UncheckedProperty for cmdProperty et al

* Properties that run an arbitrary command, such as cmdProperty
  and scriptProperty are converted to use UncheckedProperty, since
  they cannot tell on their own if the command truely made a change or not.
  (API Change)
  Transition guide:
  - When GHC complains about an UncheckedProperty, add:
  	`assume` MadeChange
  - Since these properties used to always return MadeChange, that
    change is always safe to make.
  - Or, if you know that the command should modifiy a file, use:
  	`changesFile` filename
* A few properties have had their Result improved, for example
  Apt.buldDep and Apt.autoRemove now check if a change was made or not.

1 files changed, 18 insertions, 9 deletions

diff --git a/src/Propellor/Property/Cmd.hs b/src/Propellor/Property/Cmd.hs
index 9536f71d..b02376a3 100644
--- a/src/Propellor/Property/Cmd.hs
+++ b/src/Propellor/Property/Cmd.hs
@@ -32,22 +32,31 @@ import Utility.Process (createProcess, CreateProcess, waitForProcess)
 -- | A property that can be satisfied by running a command.
 --
 -- The command must exit 0 on success.
-cmdProperty :: String -> [String] -> Property NoInfo
+--
+-- This and other properties in this module are `UncheckedProperty`,
+-- and return `NoChange`. It's up to the user to check if the command
+-- made a change to the system, perhaps by using `checkResult` or
+-- `changesFile`, or you can use @cmdProperty "foo" ["bar"] `assume` MadeChange@
+cmdProperty :: String -> [String] -> UncheckedProperty NoInfo
 cmdProperty cmd params = cmdProperty' cmd params id
 
-cmdProperty' :: String -> [String] -> (CreateProcess -> CreateProcess) -> Property NoInfo
-cmdProperty' cmd params mkprocess = property desc $ liftIO $ do
-	toResult <$> boolSystem' cmd (map Param params) mkprocess
+cmdProperty' :: String -> [String] -> (CreateProcess -> CreateProcess) -> UncheckedProperty NoInfo
+cmdProperty' cmd params mkprocess = unchecked $ property desc $ liftIO $
+	cmdResult <$> boolSystem' cmd (map Param params) mkprocess
   where
 	desc = unwords $ cmd : params
 
+cmdResult :: Bool -> Result
+cmdResult False = FailedChange
+cmdResult True = NoChange
+
 -- | A property that can be satisfied by running a command,
 -- with added environment variables in addition to the standard
 -- environment.
-cmdPropertyEnv :: String -> [String] -> [(String, String)] -> Property NoInfo
-cmdPropertyEnv cmd params env = property desc $ liftIO $ do
+cmdPropertyEnv :: String -> [String] -> [(String, String)] -> UncheckedProperty NoInfo
+cmdPropertyEnv cmd params env = unchecked $ property desc $ liftIO $ do
 	env' <- addEntries env <$> getEnvironment
-	toResult <$> boolSystemEnv cmd (map Param params) (Just env')
+	cmdResult <$> boolSystemEnv cmd (map Param params) (Just env')
   where
 	desc = unwords $ cmd : params
 
@@ -55,14 +64,14 @@ cmdPropertyEnv cmd params env = property desc $ liftIO $ do
 type Script = [String]
 
 -- | A property that can be satisfied by running a script.
-scriptProperty :: Script -> Property NoInfo
+scriptProperty :: Script -> UncheckedProperty NoInfo
 scriptProperty script = cmdProperty "sh" ["-c", shellcmd]
   where
 	shellcmd = intercalate " ; " ("set -e" : script)
 
 -- | A property that can satisfied by running a script
 -- as user (cd'd to their home directory).
-userScriptProperty :: User -> Script -> Property NoInfo
+userScriptProperty :: User -> Script -> UncheckedProperty NoInfo
 userScriptProperty (User user) script = cmdProperty "su" ["--shell", "/bin/sh", "-c", shellcmd, user]
   where
 	shellcmd = intercalate " ; " ("set -e" : "cd" : script)