From db0232fc545913a9ea6e81d84fc5ee4d9cc8a185 Mon Sep 17 00:00:00 2001
From: Albert Krewinkel <albert@zeitkraut.de>
Date: Wed, 19 Oct 2022 19:07:56 +0200
Subject: Format: add function `diffExtensions`.

---
 src/Text/Pandoc/Format.hs | 9 +++++++++
 1 file changed, 9 insertions(+)

(limited to 'src')

diff --git a/src/Text/Pandoc/Format.hs b/src/Text/Pandoc/Format.hs
index 5e5829553..afd483577 100644
--- a/src/Text/Pandoc/Format.hs
+++ b/src/Text/Pandoc/Format.hs
@@ -12,6 +12,7 @@ module Text.Pandoc.Format
   ( FlavoredFormat (..)
   , ExtensionsConfig (..)
   , ExtensionsDiff (..)
+  , diffExtensions
   , parseFlavoredFormat
   , applyExtensionsDiff
   , getExtensionsConfig
@@ -59,6 +60,14 @@ instance Monoid ExtensionsDiff where
   mempty = ExtensionsDiff mempty mempty
   mappend = (<>)
 
+-- | Calculate the change set to get from one set of extensions to
+-- another.
+diffExtensions :: Extensions -> Extensions -> ExtensionsDiff
+diffExtensions def actual = ExtensionsDiff
+  { extsToEnable = actual `disableExtensions` def
+  , extsToDisable = def `disableExtensions` actual
+  }
+
 -- | Describes the properties of a format.
 data ExtensionsConfig = ExtensionsConfig
   { extsDefault   :: Extensions -- ^ Extensions enabled by default
-- 
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