Be able to turn off instances in password-instances (#65)

password-instances/ChangeLog.md

@@ -1,5 +1,15 @@
 # Changelog for `password-instances`
 
+## 3.1.0.0
+
+-   Added cabal flags (`aeson`, `http-api-data`, `persistent`) to make
+    dependencies optional. All flags default to `True`.
+-   Added compile-time error if all flags are disabled.
+-   Split into dedicated packages
+    [#87](https://github.com/cdepillabout/password/pull/87)
+-   and add flags to parametrize dependencies
+    [#89](https://github.com/cdepillabout/password/pull/89)
+
 ## 3.0.0.0
 
 -   The `password-instances` library now depends on the new

password-instances/password-instances.cabal

@@ -1,7 +1,7 @@
 cabal-version: 1.12
 
 name:           password-instances
-version:        3.0.0.0
+version:        3.1.0.0
 category:       Security
 synopsis:       typeclass instances for password package
 description:    A library providing typeclass instances for common libraries for the types from the password package.
@@ -21,6 +21,21 @@ source-repository head
   type: git
   location: https://github.com/cdepillabout/password
 
+flag aeson
+  description: Enable instances for Aeson
+  default: True
+  manual: True
+
+flag http-api-data
+  description: Enable instances for HTTP API Data
+  default: True
+  manual: True
+
+flag persistent
+  description: Enable instances for Persistent
+  default: True
+  manual: True
+
 custom-setup
   setup-depends:
       base          >= 4.9 && < 5
@@ -35,10 +50,21 @@ library
       Paths_password_instances
   build-depends:
       base          >= 4.9 && < 5
-    , password-aeson
-    , password-http-api-data
-    , password-persistent
   ghc-options:
       -Wall
   default-language:
       Haskell2010
+  default-extensions:
+      CPP
+  if flag(aeson)
+    build-depends:
+        password-aeson
+    cpp-options: -DFLAG_AESON
+  if flag(http-api-data)
+    build-depends:
+        password-http-api-data
+    cpp-options: -DFLAG_HTTP_API_DATA
+  if flag(persistent)
+    build-depends:
+        password-persistent
+    cpp-options: -DFLAG_PERSISTENT

password-instances/src/Data/Password/Instances.hs

@@ -16,6 +16,18 @@ See the "Data.Password.Types" module for more information.
 
 module Data.Password.Instances (module E) where
 
+#if !defined(FLAG_AESON) && !defined(FLAG_HTTP_API_DATA) && !defined(FLAG_PERSISTENT)
+#error "At least one of the flags (aeson, http-api-data, persistent) must be enabled"
+#endif
+
+#ifdef FLAG_AESON
 import Data.Password.Aeson  as E
+#endif
+
+#ifdef FLAG_HTTP_API_DATA
 import Data.Password.HttpApiData as E
+#endif
+
+#ifdef FLAG_PERSISTENT
 import Data.Password.Persistent as E
+#endif