From b15c62cd52ce8e73b30779d9006bbf8cb2029997 Mon Sep 17 00:00:00 2001
From: Konrad Malawski <ktoso@apple.com>
Date: Tue, 12 May 2026 11:36:33 +0900
Subject: [PATCH] Fix extension constraint matching

All same type constraints must match, not just one of them.
This is a follow up after https://github.com/swiftlang/swift-java/pull/734#discussion_r3223126771

https://github.com/swiftlang/swift-java/pull/734
---
 .../JExtractSwiftLib/Swift2JavaVisitor.swift  | 14 ++-
 .../JNI/JNIGenericTypeTests.swift             | 98 +++++++++++++++++++
 2 files changed, 104 insertions(+), 8 deletions(-)

diff --git a/Sources/JExtractSwiftLib/Swift2JavaVisitor.swift b/Sources/JExtractSwiftLib/Swift2JavaVisitor.swift
index 9e4a838b..275b48af 100644
--- a/Sources/JExtractSwiftLib/Swift2JavaVisitor.swift
+++ b/Sources/JExtractSwiftLib/Swift2JavaVisitor.swift
@@ -648,20 +648,18 @@ final class Swift2JavaVisitor {
     }
   }
 
-  /// Check if where clause constraints match a specialization's generic arguments
+  /// Check if where clause constraints match a specialization's generic arguments.
+  /// Same-type where-clauses are conjunctive: every constraint must hold.
   private func constraintsMatchSpecialization(
     _ constraints: [(String, String)],
     specialized: ImportedNominalType,
   ) -> Bool {
     for (lhs, rhs) in constraints {
-      if specialized.genericArguments[lhs] == rhs {
-        return true
-      }
-      if specialized.genericArguments[rhs] == lhs {
-        return true
-      }
+      if specialized.genericArguments[lhs] == rhs { continue }
+      if specialized.genericArguments[rhs] == lhs { continue }
+      return false
     }
-    return false
+    return true
   }
 }
 
diff --git a/Tests/JExtractSwiftTests/JNI/JNIGenericTypeTests.swift b/Tests/JExtractSwiftTests/JNI/JNIGenericTypeTests.swift
index 1b8202d7..cdc712ed 100644
--- a/Tests/JExtractSwiftTests/JNI/JNIGenericTypeTests.swift
+++ b/Tests/JExtractSwiftTests/JNI/JNIGenericTypeTests.swift
@@ -281,4 +281,102 @@ struct JNIGenericTypeTests {
       ],
     )
   }
+
+  @Test("Constrained extensions are ignored, unless specialized")
+  func constrainedExtensionsAreIgnoredUnlessSpecialized() throws {
+    let input =
+      #"""
+      public struct Fish {
+        public var name: String
+      }
+      public struct Tool {
+        public var name: String
+      }
+
+      public protocol Animal {}
+      extension Fish: Animal {}
+
+      public struct Tank<T> {
+        public var contents: T
+      }
+
+      extension Tank where T: Animal { // currently not supported yet
+        public func feed() {}
+      }
+      extension Tank where T == Fish {
+        public func observeTheFish() {}
+      }
+      extension Tank where T == Tool {
+        public func useTheTool() {}
+      }
+
+      public typealias FishTank = Tank<Fish>
+      """#
+
+    try assertOutput(
+      input: input,
+      .jni,
+      .java,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        "public final class FishTank implements JNISwiftInstance {",
+        "observeTheFish",
+      ],
+      notExpectedChunks: [
+        "feed",
+        "useTheTool",
+      ],
+    )
+  }
+
+  @Test("Multi-constraint extensions require all constraints to match")
+  func multiConstraintExtensionsRequireAllToMatch() throws {
+    let input =
+      #"""
+      public struct Fish {
+        public var name: String
+      }
+      public struct Tool {
+        public var name: String
+      }
+      public struct Bait {
+        public var name: String
+      }
+
+      public struct Pair<A, B> {
+        public var first: A
+        public var second: B
+      }
+
+      extension Pair where A == Fish, B == Tool {
+        // OK: Both constraints match FishToolPair
+        public func bothMatch() {}
+      }
+      extension Pair where A == Fish, B == Bait {
+        // NOPE: Only A matches FishToolPair
+        public func onlyAMatches() {}
+      }
+      extension Pair where A == Tool, B == Tool {
+        // NOPE: Only B matches FishToolPair
+        public func onlyBMatches() {}
+      }
+
+      public typealias FishToolPair = Pair<Fish, Tool>
+      """#
+
+    try assertOutput(
+      input: input,
+      .jni,
+      .java,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        "public final class FishToolPair implements JNISwiftInstance {",
+        "bothMatch",
+      ],
+      notExpectedChunks: [
+        "onlyAMatches",
+        "onlyBMatches",
+      ],
+    )
+  }
 }