Resolve warnings for assignment or explicit cast of possibly null typ…

…e parameter value (#43925)

src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/BlockingCollection.cs

@@ -536,7 +536,7 @@ private bool TryAddWithNoTimeValidation(T item, int millisecondsTimeout, Cancell
         /// <remarks>A call to <see cref="Take()"/> may block until an item is available to be removed.</remarks>
         public T Take()
         {
-            T item;
+            T? item;
 
             if (!TryTake(out item, Timeout.Infinite, CancellationToken.None))
             {
@@ -560,7 +560,7 @@ public T Take()
         /// <remarks>A call to <see cref="Take(CancellationToken)"/> may block until an item is available to be removed.</remarks>
         public T Take(CancellationToken cancellationToken)
         {
-            T item;
+            T? item;
 
             if (!TryTake(out item, Timeout.Infinite, cancellationToken))
             {
@@ -1658,7 +1658,7 @@ public IEnumerable<T> GetConsumingEnumerable(CancellationToken cancellationToken
                 linkedTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, _consumersCancellationTokenSource.Token);
                 while (!IsCompleted)
                 {
-                    T item;
+                    T? item;
                     if (TryTakeWithNoTimeValidation(out item, Timeout.Infinite, cancellationToken, linkedTokenSource))
                     {
                         yield return item;

src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentBag.cs

@@ -448,7 +448,7 @@ public void Clear()
                 FreezeBag(ref lockTaken);
                 for (WorkStealingQueue? queue = _workStealingQueues; queue != null; queue = queue._nextQueue)
                 {
-                    T ignored;
+                    T? ignored;
                     while (queue.TrySteal(out ignored, take: true));
                 }
             }

src/libraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentDictionary.cs

@@ -1022,7 +1022,7 @@ public TValue this[TKey key]
         {
             get
             {
-                if (!TryGetValue(key, out TValue value))
+                if (!TryGetValue(key, out TValue? value))
                 {
                     ThrowKeyNotFoundException(key);
                 }
@@ -1132,7 +1132,7 @@ public TValue GetOrAdd(TKey key, Func<TKey, TValue> valueFactory)
             IEqualityComparer<TKey>? comparer = _comparer;
             int hashcode = comparer is null ? key.GetHashCode() : comparer.GetHashCode(key);
 
-            if (!TryGetValueInternal(key, hashcode, out TValue resultingValue))
+            if (!TryGetValueInternal(key, hashcode, out TValue? resultingValue))
             {
                 TryAddInternal(key, hashcode, valueFactory(key), updateIfExists: false, acquireLock: true, out resultingValue);
             }
@@ -1171,7 +1171,7 @@ public TValue GetOrAdd<TArg>(TKey key, Func<TKey, TArg, TValue> valueFactory, TA
             IEqualityComparer<TKey>? comparer = _comparer;
             int hashcode = comparer is null ? key.GetHashCode() : comparer.GetHashCode(key);
 
-            if (!TryGetValueInternal(key, hashcode, out TValue resultingValue))
+            if (!TryGetValueInternal(key, hashcode, out TValue? resultingValue))
             {
                 TryAddInternal(key, hashcode, valueFactory(key, factoryArgument), updateIfExists: false, acquireLock: true, out resultingValue);
             }
@@ -1201,7 +1201,7 @@ public TValue GetOrAdd(TKey key, TValue value)
             IEqualityComparer<TKey>? comparer = _comparer;
             int hashcode = comparer is null ? key.GetHashCode() : comparer.GetHashCode(key);
 
-            if (!TryGetValueInternal(key, hashcode, out TValue resultingValue))
+            if (!TryGetValueInternal(key, hashcode, out TValue? resultingValue))
             {
                 TryAddInternal(key, hashcode, value, updateIfExists: false, acquireLock: true, out resultingValue);
             }
@@ -1252,7 +1252,7 @@ public TValue AddOrUpdate<TArg>(
 
             while (true)
             {
-                if (TryGetValueInternal(key, hashcode, out TValue oldValue))
+                if (TryGetValueInternal(key, hashcode, out TValue? oldValue))
                 {
                     // key exists, try to update
                     TValue newValue = updateValueFactory(key, oldValue, factoryArgument);
@@ -1313,7 +1313,7 @@ public TValue AddOrUpdate(TKey key, Func<TKey, TValue> addValueFactory, Func<TKe
 
             while (true)
             {
-                if (TryGetValueInternal(key, hashcode, out TValue oldValue))
+                if (TryGetValueInternal(key, hashcode, out TValue? oldValue))
                 {
                     // key exists, try to update
                     TValue newValue = updateValueFactory(key, oldValue);
@@ -1367,7 +1367,7 @@ public TValue AddOrUpdate(TKey key, TValue addValue, Func<TKey, TValue, TValue>
 
             while (true)
             {
-                if (TryGetValueInternal(key, hashcode, out TValue oldValue))
+                if (TryGetValueInternal(key, hashcode, out TValue? oldValue))
                 {
                     // key exists, try to update
                     TValue newValue = updateValueFactory(key, oldValue);
@@ -1538,7 +1538,7 @@ void IDictionary<TKey, TValue>.Add(TKey key, TValue value)
         /// cref="ICollection{T}"/>; otherwise, false.</returns>
         bool ICollection<KeyValuePair<TKey, TValue>>.Contains(KeyValuePair<TKey, TValue> keyValuePair)
         {
-            if (!TryGetValue(keyValuePair.Key, out TValue value))
+            if (!TryGetValue(keyValuePair.Key, out TValue? value))
             {
                 return false;
             }
@@ -1730,7 +1730,7 @@ void IDictionary.Remove(object key)
                     ThrowHelper.ThrowKeyNullException();
                 }
 
-                if (key is TKey tkey && TryGetValue(tkey, out TValue value))
+                if (key is TKey tkey && TryGetValue(tkey, out TValue? value))
                 {
                     return value;
                 }

src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedDictionary_2.cs

@@ -196,7 +196,7 @@ public TValue this[TKey key]
             {
                 Requires.NotNullAllowStructs(key, nameof(key));
 
-                TValue value;
+                TValue? value;
                 if (this.TryGetValue(key, out value))
                 {
                     return value;

src/libraries/System.Collections/src/System/Collections/Generic/CollectionExtensions.cs

@@ -19,7 +19,7 @@ public static TValue GetValueOrDefault<TKey, TValue>(this IReadOnlyDictionary<TK
                 throw new ArgumentNullException(nameof(dictionary));
             }
 
-            TValue value;
+            TValue? value;
             return dictionary.TryGetValue(key, out value) ? value : defaultValue;
         }
 

src/libraries/System.Collections/src/System/Collections/Generic/SortedDictionary.cs

@@ -326,7 +326,7 @@ ICollection IDictionary.Values
             {
                 if (IsCompatibleKey(key))
                 {
-                    TValue value;
+                    TValue? value;
                     if (TryGetValue((TKey)key, out value))
                     {
                         return value;

src/libraries/System.Collections/src/System/Collections/Generic/SortedSet.cs

@@ -146,8 +146,8 @@ private void AddAllElements(IEnumerable<T> collection)
 
         private void RemoveAllElements(IEnumerable<T> collection)
         {
-            T min = Min;
-            T max = Max;
+            T? min = Min;
+            T? max = Max;
             foreach (T item in collection)
             {
                 if (!(comparer.Compare(item, min) < 0 || comparer.Compare(item, max) > 0) && Contains(item))
@@ -1031,7 +1031,7 @@ public virtual void IntersectWith(IEnumerable<T> other)
                 Enumerator mine = this.GetEnumerator();
                 Enumerator theirs = asSorted.GetEnumerator();
                 bool mineEnded = !mine.MoveNext(), theirsEnded = !theirs.MoveNext();
-                T max = Max;
+                T? max = Max;
 
                 while (!mineEnded && !theirsEnded && Comparer.Compare(theirs.Current, max) <= 0)
                 {
@@ -1109,8 +1109,8 @@ public void ExceptWith(IEnumerable<T> other)
                 // Outside range, no point in doing anything
                 if (comparer.Compare(asSorted.Max, Min) >= 0 && comparer.Compare(asSorted.Min, Max) <= 0)
                 {
-                    T min = Min;
-                    T max = Max;
+                    T? min = Min;
+                    T? max = Max;
                     foreach (T item in other)
                     {
                         if (comparer.Compare(item, min) < 0)

src/libraries/System.ComponentModel.Composition/src/System/ComponentModel/Composition/Hosting/AtomicCompositionExtensions.cs

@@ -18,8 +18,8 @@ internal static T GetValueAllowNull<T>(this AtomicComposition? atomicComposition
 
         internal static T GetValueAllowNull<T>(this AtomicComposition? atomicComposition, object key, T defaultResult)
         {
-            T result;
-            if (atomicComposition != null && atomicComposition.TryGetValue(key, out result))
+            T? result;
+            if (atomicComposition != null && atomicComposition.TryGetValue<T>(key, out result))
             {
                 return result;
             }

src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/Interpreter/Utilities.cs

@@ -271,7 +271,7 @@ public TValue this[TKey key]
             {
                 Debug.Assert(key != null);
 
-                TValue res;
+                TValue? res;
                 if (TryGetValue(key, out res))
                 {
                     return res;

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Partitioning/OrderedHashRepartitionEnumerator.cs

@@ -104,7 +104,7 @@ internal OrderedHashRepartitionEnumerator(
         // anyway, so having the repartitioning operator do so isn't complicating matters much at all.
         //
 
-        internal override bool MoveNext(ref Pair<TInputOutput, THashKey> currentElement, ref TOrderKey currentKey)
+        internal override bool MoveNext(ref Pair<TInputOutput, THashKey> currentElement, [AllowNull] ref TOrderKey currentKey)
         {
             if (_partitionCount == 1)
             {

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Binary/ExceptQueryOperator.cs

@@ -257,7 +257,7 @@ internal OrderedExceptQueryOperatorEnumerator(
             // Walks the two data sources, left and then right, to produce the distinct set
             //
 
-            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TInputOutput currentElement, ref TLeftKey currentKey)
+            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TInputOutput currentElement, [AllowNull] ref TLeftKey currentKey)
             {
                 Debug.Assert(_leftSource != null);
                 Debug.Assert(_rightSource != null);

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Binary/HashJoinQueryOperatorEnumerator.cs

@@ -90,7 +90,7 @@ internal HashJoinQueryOperatorEnumerator(
         // as we do for inner joins.
         //
 
-        internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TOutput currentElement, ref TOutputKey currentKey)
+        internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TOutput currentElement, [AllowNull] ref TOutputKey currentKey)
         {
             Debug.Assert(_resultSelector != null, "expected a compiled result selector");
             Debug.Assert(_leftSource != null);

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Binary/IntersectQueryOperator.cs

@@ -258,7 +258,7 @@ internal OrderedIntersectQueryOperatorEnumerator(
             // Walks the two data sources, left and then right, to produce the intersection.
             //
 
-            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TInputOutput currentElement, ref TLeftKey currentKey)
+            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TInputOutput currentElement, [AllowNull] ref TLeftKey currentKey)
             {
                 Debug.Assert(_leftSource != null);
                 Debug.Assert(_rightSource != null);

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Inlined/LongCountAggregationOperator.cs

@@ -95,8 +95,8 @@ internal LongCountAggregationOperatorEnumerator(QueryOperatorEnumerator<TSource,
 
             protected override bool MoveNextCore(ref long currentElement)
             {
-                TSource elementUnused = default(TSource)!;
-                TKey keyUnused = default(TKey)!;
+                TSource? elementUnused = default(TSource);
+                TKey? keyUnused = default(TKey);
 
                 QueryOperatorEnumerator<TSource, TKey> source = _source;
                 if (source.MoveNext(ref elementUnused, ref keyUnused))

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/QueryOperatorEnumerator.cs

@@ -23,7 +23,7 @@ internal abstract class QueryOperatorEnumerator<TElement, TKey>
     {
         // Moves the position of the enumerator forward by one, and simultaneously returns
         // the (new) current element and key. If empty, false is returned.
-        internal abstract bool MoveNext([MaybeNullWhen(false), AllowNull] ref TElement currentElement, ref TKey currentKey);
+        internal abstract bool MoveNext([MaybeNullWhen(false), AllowNull] ref TElement currentElement, [AllowNull] ref TKey currentKey);
 
         // Standard implementation of the disposable pattern.
         public void Dispose()

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Unary/DefaultIfEmptyQueryOperator.cs

@@ -139,7 +139,7 @@ internal DefaultIfEmptyQueryOperatorEnumerator(
             // Straightforward IEnumerator<T> methods.
             //
 
-            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TSource currentElement, ref TKey currentKey)
+            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TSource currentElement, [AllowNull] ref TKey currentKey)
             {
                 Debug.Assert(_source != null);
 

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Unary/DistinctQueryOperator.cs

@@ -220,7 +220,7 @@ internal OrderedDistinctQueryOperatorEnumerator(
             // Walks the single data source, skipping elements it has already seen.
             //
 
-            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TInputOutput currentElement, ref TKey currentKey)
+            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TInputOutput currentElement, [AllowNull] ref TKey currentKey)
             {
                 Debug.Assert(_source != null);
                 Debug.Assert(_hashLookup != null);

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Unary/ForAllOperator.cs

@@ -155,8 +155,8 @@ internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TInput cur
 
                 // Cancellation testing must be performed here as full enumeration occurs within this method.
                 // We only need to throw a simple exception here.. marshalling logic handled via QueryTaskGroupState.QueryEnd (called by ForAllSpoolingTask)
-                TInput element = default(TInput)!;
-                TKey keyUnused = default(TKey)!;
+                TInput? element = default(TInput);
+                TKey? keyUnused = default(TKey);
                 int i = 0;
                 while (_source.MoveNext(ref element, ref keyUnused))
                 {

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Unary/GroupByQueryOperator.cs

@@ -253,7 +253,7 @@ protected GroupByQueryOperatorEnumerator(
         // just enumerate the key-set from the hash-table, retrieving groupings of key-elements.
         //
 
-        internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref IGrouping<TGroupKey, TElement> currentElement, ref TOrderKey currentKey)
+        internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref IGrouping<TGroupKey, TElement> currentElement, [AllowNull] ref TOrderKey currentKey)
         {
             Debug.Assert(_source != null);
 
@@ -459,7 +459,7 @@ protected OrderedGroupByQueryOperatorEnumerator(QueryOperatorEnumerator<Pair<TSo
         // just enumerate the key-set from the hash-table, retrieving groupings of key-elements.
         //
 
-        internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref IGrouping<TGroupKey, TElement> currentElement, ref TOrderKey currentKey)
+        internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref IGrouping<TGroupKey, TElement> currentElement, [AllowNull] ref TOrderKey currentKey)
         {
             Debug.Assert(_source != null);
             Debug.Assert(_keySelector != null);

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Unary/ReverseQueryOperator.cs

@@ -124,7 +124,7 @@ internal ReverseQueryOperatorEnumerator(QueryOperatorEnumerator<TSource, TKey> s
             // Straightforward IEnumerator<T> methods.
             //
 
-            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TSource currentElement, ref TKey currentKey)
+            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TSource currentElement, [AllowNull] ref TKey currentKey)
             {
                 // If the buffer has not been created, we will generate it lazily on demand.
                 if (_buffer == null)

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Unary/SelectQueryOperator.cs

@@ -111,7 +111,7 @@ internal SelectQueryOperatorEnumerator(QueryOperatorEnumerator<TInput, TKey> sou
             // Straightforward IEnumerator<T> methods.
             //
 
-            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TOutput currentElement, ref TKey currentKey)
+            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TOutput currentElement, [AllowNull] ref TKey currentKey)
             {
                 // So long as the source has a next element, we have an element.
                 TInput element = default(TInput)!;

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Unary/SortQueryOperator.cs

@@ -198,7 +198,7 @@ internal SortQueryOperatorEnumerator(QueryOperatorEnumerator<TInputOutput, TKey>
         // in memory, and the data sorted.
         //
 
-        internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TInputOutput currentElement, ref TSortKey currentKey)
+        internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TInputOutput currentElement, [AllowNull] ref TSortKey currentKey)
         {
             Debug.Assert(_source != null);
 

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Unary/TakeOrSkipQueryOperator.cs

@@ -187,7 +187,7 @@ internal TakeOrSkipQueryOperatorEnumerator(
             // Straightforward IEnumerator<T> methods.
             //
 
-            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TResult currentElement, ref TKey currentKey)
+            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TResult currentElement, [AllowNull] ref TKey currentKey)
             {
                 Debug.Assert(_sharedIndices != null);
 

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Unary/TakeOrSkipWhileQueryOperator.cs

@@ -247,7 +247,7 @@ internal TakeOrSkipWhileQueryOperatorEnumerator(
             // Straightforward IEnumerator<T> methods.
             //
 
-            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TResult currentElement, ref TKey currentKey)
+            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TResult currentElement, [AllowNull] ref TKey currentKey)
             {
                 // If the buffer has not been created, we will generate it lazily on demand.
                 if (_buffer == null)

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/QueryOperators/Unary/WhereQueryOperator.cs

@@ -125,7 +125,7 @@ internal WhereQueryOperatorEnumerator(QueryOperatorEnumerator<TInputOutput, TKey
             // Moves to the next matching element in the underlying data stream.
             //
 
-            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TInputOutput currentElement, ref TKey currentKey)
+            internal override bool MoveNext([MaybeNullWhen(false), AllowNull] ref TInputOutput currentElement, [AllowNull] ref TKey currentKey)
             {
                 Debug.Assert(_predicate != null, "expected a compiled operator");
 

src/libraries/System.Linq.Parallel/src/System/Linq/Parallel/Utils/HashLookup.cs

@@ -42,7 +42,7 @@ internal HashLookup(IEqualityComparer<TKey>? comparer)
         // If value is not in set, add it and return true; otherwise return false
         internal bool Add(TKey key, TValue value)
         {
-            return !Find(key, true, false, ref value);
+            return !Find(key, true, false, ref value!);
         }
 
         // Check whether value is in set
@@ -55,7 +55,7 @@ internal TValue this[TKey key]
         {
             set
             {
-                TValue v = value;
+                TValue? v = value;
                 Find(key, false, true, ref v);
             }
         }

src/libraries/System.Linq/src/System/Linq/ElementAt.cs

@@ -17,7 +17,7 @@ public static TSource ElementAt<TSource>(this IEnumerable<TSource> source, int i
 
             if (source is IPartition<TSource> partition)
             {
-                TSource element = partition.TryGetElementAt(index, out bool found);
+                TSource? element = partition.TryGetElementAt(index, out bool found);
                 if (found)
                 {
                     return element!;