Line breaks for inline formulas (#1287)

* Line breaks for inline formulas

* Basic support for \allowbreak and \nobreak

* Fix spacing around \nobreak, and add documentation

* Backwards-compatibility _getBuilt to fix tests

* Put operator spacing on same line as operator

* One approach to ~

* Simplify \allowbreak/\nobreak, make ~/\nobreakspace prevent line breaks

* Adapt to #1295

* Prevent wrapping within a .base

* Implement \hspace* properly

* Fix flow error

* Update comment for regularSpace

* Update screenshots

* Move `width: min-content` from .katex into .base

* Fix screenshot

* Add min-width rule to .vlist-s

* Factor out hasClass method

* Cleanup nobreak test

* Pull out buildHTMLUnbreakable

* Fix \hspace* test (no longer the same as \hspace)

* Fix \nobreak handling

* Add screenshot test

test/katex-spec.js

@@ -53,8 +53,13 @@ const _getBuilt = function(expr, settings) {
     // grab the root node of the HTML rendering
     const builtHTML = rootNode.children[1];
 
-    // Remove the outer .katex and .katex-inner layers
-    return builtHTML.children[2].children;
+    // combine the non-strut children of all base spans
+    const children = [];
+    for (let i = 0; i < builtHTML.children.length; i++) {
+        children.push(...builtHTML.children[i].children.filter(
+            (node) => node.classes.indexOf("strut") < 0));
+    }
+    return children;
 };
 
 /**
@@ -2889,9 +2894,9 @@ describe("A macro expander", function() {
 
     // This may change in the future, if we support the extra features of
     // \hspace.
-    it("should treat \\hspace, \\hspace*, \\hskip like \\kern", function() {
+    it("should treat \\hspace, \\hskip like \\kern", function() {
         expect("\\hspace{1em}").toParseLike("\\kern1em");
-        expect("\\hspace*{1em}").toParseLike("\\kern1em");
+        expect("\\hskip{1em}").toParseLike("\\kern1em");
     });
 
     it("should expand \\limsup as expected", () => {

test/screenshotter/ss_data.yaml

@@ -144,6 +144,20 @@ LeftRightStyleSizing: |
 LimitControls: |
     \displaystyle\int\limits_2^3 3x^2\,dx + \sum\nolimits^n_{i=1}i +
     \textstyle\int\limits_x^y z
+LineBreak: |
+    \frac{x^2}{y^2} + z^2 =
+    z^2 + \frac{x^2}{y^2} =
+    \frac{x^2}{y^2} +\nobreak z^2 =
+    z^2 + \frac{x^2}{y^2} =
+    \frac{x^2}{y^2} + ~ z^2 =
+    z^2 + \frac{x^2}{y^2} =
+    \frac{x^2}{y^2} + \hspace{1em} z^2 =
+    z^2 + \frac{x^2}{y^2} =
+    \frac{x^2}{y^2} + z^2 = \hspace*{1em}
+    z^2 + \frac{x^2}{y^2} =
+    \frac{x^2}{y^2} + z^2 =
+    hi \allowbreak there =
+    hi \allowbreak there
 LowerAccent: |
     \begin{matrix}
         \underleftarrow{AB} \quad \underrightarrow{AB} \quad \underleftrightarrow{AB} \quad \undergroup{AB} \\