chore: move executable code to src/

src/ now contains all source code - in subdirectories, according to the
.cabal component they belong to. This will allow us to put vendored
libraries in the same place - and later split our own code into multiple
components/libraries as well.

src/library/PostgREST/Config/PgVersion.hs

@@ -0,0 +1,40 @@
+{-# LANGUAGE DeriveAnyClass #-}
+{-# LANGUAGE DeriveGeneric  #-}
+module PostgREST.Config.PgVersion
+  ( PgVersion(..)
+  , minimumPgVersion
+  , pgVersion150
+  , pgVersion180
+  , pgVersion190
+  ) where
+
+import qualified Data.Aeson as JSON
+
+import Protolude
+
+
+data PgVersion = PgVersion
+  { pgvNum      :: Int32
+  , pgvName     :: Text
+  , pgvFullName :: Text
+  }
+  deriving (Eq, Generic, JSON.ToJSON)
+
+instance Ord PgVersion where
+  (PgVersion v1 _ _) `compare` (PgVersion v2 _ _) = v1 `compare` v2
+
+-- | Tells the minimum PostgreSQL version required by this version of PostgREST
+minimumPgVersion :: PgVersion
+minimumPgVersion = pgVersion140
+
+pgVersion140 :: PgVersion
+pgVersion140 = PgVersion 140000 "14.0" "14.0"
+
+pgVersion150 :: PgVersion
+pgVersion150 = PgVersion 150000 "15.0" "15.0"
+
+pgVersion180 :: PgVersion
+pgVersion180 = PgVersion 180000 "18.0" "18.0"
+
+pgVersion190 :: PgVersion
+pgVersion190 = PgVersion 190000 "19.0" "19.0"