dotnet · GrabYourPitchforks · May 9, 2020 · May 8, 2020 · May 8, 2020 · May 9, 2020
diff --git a/eng/Versions.props b/eng/Versions.props
@@ -19,7 +19,8 @@
     <UsingToolIbcOptimization>true</UsingToolIbcOptimization>
     <UsingToolXliff>false</UsingToolXliff>
     <!-- Downgrade compiler version to fix nullability issues: https://github.com/dotnet/runtime/issues/34417. -->
-    <MicrosoftNetCompilersToolsetVersion>3.6.0-2.20166.2</MicrosoftNetCompilersToolsetVersion>
+    <!-- <MicrosoftNetCompilersToolsetVersion>3.6.0-2.20166.2</MicrosoftNetCompilersToolsetVersion> -->
+    <MicrosoftNetCompilersToolsetVersion>3.7.0-2.20258.1</MicrosoftNetCompilersToolsetVersion>
     <!-- Blob storage container that has the "Latest" channel to publish to. -->
     <ContainerName>dotnet</ContainerName>
     <ChecksumContainerName>$(ContainerName)</ChecksumContainerName>

diff --git a/src/libraries/Common/src/System/Collections/Generic/BidirectionalDictionary.cs b/src/libraries/Common/src/System/Collections/Generic/BidirectionalDictionary.cs
@@ -4,6 +4,7 @@
 
 #nullable enable
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.Collections.Generic
 {
@@ -36,12 +37,12 @@ public void Add(T1 item1, T2 item2)
             _backward.Add(item2, item1);
         }
 
-        public bool TryGetForward(T1 item1, out T2 item2)
+        public bool TryGetForward(T1 item1, [MaybeNullWhen(false)] out T2 item2)
         {
             return _forward.TryGetValue(item1, out item2);
         }
 
-        public bool TryGetBackward(T2 item2, out T1 item1)
+        public bool TryGetBackward(T2 item2, [MaybeNullWhen(false)] out T1 item1)
         {
             return _backward.TryGetValue(item2, out item1);
         }

diff --git a/src/libraries/System.Collections.Concurrent/ref/System.Collections.Concurrent.cs b/src/libraries/System.Collections.Concurrent/ref/System.Collections.Concurrent.cs
@@ -113,7 +113,7 @@ public void Clear() { }
         void System.Collections.Generic.IDictionary<TKey, TValue>.Add(TKey key, TValue value) { }
         bool System.Collections.Generic.IDictionary<TKey, TValue>.Remove(TKey key) { throw null; }
         void System.Collections.ICollection.CopyTo(System.Array array, int index) { }
-        void System.Collections.IDictionary.Add(object key, object value) { }
+        void System.Collections.IDictionary.Add(object key, object? value) { }
         bool System.Collections.IDictionary.Contains(object key) { throw null; }
         System.Collections.IDictionaryEnumerator System.Collections.IDictionary.GetEnumerator() { throw null; }
         void System.Collections.IDictionary.Remove(object key) { }

diff --git a/...ies/System.Collections.Concurrent/src/System/Collections/Concurrent/BlockingCollection.cs b/...ies/System.Collections.Concurrent/src/System/Collections/Concurrent/BlockingCollection.cs
@@ -755,7 +755,16 @@ private bool TryTakeWithNoTimeValidation([MaybeNullWhen(false)] out T item, int
                     }
                 }
             }
+
+            if (waitForSemaphoreWasSuccessful)
+            {
+                Debug.Assert(item != null);
+            }
+
+#pragma warning disable CS8762
+            // Compiler can't automatically deduce 'item' has a non-null value when returning false.
             return waitForSemaphoreWasSuccessful;
+#pragma warning restore CS8762
         }
 
 

diff --git a/...ibraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentBag.cs b/...ibraries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentBag.cs
@@ -170,7 +170,7 @@ private WorkStealingQueue CreateWorkStealingQueueForCurrentThread()
         /// <param name="result">To receive the item retrieved from the bag</param>
         /// <param name="take">Whether to remove or peek.</param>
         /// <returns>True if succeeded, false otherwise.</returns>
-        private bool TrySteal(out T result, bool take)
+        private bool TrySteal([MaybeNullWhen(false)] out T result, bool take)
         {
             if (CDSCollectionETWBCLProvider.Log.IsEnabled())
             {
@@ -219,7 +219,11 @@ private bool TrySteal(out T result, bool take)
                     (TryStealFromTo(localQueue._nextQueue, null, out result, take) || TryStealFromTo(_workStealingQueues, localQueue, out result, take));
                 if (gotItem)
                 {
+#pragma warning disable CS8762
+                    // Compiler can't automatically deduce that 'result' is set to a valid value
+                    // (which may be null if T allows it) at this exit point.
                     return true;
+#pragma warning restore CS8762
                 }
 
                 if (Interlocked.Read(ref _emptyToNonEmptyListTransitionCount) == initialEmptyToNonEmptyCounts)
@@ -248,7 +252,7 @@ private bool TryStealFromTo(WorkStealingQueue? startInclusive, WorkStealingQueue
                 }
             }
 
-            result = default(T)!;
+            result = default(T);
             return false;
         }
 
@@ -870,7 +874,7 @@ internal bool TryLocalPop([MaybeNullWhen(false)] out T result)
                 int tail = _tailIndex;
                 if (_headIndex - tail >= 0)
                 {
-                    result = default(T)!;
+                    result = default(T);
                     return false;
                 }
 
@@ -914,7 +918,7 @@ internal bool TryLocalPop([MaybeNullWhen(false)] out T result)
                         {
                             // We encountered a race condition and the element was stolen, restore the tail.
                             _tailIndex = tail + 1;
-                            result = default(T)!;
+                            result = default(T);
                             return false;
                         }
                     }
@@ -958,7 +962,7 @@ internal bool TryLocalPeek([MaybeNullWhen(false)] out T result)
                     }
                 }
 
-                result = default(T)!;
+                result = default(T);
                 return false;
             }
 
@@ -1015,7 +1019,7 @@ internal bool TrySteal([MaybeNullWhen(false)] out T result, bool take)
                 }
 
                 // The queue was empty.
-                result = default(T)!;
+                result = default(T);
                 return false;
             }
 

diff --git a/...raries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentStack.cs b/...raries/System.Collections.Concurrent/src/System/Collections/Concurrent/ConcurrentStack.cs
@@ -692,7 +692,7 @@ private static void CopyRemovedItems(Node head, T[] collection, int startIndex,
         /// <remarks>For <see cref="ConcurrentStack{T}"/>, this operation will attempt to pope the object at
         /// the top of the <see cref="ConcurrentStack{T}"/>.
         /// </remarks>
-        bool IProducerConsumerCollection<T>.TryTake(out T item)
+        bool IProducerConsumerCollection<T>.TryTake([MaybeNullWhen(false)] out T item)
         {
             return TryPop(out item);
         }

diff --git a/src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.cs b/src/libraries/System.Collections.Immutable/ref/System.Collections.Immutable.cs
@@ -702,7 +702,7 @@ public void Sort(int index, int count, System.Collections.Generic.IComparer<T>?
             System.Collections.Generic.IEnumerator<T> System.Collections.Generic.IEnumerable<T>.GetEnumerator() { throw null; }
             void System.Collections.ICollection.CopyTo(System.Array array, int arrayIndex) { }
             System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
-            int System.Collections.IList.Add(object value) { throw null; }
+            int System.Collections.IList.Add(object? value) { throw null; }
             void System.Collections.IList.Clear() { }
             bool System.Collections.IList.Contains(object? value) { throw null; }
             int System.Collections.IList.IndexOf(object? value) { throw null; }
@@ -819,7 +819,7 @@ void System.Collections.Generic.IDictionary<TKey,TValue>.Add(TKey key, TValue va
         bool System.Collections.Generic.IDictionary<TKey,TValue>.Remove(TKey key) { throw null; }
         System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<TKey, TValue>> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>>.GetEnumerator() { throw null; }
         void System.Collections.ICollection.CopyTo(System.Array array, int index) { }
-        void System.Collections.IDictionary.Add(object key, object value) { }
+        void System.Collections.IDictionary.Add(object key, object? value) { }
         void System.Collections.IDictionary.Clear() { }
         bool System.Collections.IDictionary.Contains(object key) { throw null; }
         System.Collections.IDictionaryEnumerator System.Collections.IDictionary.GetEnumerator() { throw null; }

diff --git a/src/libraries/System.Collections.Specialized/ref/System.Collections.Specialized.cs b/src/libraries/System.Collections.Specialized/ref/System.Collections.Specialized.cs
@@ -189,7 +189,7 @@ protected virtual void OnDeserialization(object? sender) { }
         public void Remove(object key) { }
         public void RemoveAt(int index) { }
         System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
-        void System.Runtime.Serialization.IDeserializationCallback.OnDeserialization(object sender) { }
+        void System.Runtime.Serialization.IDeserializationCallback.OnDeserialization(object? sender) { }
     }
     public partial class StringCollection : System.Collections.ICollection, System.Collections.IEnumerable, System.Collections.IList
     {

diff --git a/src/libraries/System.Collections/ref/System.Collections.cs b/src/libraries/System.Collections/ref/System.Collections.cs
@@ -56,7 +56,7 @@ protected Comparer() { }
         public static System.Collections.Generic.Comparer<T> Default { get { throw null; } }
         public abstract int Compare([System.Diagnostics.CodeAnalysis.AllowNullAttribute] T x, [System.Diagnostics.CodeAnalysis.AllowNullAttribute] T y);
         public static System.Collections.Generic.Comparer<T> Create(System.Comparison<T> comparison) { throw null; }
-        int System.Collections.IComparer.Compare(object x, object y) { throw null; }
+        int System.Collections.IComparer.Compare(object? x, object? y) { throw null; }
     }
     public partial class Dictionary<TKey, TValue> : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>, System.Collections.Generic.IDictionary<TKey, TValue>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TValue>>, System.Collections.Generic.IReadOnlyCollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>, System.Collections.Generic.IReadOnlyDictionary<TKey, TValue>, System.Collections.ICollection, System.Collections.IDictionary, System.Collections.IEnumerable, System.Runtime.Serialization.IDeserializationCallback, System.Runtime.Serialization.ISerializable where TKey : notnull
     {
@@ -102,7 +102,7 @@ public virtual void OnDeserialization(object? sender) { }
         bool System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>.Remove(System.Collections.Generic.KeyValuePair<TKey, TValue> keyValuePair) { throw null; }
         System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<TKey, TValue>> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TValue>>.GetEnumerator() { throw null; }
         void System.Collections.ICollection.CopyTo(System.Array array, int index) { }
-        void System.Collections.IDictionary.Add(object key, object value) { }
+        void System.Collections.IDictionary.Add(object key, object? value) { }
         bool System.Collections.IDictionary.Contains(object key) { throw null; }
         System.Collections.IDictionaryEnumerator System.Collections.IDictionary.GetEnumerator() { throw null; }
         void System.Collections.IDictionary.Remove(object key) { }
@@ -187,7 +187,7 @@ protected EqualityComparer() { }
         public static System.Collections.Generic.EqualityComparer<T> Default { get { throw null; } }
         public abstract bool Equals([System.Diagnostics.CodeAnalysis.AllowNullAttribute] T x, [System.Diagnostics.CodeAnalysis.AllowNullAttribute] T y);
         public abstract int GetHashCode([System.Diagnostics.CodeAnalysis.DisallowNullAttribute] T obj);
-        bool System.Collections.IEqualityComparer.Equals(object x, object y) { throw null; }
+        bool System.Collections.IEqualityComparer.Equals(object? x, object? y) { throw null; }
         int System.Collections.IEqualityComparer.GetHashCode(object obj) { throw null; }
     }
     public partial class HashSet<T> : System.Collections.Generic.ICollection<T>, System.Collections.Generic.IEnumerable<T>, System.Collections.Generic.IReadOnlyCollection<T>, System.Collections.Generic.ISet<T>, System.Collections.Generic.IReadOnlySet<T>, System.Collections.IEnumerable, System.Runtime.Serialization.IDeserializationCallback, System.Runtime.Serialization.ISerializable
@@ -295,7 +295,7 @@ public partial struct Enumerator : System.Collections.Generic.IEnumerator<T>, Sy
             public void Dispose() { }
             public bool MoveNext() { throw null; }
             void System.Collections.IEnumerator.Reset() { }
-            void System.Runtime.Serialization.IDeserializationCallback.OnDeserialization(object sender) { }
+            void System.Runtime.Serialization.IDeserializationCallback.OnDeserialization(object? sender) { }
             void System.Runtime.Serialization.ISerializable.GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
         }
     }
@@ -361,11 +361,11 @@ public void Sort(int index, int count, System.Collections.Generic.IComparer<T>?
         System.Collections.Generic.IEnumerator<T> System.Collections.Generic.IEnumerable<T>.GetEnumerator() { throw null; }
         void System.Collections.ICollection.CopyTo(System.Array array, int arrayIndex) { }
         System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
-        int System.Collections.IList.Add(object item) { throw null; }
-        bool System.Collections.IList.Contains(object item) { throw null; }
-        int System.Collections.IList.IndexOf(object item) { throw null; }
-        void System.Collections.IList.Insert(int index, object item) { }
-        void System.Collections.IList.Remove(object item) { }
+        int System.Collections.IList.Add(object? item) { throw null; }
+        bool System.Collections.IList.Contains(object? item) { throw null; }
+        int System.Collections.IList.IndexOf(object? item) { throw null; }
+        void System.Collections.IList.Insert(int index, object? item) { }
+        void System.Collections.IList.Remove(object? item) { }
         public T[] ToArray() { throw null; }
         public void TrimExcess() { }
         public bool TrueForAll(System.Predicate<T> match) { throw null; }
@@ -457,7 +457,7 @@ public void CopyTo(System.Collections.Generic.KeyValuePair<TKey, TValue>[] array
         bool System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>.Remove(System.Collections.Generic.KeyValuePair<TKey, TValue> keyValuePair) { throw null; }
         System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<TKey, TValue>> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TValue>>.GetEnumerator() { throw null; }
         void System.Collections.ICollection.CopyTo(System.Array array, int index) { }
-        void System.Collections.IDictionary.Add(object key, object value) { }
+        void System.Collections.IDictionary.Add(object key, object? value) { }
         bool System.Collections.IDictionary.Contains(object key) { throw null; }
         System.Collections.IDictionaryEnumerator System.Collections.IDictionary.GetEnumerator() { throw null; }
         void System.Collections.IDictionary.Remove(object key) { }
@@ -572,7 +572,7 @@ public void RemoveAt(int index) { }
         bool System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey, TValue>>.Remove(System.Collections.Generic.KeyValuePair<TKey, TValue> keyValuePair) { throw null; }
         System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<TKey, TValue>> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey, TValue>>.GetEnumerator() { throw null; }
         void System.Collections.ICollection.CopyTo(System.Array array, int arrayIndex) { }
-        void System.Collections.IDictionary.Add(object key, object value) { }
+        void System.Collections.IDictionary.Add(object key, object? value) { }
         bool System.Collections.IDictionary.Contains(object key) { throw null; }
         System.Collections.IDictionaryEnumerator System.Collections.IDictionary.GetEnumerator() { throw null; }
         void System.Collections.IDictionary.Remove(object key) { }
@@ -624,7 +624,7 @@ void System.Collections.Generic.ICollection<T>.Add(T item) { }
         System.Collections.Generic.IEnumerator<T> System.Collections.Generic.IEnumerable<T>.GetEnumerator() { throw null; }
         void System.Collections.ICollection.CopyTo(System.Array array, int index) { }
         System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
-        void System.Runtime.Serialization.IDeserializationCallback.OnDeserialization(object sender) { }
+        void System.Runtime.Serialization.IDeserializationCallback.OnDeserialization(object? sender) { }
         void System.Runtime.Serialization.ISerializable.GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
         public bool TryGetValue(T equalValue, [System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out T actualValue) { throw null; }
         public void UnionWith(System.Collections.Generic.IEnumerable<T> other) { }
@@ -637,7 +637,7 @@ public partial struct Enumerator : System.Collections.Generic.IEnumerator<T>, Sy
             public void Dispose() { }
             public bool MoveNext() { throw null; }
             void System.Collections.IEnumerator.Reset() { }
-            void System.Runtime.Serialization.IDeserializationCallback.OnDeserialization(object sender) { }
+            void System.Runtime.Serialization.IDeserializationCallback.OnDeserialization(object? sender) { }
             void System.Runtime.Serialization.ISerializable.GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
         }
     }

diff --git a/src/libraries/System.Diagnostics.TraceSource/ref/System.Diagnostics.TraceSource.cs b/src/libraries/System.Diagnostics.TraceSource/ref/System.Diagnostics.TraceSource.cs
@@ -263,10 +263,10 @@ public void Remove(System.Diagnostics.TraceListener? listener) { }
         public void Remove(string name) { }
         public void RemoveAt(int index) { }
         void System.Collections.ICollection.CopyTo(System.Array array, int index) { }
-        int System.Collections.IList.Add(object value) { throw null; }
+        int System.Collections.IList.Add(object? value) { throw null; }
         bool System.Collections.IList.Contains(object? value) { throw null; }
         int System.Collections.IList.IndexOf(object? value) { throw null; }
-        void System.Collections.IList.Insert(int index, object value) { }
+        void System.Collections.IList.Insert(int index, object? value) { }
         void System.Collections.IList.Remove(object? value) { }
     }
     [System.FlagsAttribute]