no sqlcoerce yet

changelog.md

@@ -64,6 +64,9 @@
         - The ability to `coerce` `SqlExpr` was removed. Instead, use
           `veryUnsafeCoerceSqlExpr`. See the documentation on
           `veryUnsafeCoerceSqlExpr` for safe use example.
+        - `unsafeCeorceSqlExpr` is provided as an option when the underlying
+          Haskell types are coercible. This is still unsafe, as different
+          `PersistFieldSql` instances may be at play.
     - [#420](https://github.com/bitemyapp/esqueleto/pull/421)
         - The `LockingKind` constructors are deprecated, and will be removed
           from non-Internal modules in a future release. Smart constructors

src/Database/Esqueleto/Internal/Internal.hs

@@ -2523,54 +2523,6 @@ veryUnsafeCoerceSqlExpr (ERaw m k) = ERaw m k
 unsafeCoerceSqlExpr :: (Coercible a b) => SqlExpr a -> SqlExpr b
 unsafeCoerceSqlExpr = veryUnsafeCoerceSqlExpr
 
--- | This type class provides a relation between two types @arg@ and @result@
--- such that @arg@ can be coerced into @result@ safely.
---
--- For this to be generally true, you should ensure that the 'sqlType' method
--- agrees for each type. See 'testSqlCoerce' for a function which does this.
---
--- You will likely want to write bidirectional instances. That is, for two types
--- @A@ and @B@, you'll likely want to write:
---
--- @
--- instance SqlCoerce A B
---
--- instance SqlCoerce B A
--- @
---
--- That way, you can coerce along either way.
---
--- @since 3.6.0.0
-class SqlCoerce arg result where
-    -- | A Haskell value-level witness that you can safely
-    --
-    -- @since 3.6.0.0
-    sqlCoerceWitness :: arg -> result
-
-    -- | Included as a class member to make importing the function easier.
-    -- However, this is defaulted to 'veryUnsafeCoerceSqlExpr', so you
-    -- probably don't want to define your own implementations.
-    sqlCoerce :: SqlExpr arg -> SqlExpr result
-    sqlCoerce = veryUnsafeCoerceSqlExpr
-
--- | This function can be used to test whether or not a 'SqlCoerce' instance is
--- safe or not. If the two underlying 'sqlType' are equal, then this returns
--- @'Right' ()@. Otherwise, it returns a 'Left' with the two 'TypeRep's,
--- allowing you to render failure how you'd like.
---
--- @since 3.6.0.0
-testSqlCoerce
-    :: forall arg result
-     . ( Typeable arg, PersistFieldSql arg
-       , Typeable result, PersistFieldSql result
-       , SqlCoerce arg result
-       )
-    => Either (TypeRep, TypeRep) ()
-testSqlCoerce =
-    if sqlType (Proxy @arg) == sqlType (Proxy @result)
-        then pure ()
-        else Left (typeRep (Proxy @arg), typeRep (Proxy @result))
-
 -- | Folks often want the ability to promote a Haskell function into the
 -- 'SqlExpr' expression language - and naturally reach for 'fmap'.
 -- Unfortunately, this is impossible. We cannot send *functions* to the