From f4ad0da658449033830f5a23906dd0a38942b73b Mon Sep 17 00:00:00 2001
From: Alexandre Kohler <64209066+kwy404@users.noreply.github.com>
Date: Tue, 13 Oct 2026 15:32:12 -0300
Subject: [PATCH] Fix lookaround regexes in `String.lastIndexOf` and
 `replaceLast` (#1908)

---
 .../src/main/java/org/pkl/core/stdlib/base/StringNodes.java     | 2 +-
 .../src/test/files/LanguageSnippetTests/input/api/string.pkl    | 2 ++
 .../src/test/files/LanguageSnippetTests/output/api/string.pcf   | 2 ++
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/pkl-core/src/main/java/org/pkl/core/stdlib/base/StringNodes.java b/pkl-core/src/main/java/org/pkl/core/stdlib/base/StringNodes.java
index f8af6ea49..5b84e7fe7 100644
--- a/pkl-core/src/main/java/org/pkl/core/stdlib/base/StringNodes.java
+++ b/pkl-core/src/main/java/org/pkl/core/stdlib/base/StringNodes.java
@@ -1107,7 +1107,7 @@ public final class StringNodes {
     } while (m.find());
 
     // Reset `m` to the last match before returning (should always be `true` at this point)
-    return m.region(r.start(), r.end()).lookingAt();
+    return m.find(r.start());
   }
 
   /**
diff --git a/pkl-core/src/test/files/LanguageSnippetTests/input/api/string.pkl b/pkl-core/src/test/files/LanguageSnippetTests/input/api/string.pkl
index 7891c869b..0485197b2 100644
--- a/pkl-core/src/test/files/LanguageSnippetTests/input/api/string.pkl
+++ b/pkl-core/src/test/files/LanguageSnippetTests/input/api/string.pkl
@@ -179,6 +179,7 @@ examples {
     str3.lastIndexOf(Regex("ab"))
     str3.lastIndexOf(Regex(""))
     module.catch(() -> str3.lastIndexOf(Regex("b*c")))
+    str3.lastIndexOf(Regex("ab(?=y)"))
   }
 
   ["lastIndexOfOrNull()"] {
@@ -230,6 +231,7 @@ examples {
     str6.replaceLast(".", "x")
     str6.replaceLast(Regex("."), "x")
     module.catch(() -> str4.replaceLast(Regex("cc"), "$4; no such group"))
+    str3.replaceLast(Regex("(?<=x)ab"), "-")
   }
 
   ["replaceAllMapped()"] {
diff --git a/pkl-core/src/test/files/LanguageSnippetTests/output/api/string.pcf b/pkl-core/src/test/files/LanguageSnippetTests/output/api/string.pcf
index 3c02b73c3..c15d69b67 100644
--- a/pkl-core/src/test/files/LanguageSnippetTests/output/api/string.pcf
+++ b/pkl-core/src/test/files/LanguageSnippetTests/output/api/string.pcf
@@ -144,6 +144,7 @@ examples {
     6
     9
     "String does not contain a match for regex pattern. String : \"abxabyabz\" Pattern: Regex(\"b*c\")"
+    3
   }
   ["lastIndexOfOrNull()"] {
     6
@@ -184,6 +185,7 @@ examples {
     "aabb.xaabbcc"
     "aabb..aabbcx"
     "Error replacing matches for regex `cc` with `$4; no such group`: `No group 4`"
+    "abx-yabz"
   }
   ["replaceAllMapped()"] {
     ">>aa<<bbcc>>aa<<bbcc"