From 5dc917da3ed997c6e48e22bde242f0f8e1ae5333 Mon Sep 17 00:00:00 2001
From: John MacFarlane <jgm@berkeley.edu>
Date: Thu, 20 May 2021 09:11:26 -0700
Subject: LaTeX reader siunitx: add leading 0 to numbers starting with .

---
 src/Text/Pandoc/Readers/LaTeX/SIunitx.hs | 7 +++++--
 test/command/6620.md                     | 3 ---
 test/command/6658.md                     | 9 +++++++++
 3 files changed, 14 insertions(+), 5 deletions(-)
 create mode 100644 test/command/6658.md

diff --git a/src/Text/Pandoc/Readers/LaTeX/SIunitx.hs b/src/Text/Pandoc/Readers/LaTeX/SIunitx.hs
index 5e140ef7a..1474329d4 100644
--- a/src/Text/Pandoc/Readers/LaTeX/SIunitx.hs
+++ b/src/Text/Pandoc/Readers/LaTeX/SIunitx.hs
@@ -83,8 +83,11 @@ parseNumPart =
     parseExp, parseSpace :: Parser Text () Inlines
   parseDecimalNum = try $ do
     pref <- option mempty $ (mempty <$ char '+') <|> ("\x2212" <$ char '-')
-    basenum <- (pref <>) . T.pack
-                <$> many1 (satisfy (\c -> isDigit c || c == '.'))
+    basenum' <- many1 (satisfy (\c -> isDigit c || c == '.'))
+    let basenum = pref <> T.pack
+                    (case basenum' of
+                      '.':_ -> '0':basenum'
+                      _ -> basenum')
     uncertainty <- option mempty $ T.pack <$> parseParens
     if T.null uncertainty
        then return $ str basenum
diff --git a/test/command/6620.md b/test/command/6620.md
index b19cd1972..e448ca6b5 100644
--- a/test/command/6620.md
+++ b/test/command/6620.md
@@ -9,13 +9,10 @@
 \SI{12.3(60)}{\m}
 
 \SI{10.0 \pm 3.3}{\ms}
-
-\SI{10.0 +- 3.3}{\ms}
 ^D
 <p>23 ± 2 m</p>
 <p>125 ± 12 m</p>
 <p>0.135 ± 0.021 m</p>
 <p>12.3 ± 6 m</p>
 <p>10.0 ± 3.3 ms</p>
-<p>10.0 ± 3.3 ms</p>
 ```
diff --git a/test/command/6658.md b/test/command/6658.md
new file mode 100644
index 000000000..bcd174465
--- /dev/null
+++ b/test/command/6658.md
@@ -0,0 +1,9 @@
+```
+pandoc -f latex
+\SI{10.0 +- 3.3}{\ms}
+
+\num{.3e45}
+^D
+<p>10.0 ± 3.3 ms</p>
+<p>0.3 × 10<sup>45</sup></p>
+```
-- 
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