From 46246edb9c33fbb3493b164f7af5bf3cb23c8004 Mon Sep 17 00:00:00 2001
From: Orson Peters <orsonpeters@gmail.com>
Date: Mon, 16 Jan 2023 22:03:40 +0100
Subject: [PATCH] Made backslash escape starting delimiters.

---
 contrib/auto-render/splitAtDelimiters.js     | 11 ++++++++++-
 contrib/auto-render/test/auto-render-spec.js | 18 ++++++++++++++++++
 docs/autorender.md                           |  6 ++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/contrib/auto-render/splitAtDelimiters.js b/contrib/auto-render/splitAtDelimiters.js
index 21b59030a5..1411ebbf50 100644
--- a/contrib/auto-render/splitAtDelimiters.js
+++ b/contrib/auto-render/splitAtDelimiters.js
@@ -46,15 +46,24 @@ const splitAtDelimiters = function(text, delimiters) {
         if (index === -1) {
             break;
         }
+
+        const escaped = index > 0 && text[index - 1] === "\\";
         if (index > 0) {
             data.push({
                 type: "text",
-                data: text.slice(0, index),
+                data: text.slice(0, index - (escaped ? 1 : 0)),
             });
             text = text.slice(index); // now text starts with delimiter
         }
         // ... so this always succeeds:
         const i = delimiters.findIndex((delim) => text.startsWith(delim.left));
+
+        if (escaped) {
+            data[data.length - 1].data += text.slice(0, delimiters[i].left.length);
+            text = text.slice(delimiters[i].left.length);
+            continue;
+        }
+
         index = findEndOfMath(delimiters[i].right, text, delimiters[i].left.length);
         if (index === -1) {
             break;
diff --git a/contrib/auto-render/test/auto-render-spec.js b/contrib/auto-render/test/auto-render-spec.js
index accb326195..c51fcc1b87 100644
--- a/contrib/auto-render/test/auto-render-spec.js
+++ b/contrib/auto-render/test/auto-render-spec.js
@@ -305,6 +305,24 @@ describe("A delimiter splitter", function() {
                     rawData: "$$boo$$", display: true},
             ]);
     });
+
+    it("correctly escapes start symbols", function() {
+        expect(splitAtDelimiters("test \\$40 for $foobar$$$bla$$\\$$boo",
+            [
+                {left:"$$", right:"$$", display:true},
+                {left:"$", right:"$", display:false},
+            ])).toEqual(
+            [
+                {type: "text", data: "test $"},
+                {type: "text", data: "40 for "},
+                {type: "math", data: "foobar",
+                    rawData: "$foobar$", display: false},
+                {type: "math", data: "bla",
+                    rawData: "$$bla$$", display: true},
+                {type: "text", data: "$$"},
+                {type: "text", data: "boo"},
+            ]);
+    });
 });
 
 describe("Pre-process callback", function() {
diff --git a/docs/autorender.md b/docs/autorender.md
index 00b1a9a7bf..78ea412057 100644
--- a/docs/autorender.md
+++ b/docs/autorender.md
@@ -115,6 +115,12 @@ in addition to five auto-render-specific keys:
   ]
   ```
 
+  Note that if a left delimiter is preceded by a backslash (`\`), the backslash
+  is stripped and the delimiter is ignored (math mode is not entered). So `\$40
+  is greater than \$30` gets transformed to `$40 is greater than $30`, if `$` is
+  configured to be a left delimiter. If it is not, the backslashes are left
+  untouched.
+
 - `ignoredTags`: This is a list of DOM node types to ignore when recursing
   through. The default value is
   `["script", "noscript", "style", "textarea", "pre", "code", "option"]`.