Fix issue #1600, allow \\ to escape a backslash in replacement string

SETUP/tests/jsTests/srchrepTests.js

@@ -99,6 +99,7 @@ QUnit.module("srchrep tests", (hooks) => {
         setTextValue("Example search -- and replace search text <i>value</i>.");
         $("#search").val("search");
         $("#replace").val("s\\n");
+        $("#is_regex").prop("checked", true);
         srchrep.doReplace();
         assert.strictEqual(
             window.opener.parent.docRef.editform.text_data.value,
@@ -107,4 +108,17 @@ QUnit.module("srchrep tests", (hooks) => {
         );
         assert.notOk($("#undo").prop("disabled"), "Undo should be enabled.");
     });
+
+    QUnit.test("\\n is just backslash n without regex", function (assert) {
+        setTextValue("Example search -- and replace search text <i>value</i>.");
+        $("#search").val("search");
+        $("#replace").val("s\\n");
+        srchrep.doReplace();
+        assert.strictEqual(
+            window.opener.parent.docRef.editform.text_data.value,
+            "Example s\\n -- and replace s\\n text <i>value</i>.",
+            "Search replace replaces with just \\n, not newline, without regex.",
+        );
+        assert.notOk($("#undo").prop("disabled"), "Undo should be enabled.");
+    });
 });

faq/prooffacehelp.php

@@ -619,11 +619,9 @@ function echo_row(string $name, string $tooltip, string $button_image_base, stri
         [Aa]{6} &mdash; six As of either case<br>
         A{2,8} &mdash; between 2 and 8 capital As<br>
         [hb]e &mdash; 'he' or 'be'<br>
+        \n &mdash; new line<br>
     </blockquote>
 </p>
-<p>
-    To replace matched text with a new line, \n may be used in the replace field.
-</p>
 
 <h4>Help</h4>
 <p>

tools/proofers/srchrep.js

@@ -17,14 +17,24 @@ var srchrep = (function () {
 
     function doReplace() {
         var search = document.getElementById("search").value;
-        var replacetext = document.getElementById("replace").value.replace(new RegExp("\\\\n", "g"), "\r\n");
+        var replacetext = document.getElementById("replace").value;
+
         saveText();
         if (!document.getElementById("is_regex").checked) {
             search = escapeRegExp(search);
-
             // Replace $ in replace text with $$ to avoid special replacement patterns.
             // Note, $ here is in a .replace function and must be escaped so '$$' becomes '$$$$'.
             replacetext = replacetext.replace(/\$/g, "$$$$");
+        } else {
+            // Handle \n for newline. And \<x> becomes just <x>. So \\ becomes a single \.
+            replacetext = replacetext.replace(/\\(.)/g, (match, esc) => {
+                switch (esc) {
+                    case "n":
+                        return "\r\n";
+                    default:
+                        return esc; // anything else, leave as is without the backslash
+                }
+            });
         }
         opener.parent.docRef.editform.text_data.value = opener.parent.docRef.editform.text_data.value.replace(new RegExp(search, "gum"), replacetext);
         setUndoButtonDisabled(false);