From 0ef1e51211cd35b1ddb54a5fe8bee4247f1e1801 Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Sun, 12 Mar 2017 12:42:03 +0100
Subject: Shared:  export extractIds.

This will be used to help with #1745.
---
 src/Text/Pandoc/Shared.hs | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/src/Text/Pandoc/Shared.hs b/src/Text/Pandoc/Shared.hs
index 3b9ae7501..95a53be72 100644
--- a/src/Text/Pandoc/Shared.hs
+++ b/src/Text/Pandoc/Shared.hs
@@ -64,6 +64,7 @@ module Text.Pandoc.Shared (
                      Element (..),
                      hierarchicalize,
                      uniqueIdent,
+                     extractIds,
                      inlineListToIdentifier,
                      isHeaderBlock,
                      headerShift,
@@ -529,6 +530,25 @@ headerLtEq level (Header l _ _) = l <= level
 headerLtEq level (Div ("",["references"],[]) (Header l _ _ : _))  = l <= level
 headerLtEq _ _ = False
 
+-- | Extract the identifiers from a block element.
+extractBlockIds :: Block -> Set.Set String
+extractBlockIds (Header _ (ident,_,_) _) | not (null ident) =
+  Set.singleton ident
+extractBlockIds (Div (ident,_,_) _) | not (null ident) =
+  Set.singleton ident
+extractBlockIds _ = Set.empty
+
+-- | Extract the identifiers from an inline element.
+extractInlineIds :: Inline -> Set.Set String
+extractInlineIds (Span (ident,_,_) _) | not (null ident) =
+  Set.singleton ident
+extractInlineIds _ = Set.empty
+
+-- | Extract the identifiers from a pandoc document.
+extractIds :: Pandoc -> Set.Set String
+extractIds doc =
+  query extractBlockIds doc `Set.union` query extractInlineIds doc
+
 -- | Generate a unique identifier from a list of inlines.
 -- Second argument is a list of already used identifiers.
 uniqueIdent :: [Inline] -> Set.Set String -> String
-- 
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