From 7506577e3734e011e3ee29e6e4fe8070cc05ef24 Mon Sep 17 00:00:00 2001
From: John Mager <jmageriii@gmail.com>
Date: Sat, 20 Jun 2020 20:24:45 -0400
Subject: [PATCH] Protects some sequences for being ligaturized

---
 Scripts/features.py | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/Scripts/features.py b/Scripts/features.py
index 38c9583..bbab79b 100644
--- a/Scripts/features.py
+++ b/Scripts/features.py
@@ -59,6 +59,16 @@ def rule(liga):
         rules.append(ignore([liga[-2]], liga[0], liga[1:]))
         rules.append(ignore(head=liga[0], suffix=(liga[1:] + [liga[1]])))
 
+    # Don't cut into `prefix` to complete a ligature.
+    #  i.e. regex `(?=`>  is not `(?`=>.
+    rules.extend(
+        [
+            ignore(prefix[:-n], liga[0], liga[1:])
+            for prefix in ignore_prefixes
+            for n in range(1, len(liga))
+            if prefix[-n:] == liga[:n]
+        ]
+    )
     # hardcoded ignores, i.e. `<||>`
     rules.extend(ignores[tuple(liga)])
 
@@ -198,5 +208,17 @@ ignores = defaultdict(
 )
 
 
+ignore_prefixes = [
+    ["parenleft", "question", "colon"],
+    # Regexp lookahead/lookbehind
+    ["parenleft", "question", "equal"],
+    ["parenleft", "question", "less", "equal"],
+    ["parenleft", "question", "exclam"],
+    ["parenleft", "question", "less", "exclam"],
+    # PHP <?=
+    ["less", "question", "equal"],
+]
+
+
 def indent(text, prefix):
     return '\n'.join(prefix + line for line in text.split('\n'))