From 98d1b04160c938ddca4b73809fc72c7bcb762635 Mon Sep 17 00:00:00 2001
From: Thibaut Cuvelier <dourouc05@gmail.com>
Date: Thu, 27 Jul 2023 01:21:46 -0400
Subject: [PATCH] Before this patch, each character within InsetMathClass was
 output separately, without understanding their meaning, using the default
 text output (with [] around each character). This commit changes the
 behaviour to skip the InsetMathClass during the MathML output. This
 effectively renders the inset useless for MathML (instead of controlling
 spacing), as expected, because the MathML processor is supposed to handle the
 spacing itself.

Another implementation would have been to use the lspace and rspace attributes in MathML, but they require to give the exact spacing before and after the operator instead of relying on rules like TeX.

For instance, `$a\mathbin{+}b$` resulted in this MathML output before the patch:

```
<math xmlns='http://www.w3.org/1998/Math/MathML'>
<mrow>
 <mi>a</mi><!--  -->
 <mi>[mathbin [char + mathalpha]]</mi>
 <mi>b</mi>
</mrow>
</math>
```

For comparison, this was the output with LyX 2.3.7

```
<math xmlns="http://www.w3.org/1998/Math/MathML">
 <mrow>
  <mrow><mi>a</mi><!--  -->
   <mi>[mathbin [char + mathalpha]]
   </mi><mi>b</mi>
  </mrow>
 </mrow></math>
 ```

 After this patch, it looks like:

 ```
 <math xmlns='http://www.w3.org/1998/Math/MathML'>
 <mstyle class='math'>
  <mrow>
   <mi>a</mi>
   <mo>+</mo>
   <mi>b</mi>
  </mrow>
 </mstyle>
 </math>
 ```
---
 src/mathed/InsetMathClass.cpp | 11 +++++++++++
 src/mathed/InsetMathClass.h   |  2 ++
 src/mathed/MathClass.h        |  2 +-
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/mathed/InsetMathClass.cpp b/src/mathed/InsetMathClass.cpp
index 0c22d478c7..2bfea82ce0 100644
--- a/src/mathed/InsetMathClass.cpp
+++ b/src/mathed/InsetMathClass.cpp
@@ -11,6 +11,7 @@
 #include <config.h>
 
 #include "InsetMathClass.h"
+#include "MathStream.h"
 
 #include "support/docstream.h"
 
@@ -56,6 +57,16 @@ void InsetMathClass::write(TeXMathStream & os) const
 }
 
 
+void InsetMathClass::mathmlize(MathMLStream & ms) const
+{
+	// Skip the \mathXXX macro, the MathML processor is supposed to handle
+	// spacing down the line.
+	for (size_t i = 0; i < nargs(); ++i) {
+		ms << cell(i);
+	}
+}
+
+
 docstring InsetMathClass::name() const
 {
 	return class_to_string(math_class_);
diff --git a/src/mathed/InsetMathClass.h b/src/mathed/InsetMathClass.h
index 89189f2b0d..f4308beb9b 100644
--- a/src/mathed/InsetMathClass.h
+++ b/src/mathed/InsetMathClass.h
@@ -43,6 +43,8 @@ public:
 	///
 	void write(TeXMathStream & os) const override;
 	///
+	void mathmlize(MathMLStream & ms) const override;
+	///
 	void infoize(odocstream & os) const override;
 	///
 	InsetCode lyxCode() const override { return MATH_CLASS_CODE; }
diff --git a/src/mathed/MathClass.h b/src/mathed/MathClass.h
index 169bfdb51a..af4f884cca 100644
--- a/src/mathed/MathClass.h
+++ b/src/mathed/MathClass.h
@@ -40,7 +40,7 @@ class MetricsBase;
  * + Vcent: a vbox to be centered, produced by \vcenter.
  *
  * Over, Under, Acc, Rad and Vcent are not considered in the enum
- * below. The relvant elements will be considered as Ord.
+ * below. The relevant elements will be considered as Ord.
  */
 enum MathClass {
 	MC_ORD,