Support \brace and \brack (#1453)

* Support \brace and \brack

* Update screenshots

test/katex-spec.js

@@ -477,13 +477,17 @@ describe("A frac parser", function() {
     });
 });
 
-describe("An over parser", function() {
+describe("An over/brace/brack parser", function() {
     const simpleOver = "1 \\over x";
     const complexOver = "1+2i \\over 3+4i";
+    const braceFrac = "a+b \\brace c+d";
+    const brackFrac = "a+b \\brack c+d";
 
     it("should not fail", function() {
         expect(simpleOver).toParse();
         expect(complexOver).toParse();
+        expect(braceFrac).toParse();
+        expect(brackFrac).toParse();
     });
 
     it("should produce a frac", function() {
@@ -500,6 +504,22 @@ describe("An over parser", function() {
         expect(parse.type).toEqual("genfrac");
         expect(parse.value.numer).toBeDefined();
         expect(parse.value.denom).toBeDefined();
+
+        const parseBraceFrac = getParsed(braceFrac)[0];
+
+        expect(parseBraceFrac.type).toEqual("genfrac");
+        expect(parseBraceFrac.value.numer).toBeDefined();
+        expect(parseBraceFrac.value.denom).toBeDefined();
+        expect(parseBraceFrac.value.leftDelim).toBeDefined();
+        expect(parseBraceFrac.value.rightDelim).toBeDefined();
+
+        const parseBrackFrac = getParsed(brackFrac)[0];
+
+        expect(parseBrackFrac.type).toEqual("genfrac");
+        expect(parseBrackFrac.value.numer).toBeDefined();
+        expect(parseBrackFrac.value.denom).toBeDefined();
+        expect(parseBrackFrac.value.leftDelim).toBeDefined();
+        expect(parseBrackFrac.value.rightDelim).toBeDefined();
     });
 
     it("should create a numerator from the atoms before \\over", function() {
@@ -567,6 +587,16 @@ describe("An over parser", function() {
     });
 });
 
+describe("A infix builder", function() {
+    it("should not fail", function() {
+        expect("a \\over b").toBuild();
+        expect("a \\atop b").toBuild();
+        expect("a \\choose b").toBuild();
+        expect("a \\brace b").toBuild();
+        expect("a \\brack b").toBuild();
+    });
+});
+
 describe("A sizing parser", function() {
     const sizeExpression = "\\Huge{x}\\small{x}";
 

test/screenshotter/ss_data.yaml

@@ -113,7 +113,11 @@ ExtensibleArrows: |
         \xrightleftharpoons[ab]{ABC} + \xhookrightarrow[ab]{ABC} \\
         \xtwoheadrightarrow{ABC} + \frac{\xrightarrow[ab]{ABC}}{\xrightarrow[ab]{ABC}} + \left\lvert\xrightarrow[ab]{ABC}\right\rvert
     \end{array}
-FractionTest: \dfrac{a}{b}\frac{a}{b}\tfrac{a}{b}\;-\dfrac12\;1\tfrac12\;{1 \atop 2}\; \cfrac{1}{1+\cfrac{1}{x}}
+FractionTest: |
+    \begin{array}{l}
+        \dfrac{a}{b}\frac{a}{b}\tfrac{a}{b}\;-\dfrac12\;1\tfrac12\;{1 \atop 2}\; \cfrac{1}{1+\cfrac{1}{x}} \\[2.5em]
+        {a \brace b} \; {a \brack b}
+    \end{array}
 Functions: \sin\cos\tan\ln\log
 Gathered: |
     \begin{gathered}