feat: support {equation}, {equation*}, and {split} (#2369)

* Support {equation}, {equation*}, and {split}

* Update screenshots

* Allow {split} at top level

* Move equation column number check to to ParseArray

* Add token to ParseError

* Sharpen parameters passed to parseArray

* Add token information

* Update an {array} spec in screenshotter

* Adjust {array} screenshotter spec

* Make a non-strict error call when {array} argument specifies too few columns.

* Move context checks to a helper function.

test/katex-spec.js

@@ -2727,8 +2727,6 @@ describe("An aligned environment", function() {
 });
 
 describe("AMS environments", function() {
-    const nonStrictDisplay = new Settings({displayMode: true, strict: false});
-
     it("should fail outside display mode", () => {
         expect`\begin{gather}a+b\\c+d\end{gather}`.not.toParse(nonstrictSettings);
         expect`\begin{gather*}a+b\\c+d\end{gather*}`.not.toParse(nonstrictSettings);
@@ -2736,8 +2734,11 @@ describe("AMS environments", function() {
         expect`\begin{align*}a&=b+c\\d+e&=f\end{align*}`.not.toParse(nonstrictSettings);
         expect`\begin{alignat}{2}10&x+ &3&y = 2\\3&x+&13&y = 4\end{alignat}`.not.toParse(nonstrictSettings);
         expect`\begin{alignat*}{2}10&x+ &3&y = 2\\3&x+&13&y = 4\end{alignat*}`.not.toParse(nonstrictSettings);
+        expect`\begin{equation}a=b+c\end{equation}`.not.toParse(nonstrictSettings);
+        expect`\begin{split}a &=b+c\\&=e+f\end{split}`.not.toParse(nonstrictSettings);
     });
 
+    const nonStrictDisplay = new Settings({displayMode: true, strict: false});
     it("should build if in non-strict display mode", () => {
         expect`\begin{gather}a+b\\c+d\end{gather}`.toBuild(nonStrictDisplay);
         expect`\begin{gather*}a+b\\c+d\end{gather*}`.toBuild(nonStrictDisplay);
@@ -2745,6 +2746,22 @@ describe("AMS environments", function() {
         expect`\begin{align*}a&=b+c\\d+e&=f\end{align*}`.toBuild(nonStrictDisplay);
         expect`\begin{alignat}{2}10&x+ &3&y = 2\\3&x+&13&y = 4\end{alignat}`.toBuild(nonStrictDisplay);
         expect`\begin{alignat*}{2}10&x+ &3&y = 2\\3&x+&13&y = 4\end{alignat*}`.toBuild(nonStrictDisplay);
+        expect`\begin{equation}a=b+c\end{equation}`.toBuild(nonStrictDisplay);
+        expect`\begin{equation}\begin{split}a &=b+c\\&=e+f\end{split}\end{equation}`.toBuild(nonStrictDisplay);
+        expect`\begin{split}a &=b+c\\&=e+f\end{split}`.toBuild(nonStrictDisplay);
+    });
+
+    it("{equation} should fail if argument contains two rows.", () => {
+        expect`\begin{equation}a=\cr b+c\end{equation}`.not.toParse(nonStrictDisplay);
+    });
+    it("{equation} should fail if argument contains two columns.", () => {
+        expect`\begin{equation}a &=b+c\end{equation}`.not.toBuild(nonStrictDisplay);
+    });
+    it("{split} should fail if argument contains three columns.", () => {
+        expect`\begin{equation}\begin{split}a &=b &+c\\&=e &+f\end{split}\end{equation}`.not.toBuild(nonStrictDisplay);
+    });
+    it("{array} should fail if body contains more columns than specification.", () => {
+        expect`\begin{array}{2}a & b & c\\d & e  f\end{array}`.not.toBuild(nonStrictDisplay);
     });
 });
 

test/screenshotter/ss_data.yaml

@@ -15,7 +15,7 @@
 
 Accents: \vec{A}\vec{x}\vec x^2\vec{x}_2^2\vec{A}^2\vec{xA}^2
 AccentsText: |
-    \begin{array}{l}
+    \begin{array}{lccccc}
     \text{\'\i} & \text{\.\i} & \text{\`\i} & \text{\"\i} & \text{\H\i} & \text{\r\i} \\
     \text{\'\j} & \text{\.\j} & \text{\`\j} & \text{\"\j} & \text{\H\j} & \text{\r\j} \\
     \text{\'a} & \text{\.a} & \text{\`a} & \text{\"a} & \text{\H{a}} & \text{\r{a}} \\
@@ -129,6 +129,9 @@ Dots: |
       \cdots;\dots+\dots\int\dots,\dots \\
       \cdots{};\ldots+\ldots\int\ldots,\ldots
     \end{array}
+Equation:
+    tex: \begin{equation}\begin{split}a& =b+c-d \\ & \quad +e-f \\ & =g+h \\ & =i \end{split}\end{equation}
+    display: 1
 Exponents: a^{a^a_a}_{a^a_a}
 ExtensibleArrows: |
     \begin{array}{l}