From 9ec39c73c098180ffa59a63c9f98db38f7d88ad1 Mon Sep 17 00:00:00 2001
From: Josh Goebel <me@joshgoebel.com>
Date: Fri, 31 Jan 2020 19:38:26 -0500
Subject: [PATCH 1/2] enh(parser) better regular expression detection

- fewer false positives
- Uses a look-ahead to make sure we have a WHOLE regex and not
  just a partial (which is more likely a math expression)
---
 CHANGES.md                              |  3 ++-
 src/highlight.js                        | 31 ++++++++++++++++---------
 test/markup/javascript/regex.expect.txt |  5 ++++
 test/markup/javascript/regex.txt        |  5 ++++
 4 files changed, 32 insertions(+), 12 deletions(-)
 create mode 100644 test/markup/javascript/regex.expect.txt
 create mode 100644 test/markup/javascript/regex.txt

diff --git a/CHANGES.md b/CHANGES.md
index a5542c2ccb..029a3264ae 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -10,7 +10,7 @@ New themes:
 
 Core Changes:
 
-- none.
+- Improve regular expression detect (less false-positives) [Josh Goebel][]
 
 Language Improvements:
 
@@ -22,6 +22,7 @@ Developer Tools:
 
 - none.
 
+[Josh Goebel]: https://github.com/yyyc514
 [Sam Miller]: https://github.com/smillerc
 [Robert Riebisch]: https://github.com/bttrx
 [Taufik Nurrohman]: https://github.com/taufik-nurrohman
diff --git a/src/highlight.js b/src/highlight.js
index ab8203654a..c2f078a131 100644
--- a/src/highlight.js
+++ b/src/highlight.js
@@ -1095,17 +1095,26 @@ https://highlightjs.org/
     relevance: 0
   };
   hljs.REGEXP_MODE = {
-    className: 'regexp',
-    begin: /\//, end: /\/[gimuy]*/,
-    illegal: /\n/,
-    contains: [
-      hljs.BACKSLASH_ESCAPE,
-      {
-        begin: /\[/, end: /\]/,
-        relevance: 0,
-        contains: [hljs.BACKSLASH_ESCAPE]
-      }
-    ]
+    // this outer rule makes sure we actually have a WHOLE regex and not simply
+    // an expression such as:
+    //
+    //     3 / something
+    //
+    // (which will then blow up when regex's `illegal` sees the newline)
+    begin: /(?=\/[^\/\n]*\/)/,
+    contains: [{
+      className: 'regexp',
+      begin: /\//, end: /\/[gimuy]*/,
+      illegal: /\n/,
+      contains: [
+        hljs.BACKSLASH_ESCAPE,
+        {
+          begin: /\[/, end: /\]/,
+          relevance: 0,
+          contains: [hljs.BACKSLASH_ESCAPE]
+        }
+      ]
+    }]
   };
   hljs.TITLE_MODE = {
     className: 'title',
diff --git a/test/markup/javascript/regex.expect.txt b/test/markup/javascript/regex.expect.txt
new file mode 100644
index 0000000000..21342a7889
--- /dev/null
+++ b/test/markup/javascript/regex.expect.txt
@@ -0,0 +1,5 @@
+<span class="hljs-comment">// examples that have proven problematic in the past</span>
+<span class="hljs-string">`Bad <span class="hljs-subst">${foo / <span class="hljs-number">1000</span>}</span>`</span>
+foo = <span class="hljs-number">2</span> / <span class="hljs-number">2</span> + <span class="hljs-number">2</span> / <span class="hljs-number">2</span>;
+foo = <span class="hljs-regexp">/ 2 + 2 /</span>;
+b = a++ / <span class="hljs-number">2</span>;
diff --git a/test/markup/javascript/regex.txt b/test/markup/javascript/regex.txt
new file mode 100644
index 0000000000..da0ee68a12
--- /dev/null
+++ b/test/markup/javascript/regex.txt
@@ -0,0 +1,5 @@
+// examples that have proven problematic in the past
+`Bad ${foo / 1000}`
+foo = 2 / 2 + 2 / 2;
+foo = / 2 + 2 /;
+b = a++ / 2;

From e8696e9837a0d6688c066e53d486fbf846178453 Mon Sep 17 00:00:00 2001
From: Josh Goebel <me@joshgoebel.com>
Date: Fri, 31 Jan 2020 19:39:52 -0500
Subject: [PATCH 2/2] pr #

---
 CHANGES.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGES.md b/CHANGES.md
index 029a3264ae..c9d5ff51f0 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -10,7 +10,7 @@ New themes:
 
 Core Changes:
 
-- Improve regular expression detect (less false-positives) [Josh Goebel][]
+- Improve regular expression detect (less false-positives) (#2380) [Josh Goebel][]
 
 Language Improvements: