Support \tag, \tag*, and \gdef (#1309)

* Tag sketch

* Drop objectAssign; already using Object.assign elsewhere

* Basic \gdef support

* Bug fix

* Finish \tag

* MathML numbers equations with <mlabeledtr>

* Fix flow bugs

* \gdef tests

* Add basic \tag tests

* Screenshot test for \tag

* \tag* test

* Add missing file

* Bug fix screenshot

* Major refactor

* Represent tag at top level of parse tree, requiring less hackery
  * No more \@tag function; it was essentially just doing \text
* Wrap tag in group so e.g. ( and ) are formatted the same
* Add `feed` method to MacroExpander for multiple inputs (for tag)
* Bug fixes in buildHTML, makeTextRow, _getBuilt (for display mode)
* Remove excess <mrow> wrapper when unnecessary

* Update screenshot from tag being wrapped in group

* Add maxExpand limit

test/__snapshots__/mathml-spec.js.snap

@@ -209,32 +209,30 @@ exports[`A MathML builder should render boldsymbol with the correct mathvariants
 <math>
   <semantics>
     <mrow>
-      <mrow>
-        <mi mathvariant="bold-italic">
-          A
-        </mi>
-        <mi mathvariant="bold-italic">
-          x
-        </mi>
-        <mn mathvariant="bold-italic">
-          2
-        </mn>
-        <mi mathvariant="bold-italic">
-          k
-        </mi>
-        <mi mathvariant="bold-italic">
-          ω
-        </mi>
-        <mi mathvariant="bold-italic">
-          Ω
-        </mi>
-        <mi mathvariant="bold-italic">
-          ı
-        </mi>
-        <mo mathvariant="bold-italic">
-          +
-        </mo>
-      </mrow>
+      <mi mathvariant="bold-italic">
+        A
+      </mi>
+      <mi mathvariant="bold-italic">
+        x
+      </mi>
+      <mn mathvariant="bold-italic">
+        2
+      </mn>
+      <mi mathvariant="bold-italic">
+        k
+      </mi>
+      <mi mathvariant="bold-italic">
+        ω
+      </mi>
+      <mi mathvariant="bold-italic">
+        Ω
+      </mi>
+      <mi mathvariant="bold-italic">
+        ı
+      </mi>
+      <mo mathvariant="bold-italic">
+        +
+      </mo>
     </mrow>
     <annotation encoding="application/x-tex">
       \\boldsymbol{Ax2k\\omega\\Omega\\imath+}
@@ -296,35 +294,33 @@ exports[`A MathML builder should render mathchoice as if there was nothing 2`] =
 <math>
   <semantics>
     <mrow>
-      <mrow>
-        <msubsup>
-          <mo>
-            ∑
-          </mo>
-          <mrow>
-            <mi>
-              k
-            </mi>
-            <mo>
-              =
-            </mo>
-            <mn>
-              0
-            </mn>
-          </mrow>
-          <mi mathvariant="normal">
-            ∞
-          </mi>
-        </msubsup>
-        <msup>
-          <mi>
-            x
-          </mi>
+      <msubsup>
+        <mo>
+          ∑
+        </mo>
+        <mrow>
           <mi>
             k
           </mi>
-        </msup>
-      </mrow>
+          <mo>
+            =
+          </mo>
+          <mn>
+            0
+          </mn>
+        </mrow>
+        <mi mathvariant="normal">
+          ∞
+        </mi>
+      </msubsup>
+      <msup>
+        <mi>
+          x
+        </mi>
+        <mi>
+          k
+        </mi>
+      </msup>
     </mrow>
     <annotation encoding="application/x-tex">
       \\mathchoice{D}{\\sum_{k = 0}^{\\infty} x^k}{S}{SS}
@@ -391,12 +387,10 @@ exports[`A MathML builder should set href attribute for href appropriately 1`] =
 
 <math>
   <semantics>
-    <mrow>
-      <mrow href="http://example.org">
-        <mi>
-          α
-        </mi>
-      </mrow>
+    <mrow href="http://example.org">
+      <mi>
+        α
+      </mi>
     </mrow>
     <annotation encoding="application/x-tex">
       \\href{http://example.org}{\\alpha}
@@ -505,3 +499,55 @@ exports[`A MathML builder should use <munderover> for large operators 1`] = `
 </math>
 
 `;
+
+exports[`A MathML builder tags use <mlabeledtr> 1`] = `
+
+<math>
+  <semantics>
+    <mtable side="right">
+      <mlabeledtr>
+        <mtd>
+          <mrow>
+            <mtext>
+              (
+            </mtext>
+            <mrow>
+              <mtext>
+                h
+              </mtext>
+              <mtext>
+                i
+              </mtext>
+            </mrow>
+            <mtext>
+              )
+            </mtext>
+          </mrow>
+        </mtd>
+        <mtd>
+          <mrow>
+            <mi>
+              x
+            </mi>
+            <mo>
+              +
+            </mo>
+            <msup>
+              <mi>
+                y
+              </mi>
+              <mn>
+                2
+              </mn>
+            </msup>
+          </mrow>
+        </mtd>
+      </mlabeledtr>
+    </mtable>
+    <annotation encoding="application/x-tex">
+      \\tag{hi} x+y^2
+    </annotation>
+  </semantics>
+</math>
+
+`;

test/helpers.js

@@ -11,13 +11,18 @@ export const defaultSettings = new Settings({
 export const strictSettings = new Settings({strict: true});
 
 export const _getBuilt = function(expr, settings = defaultSettings) {
-    const rootNode = katex.__renderToDomTree(expr, settings);
+    let rootNode = katex.__renderToDomTree(expr, settings);
 
     if (rootNode.classes.indexOf('katex-error') >= 0) {
         return rootNode;
     }
 
+    if (rootNode.classes.indexOf('katex-display') >= 0) {
+        rootNode = rootNode.children[0];
+    }
+
     // grab the root node of the HTML rendering
+    // rootNode.children[0] is the MathML rendering
     const builtHTML = rootNode.children[1];
 
     // combine the non-strut children of all base spans

test/katex-spec.js

@@ -2663,6 +2663,24 @@ describe("A macro expander", function() {
     //        {"\\mode": "\\TextOrMath{text}{math}"});
     //});
 
+    it("\\gdef defines macros", function() {
+        compareParseTree("\\gdef\\foo{x^2}\\foo+\\foo", "x^2+x^2");
+        compareParseTree("\\gdef{\\foo}{x^2}\\foo+\\foo", "x^2+x^2");
+        compareParseTree("\\gdef\\foo{hi}\\foo+\\text{\\foo}", "hi+\\text{hi}");
+        compareParseTree("\\gdef\\foo#1{hi #1}\\text{\\foo{Alice}, \\foo{Bob}}",
+            "\\text{hi Alice, hi Bob}");
+        compareParseTree("\\gdef\\foo#1#2{(#1,#2)}\\foo 1 2+\\foo 3 4",
+            "(1,2)+(3,4)");
+        expect("\\gdef\\foo#2{}").toNotParse();
+        expect("\\gdef\\foo#1#3{}").toNotParse();
+        expect("\\gdef\\foo#1#2#3#4#5#6#7#8#9{}").toParse();
+        expect("\\gdef\\foo#1#2#3#4#5#6#7#8#9#10{}").toNotParse();
+        expect("\\gdef\\foo#{}").toNotParse();
+        expect("\\gdef\\foo\\bar").toParse();
+        expect("\\gdef{\\foo\\bar}{}").toNotParse();
+        expect("\\gdef{}{}").toNotParse();
+    });
+
     // This may change in the future, if we support the extra features of
     // \hspace.
     it("should treat \\hspace, \\hskip like \\kern", function() {
@@ -2681,6 +2699,30 @@ describe("A macro expander", function() {
     });
 });
 
+describe("\\tag support", function() {
+    const displayMode = new Settings({displayMode: true});
+
+    it("should fail outside display mode", () => {
+        expect("\\tag{hi}x+y").toNotParse();
+    });
+
+    it("should fail with multiple tags", () => {
+        expect("\\tag{1}\\tag{2}x+y").toNotParse(displayMode);
+    });
+
+    it("should build", () => {
+        expect("\\tag{hi}x+y").toBuild(displayMode);
+    });
+
+    it("should ignore location of \\tag", () => {
+        expect("\\tag{hi}x+y").toParseLike("x+y\\tag{hi}", displayMode);
+    });
+
+    it("should handle \\tag* like \\tag", () => {
+        expect("\\tag{hi}x+y").toParseLike("\\tag*{({hi})}x+y", displayMode);
+    });
+});
+
 describe("A parser taking String objects", function() {
     it("should not fail on an empty String object", function() {
         expect(new String("")).toParse();
@@ -2862,6 +2904,20 @@ describe("The maxSize setting", function() {
     });
 });
 
+describe("The maxExpand setting", () => {
+    it("should prevent expansion", () => {
+        expect("\\gdef\\foo{1}\\foo").toParse();
+        expect("\\gdef\\foo{1}\\foo").toParse(new Settings({maxExpand: 2}));
+        expect("\\gdef\\foo{1}\\foo").toNotParse(new Settings({maxExpand: 1}));
+        expect("\\gdef\\foo{1}\\foo").toNotParse(new Settings({maxExpand: 0}));
+    });
+
+    it("should prevent infinite loops", () => {
+        expect("\\gdef\\foo{\\foo}\\foo").toNotParse(
+            new Settings({maxExpand: 10}));
+    });
+});
+
 describe("The \\mathchoice function", function() {
     const cmd = "\\sum_{k = 0}^{\\infty} x^k";
 

test/mathml-spec.js

@@ -94,8 +94,13 @@ describe("A MathML builder", function() {
             .toMatchSnapshot();
     });
 
-    it('accents turn into <mover accent="true"> in MathML', function() {
+    it('accents turn into <mover accent="true"> in MathML', () => {
         expect(getMathML("über fiancée", {unicodeTextInMathMode: true}))
             .toMatchSnapshot();
     });
+
+    it('tags use <mlabeledtr>', () => {
+        expect(getMathML("\\tag{hi} x+y^2", {displayMode: true}))
+            .toMatchSnapshot();
+    });
 });

test/screenshotter/ss_data.yaml

@@ -332,6 +332,9 @@ SvgReset:
 Symbols1: |
     \maltese\degree\pounds\$
     \text{\maltese\degree\pounds\textdollar}
+Tag:
+    tex: \tag{$+$hi} \frac{x^2}{y}+x^{2^y}
+    display: 1
 Text: \frac{a}{b}\text{c~ {ab} \ e}+fg
 TextSpace:
   \begin{array}{l}