prevent trust commands from trying to do things in a bare repo

Since they need to stage changes, they would actually, if allowed to run,
succeed, but wipe out existing trust.log content.

Command.hs

@@ -10,7 +10,7 @@ module Command where
 import Control.Monad.State (liftIO)
 import System.Directory
 import System.Posix.Files
-import Control.Monad (filterM, liftM)
+import Control.Monad (filterM, liftM, when)
 import System.Path.WildMatch
 import Text.Regex.PCRE.Light.Char8
 import Data.List
@@ -104,6 +104,13 @@ isAnnexed file a = do
 		Just v -> a v
 		Nothing -> return Nothing
 
+notBareRepo :: Annex a -> Annex a
+notBareRepo a = do
+	g <- Annex.gitRepo
+	when (Git.repoIsLocalBare g) $ do
+		error "You cannot run this subcommand in a bare repository."
+	a
+
 {- These functions find appropriate files or other things based on a
    user's parameters, and run a specified action on them. -}
 withFilesInGit :: CommandSeekStrings

Command/Semitrust.hs

@@ -22,7 +22,7 @@ seek :: [CommandSeek]
 seek = [withString start]
 
 start :: CommandStartString
-start name = do
+start name = notBareRepo $ do
 	showStart "semitrust" name
 	Remotes.readConfigs
 	r <- Remotes.byName name

Command/Trust.hs

@@ -22,7 +22,7 @@ seek :: [CommandSeek]
 seek = [withString start]
 
 start :: CommandStartString
-start name = do
+start name = notBareRepo $ do
 	showStart "trust" name
 	Remotes.readConfigs
 	r <- Remotes.byName name

Command/Untrust.hs

@@ -22,7 +22,7 @@ seek :: [CommandSeek]
 seek = [withString start]
 
 start :: CommandStartString
-start name = do
+start name = notBareRepo $ do
 	showStart "untrust" name
 	Remotes.readConfigs
 	r <- Remotes.byName name

doc/bare_repositories.mdwn

@@ -19,12 +19,9 @@ Known to work ok:
 
 There are a few caveats to keep in mind:
 
-* Using non-local bare repositories is not tested and probably broken.
 * `git annex init` can be run in a bare repository, but it cannot
   store the name you gave the repository in .git-annex/uuid.log (because
   the bare repository has no such file to commit to).
-* `git annex trust` cannot be used in a bare repository, and currently
-  does something pointless. Same for `untrust` and `semitrust`.
 * `git annex fromkey` does something pointless in a bare repository.
 * `git annex fsck` cannot detect any problems in a bare repository.
 * `git annex unused` will think everything stored in a bare repository