Renamed AtLeastOneFragment type class to AtMostOneFragment (#1727)

* Renamed `AtLeastOneFragment` to `AtMostOneFragment`

Author: DavidMazarro

changelog.d/1727

@@ -0,0 +1,10 @@
+synopsis: Renamed `AtLeastOneFragment` type class to `AtMostOneFragment`
+prs: #1720
+
+description: {
+
+The previously named `AtLeastOneFragment` type class defined in the
+`Servant.API.TypeLevel` module has been renamed to `AtMostOneFragment`,
+since the previous name was misleading.
+
+}

servant-client-core/src/Servant/Client/Core/HasClient.hs

@@ -88,7 +88,7 @@ import           Servant.API.ContentTypes
                  (contentTypes, AllMime (allMime), AllMimeUnrender (allMimeUnrender))
 import           Servant.API.Status
                  (statusFromNat)
-import           Servant.API.TypeLevel (FragmentUnique, AtLeastOneFragment)
+import           Servant.API.TypeLevel (FragmentUnique, AtMostOneFragment)
 import           Servant.API.Modifiers
                  (FoldRequired, RequiredArgument, foldRequiredArgument)
 import           Servant.API.TypeErrors
@@ -821,7 +821,7 @@ instance ( HasClient m api
 -- > getBooks = client myApi
 -- > -- then you can just use "getBooksBy" to query that endpoint.
 -- > -- 'getBooks' for all books.
-instance (AtLeastOneFragment api, FragmentUnique (Fragment a :> api), HasClient m api
+instance (AtMostOneFragment api, FragmentUnique (Fragment a :> api), HasClient m api
          ) => HasClient m (Fragment a :> api) where
 
   type Client m (Fragment a :> api) = Client m api

servant-server/src/Servant/Server/Internal.hs

@@ -114,7 +114,7 @@ import           Servant.Server.Internal.ServerError
 import           GHC.TypeLits
                  (ErrorMessage (..), TypeError)
 import           Servant.API.TypeLevel
-                 (AtLeastOneFragment, FragmentUnique)
+                 (AtMostOneFragment, FragmentUnique)
 
 class HasServer api context where
   -- | The type of a server for this API, given a monad to run effects in.
@@ -961,7 +961,7 @@ instance {-# OVERLAPPABLE #-} TypeError (NoInstanceFor (HasServer api context))
 -- > server = getBooks
 -- >   where getBooks :: Handler [Book]
 -- >         getBooks = ...return all books...
-instance (AtLeastOneFragment api, FragmentUnique (Fragment a1 :> api), HasServer api context)
+instance (AtMostOneFragment api, FragmentUnique (Fragment a1 :> api), HasServer api context)
     => HasServer (Fragment a1 :> api) context where
   type ServerT (Fragment a1 :> api) m = ServerT api m
 

servant/src/Servant/API/TypeLevel.hs

@@ -47,7 +47,7 @@ module Servant.API.TypeLevel (
     And,
     -- ** Fragment
     FragmentUnique,
-    AtLeastOneFragment
+    AtMostOneFragment
     ) where
 
 
@@ -244,14 +244,14 @@ type family ElemGo e es orig :: Constraint where
 
 -- ** Logic
 
--- | If either a or b produce an empty constraint, produce an empty constraint.
+-- | If either 'a' or 'b' produce an empty constraint, produce an empty constraint.
 type family Or (a :: Constraint) (b :: Constraint) :: Constraint where
     -- This works because of:
     -- https://ghc.haskell.org/trac/ghc/wiki/NewAxioms/CoincidentOverlap
   Or () b       = ()
   Or a ()       = ()
 
--- | If both a or b produce an empty constraint, produce an empty constraint.
+-- | If both 'a' or 'b' produce an empty constraint, produce an empty constraint.
 type family And (a :: Constraint) (b :: Constraint) :: Constraint where
   And () ()     = ()
 
@@ -263,21 +263,22 @@ families are not evaluated (see https://ghc.haskell.org/trac/ghc/ticket/12048).
 
 -- ** Fragment
 
-class FragmentUnique api => AtLeastOneFragment api
-
--- | If fragment appeared in API endpoint twice, compile-time error would be raised.
+-- | If there is more than one fragment in an API endpoint,
+-- a compile-time error is raised.
 --
--- >>> -- type FailAPI = Fragment Bool :> Fragment Int :> Get '[JSON] NoContent
--- >>> instance AtLeastOneFragment FailAPI
+-- >>> type FailAPI = Fragment Bool :> Fragment Int :> Get '[JSON] NoContent
+-- >>> instance AtMostOneFragment FailAPI
 -- ...
 -- ...Only one Fragment allowed per endpoint in api...
 -- ...
 -- ...In the instance declaration for...
-instance AtLeastOneFragment (Verb m s ct typ)
+class FragmentUnique api => AtMostOneFragment api
+
+instance AtMostOneFragment (Verb m s ct typ)
 
-instance AtLeastOneFragment (UVerb m cts as)
+instance AtMostOneFragment (UVerb m cts as)
 
-instance AtLeastOneFragment (Fragment a)
+instance AtMostOneFragment (Fragment a)
 
 type family FragmentUnique api :: Constraint where
   FragmentUnique (sa :<|> sb)       = And (FragmentUnique sa) (FragmentUnique sb)