feat: Support \mathstrut (#2416)

* feat: Support \mathstrut

* Update screenshots

docs/support_table.md

@@ -659,7 +659,7 @@ use `\ce` instead|
 |\mathscr|$\mathscr{AB}$|`\mathscr{AaBb123}`<br>KaTeX supports A-Z|
 |\mathsf|$\mathsf{AaBb123}$|`\mathsf{AaBb123}`|
 |\mathsterling|$\mathsterling$||
-|\mathstrut|<span style="color:firebrick;">Not supported</span>||
+|\mathstrut|$\sqrt{\mathstrut a}$|`\sqrt{\mathstrut a}`|
 |\mathtip|<span style="color:firebrick;">Not supported</span>||
 |\mathtt|$\mathtt{AaBb123}$|`\mathtt{AaBb123}`|
 |\matrix|<span style="color:firebrick;">Not supported</span>|See `{matrix}`|

docs/supported.md

@@ -268,7 +268,7 @@ KaTeX also supports `\llap`, `\rlap`, and `\clap`, but they will take only text,
 | `~`             | non-breaking space | `\negthinspace`      | – ³∕₁₈ em space
 | `\<space>`      | space              | `\negmedspace`       | – ⁴∕₁₈ em space
 | `\nobreakspace` | non-breaking space | `\negthickspace`     | – ⁵∕₁₈ em space
-| `\space`        | space              |
+| `\space`        | space              | `\mathstrut`         | `\vphantom{(}`
 
 </div>
 

src/macros.js

@@ -361,6 +361,9 @@ defineMacro("\\llap", "\\mathllap{\\textrm{#1}}");
 defineMacro("\\rlap", "\\mathrlap{\\textrm{#1}}");
 defineMacro("\\clap", "\\mathclap{\\textrm{#1}}");
 
+// \mathstrut from the TeXbook, p 360
+defineMacro("\\mathstrut", "\\vphantom{(}");
+
 // \not is defined by base/fontmath.ltx via
 // \DeclareMathSymbol{\not}{\mathrel}{symbols}{"36}
 // It's thus treated like a \mathrel, but defined by a symbol that has zero

test/katex-spec.js

@@ -2505,6 +2505,7 @@ describe("A phantom builder", function() {
         expect`\phantom{x^2}`.toBuild();
         expect`\phantom{x}^2`.toBuild();
         expect`\phantom x`.toBuild();
+        expect `\mathstrut`.toBuild();
 
         expect`\hphantom{x}`.toBuild();
         expect`\hphantom{x^2}`.toBuild();

test/screenshotter/ss_data.yaml

@@ -315,7 +315,8 @@ OverUnderset: |
     \end{array}
 Phantom: \begin{array}{l}
             \dfrac{1+\phantom{x^{\blue{2}}} = x}{1+x^{\blue{2}} = x} \left(\vphantom{\int_t} zzz \right) \left( X \hphantom{\frac{\frac X X}{X}} \right)\\
-            \text{a \phantom{123}} b \hphantom{\frac{1}{2}}=c \vphantom{101112} d
+            \text{a \phantom{123}} b \hphantom{\frac{1}{2}}=c \vphantom{101112} d \\
+            \sqrt{\mathstrut a} + \sqrt{\mathstrut d}
          \end{array}
 Pmb: \mu\pmb{\mu}\pmb{=}\mu\pmb{+}\mu
 PrimeSpacing: f'+f_2'+f^{f'}