From 8331570aafe66d35a0416c5033d1e50e1ab2568a Mon Sep 17 00:00:00 2001
From: Alexandre Kohler <64209066+kwy404@users.noreply.github.com>
Date: Wed, 30 Sep 2026 01:52:12 -0300
Subject: [PATCH] Fix `String.endsWith` for overlapping regex matches (#1880)

---
 .../java/org/pkl/core/stdlib/base/StringNodes.java    | 11 +++++------
 .../files/LanguageSnippetTests/input/api/string.pkl   |  5 +++++
 .../files/LanguageSnippetTests/output/api/string.pcf  |  5 +++++
 3 files changed, 15 insertions(+), 6 deletions(-)

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 c92da1ffe..c125bd7b3 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
@@ -333,14 +333,13 @@ public final class StringNodes {
 
     @TruffleBoundary
     @Specialization
-    // inefficient but at least correct
     protected boolean eval(String self, VmRegex regex) {
-      var matcher = regex.matcher(self);
-      var end = -1;
-      while (matcher.find()) {
-        end = matcher.end();
+      // try every suffix; `find()` would skip matches that overlap an earlier one
+      var matcher = regex.matcher(self).useTransparentBounds(true).useAnchoringBounds(false);
+      for (var start = self.length(); ; start = self.offsetByCodePoints(start, -1)) {
+        if (matcher.region(start, self.length()).matches()) return true;
+        if (start == 0) return false;
       }
-      return end == self.length();
     }
   }
 
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 29939fac7..a5ab43ee7 100644
--- a/pkl-core/src/test/files/LanguageSnippetTests/input/api/string.pkl
+++ b/pkl-core/src/test/files/LanguageSnippetTests/input/api/string.pkl
@@ -76,7 +76,12 @@ facts {
   ["endsWith()"] {
     str1.endsWith("")
     str1.endsWith("efg")
+    str1.endsWith(Regex(#"\w"#))
+    "aaa".endsWith(Regex("aa"))
     !str1.endsWith("efx")
+    !str1.endsWith(Regex(#"\d"#))
+    !str1.endsWith(Regex(#"\bfg"#))
+    !str1.endsWith(Regex("^fg"))
   }
 
   ["isRegex"] {
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 1c39c1683..bda6f39e8 100644
--- a/pkl-core/src/test/files/LanguageSnippetTests/output/api/string.pcf
+++ b/pkl-core/src/test/files/LanguageSnippetTests/output/api/string.pcf
@@ -59,6 +59,11 @@ facts {
     true
     true
     true
+    true
+    true
+    true
+    true
+    true
   }
   ["isRegex"] {
     true