LaTeX reader/writer: change handling of math environments.

Certain environments in LaTeX will trigger math mode and can't
occur within math mode: e.g., `align` or `equation`.  Previously
we "downshifted" these, parsing an `align` environment as a
Math element with `aligned`, and an `equation` environment as a
regular display math element.  With this shift, we put these in
Math inlines but retain the original environments.

This works because:

1) texmath handles these environments just fine,
2) and so does MathJax;
3) when writing LaTeX we detect these environments in Math elements
   and emit them verbatim instead of putting them in `$..$` or
   `$$..$$`.

Closes #9711. Closes #9296.

8 files changed, 59 insertions, 21 deletions

diff --git a/src/Text/Pandoc/Readers/LaTeX/Math.hs b/src/Text/Pandoc/Readers/LaTeX/Math.hs
index 9f82618e0..1f4dc4f8c 100644
--- a/src/Text/Pandoc/Readers/LaTeX/Math.hs
+++ b/src/Text/Pandoc/Readers/LaTeX/Math.hs
@@ -98,20 +98,21 @@ inlineEnvironments :: PandocMonad m => M.Map Text (LP m Inlines)
 inlineEnvironments = M.fromList [
     ("displaymath", mathEnvWith id Nothing "displaymath")
   , ("math", math <$> mathEnv "math")
-  , ("equation", mathEnvWith id Nothing "equation")
-  , ("equation*", mathEnvWith id Nothing "equation*")
-  , ("gather", mathEnvWith id (Just "gathered") "gather")
-  , ("gather*", mathEnvWith id (Just "gathered") "gather*")
-  , ("multline", mathEnvWith id (Just "gathered") "multline")
-  , ("multline*", mathEnvWith id (Just "gathered") "multline*")
-  , ("eqnarray", mathEnvWith id (Just "aligned") "eqnarray")
-  , ("eqnarray*", mathEnvWith id (Just "aligned") "eqnarray*")
-  , ("align", mathEnvWith id (Just "aligned") "align")
-  , ("align*", mathEnvWith id (Just "aligned") "align*")
-  , ("alignat", mathEnvWith id (Just "aligned") "alignat")
-  , ("alignat*", mathEnvWith id (Just "aligned") "alignat*")
-  , ("flalign", mathEnvWith id (Just "aligned") "flalign")
-  , ("flalign*", mathEnvWith id (Just "aligned") "flalign*")
+  , ("equation", mathEnvWith id (Just "equation") "equation")
+  , ("equation*", mathEnvWith id (Just "equation*") "equation*")
+  , ("gather", mathEnvWith id (Just "gather") "gather")
+  , ("gather*", mathEnvWith id (Just "gather*") "gather*")
+  , ("multline", mathEnvWith id (Just "multline") "multline")
+  , ("multline*", mathEnvWith id (Just "multline*") "multline*")
+  , ("eqnarray", mathEnvWith id (Just "eqnarray") "eqnarray")
+  , ("eqnarray*", mathEnvWith id (Just "eqnarray*") "eqnarray*")
+  , ("align", mathEnvWith id (Just "align") "align")
+  , ("align*", mathEnvWith id (Just "align*") "align*")
+  , ("alignat", mathEnvWith id (Just "alignat") "alignat")
+  , ("alignat*", mathEnvWith id (Just "alignat*") "alignat*")
+  , ("flalign", mathEnvWith id (Just "flalign") "flalign")
+  , ("flalign*", mathEnvWith id (Just "flalign*") "flalign*")
+  -- the following are not yet handled by texmath, so we use substitutes:
   , ("dmath", mathEnvWith id Nothing "dmath")
   , ("dmath*", mathEnvWith id Nothing "dmath*")
   , ("dgroup", mathEnvWith id (Just "aligned") "dgroup")
diff --git a/src/Text/Pandoc/Writers/LaTeX.hs b/src/Text/Pandoc/Writers/LaTeX.hs
index b3d545a6b..9f5f6ed69 100644
--- a/src/Text/Pandoc/Writers/LaTeX.hs
+++ b/src/Text/Pandoc/Writers/LaTeX.hs
@@ -1021,6 +1021,10 @@ inlineToLaTeX (Quoted qt lst) = do
 inlineToLaTeX (Str str) = do
   setEmptyLine False
   liftM literal $ stringToLaTeX TextString str
+inlineToLaTeX (Math _ str)
+  | isMathEnv str -- see #9711
+  = do setEmptyLine False
+       pure $ literal str
 inlineToLaTeX (Math InlineMath str) = do
   setEmptyLine False
   inSoul <- gets stInSoulCommand
@@ -1310,3 +1314,23 @@ ldfLanguages =
   , "galician"
   , "slovene"
   ]
+
+isMathEnv :: Text -> Bool
+isMathEnv t =
+  case T.stripPrefix "\\begin{" t of
+    Nothing -> False
+    Just t' -> T.takeWhile (/= '}') t' `elem`
+      [ "align", "align*"
+      , "flalign", "flalign*"
+      , "alignat", "alignat*"
+      , "dmath", "dmath*"
+      , "dgroup", "dgroup*"
+      , "darray", "darray*"
+      , "gather", "gather*"
+      , "multline", "multline*"
+      , "split"
+      , "subequations"
+      , "equation", "equation*"
+      , "eqnarray"
+      , "displaymath"
+      ]
diff --git a/test/command/10160.md b/test/command/10160.md
index fa3e97cd5..52e512b5a 100644
--- a/test/command/10160.md
+++ b/test/command/10160.md
@@ -7,5 +7,9 @@
 \begin{table}[h]
 \end{table}
 ^D
-[ Para [ Math DisplayMath "[0,1)" ] ]
+[ Para
+    [ Math
+        DisplayMath "\\begin{equation}\n  [0,1)\n\\end{equation}"
+    ]
+]
 ```
diff --git a/test/command/3113.md b/test/command/3113.md
index 7746ec14f..96403905e 100644
--- a/test/command/3113.md
+++ b/test/command/3113.md
@@ -11,7 +11,7 @@ E&=&F
 [ Para
     [ Math
         DisplayMath
-        "\\begin{aligned}\nA&=&B,\\\\\nC&=&D,\\\\\n%\\end{eqnarray}\n%\\begin{eqnarray}\nE&=&F\n\\end{aligned}"
+        "\\begin{eqnarray}\nA&=&B,\\\\\nC&=&D,\\\\\n%\\end{eqnarray}\n%\\begin{eqnarray}\nE&=&F\n\\end{eqnarray}"
     ]
 ]
 ```
diff --git a/test/command/7512.md b/test/command/7512.md
index 032cfe565..618739acd 100644
--- a/test/command/7512.md
+++ b/test/command/7512.md
@@ -4,7 +4,12 @@
 [d,\delta]=0.
 \end{equation*}
 ^D
-[ Para [ Math DisplayMath "[d,\\delta]=0." ] ]
+[ Para
+    [ Math
+        DisplayMath
+        "\\begin{equation*}\n[d,\\delta]=0.\n\\end{equation*}"
+    ]
+]
 ```
 
 ```
diff --git a/test/command/982.md b/test/command/982.md
index 4b997c4c4..bc18fc11c 100644
--- a/test/command/982.md
+++ b/test/command/982.md
@@ -7,5 +7,9 @@
 y=x^2
 \EEQ
 ^D
-[ Para [ Math DisplayMath "y=x^2" ] ]
+[ Para
+    [ Math
+        DisplayMath "\\begin{equation}\ny=x^2\n\\end{equation}"
+    ]
+]
 ```
diff --git a/test/command/macros.md b/test/command/macros.md
index 86f10ea1b..d90498e35 100644
--- a/test/command/macros.md
+++ b/test/command/macros.md
@@ -61,9 +61,9 @@ x &= y\\
 ^D
 \(5-67\)
 
-\[\begin{aligned}
+\begin{align}
 x &= y\\
-\end{aligned}\]
+\end{align}
 
 \emph{hi}
 
diff --git a/test/command/refs.md b/test/command/refs.md
index f54f4fa8d..63daf81a7 100644
--- a/test/command/refs.md
+++ b/test/command/refs.md
@@ -118,7 +118,7 @@ Accuracy~\eqref{eq:Accuracy} is the proportion, measuring true results among all
 , Para
     [ Math
         DisplayMath
-        "\\label{eq:Accuracy}\n  Accuracy = \\frac{t_p + t_n}{t_p + f_p + f_n + t_n}"
+        "\\begin{equation}\n  \\label{eq:Accuracy}\n  Accuracy = \\frac{t_p + t_n}{t_p + f_p + f_n + t_n}\n\\end{equation}"
     ]
 ]
 ```