Fix \nobreakspace, refactor "regular space" checking (#1200)

* Fix \nobreakspace, refactor "regular space" checking

Fix #1199 by adding \nobreakspace to the list of commands/symbols that
behave like a regular space character.  Refactor to put that list in one
place, and use an object so it checks instantly instead of sequentially.

* Copy test from #1201

src/buildCommon.js

@@ -682,6 +682,16 @@ const spacingFunctions: {[string]: {| size: string, className: string |}} = {
     },
 };
 
+// A lookup table to determine whether a spacing function/symbol should be
+// treated like a regular space character.
+const regularSpace: {[string]: boolean} = {
+    " ": true,
+    "\\ ": true,
+    "~": true,
+    "\\space": true,
+    "\\nobreakspace": true,
+};
+
 /**
  * Maps TeX font commands to objects containing:
  * - variant: string used for "mathvariant" attribute in buildMathML.js
@@ -777,4 +787,5 @@ export default {
     svgData,
     tryCombineChars,
     spacingFunctions,
+    regularSpace,
 };

src/buildHTML.js

@@ -419,8 +419,7 @@ groupTypes.supsub = function(group, options) {
 };
 
 groupTypes.spacing = function(group, options) {
-    if (group.value === "\\ " || group.value === "\\space" ||
-        group.value === " " || group.value === "~") {
+    if (buildCommon.regularSpace.hasOwnProperty(group.value)) {
         // Spaces are generated by adding an actual space. Each of these
         // things has an entry in the symbols table, so these will be turned
         // into appropriate outputs.

src/buildMathML.js

@@ -228,8 +228,7 @@ groupTypes.supsub = function(group, options) {
 groupTypes.spacing = function(group) {
     let node;
 
-    if (group.value === "\\ " || group.value === "\\space" ||
-        group.value === " " || group.value === "~") {
+    if (buildCommon.regularSpace.hasOwnProperty(group.value)) {
         node = new mathMLTree.MathNode(
             "mtext", [new mathMLTree.TextNode("\u00a0")]);
     } else {

test/katex-spec.js

@@ -875,6 +875,11 @@ describe("A text parser", function() {
         expect(textWithEmbeddedMath).toParse();
     });
 
+    it("should parse spacing functions", function() {
+        expect("a b\\, \\; \\! \\: ~ \\thinspace \\medspace \\quad \\ ").toBuild();
+        expect("\\enspace \\thickspace \\qquad \\space \\nobreakspace").toBuild();
+    });
+
     it("should omit spaces after commands", function() {
         expect("\\text{\\textellipsis !}")
             .toParseLike("\\text{\\textellipsis!}");
@@ -2999,11 +3004,11 @@ describe("The \\mathchoice function", function() {
 
 describe("Symbols", function() {
     it("should parse \\text{\\i\\j}", () => {
-        expect("\\text{\\i\\j}").toParse();
+        expect("\\text{\\i\\j}").toBuild();
     });
 
     it("should parse spacing functions in math or text mode", () => {
-        expect("A\\;B\\,C\\nobreakspace \\text{A\\;B\\,C\\nobreakspace}").toParse();
+        expect("A\\;B\\,C\\nobreakspace \\text{A\\;B\\,C\\nobreakspace}").toBuild();
     });
 
     it("should render ligature commands like their unicode characters", () => {