[FIX] Parser: parse <br> consistently with Renderer behaviour

Until this commit, the Parser just added a LINE_BREAK in VDocument for
each <br>. But our own Renderer doesn't render a single <br> for each
LINE_BREAK. This commit makes the Parser consistent with that behaviour.
Also includes tests to account for that.

src/core/utils/Parser.ts

@@ -89,6 +89,19 @@ function parseElementNode(currentContext: ParsingContext): ParsingContext {
     const context = { ...currentContext };
 
     const node = context.node;
+    // A <br/> with no siblings is there only to make its parent visible.
+    // Consume it since it was just parsed as its parent element node.
+    // TODO: do this less naively to account for formatting space.
+    if (node.childNodes.length === 1 && node.childNodes[0].nodeName === 'BR') {
+        context.node = node.childNodes[0];
+    }
+    // A trailing <br/> after another <br/> is there only to make its previous
+    // sibling visible. Consume it since it was just parsed as a single BR
+    // within our abstraction.
+    // TODO: do this less naively to account for formatting space.
+    if (node.nodeName === 'BR' && node.nextSibling && node.nextSibling.nodeName === 'BR') {
+        context.node = node.nextSibling;
+    }
     if (Format.tags.includes(context.node.nodeName)) {
         // Format nodes (e.g. B, I, U) are parsed differently than regular
         // elements since they are not represented by a proper VNode in our

test/utils/Parser.test.ts

@@ -18,7 +18,24 @@ describe('utils', () => {
                 expect(p.children[0].type).to.equal(VNodeType.CHAR);
                 expect(p.children[0].value).to.equal('a');
             });
-
+            it('should parse a "p" tag with no content', () => {
+                const element = document.createElement('div');
+                element.innerHTML = '<p><br></p>';
+                const vDocument = Parser.parse(element);
+                const p = vDocument.root.firstChild();
+                // The placeholder <br> should not be parsed.
+                expect(p.hasChildren()).to.be.false;
+            });
+            it('should parse two trailing consecutive <br> as one LINE_BREAK', () => {
+                const element = document.createElement('div');
+                element.innerHTML = '<p>a<br><br>';
+                const vDocument = Parser.parse(element);
+                const p = vDocument.root.firstChild();
+                // Only one <br> should be parsed.
+                expect(p.children.length).to.equal(2);
+                expect(p.lastChild().type).to.equal(VNodeType.LINE_BREAK);
+                expect(p.lastChild().previousSibling().value).to.equal('a');
+            });
             it('handles nested formatted nodes', () => {
                 const element = document.createElement('div');
                 element.innerHTML = '<p>a<i>b<b>c</b>d</i></p>';