Add test to check package id extraction

This commit add a failing test to check extracting package id. The test will
fail with the following output for now:

1) Cradle.getPackageDbPackages find a config file and extracts packages with their ids
expected: [("template-haskell",Just "template-haskell-2.8.0.0-32d4f24abdbb6bf41272b183b2e23e9c")]
 but got: []

Language/Haskell/GhcMod/Cradle.hs

@@ -4,6 +4,7 @@ module Language.Haskell.GhcMod.Cradle (
     findCradle
   , findCradleWithoutSandbox
   , getPackageDbDir
+  , getPackageDbPackages
   ) where
 
 import Data.Char (isSpace)
@@ -141,3 +142,43 @@ extractGhcVer dir = ver
     (verStr1,_:left) = break (== '.') $ findVer file
     (verStr2,_)      = break (== '.') left
     ver = read verStr1 * 100 + read verStr2
+
+-- | Obtaining packages installed in a package db directory.
+getPackageDbPackages :: FilePath -> IO [Package]
+getPackageDbPackages cdir = (getPkgDb >>= listDbPackages) `E.catch` handler
+  where
+    getPkgDb = getPackageDbDir (cdir </> configFile)
+    handler :: SomeException -> IO [Package]
+    handler _ = return []
+
+listDbPackages :: FilePath -> IO [Package]
+listDbPackages pkgdir = do
+  files <- filter (".conf" `isSuffixOf`) <$> getDirectoryContents pkgdir
+  mapM extractPackage $ map (pkgdir </>) files
+
+extractPackage :: FilePath -> IO Package
+extractPackage pconf = do
+  contents <- lines <$> readFile pconf
+  -- Be strict to ensure that an error can be caught.
+  let !name = extractName $ parseName contents
+      !pid = extractId $ parseId contents
+  return (name, Just pid)
+  where
+    parseName = parse nameKey
+    extractName = extract nameKeyLength
+    parseId = parse idKey
+    extractId = extract idKeyLength
+    parse key = head . filter (key `isPrefixOf`)
+    extract keylen = fst . break isSpace . dropWhile isSpace . drop keylen
+
+nameKey :: String
+nameKey = "name:"
+
+idKey :: String
+idKey = "id:"
+
+nameKeyLength :: Int
+nameKeyLength = length nameKey
+
+idKeyLength :: Int
+idKeyLength = length idKey

test/CradleSpec.hs

@@ -53,6 +53,11 @@ spec = do
         it "throws an error if a config file is broken" $ do
             getPackageDbDir "test/data/bad.config" `shouldThrow` anyException
 
+    describe "getPackageDbPackages" $ do
+        it "find a config file and extracts packages with their ids" $ do
+            pkgs <- getPackageDbPackages "test/data/check-packageid"
+            pkgs `shouldBe` [("template-haskell", Just "template-haskell-2.8.0.0-32d4f24abdbb6bf41272b183b2e23e9c")]
+
 relativeCradle :: FilePath -> Cradle -> Cradle
 relativeCradle dir cradle = cradle {
     cradleCurrentDir    = toRelativeDir dir  $  cradleCurrentDir    cradle

test/data/check-packageid/.cabal-sandbox/i386-osx-ghc-7.6.3-packages.conf.d/template-haskell-2.8.0.0-32d4f24abdbb6bf41272b183b2e23e9c.conf

@@ -0,0 +1,37 @@
+name: template-haskell
+version: 2.8.0.0
+id: template-haskell-2.8.0.0-32d4f24abdbb6bf41272b183b2e23e9c
+license: BSD3
+copyright:
+maintainer: libraries@haskell.org
+stability:
+homepage:
+package-url:
+synopsis:
+description: Facilities for manipulating Haskell source code using Template Haskell.
+category:
+author:
+exposed: True
+exposed-modules: Language.Haskell.TH.Syntax
+                 Language.Haskell.TH.PprLib Language.Haskell.TH.Ppr
+                 Language.Haskell.TH.Lib Language.Haskell.TH.Quote
+                 Language.Haskell.TH
+hidden-modules:
+trusted: False
+import-dirs: /usr/lib64/ghc-7.6.3/template-haskell-2.8.0.0
+library-dirs: /usr/lib64/ghc-7.6.3/template-haskell-2.8.0.0
+hs-libraries: HStemplate-haskell-2.8.0.0
+extra-libraries:
+extra-ghci-libraries:
+include-dirs:
+includes:
+depends: base-4.6.0.1-2bc8d09dc7b7883c4b97d1eb4a9d4ac8
+         containers-0.5.0.0-120bacdd7a06bf9f1f601811aa72d6c3
+         pretty-1.1.1.0-65070790589ca7952412e425f427ac56
+hugs-options:
+cc-options:
+ld-options:
+framework-dirs:
+frameworks:
+haddock-interfaces: /usr/share/doc/ghc-7.6.3/html/libraries/template-haskell-2.8.0.0/template-haskell.haddock
+haddock-html: /usr/share/doc/ghc-7.6.3/html/libraries/template-haskell-2.8.0.0

test/data/check-packageid/cabal.sandbox.config

@@ -0,0 +1,25 @@
+-- This is a Cabal package environment file.
+-- THIS FILE IS AUTO-GENERATED. DO NOT EDIT DIRECTLY.
+-- Please create a 'cabal.config' file in the same directory
+-- if you want to change the default settings for this sandbox.
+
+
+local-repo: /home/me/work/ghc-mod/test/data/.cabal-sandbox/packages
+logs-dir: /home/me/work/ghc-mod/test/data/.cabal-sandbox/logs
+world-file: /home/me/work/ghc-mod/test/data/.cabal-sandbox/world
+user-install: False
+package-db: test/data/check-packageid/.cabal-sandbox/i386-osx-ghc-7.6.3-packages.conf.d
+build-summary: /home/me/work/ghc-mod/test/data/.cabal-sandbox/logs/build.log
+
+install-dirs 
+  prefix: /home/me/work/ghc-mod/test/data/.cabal-sandbox
+  bindir: $prefix/bin
+  libdir: $prefix/lib
+  libsubdir: $arch-$os-$compiler/$pkgid
+  libexecdir: $prefix/libexec
+  datadir: $prefix/share
+  datasubdir: $arch-$os-$compiler/$pkgid
+  docdir: $datadir/doc/$arch-$os-$compiler/$pkgid
+  htmldir: $docdir/html
+  haddockdir: $htmldir
+  sysconfdir: $prefix/etc