[0.1.0.3] no overlapping instances, mimeUnrenderXML

CHANGELOG.md

 # Revision history for servant-xml-conduit
 
+## [0.1.0.3] - 2023-11-23
+
+### Fixed
+
+- documentation generation (add `cabal.project` with `allow-newer` for `base`)
+- fix overlapping instances
+
+## [0.1.0.2] - 2023-11-23
+
+### Added
+
+- `.cabal`: added homepage, bug-reports, source-repository
+
 ## [0.1.0.1] - 2023-11 23
 
 ### Fixed

cabal.project

+with-compiler: ghc-8.10.7
+
+allow-newer: base
+
+packages:
+        ./

servant-xml-conduit.cabal

@@ -20,14 +20,14 @@ name:               servant-xml-conduit
 -- PVP summary:     +-+------- breaking API changes
 --                  | | +----- non-breaking API additions
 --                  | | | +--- code changes with no API change
-version:            0.1.0.1
+version:            0.1.0.3
 
 -- A short (one-line) description of the package.
 synopsis: Servant XML content-type with support for xml-conduit
 
 -- A longer description of the package.
 description: This is similar in spirit to `servant-xml` but uses `xml-conduit` instead of `xmlbf`.
-
+             
 -- The license under which the package is released.
 license:            AGPL-3.0-or-later
 
@@ -40,6 +40,9 @@ author:             Gargantext
 -- An email address to which users can send suggestions, bug reports, and patches.
 maintainer:         pk@intrepidus.pl
 
+homepage:           https://gitlab.iscpif.fr/gargantext/servant-xml-conduit
+bug-reports:        https://gitlab.iscpif.fr/gargantext/servant-xml-conduit/issues
+
 -- A copyright notice.
 -- copyright:
 category:           Web
@@ -51,6 +54,10 @@ extra-doc-files:    CHANGELOG.md
 -- Extra source files to be distributed with the package, such as examples, or a tutorial module.
 -- extra-source-files:
 
+source-repository head
+  type: git
+  location: https://gitlab.iscpif.fr/gargantext/servant-xml-conduit
+   
 common warnings
     ghc-options: -Wall
 

src/Servant/XML/Conduit.hs

-{-# LANGUAGE FlexibleContexts #-}
-{-# LANGUAGE UndecidableInstances #-}
-
 {-|
 Module      : Servant.XML.Conduit
 Description : Servant bindings for XML using xml-conduit
@@ -14,6 +11,7 @@ Portability : POSIX
 module Servant.XML.Conduit where
 
 import Data.Bifunctor (first)
+import Data.ByteString.Lazy qualified as BSL
 import Network.HTTP.Media qualified as M
 import Servant.API
 import Text.XML qualified as XML
@@ -24,7 +22,42 @@ data XML
 instance Accept XML where
   contentType _ = "application" M.// "xml" M./: ("charset", "utf-8")
 
-instance {-# OVERLAPPING #-} MimeUnrender XML XML.Document where
-  mimeUnrender _ bs = first show $ XML.parseLBS XML.def bs
 instance MimeRender XML XML.Document where
   mimeRender _ doc = XML.renderLBS XML.def doc
+
+{-| Function to decode a lazy `ByteString' into 'XML.Document'. The
+  reason we don't privde a @'MimeUnrender' 'XML' 'XML.Document'@ instance is
+  that we don't want to force users with a predefined 'FromXML'
+  typeclass.
+
+  If we added
+
+  @
+    instance 'MimeUnrender' 'XML' 'XML.Document' where
+      mimeUnrender _ bs = first show $ 'XML.parseLBS' 'XML.def' bs
+  @
+
+  we immediately arrive at overlapping instances problem when we try to define
+
+  @
+    instance FromXML a => 'MimeUnrender' 'XML' a ...
+  @
+
+  So, just define this in your code:
+
+  @
+    data ParseError =
+      ErrorNoElementFound Text
+      | ...
+
+    class FromXML a where
+      fromXML :: (Functor m, Applicative m, MonadError ParseError m) => 'Text.XML.Cursor.Cursor' -> m a
+
+    instance (FromXML a) => 'MimeUnrender' 'XML' a where
+      mimeUnrender _ctype bs = case 'mimeUnrenderXML' bs of
+        Left err -> Left err
+        Right doc -> first show $ fromXML ('Text.XML.Cursor.fromDocument' doc)
+  @
+-}
+mimeUnrenderXML :: BSL.ByteString -> Either String XML.Document
+mimeUnrenderXML bs = first show $ XML.parseLBS XML.def bs