Fix build error for linux builds and add basic validation test

Author: rctcwyvrn

stdlib/public/core/Dictionary.swift

@@ -608,9 +608,9 @@ extension Dictionary {
   public __consuming func filter(
     _ isIncluded: (Element) throws -> Bool
   ) rethrows -> [Key: Value] {
-    if _variant.isNative {
-      return Dictionary(_native: try _variant.asNative.filter(isIncluded))
-    } else {
+  #if _runtime(_ObjC)
+    guard _variant.isNative else {
+      // Slow path for bridged dictionaries
       var result = _NativeDictionary<Key, Value>()
       for element in self {
         if try isIncluded(element) {
@@ -619,6 +619,8 @@ extension Dictionary {
       }
       return Dictionary(_native: result)
     }
+  #endif
+    return Dictionary(_native: try _variant.asNative.filter(isIncluded))
   }
 }
 

stdlib/public/core/NativeDictionary.swift

@@ -798,18 +798,18 @@ extension _NativeDictionary { // High-level operations
     _ isIncluded: (Element) throws -> Bool
   ) rethrows -> _NativeDictionary<Key, Value> {
     try _UnsafeBitset.withTemporaryBitset(
-        capacity: _storage._bucketCount
-      ) { bitset in
-        var count = 0
-        for bucket in hashTable {
-          if try isIncluded(
-            (uncheckedKey(at: bucket), uncheckedValue(at: bucket))
-          ) {
-            bitset.uncheckedInsert(bucket.offset)
-            count += 1
-          }
+      capacity: _storage._bucketCount
+    ) { bitset in
+      var count = 0
+      for bucket in hashTable {
+        if try isIncluded(
+          (uncheckedKey(at: bucket), uncheckedValue(at: bucket))
+        ) {
+          bitset.uncheckedInsert(bucket.offset)
+          count += 1
         }
-        return extractDictionary(using: bitset, count: count)
+      }
+      return extractDictionary(using: bitset, count: count)
     }
   }
 }

validation-test/stdlib/Dictionary.swift

@@ -2013,6 +2013,19 @@ DictionaryTestSuite.test("mapValues(_:)") {
   }
 }
 
+DictionaryTestSuite.test("filter(_:)") {
+  let d1 = [1: 1, 2: 2, 3: 100, 4: 4, 5: 100, 6: 6]
+  let d2 = d1.filter() {key, value in key == value}
+
+  expectEqual(d2.count, 4)
+  for (key, value) in d2 {
+    expectEqual(key, value)
+  }
+
+  expectNil(d2[3])
+  expectNil(d2[5])
+}
+
 DictionaryTestSuite.test("capacity/init(minimumCapacity:)") {
   let d0 = Dictionary<String, Int>(minimumCapacity: 0)
   expectGE(d0.capacity, 0)