fix: acknowledge self-closing flag on foreign integration points

src/Parser.events.spec.ts

@@ -215,6 +215,28 @@ describe("Events", () => {
             recognizeSelfClosing: true,
         }));
 
+    it("Self-closing SVG integration point acknowledges the slash", () =>
+        runTest("<svg><foreignObject/>x</svg>"));
+
+    it("Self-closing SVG title acknowledges the slash", () =>
+        runTest("<svg><title/>x</svg>"));
+
+    it("Self-closing SVG desc acknowledges the slash", () =>
+        runTest("<svg><desc/>x</svg>"));
+
+    it("Self-closing MathML integration point acknowledges the slash", () =>
+        runTest("<math><mi/>x</math>"));
+
+    it("Self-closing MathML annotation-xml acknowledges the slash", () =>
+        runTest("<math><annotation-xml/>x</math>"));
+
+    it("Self-closing HTML descendant of an integration point ignores the slash", () =>
+        /*
+         * `title` here is HTML (inside foreignObject's HTML context), not a
+         * foreign integration point, so its slash must not be acknowledged.
+         */
+        runTest("<svg><foreignObject><title/>x</foreignObject></svg>"));
+
     it("HTML image alias", () => runTest("<image></image>"));
 
     it("SVG image is not aliased", () => runTest("<svg><image></image></svg>"));

src/Parser.ts

@@ -338,6 +338,25 @@ export class Parser implements Callbacks {
         return this.foreignContext[0] !== ForeignContext.None;
     }
 
+    /**
+     * Whether the element currently being opened is a foreign (SVG/MathML)
+     * element. Foreign elements acknowledge the self-closing flag even in HTML
+     * mode.
+     *
+     * HTML integration points (e.g. `<foreignObject>`, or `<title>` inside
+     * `<svg>`) switch their *children* back to the HTML context, so
+     * `isInForeignContext()` reports `false` for them even though the element
+     * itself is foreign. For those, check the enclosing context instead.
+     */
+    private currentTagIsForeign(): boolean {
+        return (
+            this.isInForeignContext() ||
+            (this.htmlMode &&
+                htmlIntegrationElements.has(this.tagname) &&
+                this.foreignContext[1] !== ForeignContext.None)
+        );
+    }
+
     /**
      * Checks if the current tag is a void element. Override this if you want
      * to specify your own additional void elements.
@@ -503,7 +522,7 @@ export class Parser implements Callbacks {
      */
     onselfclosingtag(endIndex: number): void {
         this.endIndex = endIndex;
-        if (this.recognizeSelfClosing || this.isInForeignContext()) {
+        if (this.recognizeSelfClosing || this.currentTagIsForeign()) {
             this.closeCurrentTag(false);
 
             // Set `startIndex` for next node