Text/Pandoc/Reader/Docx/Parse.hs handles complex fields as if the "separate" field char and subsequent runs were obligatory, but they are optional.

While working on other things, I came across this snippet of docx XML (simplified here):

<w:r><w:fldChar w:fldCharType="begin"/></w:r>
<w:r>
  <w:instrText xml:space="preserve"> SEQ CHAPTER \h \r 1</w:instrText>
</w:r>
<w:r><w:fldChar w:fldCharType="end"/></w:r>

ECMA-376-1:2016, 17.16.2 (p. 1165), however, marks these parts as optional.

Parsing this had the FldCharState transition from Closed -begin-> Open -instr-> FieldInfo, and then ignoring the end. Only when a later field contained a separator, it would continue to -sebarate-> CharContent -end-> Closed.

As a fix, I added a case when end is encountered in the FieldInfo state:

Fixed a bug in complex field handling: separator fields and rendition runs are optional.

---
 src/Text/Pandoc/Readers/Docx/Parse.hs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/Text/Pandoc/Readers/Docx/Parse.hs b/src/Text/Pandoc/Readers/Docx/Parse.hs
index 221260f42..b5226a95a 100644
--- a/src/Text/Pandoc/Readers/Docx/Parse.hs
+++ b/src/Text/Pandoc/Readers/Docx/Parse.hs
@@ -830,9 +830,12 @@ elemToParPart ns element
         FldCharClosed | fldCharType == "begin" -> do
           modify $ \st -> st {stateFldCharState = FldCharOpen}
           return NullParPart
-        FldCharFieldInfo info | fldCharType == "separate" -> do
+        FldCharFieldInfo info | fldCharType == "separate" -> do -- optional separator before rendition
           modify $ \st -> st {stateFldCharState = FldCharContent info []}
           return NullParPart
+        FldCharFieldInfo info | fldCharType == "end" -> do -- direct end, without rendition
+          modify $ \st -> st {stateFldCharState = FldCharClosed}
+          return $ Field info []
         FldCharContent info runs | fldCharType == "end" -> do -- fxg: End in same par
           modify $ \st -> st {stateFldCharState = FldCharClosed}
           return $ Field info $ reverse runs
-- 
2.11.0

I tested that with the current pandoc git master HEAD, versioned 2.2.1