fix: restructure TableNotCompatibleError to TableUnionNotCompatibleError

src/Database/LSMTree.hs

@@ -16,7 +16,7 @@ module Database.LSMTree (
   , Common.TableClosedError (..)
   , Common.TableCorruptedError (..)
   , Common.TableTooLargeError (..)
-  , Common.TableNotCompatibleError (..)
+  , Common.TableUnionNotCompatibleError (..)
   , Common.SnapshotExistsError (..)
   , Common.SnapshotDoesNotExistError (..)
   , Common.SnapshotCorruptedError (..)
@@ -129,7 +129,8 @@ import           Data.Bifunctor (Bifunctor (..))
 import           Data.Coerce (coerce)
 import           Data.Kind (Type)
 import           Data.List.NonEmpty (NonEmpty (..))
-import           Data.Typeable (Proxy (..), Typeable, eqT, type (:~:) (Refl))
+import           Data.Typeable (Proxy (..), Typeable, eqT, type (:~:) (Refl),
+                     typeRep)
 import qualified Data.Vector as V
 import           Database.LSMTree.Common (BlobRef (BlobRef), IOLike, Range (..),
                      SerialiseKey, SerialiseValue, Session, UnionCredits (..),
@@ -570,7 +571,7 @@ unions (t :| ts) =
       -> m (Internal.Table m h)
     checkTableType _ i (Internal.Table' (t' :: Internal.Table m h'))
       | Just Refl <- eqT @h @h' = pure t'
-      | otherwise = throwIO (Common.ErrTableTypeMismatch 0 i)
+      | otherwise = throwIO $ Common.ErrTableUnionHandleTypeMismatch 0 (typeRep $ Proxy @h) i (typeRep $ Proxy @h')
 
 {-# SPECIALISE remainingUnionDebt :: Table IO k v b -> IO UnionDebt #-}
 remainingUnionDebt :: IOLike m => Table m k v b -> m UnionDebt

src/Database/LSMTree/Common.hs

@@ -9,7 +9,7 @@ module Database.LSMTree.Common (
   , Internal.TableClosedError (..)
   , Internal.TableCorruptedError (..)
   , Internal.TableTooLargeError (..)
-  , Internal.TableNotCompatibleError (..)
+  , Internal.TableUnionNotCompatibleError (..)
   , Internal.SnapshotExistsError (..)
   , Internal.SnapshotDoesNotExistError (..)
   , Internal.SnapshotCorruptedError (..)

src/Database/LSMTree/Internal.hs

@@ -28,7 +28,7 @@ module Database.LSMTree.Internal (
   , TableClosedError (..)
   , TableCorruptedError (..)
   , TableTooLargeError (..)
-  , TableNotCompatibleError (..)
+  , TableUnionNotCompatibleError (..)
   , SnapshotExistsError (..)
   , SnapshotDoesNotExistError (..)
   , SnapshotCorruptedError (..)
@@ -1534,27 +1534,30 @@ duplicate t@Table{..} = do
             tableArenaManager
             content
 
-
 {-------------------------------------------------------------------------------
    Table union
 -------------------------------------------------------------------------------}
 
--- | An operation was called with two tables that are not compatible.
-data TableNotCompatibleError
-    = -- | An operation was called with two tables that are not of the same type.
-      --
-      --   TODO: This error is no longer used by 'unions'.
-      ErrTableTypeMismatch
-        -- | Vector index of table @t1@ involved in the mismatch
-        Int
-        -- | Vector index of table @t2@ involved in the mismatch
-        Int
-    | -- | An operation was called with two tables that are not in the same session.
-      ErrTableSessionMismatch
-        -- | Vector index of table @t1@ involved in the mismatch
-        Int
-        -- | Vector index of table @t2@ involved in the mismatch
-        Int
+-- | A table union was constructed with two tables that are not compatible.
+data TableUnionNotCompatibleError
+    = ErrTableUnionHandleTypeMismatch
+        -- | The index of the first table.
+        !Int
+        -- | The type of the filesystem handle of the first table.
+        !TypeRep
+        -- | The index of the second table.
+        !Int
+        -- | The type of the filesystem handle of the second table.
+        !TypeRep
+    | ErrTableUnionSessionMismatch
+        -- | The index of the first table.
+        !Int
+        -- | The session directory of the first table.
+        !FsErrorPath
+        -- | The index of the second table.
+        !Int
+        -- | The session directory of the second table.
+        !FsErrorPath
     deriving stock (Show, Eq)
     deriving anyclass (Exception)
 
@@ -1565,10 +1568,7 @@ unions ::
   => NonEmpty (Table m h)
   -> m (Table m h)
 unions ts = do
-    sesh <-
-      matchSessions ts >>= \case
-        Left (i, j) -> throwIO $ ErrTableSessionMismatch i j
-        Right sesh  -> pure sesh
+    sesh <- ensureSessionsMatch ts
 
     traceWith (sessionTracer sesh) $ TraceUnions (NE.map tableId ts)
 
@@ -1706,37 +1706,34 @@ writeBufferToNewRun SessionEnv {
       tableWriteBuffer
       tableWriteBufferBlobs
 
--- | Check that all tables in the session match. If so, return the matched
--- session. If there is a mismatch, return the list indices of the mismatching
--- tables.
---
--- TODO: compare LockFileHandle instead of SessionRoot (?). We can write an Eq
--- instance for LockFileHandle based on pointer equality, just like base does
--- for Handle.
-matchSessions ::
+{-# SPECIALISE ensureSessionsMatch ::
+     NonEmpty (Table IO h)
+  -> IO (Session IO h) #-}
+-- | Check if all tables have the same session.
+--   If so, return the session.
+--   Otherwise, throw a 'TableUnionNotCompatibleError'.
+ensureSessionsMatch ::
      (MonadSTM m, MonadThrow m)
   => NonEmpty (Table m h)
-  -> m (Either (Int, Int) (Session m h))
-matchSessions = \(t :| ts) ->
-    withSessionRoot t $ \root -> do
-      eith <- go root 1 ts
-      pure $ case eith of
-        Left i   -> Left (0, i)
-        Right () -> Right (tableSession t)
-  where
+  -> m (Session m h)
+ensureSessionsMatch (t :| ts) = do
+  let sesh = tableSession t
+  withOpenSession sesh $ \seshEnv -> do
+    let root = FS.mkFsErrorPath (sessionHasFS seshEnv) (getSessionRoot (sessionRoot seshEnv))
     -- Check that the session roots for all tables are the same. There can only
     -- be one *open/active* session per directory because of cooperative file
     -- locks, so each unique *open* session has a unique session root. We check
     -- that all the table's sessions are open at the same time while comparing
     -- the session roots.
-    go _ _ [] = pure (Right ())
-    go root !i (t':ts') =
-        withSessionRoot t' $ \root' ->
-          if root == root'
-            then go root (i+1) ts'
-            else pure (Left i)
-
-    withSessionRoot t k =  withOpenSession (tableSession t) $ k . sessionRoot
+    for_ (zip [1..] ts) $ \(i, t') -> do
+      let sesh' = tableSession t'
+      withOpenSession sesh' $ \seshEnv' -> do
+        let root' = FS.mkFsErrorPath (sessionHasFS seshEnv') (getSessionRoot (sessionRoot seshEnv'))
+        -- TODO: compare LockFileHandle instead of SessionRoot (?).
+        -- We can write an Eq instance for LockFileHandle based on pointer equality,
+        -- just like base does for Handle.
+        unless (root == root') $ throwIO $ ErrTableUnionSessionMismatch 0 root i root'
+    pure sesh
 
 {-------------------------------------------------------------------------------
   Table union: debt and credit

src/Database/LSMTree/Monoidal.hs

@@ -31,7 +31,7 @@ module Database.LSMTree.Monoidal (
   , Common.TableClosedError (..)
   , Common.TableCorruptedError (..)
   , Common.TableTooLargeError (..)
-  , Common.TableNotCompatibleError (..)
+  , Common.TableUnionNotCompatibleError (..)
   , Common.SnapshotExistsError (..)
   , Common.SnapshotDoesNotExistError (..)
   , Common.SnapshotCorruptedError (..)
@@ -149,8 +149,8 @@ import           Data.Coerce (coerce)
 import           Data.Kind (Type)
 import           Data.List.NonEmpty (NonEmpty (..))
 import           Data.Monoid (Sum (..))
-import           Data.Proxy (Proxy (Proxy))
-import           Data.Typeable (Typeable, eqT, type (:~:) (Refl))
+import           Data.Typeable (Proxy (..), Typeable, eqT, type (:~:) (Refl),
+                     typeRep)
 import qualified Data.Vector as V
 import           Database.LSMTree.Common (IOLike, Range (..), SerialiseKey,
                      SerialiseValue (..), Session, UnionCredits (..),
@@ -719,7 +719,7 @@ unions (t :| ts) =
       -> m (Internal.Table m h)
     checkTableType _ i (Internal.MonoidalTable (t' :: Internal.Table m h'))
       | Just Refl <- eqT @h @h' = pure t'
-      | otherwise = throwIO (Common.ErrTableTypeMismatch 0 i)
+      | otherwise = throwIO $ Common.ErrTableUnionHandleTypeMismatch 0 (typeRep $ Proxy @h) i (typeRep $ Proxy @h')
 
 {-# SPECIALISE remainingUnionDebt :: Table IO k v -> IO UnionDebt #-}
 -- | Return the current union debt. This debt can be reduced until it is paid

src/Database/LSMTree/Normal.hs

@@ -30,7 +30,7 @@ module Database.LSMTree.Normal (
   , Common.TableClosedError (..)
   , Common.TableCorruptedError (..)
   , Common.TableTooLargeError (..)
-  , Common.TableNotCompatibleError (..)
+  , Common.TableUnionNotCompatibleError (..)
   , Common.SnapshotExistsError (..)
   , Common.SnapshotDoesNotExistError (..)
   , Common.SnapshotCorruptedError (..)
@@ -140,7 +140,8 @@ import           Control.Monad.Class.MonadThrow
 import           Data.Bifunctor (Bifunctor (..))
 import           Data.Kind (Type)
 import           Data.List.NonEmpty (NonEmpty (..))
-import           Data.Typeable (Typeable, eqT, type (:~:) (Refl))
+import           Data.Typeable (Proxy (..), Typeable, eqT, type (:~:) (Refl),
+                     typeRep)
 import qualified Data.Vector as V
 import           Database.LSMTree.Common (BlobRef (BlobRef), IOLike, Range (..),
                      SerialiseKey, SerialiseValue, Session, UnionCredits (..),
@@ -839,7 +840,7 @@ unions (t :| ts) =
       -> m (Internal.Table m h)
     checkTableType _ i (Internal.NormalTable (t' :: Internal.Table m h'))
       | Just Refl <- eqT @h @h' = pure t'
-      | otherwise = throwIO (Common.ErrTableTypeMismatch 0 i)
+      | otherwise = throwIO $ Common.ErrTableUnionHandleTypeMismatch 0 (typeRep $ Proxy @h) i (typeRep $ Proxy @h')
 
 {-# SPECIALISE remainingUnionDebt :: Table IO k v b -> IO UnionDebt #-}
 -- | Return the current union debt. This debt can be reduced until it is paid

test/Database/LSMTree/Model/Session.hs

@@ -267,8 +267,8 @@ data Err
   | ErrSessionClosed
   | ErrTableClosed
   | ErrTableCorrupted
-  | ErrTableTypeMismatch
-  | ErrTableSessionMismatch
+  | ErrTableUnionHandleTypeMismatch
+  | ErrTableUnionSessionMismatch
   | ErrSnapshotExists !SnapshotName
   | ErrSnapshotDoesNotExist !SnapshotName
   | ErrSnapshotCorrupted !SnapshotName

test/Test/Database/LSMTree/StateMachine.hs

@@ -94,7 +94,8 @@ import           Database.LSMTree.Common (BlobRefInvalidError (..),
                      SessionDirLockedError (..), SnapshotCorruptedError (..),
                      SnapshotDoesNotExistError (..), SnapshotExistsError (..),
                      SnapshotNotCompatibleError (..), TableClosedError (..),
-                     TableCorruptedError (..), TableNotCompatibleError (..))
+                     TableCorruptedError (..),
+                     TableUnionNotCompatibleError (..))
 import           Database.LSMTree.Extras (showPowersOf)
 import           Database.LSMTree.Extras.Generators (KeyForIndexCompact)
 import           Database.LSMTree.Extras.NoThunks (propNoThunks)
@@ -483,7 +484,7 @@ handleSomeException e =
     , handleSessionClosedError <$> fromException e
     , handleTableClosedError <$> fromException e
     , handleTableCorruptedError <$> fromException e
-    , handleTableNotCompatibleError <$> fromException e
+    , handleTableUnionNotCompatibleError <$> fromException e
     , handleSnapshotExistsError <$> fromException e
     , handleSnapshotDoesNotExistError <$> fromException e
     , handleSnapshotCorruptedError <$> fromException e
@@ -528,12 +529,12 @@ handleTableClosedError = \case
 
 handleTableCorruptedError :: TableCorruptedError -> Model.Err
 handleTableCorruptedError = \case
-  ErrLookupByteCountDiscrepancy _ _ -> Model.ErrTableCorrupted
+  ErrLookupByteCountDiscrepancy{} -> Model.ErrTableCorrupted
 
-handleTableNotCompatibleError :: TableNotCompatibleError -> Model.Err
-handleTableNotCompatibleError = \case
-  ErrTableTypeMismatch _ _ -> Model.ErrTableTypeMismatch
-  ErrTableSessionMismatch _ _ -> Model.ErrTableSessionMismatch
+handleTableUnionNotCompatibleError :: TableUnionNotCompatibleError -> Model.Err
+handleTableUnionNotCompatibleError = \case
+  ErrTableUnionHandleTypeMismatch{} -> Model.ErrTableUnionHandleTypeMismatch
+  ErrTableUnionSessionMismatch{} -> Model.ErrTableUnionSessionMismatch
 
 handleSnapshotExistsError :: SnapshotExistsError -> Model.Err
 handleSnapshotExistsError = \case