Ignore whitespace following \text

Summary:
In something like `\text {hello, world}` we want to ignore the first space but not the second. This suggests to me that perhaps we shouldn't be in text-lexing mode until we actually see the first curly brace, so this changes us to do that.

Note that this disallows doing unbraced text things now; it seemed nontrivial to lex a single text character while ignoring spaces. We should probably fix it sometime, but for now we'll fall back to MathJax anyway so I'm not super concerned.

We should also add a huxley test for this.

Test Plan: `\text {2x 2}` rendered `2x 2` in a non-italic font.

Reviewers: jack, emily

Reviewed By: emily

Differential Revision: http://phabricator.khanacademy.org/D9376

Parser.js

@@ -223,6 +223,28 @@ Parser.prototype.parseColorGroup = function(pos, mode) {
     }
 };
 
+// Parses a text group, which looks like "{#ffffff}"
+Parser.prototype.parseTextGroup = function(pos, mode) {
+    var start = this.lexer.lex(pos, mode);
+    // Try to parse an open brace
+    if (start.type === "{") {
+        // Parse the text
+        var text = this.parseExpression(start.position, "text");
+        // Make sure we get a close brace
+        var closeBrace = this.lexer.lex(text.position, mode);
+        this.expect(closeBrace, "}");
+        return new ParseResult(
+            new ParseNode("ordgroup", text.result, "text"),
+            closeBrace.position);
+    } else {
+        // It has to have an open brace, so if it doesn't we throw
+        throw new ParseError(
+            "There must be braces around text",
+            this.lexer, pos
+        );
+    }
+};
+
 // A list of 1-argument color functions
 var colorFuncs = [
     "\\blue", "\\orange", "\\pink", "\\red", "\\green", "\\gray", "\\purple"
@@ -333,7 +355,7 @@ Parser.prototype.parseNucleus = function(pos, mode) {
             );
         }
     } else if (mode === "math" && nucleus.type === "\\text") {
-        var group = this.parseGroup(nucleus.position, "text");
+        var group = this.parseTextGroup(nucleus.position, mode);
         if (group) {
             return new ParseResult(
                 new ParseNode(nucleus.type.slice(1), group.result, mode),

test/katex-tests.js

@@ -451,8 +451,10 @@ describe("A sizing parser", function() {
 describe("A text parser", function() {
     var textExpression = "\\text{a b}";
     var badTextExpression = "\\text{a b%}";
+    var badTextExpression2 = "\\text x";
     var nestedTextExpression = "\\text{a {b} \\blue{c}}";
     var spaceTextExpression = "\\text{  a \\ }";
+    var leadingSpaceTextExpression = "\\text {moo}";
 
     it("should not fail", function() {
         expect(function() {
@@ -478,6 +480,9 @@ describe("A text parser", function() {
         expect(function() {
             parseTree(badTextExpression);
         }).toThrow();
+        expect(function() {
+            parseTree(badTextExpression2);
+        }).toThrow();
     });
 
     it("should parse nested expressions", function() {
@@ -495,6 +500,15 @@ describe("A text parser", function() {
         expect(group[2].type).toMatch("spacing");
         expect(group[3].type).toMatch("spacing");
     });
+
+    it("should ignore a space before the text group", function() {
+        var parse = parseTree(leadingSpaceTextExpression)[0];
+        // [m, o, o]
+        expect(parse.value.value.length).toBe(3);
+        expect(
+            parse.value.value.map(function(n) { return n.value; }).join("")
+        ).toBe("moo");
+    });
 });
 
 describe("A color parser", function() {