Merge pull request #26010 from VSadov/useNewFeatures

Use 7.2 language features in Roslyn

build/Targets/Packages.props

@@ -55,7 +55,7 @@
     <MicrosoftMSXMLVersion>8.0.0.0-alpha</MicrosoftMSXMLVersion>
     <!-- Using a private build of Microsoft.Net.Test.SDK to work around issue https://github.com/Microsoft/vstest/issues/373 -->
     <MicrosoftNETTestSdkVersion>15.6.0-dev</MicrosoftNETTestSdkVersion>
-    <MicrosoftNetCompilersVersion>2.6.1</MicrosoftNetCompilersVersion>
+    <MicrosoftNetCompilersVersion>2.7.0</MicrosoftNetCompilersVersion>
     <MicrosoftNetRoslynDiagnosticsVersion>2.6.1-beta1-62702-01</MicrosoftNetRoslynDiagnosticsVersion>
     <MicrosoftNetCoreILAsmVersion>2.0.0</MicrosoftNetCoreILAsmVersion>
     <MicrosoftNETCoreCompilersVersion>2.8.0-beta2-62712-07</MicrosoftNETCoreCompilersVersion>

src/Compilers/CSharp/Portable/Parser/BlendedNode.cs

@@ -6,7 +6,7 @@
 
 namespace Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax
 {
-    internal struct BlendedNode
+    internal readonly struct BlendedNode
     {
         internal readonly CSharp.CSharpSyntaxNode Node;
         internal readonly SyntaxToken Token;

src/Compilers/CSharp/Portable/Parser/Blender.cs

@@ -11,7 +11,7 @@
 
 namespace Microsoft.CodeAnalysis.CSharp.Syntax.InternalSyntax
 {
-    internal partial struct Blender
+    internal readonly partial struct Blender
     {
         private readonly Lexer _lexer;
         private readonly Cursor _oldTreeCursor;

src/Compilers/CSharp/Portable/Parser/SyntaxParser.cs

@@ -333,7 +333,7 @@ private void AddNewToken()
         }
 
         // adds token to end of current token array
-        private void AddToken(BlendedNode tokenResult)
+        private void AddToken(in BlendedNode tokenResult)
         {
             Debug.Assert(tokenResult.Token != null);
             if (_tokenCount >= _blendedTokens.Length)

src/Compilers/Core/Portable/Diagnostic/SourceLocation.cs

@@ -26,17 +26,17 @@ public SourceLocation(SyntaxNode node)
         {
         }
 
-        public SourceLocation(SyntaxToken token)
+        public SourceLocation(in SyntaxToken token)
             : this(token.SyntaxTree, token.Span)
         {
         }
 
-        public SourceLocation(SyntaxNodeOrToken nodeOrToken)
+        public SourceLocation(in SyntaxNodeOrToken nodeOrToken)
             : this(nodeOrToken.SyntaxTree, nodeOrToken.Span)
         {
         }
 
-        public SourceLocation(SyntaxTrivia trivia)
+        public SourceLocation(in SyntaxTrivia trivia)
             : this(trivia.SyntaxTree, trivia.Span)
         {
         }

src/Compilers/Core/Portable/InternalUtilities/EnumField.cs

@@ -8,7 +8,7 @@
 namespace Roslyn.Utilities
 {
     [DebuggerDisplay("{GetDebuggerDisplay(), nq}")]
-    internal struct EnumField
+    internal readonly struct EnumField
     {
         public static readonly IComparer<EnumField> Comparer = new EnumFieldComparer();
 

src/Compilers/Core/Portable/InternalUtilities/TextKeyedCache.cs

@@ -15,26 +15,6 @@ namespace Roslyn.Utilities
 {
     internal class TextKeyedCache<T> where T : class
     {
-        // entry in the local cache
-        private struct LocalEntry
-        {
-            // full text of the item
-            public string Text;
-
-            // hash code of the entry
-            public int HashCode;
-
-            // item
-            public T Item;
-        }
-
-        // entry in the shared cache
-        private struct SharedEntry
-        {
-            public int HashCode;
-            public SharedEntryValue Entry;
-        }
-
         // immutable tuple - text and corresponding item
         // reference type because we want atomic assignments
         private class SharedEntryValue
@@ -71,17 +51,17 @@ public SharedEntryValue(string Text, T item)
         // local cache
         // simple fast and not threadsafe cache 
         // with limited size and "last add wins" expiration policy
-        private readonly LocalEntry[] _localTable = new LocalEntry[LocalSize];
+        private readonly (string Text, int HashCode, T Item)[] _localTable = new(string Text, int HashCode, T Item)[LocalSize];
 
         // shared threadsafe cache
         // slightly slower than local cache
         // we read this cache when having a miss in local cache
         // writes to local cache will update shared cache as well.
-        private static readonly SharedEntry[] s_sharedTable = new SharedEntry[SharedSize];
+        private static readonly (int HashCode, SharedEntryValue Entry)[] s_sharedTable = new(int HashCode, SharedEntryValue Entry)[SharedSize];
 
         // store a reference to shared cache locally
         // accessing a static field of a generic type could be nontrivial
-        private readonly SharedEntry[] _sharedTableInst = s_sharedTable;
+        private readonly (int HashCode, SharedEntryValue Entry)[] _sharedTableInst = s_sharedTable;
 
         private readonly StringTable _strings;
 
@@ -131,31 +111,27 @@ public void Free()
 
         internal T FindItem(char[] chars, int start, int len, int hashCode)
         {
-            // capture array to avoid extra range checks
-            var arr = _localTable;
-            var idx = LocalIdxFromHash(hashCode);
+            // get direct element reference to avoid extra range checks
+            ref var localSlot = ref _localTable[LocalIdxFromHash(hashCode)];
 
-            var text = arr[idx].Text;
+            var text = localSlot.Text;
 
-            if (text != null && arr[idx].HashCode == hashCode)
+            if (text != null && localSlot.HashCode == hashCode)
             {
                 if (StringTable.TextEquals(text, chars, start, len))
                 {
-                    return arr[idx].Item;
+                    return localSlot.Item;
                 }
             }
 
             SharedEntryValue e = FindSharedEntry(chars, start, len, hashCode);
             if (e != null)
             {
-                // PERF: the following code does element-wise assignment of a struct
-                //       because current JIT produces better code compared to
-                //       arr[idx] = new LocalEntry(...)
-                arr[idx].HashCode = hashCode;
-                arr[idx].Text = e.Text;
+                localSlot.HashCode = hashCode;
+                localSlot.Text = e.Text;
 
                 var tk = e.Item;
-                arr[idx].Item = tk;
+                localSlot.Item = tk;
 
                 return tk;
             }
@@ -169,12 +145,13 @@ private SharedEntryValue FindSharedEntry(char[] chars, int start, int len, int h
             int idx = SharedIdxFromHash(hashCode);
 
             SharedEntryValue e = null;
+            int hash;
+
             // we use quadratic probing here
             // bucket positions are (n^2 + n)/2 relative to the masked hashcode
             for (int i = 1; i < SharedBucketSize + 1; i++)
             {
-                e = arr[idx].Entry;
-                int hash = arr[idx].HashCode;
+                (hash, e) = arr[idx];
 
                 if (e != null)
                 {
@@ -207,11 +184,10 @@ internal void AddItem(char[] chars, int start, int len, int hashCode, T item)
             AddSharedEntry(hashCode, e);
 
             // add to the local table too
-            var arr = _localTable;
-            var idx = LocalIdxFromHash(hashCode);
-            arr[idx].HashCode = hashCode;
-            arr[idx].Text = text;
-            arr[idx].Item = item;
+            ref var localSlot = ref _localTable[LocalIdxFromHash(hashCode)];
+            localSlot.HashCode = hashCode;
+            localSlot.Text = text;
+            localSlot.Item = item;
         }
 
         private void AddSharedEntry(int hashCode, SharedEntryValue e)

src/Compilers/Core/Portable/Optional.cs

@@ -9,7 +9,7 @@ namespace Microsoft.CodeAnalysis
     /// indicating whether or not that value is meaningful.
     /// </summary>
     /// <typeparam name="T">The type of the value.</typeparam>
-    public struct Optional<T>
+    public readonly struct Optional<T>
     {
         private readonly bool _hasValue;
         private readonly T _value;

src/Compilers/Core/Portable/PublicAPI.Shipped.txt

@@ -2210,7 +2210,6 @@ Microsoft.CodeAnalysis.SyntaxTokenList.Reverse() -> Microsoft.CodeAnalysis.Synta
 Microsoft.CodeAnalysis.SyntaxTokenList.Reversed
 Microsoft.CodeAnalysis.SyntaxTokenList.Reversed.Enumerator
 Microsoft.CodeAnalysis.SyntaxTokenList.Reversed.Enumerator.Current.get -> Microsoft.CodeAnalysis.SyntaxToken
-Microsoft.CodeAnalysis.SyntaxTokenList.Reversed.Enumerator.Enumerator(ref Microsoft.CodeAnalysis.SyntaxTokenList list) -> void
 Microsoft.CodeAnalysis.SyntaxTokenList.Reversed.Enumerator.MoveNext() -> bool
 Microsoft.CodeAnalysis.SyntaxTokenList.Reversed.Equals(Microsoft.CodeAnalysis.SyntaxTokenList.Reversed other) -> bool
 Microsoft.CodeAnalysis.SyntaxTokenList.Reversed.GetEnumerator() -> Microsoft.CodeAnalysis.SyntaxTokenList.Reversed.Enumerator
@@ -2282,7 +2281,6 @@ Microsoft.CodeAnalysis.SyntaxTriviaList.Reverse() -> Microsoft.CodeAnalysis.Synt
 Microsoft.CodeAnalysis.SyntaxTriviaList.Reversed
 Microsoft.CodeAnalysis.SyntaxTriviaList.Reversed.Enumerator
 Microsoft.CodeAnalysis.SyntaxTriviaList.Reversed.Enumerator.Current.get -> Microsoft.CodeAnalysis.SyntaxTrivia
-Microsoft.CodeAnalysis.SyntaxTriviaList.Reversed.Enumerator.Enumerator(ref Microsoft.CodeAnalysis.SyntaxTriviaList list) -> void
 Microsoft.CodeAnalysis.SyntaxTriviaList.Reversed.Enumerator.MoveNext() -> bool
 Microsoft.CodeAnalysis.SyntaxTriviaList.Reversed.Equals(Microsoft.CodeAnalysis.SyntaxTriviaList.Reversed other) -> bool
 Microsoft.CodeAnalysis.SyntaxTriviaList.Reversed.GetEnumerator() -> Microsoft.CodeAnalysis.SyntaxTriviaList.Reversed.Enumerator

src/Compilers/Core/Portable/Syntax/ChildSyntaxList.Enumerator.cs

@@ -62,10 +62,11 @@ public void Reset()
                 _childIndex = -1;
             }
 
-            internal bool TryMoveNextAndGetCurrent(ref SyntaxNodeOrToken current)
+            internal bool TryMoveNextAndGetCurrent(out SyntaxNodeOrToken current)
             {
                 if (!MoveNext())
                 {
+                    current = default;
                     return false;
                 }
 

src/Compilers/Core/Portable/Syntax/ChildSyntaxList.Reversed.cs

@@ -11,9 +11,9 @@
 
 namespace Microsoft.CodeAnalysis
 {
-    public partial struct ChildSyntaxList
+    public readonly partial struct ChildSyntaxList
     {
-        public partial struct Reversed : IEnumerable<SyntaxNodeOrToken>, IEquatable<Reversed>
+        public readonly partial struct Reversed : IEnumerable<SyntaxNodeOrToken>, IEquatable<Reversed>
         {
             private readonly SyntaxNode _node;
             private readonly int _count;

src/Compilers/Core/Portable/Syntax/ChildSyntaxList.cs

@@ -10,7 +10,7 @@
 
 namespace Microsoft.CodeAnalysis
 {
-    public partial struct ChildSyntaxList : IEquatable<ChildSyntaxList>, IReadOnlyList<SyntaxNodeOrToken>
+    public readonly partial struct ChildSyntaxList : IEquatable<ChildSyntaxList>, IReadOnlyList<SyntaxNodeOrToken>
     {
         private readonly SyntaxNode _node;
         private readonly int _count;

src/Compilers/Core/Portable/Syntax/InternalSyntax/SeparatedSyntaxList.cs

@@ -73,12 +73,12 @@ public SyntaxList<GreenNode> GetWithSeparators()
             return _list;
         }
 
-        public static bool operator ==(SeparatedSyntaxList<TNode> left, SeparatedSyntaxList<TNode> right)
+        public static bool operator ==(in SeparatedSyntaxList<TNode> left, in SeparatedSyntaxList<TNode> right)
         {
             return left.Equals(right);
         }
 
-        public static bool operator !=(SeparatedSyntaxList<TNode> left, SeparatedSyntaxList<TNode> right)
+        public static bool operator !=(in SeparatedSyntaxList<TNode> left, in SeparatedSyntaxList<TNode> right)
         {
             return !left.Equals(right);
         }

src/Compilers/Core/Portable/Syntax/InternalSyntax/SeparatedSyntaxListBuilder.cs

@@ -78,12 +78,12 @@ public void AddRange(TNode[] items, int offset, int length)
             _builder.AddRange(items, offset, length);
         }
 
-        public void AddRange(SeparatedSyntaxList<TNode> nodes)
+        public void AddRange(in SeparatedSyntaxList<TNode> nodes)
         {
             _builder.AddRange(nodes.GetWithSeparators());
         }
 
-        public void AddRange(SeparatedSyntaxList<TNode> nodes, int count)
+        public void AddRange(in SeparatedSyntaxList<TNode> nodes, int count)
         {
             var list = nodes.GetWithSeparators();
             this._builder.AddRange(list, this.Count, Math.Min(count * 2, list.Count));
@@ -115,12 +115,12 @@ internal SyntaxListBuilder UnderlyingBuilder
             get { return _builder; }
         }
 
-        public static implicit operator SeparatedSyntaxList<TNode>(SeparatedSyntaxListBuilder<TNode> builder)
+        public static implicit operator SeparatedSyntaxList<TNode>(in SeparatedSyntaxListBuilder<TNode> builder)
         {
             return builder.ToList();
         }
 
-        public static implicit operator SyntaxListBuilder(SeparatedSyntaxListBuilder<TNode> builder)
+        public static implicit operator SyntaxListBuilder(in SeparatedSyntaxListBuilder<TNode> builder)
         {
             return builder._builder;
         }

src/Compilers/Core/Portable/Syntax/InternalSyntax/SyntaxListPool.cs

@@ -50,7 +50,7 @@ internal SyntaxListBuilder Allocate()
             return new SeparatedSyntaxListBuilder<TNode>(this.Allocate());
         }
 
-        internal void Free<TNode>(SeparatedSyntaxListBuilder<TNode> item) where TNode : GreenNode
+        internal void Free<TNode>(in SeparatedSyntaxListBuilder<TNode> item) where TNode : GreenNode
         {
             Free(item.UnderlyingBuilder);
         }

src/Compilers/Core/Portable/Syntax/SeparatedSyntaxList.Enumerator.cs

@@ -18,7 +18,7 @@ public struct Enumerator
             private readonly SeparatedSyntaxList<TNode> _list;
             private int _index;
 
-            internal Enumerator(SeparatedSyntaxList<TNode> list)
+            internal Enumerator(in SeparatedSyntaxList<TNode> list)
             {
                 _list = list;
                 _index = -1;
@@ -65,9 +65,9 @@ private class EnumeratorImpl : IEnumerator<TNode>
         {
             private Enumerator _e;
 
-            internal EnumeratorImpl(SeparatedSyntaxList<TNode> list)
+            internal EnumeratorImpl(in SeparatedSyntaxList<TNode> list)
             {
-                _e = new Enumerator(list);
+                _e = new Enumerator(in list);
             }
 
             public TNode Current

src/Compilers/Core/Portable/Syntax/SeparatedSyntaxList.cs

@@ -10,7 +10,7 @@
 
 namespace Microsoft.CodeAnalysis
 {
-    public partial struct SeparatedSyntaxList<TNode> : IEquatable<SeparatedSyntaxList<TNode>>, IReadOnlyList<TNode> where TNode : SyntaxNode
+    public readonly partial struct SeparatedSyntaxList<TNode> : IEquatable<SeparatedSyntaxList<TNode>>, IReadOnlyList<TNode> where TNode : SyntaxNode
     {
         private readonly SyntaxNodeOrTokenList _list;
         private readonly int _count;
@@ -414,7 +414,7 @@ public SeparatedSyntaxList<TNode> InsertRange(int index, IEnumerable<TNode> node
             return new SeparatedSyntaxList<TNode>(nodesWithSeps.InsertRange(insertionIndex, nodesToInsertWithSeparators));
         }
 
-        private static bool KeepSeparatorWithPreviousNode(SyntaxToken separator)
+        private static bool KeepSeparatorWithPreviousNode(in SyntaxToken separator)
         {
             // if the trivia after the separator contains an explicit end of line or a single line comment
             // then it should stay associated with previous node

src/Compilers/Core/Portable/Syntax/SeparatedSyntaxListBuilder.cs

@@ -70,7 +70,7 @@ public SeparatedSyntaxListBuilder<TNode> Add(TNode node)
             return this;
         }
 
-        public SeparatedSyntaxListBuilder<TNode> AddSeparator(SyntaxToken separatorToken)
+        public SeparatedSyntaxListBuilder<TNode> AddSeparator(in SyntaxToken separatorToken)
         {
             CheckExpectedSeparator();
             _expectedSeparator = false;
@@ -78,7 +78,7 @@ public SeparatedSyntaxListBuilder<TNode> AddSeparator(SyntaxToken separatorToken
             return this;
         }
 
-        public SeparatedSyntaxListBuilder<TNode> AddRange(SeparatedSyntaxList<TNode> nodes)
+        public SeparatedSyntaxListBuilder<TNode> AddRange(in SeparatedSyntaxList<TNode> nodes)
         {
             CheckExpectedElement();
             SyntaxNodeOrTokenList list = nodes.GetWithSeparators();
@@ -87,7 +87,7 @@ public SeparatedSyntaxListBuilder<TNode> AddRange(SeparatedSyntaxList<TNode> nod
             return this;
         }
 
-        public SeparatedSyntaxListBuilder<TNode> AddRange(SeparatedSyntaxList<TNode> nodes, int count)
+        public SeparatedSyntaxListBuilder<TNode> AddRange(in SeparatedSyntaxList<TNode> nodes, int count)
         {
             CheckExpectedElement();
             SyntaxNodeOrTokenList list = nodes.GetWithSeparators();
@@ -116,12 +116,12 @@ public SeparatedSyntaxList<TNode> ToList()
             return _builder.ToSeparatedList<TDerived>();
         }
 
-        public static implicit operator SyntaxListBuilder(SeparatedSyntaxListBuilder<TNode> builder)
+        public static implicit operator SyntaxListBuilder(in SeparatedSyntaxListBuilder<TNode> builder)
         {
             return builder._builder;
         }
 
-        public static implicit operator SeparatedSyntaxList<TNode>(SeparatedSyntaxListBuilder<TNode> builder)
+        public static implicit operator SeparatedSyntaxList<TNode>(in SeparatedSyntaxListBuilder<TNode> builder)
         {
             if (builder._builder != null)
             {

src/Compilers/Core/Portable/Syntax/SyntaxDiffer.cs

@@ -336,7 +336,7 @@ private static void ReplaceFirstWithChildren(Stack<SyntaxNodeOrToken> stack)
             }
         }
 
-        private void FindBestMatch(Stack<SyntaxNodeOrToken> stack, SyntaxNodeOrToken node, out int index, out int similarity, int startIndex = 0)
+        private void FindBestMatch(Stack<SyntaxNodeOrToken> stack, in SyntaxNodeOrToken node, out int index, out int similarity, int startIndex = 0)
         {
             index = -1;
             similarity = -1;
@@ -419,7 +419,7 @@ private void FindBestMatch(Stack<SyntaxNodeOrToken> stack, SyntaxNodeOrToken nod
             }
         }
 
-        private int GetSimilarity(SyntaxNodeOrToken node1, SyntaxNodeOrToken node2)
+        private int GetSimilarity(in SyntaxNodeOrToken node1, in SyntaxNodeOrToken node2)
         {
             // count the characters in the common/identical nodes
             int w = 0;
@@ -495,12 +495,12 @@ private int GetSimilarity(SyntaxNodeOrToken node1, SyntaxNodeOrToken node2)
             return w;
         }
 
-        private static bool AreIdentical(SyntaxNodeOrToken node1, SyntaxNodeOrToken node2)
+        private static bool AreIdentical(in SyntaxNodeOrToken node1, in SyntaxNodeOrToken node2)
         {
             return node1.UnderlyingNode == node2.UnderlyingNode;
         }
 
-        private static bool AreSimilar(SyntaxNodeOrToken node1, SyntaxNodeOrToken node2)
+        private static bool AreSimilar(in SyntaxNodeOrToken node1, in SyntaxNodeOrToken node2)
         {
             return node1.RawKind == node2.RawKind;
         }
@@ -582,7 +582,7 @@ private void RecordChange(ChangeRecord change)
             _changes.Add(change);
         }
 
-        private void RecordChange(TextChangeRange textChangeRange, SyntaxNodeOrToken removedNode, SyntaxNodeOrToken insertedNode)
+        private void RecordChange(TextChangeRange textChangeRange, in SyntaxNodeOrToken removedNode, SyntaxNodeOrToken insertedNode)
         {
             if (_changes.Count > 0)
             {

src/Compilers/Core/Portable/Syntax/SyntaxList`1.Enumerator.cs

@@ -7,12 +7,12 @@
 
 namespace Microsoft.CodeAnalysis
 {
-    public partial struct SyntaxList<TNode>
+    public readonly partial struct SyntaxList<TNode>
     {
         [SuppressMessage("Performance", "CA1067", Justification = "Equality not actually implemented")]
         public struct Enumerator
         {
-            private SyntaxList<TNode> _list;
+            private readonly SyntaxList<TNode> _list;
             private int _index;
 
             internal Enumerator(SyntaxList<TNode> list)
@@ -61,7 +61,7 @@ private class EnumeratorImpl : IEnumerator<TNode>
         {
             private Enumerator _e;
 
-            internal EnumeratorImpl(SyntaxList<TNode> list)
+            internal EnumeratorImpl(in SyntaxList<TNode> list)
             {
                 _e = new Enumerator(list);
             }

src/Compilers/Core/Portable/Syntax/SyntaxList`1.cs

@@ -14,7 +14,7 @@ namespace Microsoft.CodeAnalysis
     /// <summary>
     /// A list of <see cref="SyntaxNode"/>.
     /// </summary>
-    public partial struct SyntaxList<TNode> : IReadOnlyList<TNode>, IEquatable<SyntaxList<TNode>>
+    public readonly partial struct SyntaxList<TNode> : IReadOnlyList<TNode>, IEquatable<SyntaxList<TNode>>
         where TNode : SyntaxNode
     {
         private readonly SyntaxNode _node;

src/Compilers/Core/Portable/Syntax/SyntaxNavigator.cs

@@ -57,32 +57,32 @@ private static bool Matches(Func<SyntaxToken, bool> predicate, SyntaxToken token
             return predicate == null || ReferenceEquals(predicate, SyntaxToken.Any) || predicate(token);
         }
 
-        internal SyntaxToken GetFirstToken(SyntaxNode current, bool includeZeroWidth, bool includeSkipped, bool includeDirectives, bool includeDocumentationComments)
+        internal SyntaxToken GetFirstToken(in SyntaxNode current, bool includeZeroWidth, bool includeSkipped, bool includeDirectives, bool includeDocumentationComments)
         {
             return GetFirstToken(current, GetPredicateFunction(includeZeroWidth), GetStepIntoFunction(includeSkipped, includeDirectives, includeDocumentationComments));
         }
 
-        internal SyntaxToken GetLastToken(SyntaxNode current, bool includeZeroWidth, bool includeSkipped, bool includeDirectives, bool includeDocumentationComments)
+        internal SyntaxToken GetLastToken(in SyntaxNode current, bool includeZeroWidth, bool includeSkipped, bool includeDirectives, bool includeDocumentationComments)
         {
             return GetLastToken(current, GetPredicateFunction(includeZeroWidth), GetStepIntoFunction(includeSkipped, includeDirectives, includeDocumentationComments));
         }
 
-        internal SyntaxToken GetPreviousToken(SyntaxToken current, bool includeZeroWidth, bool includeSkipped, bool includeDirectives, bool includeDocumentationComments)
+        internal SyntaxToken GetPreviousToken(in SyntaxToken current, bool includeZeroWidth, bool includeSkipped, bool includeDirectives, bool includeDocumentationComments)
         {
             return GetPreviousToken(current, GetPredicateFunction(includeZeroWidth), GetStepIntoFunction(includeSkipped, includeDirectives, includeDocumentationComments));
         }
 
-        internal SyntaxToken GetNextToken(SyntaxToken current, bool includeZeroWidth, bool includeSkipped, bool includeDirectives, bool includeDocumentationComments)
+        internal SyntaxToken GetNextToken(in SyntaxToken current, bool includeZeroWidth, bool includeSkipped, bool includeDirectives, bool includeDocumentationComments)
         {
             return GetNextToken(current, GetPredicateFunction(includeZeroWidth), GetStepIntoFunction(includeSkipped, includeDirectives, includeDocumentationComments));
         }
 
-        internal SyntaxToken GetPreviousToken(SyntaxToken current, Func<SyntaxToken, bool> predicate, Func<SyntaxTrivia, bool> stepInto)
+        internal SyntaxToken GetPreviousToken(in SyntaxToken current, Func<SyntaxToken, bool> predicate, Func<SyntaxTrivia, bool> stepInto)
         {
             return GetPreviousToken(current, predicate, stepInto != null, stepInto);
         }
 
-        internal SyntaxToken GetNextToken(SyntaxToken current, Func<SyntaxToken, bool> predicate, Func<SyntaxTrivia, bool> stepInto)
+        internal SyntaxToken GetNextToken(in SyntaxToken current, Func<SyntaxToken, bool> predicate, Func<SyntaxTrivia, bool> stepInto)
         {
             return GetNextToken(current, predicate, stepInto != null, stepInto);
         }
@@ -523,7 +523,7 @@ internal SyntaxToken GetLastToken(SyntaxNode current, Func<SyntaxToken, bool> pr
             return default(SyntaxToken);
         }
 
-        internal SyntaxToken GetNextToken(SyntaxToken current, Func<SyntaxToken, bool> predicate, bool searchInsideCurrentTokenTrailingTrivia, Func<SyntaxTrivia, bool> stepInto)
+        internal SyntaxToken GetNextToken(in SyntaxToken current, Func<SyntaxToken, bool> predicate, bool searchInsideCurrentTokenTrailingTrivia, Func<SyntaxTrivia, bool> stepInto)
         {
             Debug.Assert(searchInsideCurrentTokenTrailingTrivia == false || stepInto != null);
             if (current.Parent != null)
@@ -575,7 +575,7 @@ internal SyntaxToken GetNextToken(SyntaxToken current, Func<SyntaxToken, bool> p
             return default(SyntaxToken);
         }
 
-        internal SyntaxToken GetPreviousToken(SyntaxToken current, Func<SyntaxToken, bool> predicate, bool searchInsideCurrentTokenLeadingTrivia,
+        internal SyntaxToken GetPreviousToken(in SyntaxToken current, Func<SyntaxToken, bool> predicate, bool searchInsideCurrentTokenLeadingTrivia,
             Func<SyntaxTrivia, bool> stepInto)
         {
             Debug.Assert(searchInsideCurrentTokenLeadingTrivia == false || stepInto != null);

src/Compilers/Core/Portable/Syntax/SyntaxNode.Iterators.cs

@@ -32,7 +32,7 @@ private IEnumerable<SyntaxTrivia> DescendantTriviaImpl(TextSpan span, Func<Synta
                 : DescendantTriviaOnly(span, descendIntoChildren);
         }
 
-        private static bool IsInSpan(ref TextSpan span, TextSpan childSpan)
+        private static bool IsInSpan(in TextSpan span, TextSpan childSpan)
         {
             return span.OverlapsWith(childSpan)
                 // special case for zero-width tokens (OverlapsWith never returns true for these)
@@ -63,13 +63,11 @@ public ChildSyntaxListEnumeratorStack(SyntaxNode startingNode, Func<SyntaxNode,
 
             public bool IsNotEmpty { get { return _stackPtr >= 0; } }
 
-            public bool TryGetNextInSpan(ref /*readonly*/ TextSpan span, out SyntaxNodeOrToken value)
+            public bool TryGetNextInSpan(in TextSpan span, out SyntaxNodeOrToken value)
             {
-                value = default(SyntaxNodeOrToken);
-
-                while (_stack[_stackPtr].TryMoveNextAndGetCurrent(ref value))
+                while (_stack[_stackPtr].TryMoveNextAndGetCurrent(out value))
                 {
-                    if (IsInSpan(ref span, value.FullSpan))
+                    if (IsInSpan(in span, value.FullSpan))
                     {
                         return true;
                     }
@@ -79,12 +77,12 @@ public bool TryGetNextInSpan(ref /*readonly*/ TextSpan span, out SyntaxNodeOrTok
                 return false;
             }
 
-            public SyntaxNode TryGetNextAsNodeInSpan(ref /*readonly*/ TextSpan span)
+            public SyntaxNode TryGetNextAsNodeInSpan(in TextSpan span)
             {
                 SyntaxNode nodeValue;
                 while ((nodeValue = _stack[_stackPtr].TryMoveNextAndGetCurrentAsNode()) != null)
                 {
-                    if (IsInSpan(ref span, nodeValue.FullSpan))
+                    if (IsInSpan(in span, nodeValue.FullSpan))
                     {
                         return nodeValue;
                     }
@@ -133,9 +131,7 @@ private struct TriviaListEnumeratorStack : IDisposable
 
             public bool TryGetNext(out SyntaxTrivia value)
             {
-                value = default(SyntaxTrivia);
-
-                if (_stack[_stackPtr].TryMoveNextAndGetCurrent(ref value))
+                if (_stack[_stackPtr].TryMoveNextAndGetCurrent(out value))
                 {
                     return true;
                 }
@@ -144,16 +140,16 @@ public bool TryGetNext(out SyntaxTrivia value)
                 return false;
             }
 
-            public void PushLeadingTrivia(ref SyntaxToken token)
+            public void PushLeadingTrivia(in SyntaxToken token)
             {
                 Grow();
-                _stack[_stackPtr].InitializeFromLeadingTrivia(ref token);
+                _stack[_stackPtr].InitializeFromLeadingTrivia(in token);
             }
 
-            public void PushTrailingTrivia(ref SyntaxToken token)
+            public void PushTrailingTrivia(in SyntaxToken token)
             {
                 Grow();
-                _stack[_stackPtr].InitializeFromTrailingTrivia(ref token);
+                _stack[_stackPtr].InitializeFromTrailingTrivia(in token);
             }
 
             private void Grow()
@@ -216,9 +212,9 @@ public Which PeekNext()
                 return _discriminatorStack.Peek();
             }
 
-            public bool TryGetNextInSpan(ref TextSpan span, out SyntaxNodeOrToken value)
+            public bool TryGetNextInSpan(in TextSpan span, out SyntaxNodeOrToken value)
             {
-                if (_nodeStack.TryGetNextInSpan(ref span, out value))
+                if (_nodeStack.TryGetNextInSpan(in span, out value))
                 {
                     return true;
                 }
@@ -247,15 +243,15 @@ public void PushChildren(SyntaxNode node, Func<SyntaxNode, bool> descendIntoChil
                 }
             }
 
-            public void PushLeadingTrivia(ref SyntaxToken token)
+            public void PushLeadingTrivia(in SyntaxToken token)
             {
-                _triviaStack.PushLeadingTrivia(ref token);
+                _triviaStack.PushLeadingTrivia(in token);
                 _discriminatorStack.Push(Which.Trivia);
             }
 
-            public void PushTrailingTrivia(ref SyntaxToken token)
+            public void PushTrailingTrivia(in SyntaxToken token)
             {
-                _triviaStack.PushTrailingTrivia(ref token);
+                _triviaStack.PushTrailingTrivia(in token);
                 _discriminatorStack.Push(Which.Trivia);
             }
 
@@ -305,9 +301,9 @@ public Which PeekNext()
                 return _discriminatorStack.Peek();
             }
 
-            public bool TryGetNextInSpan(ref TextSpan span, out SyntaxNodeOrToken value)
+            public bool TryGetNextInSpan(in TextSpan span, out SyntaxNodeOrToken value)
             {
-                if (_nodeStack.TryGetNextInSpan(ref span, out value))
+                if (_nodeStack.TryGetNextInSpan(in span, out value))
                 {
                     return true;
                 }
@@ -342,19 +338,19 @@ public void PushChildren(SyntaxNode node, Func<SyntaxNode, bool> descendIntoChil
                 }
             }
 
-            public void PushLeadingTrivia(ref SyntaxToken token)
+            public void PushLeadingTrivia(in SyntaxToken token)
             {
-                _triviaStack.PushLeadingTrivia(ref token);
+                _triviaStack.PushLeadingTrivia(in token);
                 _discriminatorStack.Push(Which.Trivia);
             }
 
-            public void PushTrailingTrivia(ref SyntaxToken token)
+            public void PushTrailingTrivia(in SyntaxToken token)
             {
-                _triviaStack.PushTrailingTrivia(ref token);
+                _triviaStack.PushTrailingTrivia(in token);
                 _discriminatorStack.Push(Which.Trivia);
             }
 
-            public void PushToken(ref SyntaxNodeOrToken value)
+            public void PushToken(in SyntaxNodeOrToken value)
             {
                 _tokenStack.Push(value);
                 _discriminatorStack.Push(Which.Token);
@@ -371,7 +367,7 @@ public void Dispose()
 
         private IEnumerable<SyntaxNode> DescendantNodesOnly(TextSpan span, Func<SyntaxNode, bool> descendIntoChildren, bool includeSelf)
         {
-            if (includeSelf && IsInSpan(ref span, this.FullSpan))
+            if (includeSelf && IsInSpan(in span, this.FullSpan))
             {
                 yield return this;
             }
@@ -380,7 +376,7 @@ private IEnumerable<SyntaxNode> DescendantNodesOnly(TextSpan span, Func<SyntaxNo
             {
                 while (stack.IsNotEmpty)
                 {
-                    SyntaxNode nodeValue = stack.TryGetNextAsNodeInSpan(ref span);
+                    SyntaxNode nodeValue = stack.TryGetNextAsNodeInSpan(in span);
                     if (nodeValue != null)
                     {
                         // PERF: Push before yield return so that "nodeValue" is 'dead' after the yield
@@ -396,7 +392,7 @@ private IEnumerable<SyntaxNode> DescendantNodesOnly(TextSpan span, Func<SyntaxNo
 
         private IEnumerable<SyntaxNodeOrToken> DescendantNodesAndTokensOnly(TextSpan span, Func<SyntaxNode, bool> descendIntoChildren, bool includeSelf)
         {
-            if (includeSelf && IsInSpan(ref span, this.FullSpan))
+            if (includeSelf && IsInSpan(in span, this.FullSpan))
             {
                 yield return this;
             }
@@ -406,7 +402,7 @@ private IEnumerable<SyntaxNodeOrToken> DescendantNodesAndTokensOnly(TextSpan spa
                 while (stack.IsNotEmpty)
                 {
                     SyntaxNodeOrToken value;
-                    if (stack.TryGetNextInSpan(ref span, out value))
+                    if (stack.TryGetNextInSpan(in span, out value))
                     {
                         // PERF: Push before yield return so that "value" is 'dead' after the yield
                         // and therefore doesn't need to be stored in the iterator state machine. This
@@ -425,7 +421,7 @@ private IEnumerable<SyntaxNodeOrToken> DescendantNodesAndTokensOnly(TextSpan spa
 
         private IEnumerable<SyntaxNodeOrToken> DescendantNodesAndTokensIntoTrivia(TextSpan span, Func<SyntaxNode, bool> descendIntoChildren, bool includeSelf)
         {
-            if (includeSelf && IsInSpan(ref span, this.FullSpan))
+            if (includeSelf && IsInSpan(in span, this.FullSpan))
             {
                 yield return this;
             }
@@ -438,7 +434,7 @@ private IEnumerable<SyntaxNodeOrToken> DescendantNodesAndTokensIntoTrivia(TextSp
                     {
                         case ThreeEnumeratorListStack.Which.Node:
                             SyntaxNodeOrToken value;
-                            if (stack.TryGetNextInSpan(ref span, out value))
+                            if (stack.TryGetNextInSpan(in span, out value))
                             {
                                 // PERF: The following code has an unusual structure (note the 'break' out of
                                 // the case statement from inside an if body) in order to convince the compiler
@@ -458,16 +454,16 @@ private IEnumerable<SyntaxNodeOrToken> DescendantNodesAndTokensIntoTrivia(TextSp
                                         // trailing trivia comes last
                                         if (token.HasTrailingTrivia)
                                         {
-                                            stack.PushTrailingTrivia(ref token);
+                                            stack.PushTrailingTrivia(in token);
                                         }
 
                                         // tokens come between leading and trailing trivia
-                                        stack.PushToken(ref value);
+                                        stack.PushToken(in value);
 
                                         // leading trivia comes first
                                         if (token.HasLeadingTrivia)
                                         {
-                                            stack.PushLeadingTrivia(ref token);
+                                            stack.PushLeadingTrivia(in token);
                                         }
 
                                         // Exit the case block without yielding (see PERF note above)
@@ -489,7 +485,7 @@ private IEnumerable<SyntaxNodeOrToken> DescendantNodesAndTokensIntoTrivia(TextSp
                             SyntaxTrivia trivia;
                             if (stack.TryGetNext(out trivia))
                             {
-                                if (trivia.HasStructure && IsInSpan(ref span, trivia.FullSpan))
+                                if (trivia.HasStructure && IsInSpan(in span, trivia.FullSpan))
                                 {
                                     var structureNode = trivia.GetStructure();
 
@@ -520,7 +516,7 @@ private IEnumerable<SyntaxTrivia> DescendantTriviaOnly(TextSpan span, Func<Synta
                 while (stack.IsNotEmpty)
                 {
                     SyntaxNodeOrToken value;
-                    if (stack.TryGetNextInSpan(ref span, out value))
+                    if (stack.TryGetNextInSpan(in span, out value))
                     {
                         if (value.IsNode)
                         {
@@ -534,7 +530,7 @@ private IEnumerable<SyntaxTrivia> DescendantTriviaOnly(TextSpan span, Func<Synta
 
                             foreach (var trivia in token.LeadingTrivia)
                             {
-                                if (IsInSpan(ref span, trivia.FullSpan))
+                                if (IsInSpan(in span, trivia.FullSpan))
                                 {
                                     yield return trivia;
                                 }
@@ -542,7 +538,7 @@ private IEnumerable<SyntaxTrivia> DescendantTriviaOnly(TextSpan span, Func<Synta
 
                             foreach (var trivia in token.TrailingTrivia)
                             {
-                                if (IsInSpan(ref span, trivia.FullSpan))
+                                if (IsInSpan(in span, trivia.FullSpan))
                                 {
                                     yield return trivia;
                                 }
@@ -563,7 +559,7 @@ private IEnumerable<SyntaxTrivia> DescendantTriviaIntoTrivia(TextSpan span, Func
                     {
                         case TwoEnumeratorListStack.Which.Node:
                             SyntaxNodeOrToken value;
-                            if (stack.TryGetNextInSpan(ref span, out value))
+                            if (stack.TryGetNextInSpan(in span, out value))
                             {
                                 if (value.IsNode)
                                 {
@@ -576,12 +572,12 @@ private IEnumerable<SyntaxTrivia> DescendantTriviaIntoTrivia(TextSpan span, Func
 
                                     if (token.HasTrailingTrivia)
                                     {
-                                        stack.PushTrailingTrivia(ref token);
+                                        stack.PushTrailingTrivia(in token);
                                     }
 
                                     if (token.HasLeadingTrivia)
                                     {
-                                        stack.PushLeadingTrivia(ref token);
+                                        stack.PushLeadingTrivia(in token);
                                     }
                                 }
                             }
@@ -602,7 +598,7 @@ private IEnumerable<SyntaxTrivia> DescendantTriviaIntoTrivia(TextSpan span, Func
                                     stack.PushChildren(structureNode, descendIntoChildren);
                                 }
 
-                                if (IsInSpan(ref span, trivia.FullSpan))
+                                if (IsInSpan(in span, trivia.FullSpan))
                                 {
                                     yield return trivia;
                                 }

src/Compilers/Core/Portable/Syntax/SyntaxNode.cs

@@ -1368,7 +1368,7 @@ protected virtual SyntaxToken FindTokenCore(int position, Func<SyntaxTrivia, boo
             return token;
         }
 
-        internal static SyntaxTrivia GetTriviaFromSyntaxToken(int position, SyntaxToken token)
+        internal static SyntaxTrivia GetTriviaFromSyntaxToken(int position, in SyntaxToken token)
         {
             var span = token.Span;
             var trivia = new SyntaxTrivia();
@@ -1384,7 +1384,7 @@ internal static SyntaxTrivia GetTriviaFromSyntaxToken(int position, SyntaxToken
             return trivia;
         }
 
-        internal static SyntaxTrivia GetTriviaThatContainsPosition(SyntaxTriviaList list, int position)
+        internal static SyntaxTrivia GetTriviaThatContainsPosition(in SyntaxTriviaList list, int position)
         {
             foreach (var trivia in list)
             {

src/Compilers/Core/Portable/Syntax/SyntaxNodeOrToken.cs

@@ -19,7 +19,7 @@ namespace Microsoft.CodeAnalysis
     /// </remarks>
     [StructLayout(LayoutKind.Auto)]
     [DebuggerDisplay("{GetDebuggerDisplay(), nq}")]
-    public struct SyntaxNodeOrToken : IEquatable<SyntaxNodeOrToken>
+    public readonly struct SyntaxNodeOrToken : IEquatable<SyntaxNodeOrToken>
     {
         // In a case if we are wrapping a SyntaxNode this is the SyntaxNode itself.
         // In a case where we are wrapping a token, this is the token's parent.
@@ -801,7 +801,7 @@ internal IList<TDirective> GetDirectives<TDirective>(Func<TDirective, bool> filt
             return directives ?? SpecializedCollections.EmptyList<TDirective>();
         }
 
-        private static void GetDirectives<TDirective>(SyntaxNodeOrToken node, Func<TDirective, bool> filter, ref List<TDirective> directives)
+        private static void GetDirectives<TDirective>(in SyntaxNodeOrToken node, Func<TDirective, bool> filter, ref List<TDirective> directives)
             where TDirective : SyntaxNode
         {
             if (node._token != null)
@@ -836,7 +836,7 @@ private static void GetDirectives<TDirective>(SyntaxToken token, Func<TDirective
             }
         }
 
-        private static void GetDirectives<TDirective>(SyntaxTriviaList trivia, Func<TDirective, bool> filter, ref List<TDirective> directives)
+        private static void GetDirectives<TDirective>(in SyntaxTriviaList trivia, Func<TDirective, bool> filter, ref List<TDirective> directives)
             where TDirective : SyntaxNode
         {
             foreach (var tr in trivia)

src/Compilers/Core/Portable/Syntax/SyntaxNodeOrTokenList.cs

@@ -15,7 +15,7 @@ namespace Microsoft.CodeAnalysis
     /// <summary>
     /// A list of <see cref="SyntaxNodeOrToken"/> structures.
     /// </summary>
-    public struct SyntaxNodeOrTokenList : IEquatable<SyntaxNodeOrTokenList>, IReadOnlyCollection<SyntaxNodeOrToken>
+    public readonly struct SyntaxNodeOrTokenList : IEquatable<SyntaxNodeOrTokenList>, IReadOnlyCollection<SyntaxNodeOrToken>
     {
         /// <summary>
         /// The underlying field
@@ -500,7 +500,7 @@ public struct Enumerator : IEnumerator<SyntaxNodeOrToken>
             private SyntaxNodeOrTokenList _list;
             private int _index;
 
-            internal Enumerator(SyntaxNodeOrTokenList list)
+            internal Enumerator(in SyntaxNodeOrTokenList list)
                 : this()
             {
                 _list = list;

src/Compilers/Core/Portable/Syntax/SyntaxNodeOrTokenListBuilder.cs

@@ -63,7 +63,17 @@ internal void Add(GreenNode item)
             _nodes[_count++] = item;
         }
 
-        public void Add(SyntaxNodeOrToken item)
+        public void Add(SyntaxNode item)
+        {
+            this.Add(item.Green);
+        }
+
+        public void Add(in SyntaxToken item)
+        {
+            this.Add(item.Node);
+        }
+
+        public void Add(in SyntaxNodeOrToken item)
         {
             this.Add(item.UnderlyingNode);
         }

src/Compilers/Core/Portable/Syntax/SyntaxToken.cs

@@ -18,7 +18,7 @@ namespace Microsoft.CodeAnalysis
 #pragma warning restore CA1200 // Avoid using cref tags with a prefix
     [StructLayout(LayoutKind.Auto)]
     [DebuggerDisplay("{GetDebuggerDisplay(), nq}")]
-    public struct SyntaxToken : IEquatable<SyntaxToken>
+    public readonly struct SyntaxToken : IEquatable<SyntaxToken>
     {
         private static readonly Func<DiagnosticInfo, Diagnostic> s_createDiagnosticWithoutLocation = Diagnostic.Create;
 

src/Compilers/Core/Portable/Syntax/SyntaxTokenList.Enumerator.cs

@@ -54,7 +54,7 @@ public struct Enumerator
             private GreenNode _current;
             private int _position;
 
-            internal Enumerator(ref SyntaxTokenList list)
+            internal Enumerator(in SyntaxTokenList list)
             {
                 _parent = list._parent;
                 _singleNodeOrList = list.Node;
@@ -129,9 +129,9 @@ private class EnumeratorImpl : IEnumerator<SyntaxToken>
             private Enumerator _enumerator;
 
             // SyntaxTriviaList is a relatively big struct so is passed by ref
-            internal EnumeratorImpl(ref SyntaxTokenList list)
+            internal EnumeratorImpl(in SyntaxTokenList list)
             {
-                _enumerator = new Enumerator(ref list);
+                _enumerator = new Enumerator(in list);
             }
 
             public SyntaxToken Current => _enumerator.Current;

src/Compilers/Core/Portable/Syntax/SyntaxTokenList.Reversed.cs

@@ -14,9 +14,9 @@ public partial struct SyntaxTokenList
         /// <summary>
         /// Reversed enumerable.
         /// </summary>
-        public struct Reversed : IEnumerable<SyntaxToken>, IEquatable<Reversed>
+        public readonly struct Reversed : IEnumerable<SyntaxToken>, IEquatable<Reversed>
         {
-            private SyntaxTokenList _list;
+            private readonly SyntaxTokenList _list;
 
             public Reversed(SyntaxTokenList list)
             {
@@ -25,7 +25,7 @@ public Reversed(SyntaxTokenList list)
 
             public Enumerator GetEnumerator()
             {
-                return new Enumerator(ref _list);
+                return new Enumerator(in _list);
             }
 
             IEnumerator<SyntaxToken> IEnumerable<SyntaxToken>.GetEnumerator()
@@ -35,7 +35,7 @@ IEnumerator<SyntaxToken> IEnumerable<SyntaxToken>.GetEnumerator()
                     return SpecializedCollections.EmptyEnumerator<SyntaxToken>();
                 }
 
-                return new EnumeratorImpl(ref _list);
+                return new EnumeratorImpl(in _list);
             }
 
             IEnumerator IEnumerable.GetEnumerator()
@@ -45,7 +45,7 @@ IEnumerator IEnumerable.GetEnumerator()
                     return SpecializedCollections.EmptyEnumerator<SyntaxToken>();
                 }
 
-                return new EnumeratorImpl(ref _list);
+                return new EnumeratorImpl(in _list);
             }
 
             public override bool Equals(object obj)
@@ -76,7 +76,7 @@ public struct Enumerator
                 private GreenNode _current;
                 private int _position;
 
-                public Enumerator(ref SyntaxTokenList list)
+                internal Enumerator(in SyntaxTokenList list)
                     : this()
                 {
                     if (list.Any())
@@ -139,9 +139,9 @@ private class EnumeratorImpl : IEnumerator<SyntaxToken>
                 private Enumerator _enumerator;
 
                 // SyntaxTriviaList is a relatively big struct so is passed as ref
-                internal EnumeratorImpl(ref SyntaxTokenList list)
+                internal EnumeratorImpl(in SyntaxTokenList list)
                 {
-                    _enumerator = new Enumerator(ref list);
+                    _enumerator = new Enumerator(in list);
                 }
 
                 public SyntaxToken Current => _enumerator.Current;

src/Compilers/Core/Portable/Syntax/SyntaxTokenList.cs

@@ -16,7 +16,7 @@ namespace Microsoft.CodeAnalysis
     /// Represents a read-only list of <see cref="SyntaxToken"/>.
     /// </summary>
     [StructLayout(LayoutKind.Auto)]
-    public partial struct SyntaxTokenList : IEquatable<SyntaxTokenList>, IReadOnlyList<SyntaxToken>
+    public readonly partial struct SyntaxTokenList : IEquatable<SyntaxTokenList>, IReadOnlyList<SyntaxToken>
     {
         private readonly SyntaxNode _parent;
         private readonly int _index;
@@ -431,7 +431,7 @@ public SyntaxTokenList ReplaceRange(SyntaxToken tokenInList, IEnumerable<SyntaxT
         /// </summary>
         public Enumerator GetEnumerator()
         {
-            return new Enumerator(ref this);
+            return new Enumerator(in this);
         }
 
         IEnumerator<SyntaxToken> IEnumerable<SyntaxToken>.GetEnumerator()
@@ -441,7 +441,7 @@ IEnumerator<SyntaxToken> IEnumerable<SyntaxToken>.GetEnumerator()
                 return SpecializedCollections.EmptyEnumerator<SyntaxToken>();
             }
 
-            return new EnumeratorImpl(ref this);
+            return new EnumeratorImpl(in this);
         }
 
         IEnumerator IEnumerable.GetEnumerator()
@@ -451,7 +451,7 @@ IEnumerator IEnumerable.GetEnumerator()
                 return SpecializedCollections.EmptyEnumerator<SyntaxToken>();
             }
 
-            return new EnumeratorImpl(ref this);
+            return new EnumeratorImpl(in this);
         }
 
         /// <summary>

src/Compilers/Core/Portable/Syntax/SyntaxTrivia.cs

@@ -17,11 +17,11 @@ namespace Microsoft.CodeAnalysis
 #pragma warning restore CA1200 // Avoid using cref tags with a prefix
     [DebuggerDisplay("{GetDebuggerDisplay(), nq}")]
     [StructLayout(LayoutKind.Auto)]
-    public struct SyntaxTrivia : IEquatable<SyntaxTrivia>
+    public readonly struct SyntaxTrivia : IEquatable<SyntaxTrivia>
     {
         internal static readonly Func<SyntaxTrivia, bool> Any = t => true;
 
-        internal SyntaxTrivia(SyntaxToken token, GreenNode triviaNode, int position, int index)
+        internal SyntaxTrivia(in SyntaxToken token, GreenNode triviaNode, int position, int index)
         {
             Token = token;
             UnderlyingNode = triviaNode;

src/Compilers/Core/Portable/Syntax/SyntaxTriviaList.Enumerator.cs

@@ -21,7 +21,7 @@ public struct Enumerator
             private GreenNode _current;
             private int _position;
 
-            internal Enumerator(ref SyntaxTriviaList list)
+            internal Enumerator(in SyntaxTriviaList list)
             {
                 _token = list.Token;
                 _singleNodeOrList = list.Node;
@@ -34,7 +34,7 @@ internal Enumerator(ref SyntaxTriviaList list)
             }
 
             // PERF: Passing SyntaxToken by ref since it's a non-trivial struct
-            private void InitializeFrom(ref SyntaxToken token, GreenNode greenNode, int index, int position)
+            private void InitializeFrom(in SyntaxToken token, GreenNode greenNode, int index, int position)
             {
                 _token = token;
                 _singleNodeOrList = greenNode;
@@ -49,15 +49,15 @@ private void InitializeFrom(ref SyntaxToken token, GreenNode greenNode, int inde
             // PERF: Used to initialize an enumerator for leading trivia directly from a token.
             // This saves constructing an intermediate SyntaxTriviaList. Also, passing token
             // by ref since it's a non-trivial struct
-            internal void InitializeFromLeadingTrivia(ref SyntaxToken token)
+            internal void InitializeFromLeadingTrivia(in SyntaxToken token)
             {
-                InitializeFrom(ref token, token.Node.GetLeadingTriviaCore(), 0, token.Position);
+                InitializeFrom(in token, token.Node.GetLeadingTriviaCore(), 0, token.Position);
             }
 
             // PERF: Used to initialize an enumerator for trailing trivia directly from a token.
             // This saves constructing an intermediate SyntaxTriviaList. Also, passing token
             // by ref since it's a non-trivial struct
-            internal void InitializeFromTrailingTrivia(ref SyntaxToken token)
+            internal void InitializeFromTrailingTrivia(in SyntaxToken token)
             {
                 var leading = token.Node.GetLeadingTriviaCore();
                 int index = 0;
@@ -73,7 +73,7 @@ internal void InitializeFromTrailingTrivia(ref SyntaxToken token)
                     trailingPosition -= trailingGreen.FullWidth;
                 }
 
-                InitializeFrom(ref token, trailingGreen, index, trailingPosition);
+                InitializeFrom(in token, trailingGreen, index, trailingPosition);
             }
 
             public bool MoveNext()
@@ -110,10 +110,11 @@ public SyntaxTrivia Current
                 }
             }
 
-            internal bool TryMoveNextAndGetCurrent(ref SyntaxTrivia current)
+            internal bool TryMoveNextAndGetCurrent(out SyntaxTrivia current)
             {
                 if (!MoveNext())
                 {
+                    current = default;
                     return false;
                 }
 
@@ -127,9 +128,9 @@ private class EnumeratorImpl : IEnumerator<SyntaxTrivia>
             private Enumerator _enumerator;
 
             // SyntaxTriviaList is a relatively big struct so is passed as ref
-            internal EnumeratorImpl(ref SyntaxTriviaList list)
+            internal EnumeratorImpl(in SyntaxTriviaList list)
             {
-                _enumerator = new Enumerator(ref list);
+                _enumerator = new Enumerator(in list);
             }
 
             public SyntaxTrivia Current => _enumerator.Current;

src/Compilers/Core/Portable/Syntax/SyntaxTriviaList.Reversed.cs

@@ -13,9 +13,9 @@ public partial struct SyntaxTriviaList
         /// <summary>
         /// Reversed enumerable.
         /// </summary>
-        public struct Reversed : IEnumerable<SyntaxTrivia>, IEquatable<Reversed>
+        public readonly struct Reversed : IEnumerable<SyntaxTrivia>, IEquatable<Reversed>
         {
-            private SyntaxTriviaList _list;
+            private readonly SyntaxTriviaList _list;
 
             public Reversed(SyntaxTriviaList list)
             {
@@ -24,7 +24,7 @@ public Reversed(SyntaxTriviaList list)
 
             public Enumerator GetEnumerator()
             {
-                return new Enumerator(ref _list);
+                return new Enumerator(in _list);
             }
 
             IEnumerator<SyntaxTrivia> IEnumerable<SyntaxTrivia>.GetEnumerator()
@@ -34,7 +34,7 @@ IEnumerator<SyntaxTrivia> IEnumerable<SyntaxTrivia>.GetEnumerator()
                     return SpecializedCollections.EmptyEnumerator<SyntaxTrivia>();
                 }
 
-                return new ReversedEnumeratorImpl(ref _list);
+                return new ReversedEnumeratorImpl(in _list);
             }
 
             IEnumerator
@@ -45,7 +45,7 @@ IEnumerator<SyntaxTrivia> IEnumerable<SyntaxTrivia>.GetEnumerator()
                     return SpecializedCollections.EmptyEnumerator<SyntaxTrivia>();
                 }
 
-                return new ReversedEnumeratorImpl(ref _list);
+                return new ReversedEnumeratorImpl(in _list);
             }
 
             public override int GetHashCode()
@@ -75,7 +75,7 @@ public struct Enumerator
                 private GreenNode _current;
                 private int _position;
 
-                public Enumerator(ref SyntaxTriviaList list)
+                internal Enumerator(in SyntaxTriviaList list)
                     : this()
                 {
                     if (list.Any())
@@ -128,9 +128,9 @@ private class ReversedEnumeratorImpl : IEnumerator<SyntaxTrivia>
                 private Enumerator _enumerator;
 
                 // SyntaxTriviaList is a relatively big struct so is passed as ref
-                internal ReversedEnumeratorImpl(ref SyntaxTriviaList list)
+                internal ReversedEnumeratorImpl(in SyntaxTriviaList list)
                 {
-                    _enumerator = new Enumerator(ref list);
+                    _enumerator = new Enumerator(in list);
                 }
 
                 public SyntaxTrivia Current => _enumerator.Current;

src/Compilers/Core/Portable/Syntax/SyntaxTriviaList.cs

@@ -17,11 +17,11 @@ namespace Microsoft.CodeAnalysis
     /// Represents a read-only list of <see cref="SyntaxTrivia"/>.
     /// </summary>
     [StructLayout(LayoutKind.Auto)]
-    public partial struct SyntaxTriviaList : IEquatable<SyntaxTriviaList>, IReadOnlyList<SyntaxTrivia>
+    public readonly partial struct SyntaxTriviaList : IEquatable<SyntaxTriviaList>, IReadOnlyList<SyntaxTrivia>
     {
         public static SyntaxTriviaList Empty => default(SyntaxTriviaList);
 
-        internal SyntaxTriviaList(SyntaxToken token, GreenNode node, int position, int index = 0)
+        internal SyntaxTriviaList(in SyntaxToken token, GreenNode node, int position, int index = 0)
         {
             Token = token;
             Node = node;
@@ -29,7 +29,7 @@ internal SyntaxTriviaList(SyntaxToken token, GreenNode node, int position, int i
             Index = index;
         }
 
-        internal SyntaxTriviaList(SyntaxToken token, GreenNode node)
+        internal SyntaxTriviaList(in SyntaxToken token, GreenNode node)
         {
             Token = token;
             Node = node;
@@ -205,7 +205,7 @@ public Reversed Reverse()
 
         public Enumerator GetEnumerator()
         {
-            return new Enumerator(ref this);
+            return new Enumerator(in this);
         }
 
         public int IndexOf(SyntaxTrivia triviaInList)
@@ -411,7 +411,7 @@ IEnumerator<SyntaxTrivia> IEnumerable<SyntaxTrivia>.GetEnumerator()
                 return SpecializedCollections.EmptyEnumerator<SyntaxTrivia>();
             }
 
-            return new EnumeratorImpl(ref this);
+            return new EnumeratorImpl(in this);
         }
 
         IEnumerator IEnumerable.GetEnumerator()
@@ -421,7 +421,7 @@ IEnumerator IEnumerable.GetEnumerator()
                 return SpecializedCollections.EmptyEnumerator<SyntaxTrivia>();
             }
 
-            return new EnumeratorImpl(ref this);
+            return new EnumeratorImpl(in this);
         }
 
         /// <summary>

src/Compilers/Core/Portable/Syntax/SyntaxTriviaListBuilder.cs

@@ -94,12 +94,12 @@ public void Add(SyntaxTrivia[] items, int offset, int length)
             _count += length;
         }
 
-        public void Add(SyntaxTriviaList list)
+        public void Add(in SyntaxTriviaList list)
         {
             this.Add(list, 0, list.Count);
         }
 
-        public void Add(SyntaxTriviaList list, int offset, int length)
+        public void Add(in SyntaxTriviaList list, int offset, int length)
         {
             if (_nodes == null || _count + length > _nodes.Length)
             {

src/Compilers/Core/Portable/Syntax/SyntaxWalker.cs

@@ -66,7 +66,7 @@ protected virtual void VisitToken(SyntaxToken token)
             }
         }
 
-        private void VisitLeadingTrivia(SyntaxToken token)
+        private void VisitLeadingTrivia(in SyntaxToken token)
         {
             if (token.HasLeadingTrivia)
             {
@@ -77,7 +77,7 @@ private void VisitLeadingTrivia(SyntaxToken token)
             }
         }
 
-        private void VisitTrailingTrivia(SyntaxToken token)
+        private void VisitTrailingTrivia(in SyntaxToken token)
         {
             if (token.HasTrailingTrivia)
             {

src/Compilers/Core/Portable/Text/LinePosition.cs

@@ -8,7 +8,7 @@ namespace Microsoft.CodeAnalysis.Text
     /// <summary>
     /// Immutable representation of a line number and position within a SourceText instance.
     /// </summary>
-    public struct LinePosition : IEquatable<LinePosition>, IComparable<LinePosition>
+    public readonly struct LinePosition : IEquatable<LinePosition>, IComparable<LinePosition>
     {
         /// <summary>
         /// A <see cref="LinePosition"/> that represents position 0 at line 0.

src/Compilers/Core/Portable/Text/LinePositionSpan.cs

@@ -8,7 +8,7 @@ namespace Microsoft.CodeAnalysis.Text
     /// <summary>
     /// Immutable span represented by a pair of line number and index within the line.
     /// </summary>
-    public struct LinePositionSpan : IEquatable<LinePositionSpan>
+    public readonly struct LinePositionSpan : IEquatable<LinePositionSpan>
     {
         private readonly LinePosition _start;
         private readonly LinePosition _end;

src/Compilers/Core/Portable/Text/TextChange.cs

@@ -10,7 +10,7 @@ namespace Microsoft.CodeAnalysis.Text
     /// <summary>
     /// Describes a single change when a particular span is replaced with a new text.
     /// </summary>
-    public struct TextChange : IEquatable<TextChange>
+    public readonly struct TextChange : IEquatable<TextChange>
     {
         /// <summary>
         /// The original span of the changed text. 

src/Compilers/Core/Portable/Text/TextChangeRange.cs

@@ -10,7 +10,7 @@ namespace Microsoft.CodeAnalysis.Text
     /// <summary>
     /// Represents the change to a span of text.
     /// </summary>
-    public struct TextChangeRange : IEquatable<TextChangeRange>
+    public readonly struct TextChangeRange : IEquatable<TextChangeRange>
     {
         /// <summary>
         /// The span of text before the edit which is being changed

src/Compilers/Core/Portable/Text/TextLine.cs

@@ -8,7 +8,7 @@ namespace Microsoft.CodeAnalysis.Text
     /// <summary>
     /// Information about the character boundaries of a single line of text.
     /// </summary>
-    public struct TextLine : IEquatable<TextLine>
+    public readonly struct TextLine : IEquatable<TextLine>
     {
         private readonly SourceText _text;
         private readonly int _start;

src/Compilers/Core/Portable/Text/TextSpan.cs

@@ -9,7 +9,7 @@ namespace Microsoft.CodeAnalysis.Text
     /// Immutable abstract representation of a span of text.  For example, in an error diagnostic that reports a
     /// location, it could come from a parsed string, text from a tool editor buffer, etc.
     /// </summary>
-    public struct TextSpan : IEquatable<TextSpan>, IComparable<TextSpan>
+    public readonly struct TextSpan : IEquatable<TextSpan>, IComparable<TextSpan>
     {
         /// <summary>
         /// Creates a TextSpan instance beginning with the position Start and having the Length