feat: Support bold Fraktur (#3777)

* feat: Support bold Fraktur

* Evade wideCharacterFont() when inapplicable

* Avoid creating array when uneccesary

---------

Co-authored-by: Erik Demaine <edemaine@mit.edu>

Author: ronkok

docs/supported.md

@@ -205,7 +205,8 @@ Math-mode Unicode (sub|super)script characters will render as if you had written
 | Italic      | $\text{𝐴-𝑍 𝑎-𝑧}$      | Sans serif        | $\text{𝖠-𝖹 𝖺-𝗓 𝟢-𝟫}$
 | Bold Italic | $\text{𝑨-𝒁 𝒂-𝒛}$      | Sans serif bold   | $\text{𝗔-𝗭 𝗮-𝘇 𝟬-𝟵}$
 | Script      | $\text{𝒜-𝒵}$         | Sans serif italic | $\text{𝘈-𝘡 𝘢-𝘻}$
-|  Fractur    | $\text{𝔄-}ℨ\text{ 𝔞-𝔷}$| Monospace        | $\text{𝙰-𝚉 𝚊-𝚣 𝟶-𝟿}$
+|  Fractur    | $\text{𝔄-ℨ}\text{ 𝔞-𝔷}$| Monospace        | $\text{𝙰-𝚉 𝚊-𝚣 𝟶-𝟿}$
+| Bold Fractur | $\text{𝕬-𝖅}\text{𝖆-𝖟}$ | |
 
 </div>
 <div class="katex-hopscotch">

src/buildCommon.js

@@ -165,9 +165,13 @@ const makeOrd = function<NODETYPE: "spacing" | "mathord" | "textord">(
     // Math mode or Old font (i.e. \rm)
     const isFont = mode === "math" || (mode === "text" && options.font);
     const fontOrFamily = isFont ? options.font : options.fontFamily;
+    let wideFontName = "";
+    let wideFontClass = "";
     if (text.charCodeAt(0) === 0xD835) {
+        [wideFontName, wideFontClass] = wideCharacterFont(text, mode);
+    }
+    if (wideFontName.length > 0) {
         // surrogate pairs get special treatment
-        const [wideFontName, wideFontClass] = wideCharacterFont(text, mode);
         return makeSymbol(text, wideFontName, mode, options,
             classes.concat(wideFontClass));
     } else if (fontOrFamily) {

src/katex.less

@@ -129,6 +129,12 @@
         font-family: KaTeX_Fraktur;
     }
 
+    .mathboldfrak,
+    .textboldfrak {
+        font-family: KaTeX_Fraktur;
+        font-weight: bold;
+    }
+
     .mathtt {
         font-family: KaTeX_Typewriter;
     }

src/symbols.js

@@ -816,6 +816,10 @@ for (let i = 0; i < letters.length; i++) {
     defineSymbol(math, main, mathord, ch, wideChar);
     defineSymbol(text, main, textord, ch, wideChar);
 
+    wideChar = String.fromCharCode(0xD835, 0xDD6C + i);  // A-Z a-z bold Fractur
+    defineSymbol(math, main, mathord, ch, wideChar);
+    defineSymbol(text, main, textord, ch, wideChar);
+
     wideChar = String.fromCharCode(0xD835, 0xDDA0 + i);  // A-Z a-z sans-serif
     defineSymbol(math, main, mathord, ch, wideChar);
     defineSymbol(text, main, textord, ch, wideChar);

src/wide-character.js

@@ -45,8 +45,9 @@ const wideLatinLetterData: Array<[string, string, string]> = [
     ["mathbb", "textbb", "AMS-Regular"],            // A-Z double-struck
     ["mathbb", "textbb", "AMS-Regular"],            // k double-struck
 
-    ["", "", ""],                           // A-Z bold Fraktur No font metrics
-    ["", "", ""],                           // a-z bold Fraktur.   No font.
+    // Note that we are using a bold font, but font metrics for regular Fraktur.
+    ["mathboldfrak", "textboldfrak", "Fraktur-Regular"],  // A-Z bold Fraktur
+    ["mathboldfrak", "textboldfrak", "Fraktur-Regular"],  // a-z bold Fraktur
 
     ["mathsf", "textsf", "SansSerif-Regular"],      // A-Z sans-serif
     ["mathsf", "textsf", "SansSerif-Regular"],      // a-z sans-serif

test/katex-spec.js

@@ -3919,6 +3919,7 @@ describe("Unicode", function() {
         wideCharStr += String.fromCharCode(0xD835, 0xDC00);   // bold A
         wideCharStr += String.fromCharCode(0xD835, 0xDC68);   // bold italic A
         wideCharStr += String.fromCharCode(0xD835, 0xDD04);   // Fraktur A
+        wideCharStr += String.fromCharCode(0xD835, 0xDD6C);   // bold Fraktur A
         wideCharStr += String.fromCharCode(0xD835, 0xDD38);   // double-struck
         wideCharStr += String.fromCharCode(0xD835, 0xDC9C);   // script A
         wideCharStr += String.fromCharCode(0xD835, 0xDDA0);   // sans serif A
@@ -3935,6 +3936,7 @@ describe("Unicode", function() {
         wideCharText += String.fromCharCode(0xD835, 0xDC00);   // bold A
         wideCharText += String.fromCharCode(0xD835, 0xDC68);   // bold italic A
         wideCharText += String.fromCharCode(0xD835, 0xDD04);   // Fraktur A
+        wideCharStr += String.fromCharCode(0xD835, 0xDD6C);    // bold Fraktur A
         wideCharText += String.fromCharCode(0xD835, 0xDD38);   // double-struck
         wideCharText += String.fromCharCode(0xD835, 0xDC9C);   // script A
         wideCharText += String.fromCharCode(0xD835, 0xDDA0);   // sans serif A