal's message with those produced by other tools under the same conditions:

• curl: Could not resolve host: google.com
• ping: connect: Network is unreachable
• chrome: Unable to connect to the Internet
• gem: ERROR: Could not find a valid gem 'ruby' (>= 0), here is why: Unable to download data from https://rubygems.org/ - no such name (https://rubygems.org/latest_specs.4.8.gz)

[23Skidoo]

Yes, this should be fixed. cabal install -v3 probably produces a better message.

[vincenthz]

A different issue but somewhat related, is that truncated error log (10 last lines) are completely useless. Specially with ghc being on the verbose side, it's very often that the line number is not even displayed if there's an error.

Is there a reason that the error log are reported truncated in the first place ? and would it make sense to have a bigger default value (50 ? 100 ?) ?

[23Skidoo]

@vincenthz

A different issue but somewhat related, is that truncated error log (10 last lines) are completely useless.

This is fixed in master, we print the full error log now.

[vincenthz]

@23Skidoo: awesome, thanks. I'll update my versions.

[crockeea]

I think I just got the same behavior:

# ~ $ cabal update
Downloading the latest package list from hackage.haskell.org
# ~ $ cabal install hdevtools
Resolving dependencies...
Downloading cmdargs-0.10.12...
Downloading ghc-paths-0.1.0.9...
Failed to install ghc-paths-0.1.0.9
Build log ( ~/.cabal/logs/ghc-paths-0.1.0.9.log ):
cabal: ~/.cabal/logs/ghc-paths-0.1.0.9.log: does not exist
# ~ $ cabal install ghc-paths
Resolving dependencies...
Downloading ghc-paths-0.1.0.9...
Configuring ghc-paths-0.1.0.9...
Building ghc-paths-0.1.0.9...
Installed ghc-paths-0.1.0.9

So ghc-paths failed to install, then immediately installed without complaint.

[tendril]

I encountered this issue; the cause was that packages in the repo-cache were owned by root and not readable by the user account.

Deleting the package from the repo-cache resolved the issue

Improved error reporting would help a great deal.

[Blaisorblade]

cabal update also suffers this problem — it prints "does not exist" on a network failure (in my actual scenario, we needed a proxy but none was set; FWIW, this user suffered this problem for months).
I've fixed the problem thanks to http://www.yesodweb.com/blog/2015/06/cabals-does-not-exist-error-message

So I managed to trigger (a variant of) this error in a simple way — just set a non-existent proxy (I use http_proxy=http://127.0.0.1). This might be a bit more convenient to reproduce.

cabal install -v3 probably produces a better message.
Unfortunately not, in either case. Traces below.

$ http_proxy=http://127.0.0.1 cabal update -v3
Downloading the latest package list from hackage.haskell.org
Sending:
GET http://hackage.haskell.org/packages/archive/00-index.tar.gz HTTP/1.1
User-Agent: cabal-install/1.20.0.3 (osx; x86_64)
If-None-Match: "2ed1a621df9edcca3a9f3a9c3a4335c3"
Host: hackage.haskell.org

proxy uri host: 127.0.0.1, port:
Creating new connection to 127.0.0.1
cabal: does not exist

$ http_proxy=http://127.0.0.1 cabal install -v3 base-orphans
Searching for ghc in path.
Found ghc at /usr/bin/ghc
("/usr/bin/ghc",["--numeric-version"])
/usr/bin/ghc is version 7.8.3
looking for tool ghc-pkg near compiler in /usr/bin
found ghc-pkg in /usr/bin/ghc-pkg
("/usr/bin/ghc-pkg",["--version"])
/usr/bin/ghc-pkg is version 7.8.3
("/usr/bin/ghc",["--supported-languages"])
("/usr/bin/ghc",["--info"])
Reading installed packages...
("/usr/bin/ghc-pkg",["dump","--global","-v0"])
("/usr/bin/ghc-pkg",["dump","--user","-v0"])
("/usr/bin/ghc",["--print-libdir"])
Reading available packages...
Choosing modular solver.
Resolving dependencies...
[__0] trying: base-orphans-0.4.4 (user goal)
[__1] trying: base-4.7.0.1/installed-df2... (dependency of base-orphans-0.4.4)
[__2] trying: rts-1.0/installedbuil... (dependency of base-4.7.0.1/installed-df2...)
[__3] trying: integer-gmp-0.5.1.0/installed-d42... (dependency of base-4.7.0.1/installed-df2...)
[__4] trying: base-orphans-0.4.4:!test
[__5] next goal: ghc-prim (dependency of base-orphans-0.4.4)
[__5] trying: ghc-prim-0.3.1.0/installed-954...
[__6] done
Ready to install base-orphans-0.4.4
Downloading base-orphans-0.4.4...
Sending:
GET
http://hackage.haskell.org/packages/archive/base-orphans/0.4.4/base-orphans-0.4.4.tar.gz
HTTP/1.1
User-Agent: cabal-install/1.20.0.3 (osx; x86_64)
Host: hackage.haskell.org

proxy uri host: 127.0.0.1, port:
Creating new connection to 127.0.0.1
Waiting for install task to finish...
Failed to install base-orphans-0.4.4
Build log ( /Users/pgiarrusso/.cabal/logs/base-orphans-0.4.4.log ):
cabal: /Users/pgiarrusso/.cabal/logs/base-orphans-0.4.4.log: does not exist

[Blaisorblade]

Closing in favor of more "synthetic" #3073.