Show math icon if Mathjax is empty

ts/editable/BUILD.bazel

@@ -3,7 +3,7 @@ load("//ts/svelte:svelte.bzl", "compile_svelte", "svelte_check")
 load("//ts:prettier.bzl", "prettier_test")
 load("//ts:eslint.bzl", "eslint_test")
 load("//ts:esbuild.bzl", "esbuild")
-load("//ts:vendor.bzl", "copy_bootstrap_icons", "copy_mdi_icons")
+load("//ts:vendor.bzl", "copy_mdi_icons")
 load("//ts:compile_sass.bzl", "compile_sass")
 
 svelte_files = glob(["*.svelte"])
@@ -37,6 +37,14 @@ compile_sass(
     ],
 )
 
+copy_mdi_icons(
+    name = "mdi-icons",
+    icons = [
+        "math-integral-box.svg",
+    ],
+    visibility = ["//visibility:public"],
+)
+
 ts_library(
     name = "editable",
     srcs = glob(["*.ts"]),
@@ -65,6 +73,7 @@ esbuild(
     output_css = "editable-build.css",
     visibility = ["//visibility:public"],
     deps = [
+        "mdi-icons",
         "editable",
         "editable_scss",
         "svelte_components",

ts/editable/icons.ts

@@ -0,0 +1,4 @@
+// Copyright: Ankitects Pty Ltd and contributors
+// License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
+
+export { default as mathIcon } from "./math-integral-box.svg";

ts/editable/mathjax.ts

@@ -1,14 +1,48 @@
 // Copyright: Ankitects Pty Ltd and contributors
 // License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
-export function convertMathjax(input: string): string {
-    const svg = globalThis.MathJax.tex2svg(input).children[0];
+import { mathIcon } from "./icons";
 
+const parser = new DOMParser();
+const errorPattern = /<title>(.*?)<\/title>/gsu;
+
+function getStyle(): HTMLStyleElement {
     const style = document.createElement("style") as HTMLStyleElement;
+    const css = `svg { color: white; fill: white; font-size: 20px; }`;
+    style.appendChild(document.createTextNode(css));
 
-    const styles = `svg { color: white; font-size: 24px; }`;
-    style.appendChild(document.createTextNode(styles));
+    return style;
+}
 
+function getEmptyIcon(): string {
+    const style = getStyle();
+
+    const icon = parser.parseFromString(mathIcon, "image/svg+xml");
+    const svg = icon.children[0];
     svg.insertBefore(style, svg.children[0]);
+
     return svg.outerHTML;
 }
+
+export function convertMathjax(input: string): string {
+    if (input.trim().length === 0) {
+        return getEmptyIcon();
+    }
+
+    const output = globalThis.MathJax.tex2svg(input);
+    const svg = output.children[0];
+
+    if (svg.viewBox.baseVal.height === 16) {
+        return getEmptyIcon();
+    }
+
+    if (!svg.innerHTML.includes("data-mjx-error")) {
+        const style = getStyle();
+        svg.insertBefore(style, svg.children[0]);
+
+        return svg.outerHTML;
+    } else {
+        const match = errorPattern.exec(svg.innerHTML);
+        throw match ? match[1] : "Unknown error";
+    }
+}

ts/editor/BUILD.bazel

@@ -151,6 +151,7 @@ esbuild(
         "mdi-icons",
         "svelte_components",
         "//ts/editable",
+        "//ts/editable:mdi-icons",
         "//ts/components",
         "//ts/components:svelte_components",
         "//ts/editable:svelte_components",