Automatic mrel/mbin spacing for \boldsymbol (#1388)

* Automatic mrel/mbin spacing for \boldsymbol

Fix #1154

* Add test

* Add missing mode

* Separate out \boldsymbol support to correct flow types

* Fix ternaries thanks to @ronkok's comment

* Revert package-lock.json

* Add screenshot test

src/functions/font.js

@@ -30,15 +30,15 @@ const fontAliases = {
 defineFunction({
     type: "font",
     names: [
-        // styles
-        "\\mathrm", "\\mathit", "\\mathbf", "\\boldsymbol",
+        // styles, except \boldsymbol defined below
+        "\\mathrm", "\\mathit", "\\mathbf",
 
         // families
         "\\mathbb", "\\mathcal", "\\mathfrak", "\\mathscr", "\\mathsf",
         "\\mathtt",
 
-        // aliases
-        "\\Bbb", "\\bold", "\\frak", "\\bm",
+        // aliases, except \bm defined below
+        "\\Bbb", "\\bold", "\\frak",
     ],
     props: {
         numArgs: 1,
@@ -53,13 +53,44 @@ defineFunction({
         return new ParseNode("font", {
             type: "font",
             font: func.slice(1),
-            body: body,
+            body,
         }, parser.mode);
     },
     htmlBuilder,
     mathmlBuilder,
 });
 
+defineFunction({
+    type: "mclass",
+    names: ["\\boldsymbol", "\\bm"],
+    props: {
+        numArgs: 1,
+        greediness: 2,
+    },
+    handler: ({parser}, args) => {
+        const body = args[0];
+        // amsbsy.sty's \boldsymbol inherits the argument's bin|rel|ord status
+        // (similar to \stackrel in functions/mclass.js)
+        let mclass = "mord";
+        const atomType = (body.type === "ordgroup" && body.value.length ?
+            body.value[0].type : body.type);
+        if (/^(bin|rel)$/.test(atomType)) {
+            mclass = "m" + atomType;
+        }
+        return new ParseNode("mclass", {
+            type: "mclass",
+            mclass,
+            value: [
+                new ParseNode("font", {
+                    type: "font",
+                    font: "boldsymbol",
+                    body,
+                }, parser.mode),
+            ],
+        }, parser.mode);
+    },
+});
+
 const oldFontFuncsMap = {
     "\\rm": "mathrm",
     "\\sf": "mathsf",

src/functions/mclass.js

@@ -57,12 +57,8 @@ defineFunction({
             // LaTeX applies \binrel spacing to \overset and \underset. \binrel
             // spacing varies with (bin|rel|ord) of the atom in the argument.
             // We'll do the same.
-            let atomType = "";
-            if (baseArg.type === "ordgroup") {
-                atomType = baseArg.value[0].type;
-            } else {
-                atomType = baseArg.type;
-            }
+            const atomType = (baseArg.type === "ordgroup" &&
+                baseArg.value.length ? baseArg.value[0].type : baseArg.type);
             if (/^(bin|rel)$/.test(atomType)) {
                 mclass = "m" + atomType;
             } else {