Enable C# nullable reference types in Transformations project

src/QsCompiler/CompilationManager/AssemblyLoader.cs

@@ -13,6 +13,7 @@
 using Microsoft.Quantum.QsCompiler.ReservedKeywords;
 using Microsoft.Quantum.QsCompiler.Serialization;
 using Microsoft.Quantum.QsCompiler.SyntaxTree;
+using Microsoft.Quantum.QsCompiler.Transformations;
 using Newtonsoft.Json.Bson;
 
 namespace Microsoft.Quantum.QsCompiler

src/QsCompiler/CompilationManager/CompilationUnit.cs

@@ -904,7 +904,7 @@ public QsCompilation Build()
         /// imported within a certain source file for the given namespace.
         /// Throws an ArgumentException if no namespace with the given name exists.
         /// </summary>
-        public ILookup<NonNullable<string>, (NonNullable<string>, string)> GetOpenDirectives(NonNullable<string> nsName)
+        public ILookup<NonNullable<string>, (NonNullable<string>, string?)> GetOpenDirectives(NonNullable<string> nsName)
         {
             this.syncRoot.EnterReadLock();
             try

src/QsCompiler/CompilationManager/CompilationUnitManager.cs

@@ -14,6 +14,7 @@
 using Microsoft.Quantum.QsCompiler.SyntaxProcessing;
 using Microsoft.Quantum.QsCompiler.SyntaxTokens;
 using Microsoft.Quantum.QsCompiler.SyntaxTree;
+using Microsoft.Quantum.QsCompiler.Transformations;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
 
 namespace Microsoft.Quantum.QsCompiler.CompilationBuilder
@@ -930,7 +931,7 @@ public class Compilation
             /// Contains a dictionary that maps the name of each namespace defined in the compilation to a look-up
             /// containing the names and corresponding short form (if any) of all opened namespaces for that (part of the) namespace in a particular source file.
             /// </summary>
-            private readonly ImmutableDictionary<NonNullable<string>, ILookup<NonNullable<string>, (NonNullable<string>, string)>> openDirectivesForEachFile;
+            private readonly ImmutableDictionary<NonNullable<string>, ILookup<NonNullable<string>, (NonNullable<string>, string?)>> openDirectivesForEachFile;
 
             /// <summary>
             /// Contains a dictionary that given the ID of a file included in the compilation
@@ -1022,11 +1023,10 @@ public QsComments NamespaceComments(NonNullable<string> sourceFile, NonNullable<
             /// returns the names and corresponding short form (if any) of all opened namespaces for the (part of the) namespace in that file.
             /// Returns an empy sequence if no source file with the given ID and/or namespace with the given name exists in the compilation.
             /// </summary>
-            public IEnumerable<(NonNullable<string>, string)> OpenDirectives(NonNullable<string> sourceFile, NonNullable<string> nsName) =>
-                this.openDirectivesForEachFile
-                    .TryGetValue(nsName, out ILookup<NonNullable<string>, (NonNullable<string>, string)> lookUp)
-                        ? lookUp[sourceFile]
-                        : Enumerable.Empty<(NonNullable<string>, string)>();
+            public IEnumerable<(NonNullable<string>, string?)> OpenDirectives(NonNullable<string> sourceFile, NonNullable<string> nsName) =>
+                this.openDirectivesForEachFile.TryGetValue(nsName, out var lookUp)
+                    ? lookUp[sourceFile]
+                    : Enumerable.Empty<(NonNullable<string>, string?)>();
 
             /// <summary>
             /// Returns all the names of all callable and types defined in the namespace with the given name.

src/QsCompiler/CompilationManager/EditorSupport/CodeActions.cs

@@ -12,6 +12,7 @@
 using Microsoft.Quantum.QsCompiler.SyntaxProcessing;
 using Microsoft.Quantum.QsCompiler.SyntaxTokens;
 using Microsoft.Quantum.QsCompiler.TextProcessing;
+using Microsoft.Quantum.QsCompiler.Transformations;
 using Microsoft.Quantum.QsCompiler.Transformations.QsCodeOutput;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
 using Lsp = Microsoft.VisualStudio.LanguageServer.Protocol;

src/QsCompiler/CompilationManager/EditorSupport/CodeCompletion.cs

@@ -12,6 +12,7 @@
 using Microsoft.Quantum.QsCompiler.SyntaxTree;
 using Microsoft.Quantum.QsCompiler.TextProcessing;
 using Microsoft.Quantum.QsCompiler.TextProcessing.CodeCompletion;
+using Microsoft.Quantum.QsCompiler.Transformations;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
 using static Microsoft.Quantum.QsCompiler.SyntaxGenerator;
 using static Microsoft.Quantum.QsCompiler.TextProcessing.CodeCompletion.FragmentParsing;
@@ -538,14 +539,15 @@ private static IEnumerable<CompletionItem> GetNamespaceAliasCompletions(
             {
                 prefix += ".";
             }
-            var @namespace = file.TryGetNamespaceAt(position);
-            if (@namespace == null || !compilation.GlobalSymbols.NamespaceExists(NonNullable<string>.New(@namespace)))
+            var ns = file.TryGetNamespaceAt(position);
+            if (ns == null || !compilation.GlobalSymbols.NamespaceExists(NonNullable<string>.New(ns)))
             {
                 return Array.Empty<CompletionItem>();
             }
             return compilation
-                .GetOpenDirectives(NonNullable<string>.New(@namespace))[file.FileName]
-                .Where(open => open.Item2 != null && open.Item2.StartsWith(prefix))
+                .GetOpenDirectives(NonNullable<string>.New(ns))[file.FileName]
+                .SelectNotNull(open => open.Item2?.Apply(alias => (open.Item1, alias)))
+                .Where(open => open.Item2.StartsWith(prefix))
                 .GroupBy(open => NextNamespacePart(open.Item2, prefix.Length))
                 .Select(open => new CompletionItem()
                 {

src/QsCompiler/CompilationManager/ProjectManager.cs

@@ -12,6 +12,7 @@
 using Microsoft.Quantum.QsCompiler.DataTypes;
 using Microsoft.Quantum.QsCompiler.Diagnostics;
 using Microsoft.Quantum.QsCompiler.ReservedKeywords;
+using Microsoft.Quantum.QsCompiler.Transformations;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
 
 namespace Microsoft.Quantum.QsCompiler.CompilationBuilder

src/QsCompiler/CompilationManager/TypeChecking.cs

@@ -15,8 +15,8 @@
 using Microsoft.Quantum.QsCompiler.SyntaxTokens;
 using Microsoft.Quantum.QsCompiler.SyntaxTree;
 using Microsoft.Quantum.QsCompiler.TextProcessing;
+using Microsoft.Quantum.QsCompiler.Transformations;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
-using Lsp = Microsoft.VisualStudio.LanguageServer.Protocol;
 using Position = Microsoft.Quantum.QsCompiler.DataTypes.Position;
 using Range = Microsoft.Quantum.QsCompiler.DataTypes.Range;
 

src/QsCompiler/CompilationManager/Utils.cs

@@ -152,16 +152,6 @@ internal static string GetTextChangedLines(FileContentManager file, TextDocument
 
         // general purpose type extensions
 
-        /// <summary>
-        /// Applies the action <paramref name="f"/> to the value <paramref name="x"/>.
-        /// </summary>
-        internal static void Apply<T>(this T x, Action<T> f) => f(x);
-
-        /// <summary>
-        /// Applies the function <paramref name="f"/> to the value <paramref name="x"/> and returns the result.
-        /// </summary>
-        internal static TOut Apply<TIn, TOut>(this TIn x, Func<TIn, TOut> f) => f(x);
-
         /// <summary>
         /// Partitions the given IEnumerable into the elements for which predicate returns true and those for which it returns false.
         /// Throws an ArgumentNullException if the given IEnumerable or predicate is null.
@@ -179,28 +169,6 @@ public static (List<T>, List<T>) Partition<T>(this IEnumerable<T> collection, Fu
             return (collection.Where(predicate).ToList(), collection.Where(x => !predicate(x)).ToList());
         }
 
-        /// <summary>
-        /// Projects each element of a sequence into a new form and discards null values.
-        /// </summary>
-        /// <remarks>Overload for reference types.</remarks>
-        internal static IEnumerable<TResult> SelectNotNull<TSource, TResult>(
-            this IEnumerable<TSource> source, Func<TSource, TResult?> selector)
-            where TResult : class =>
-            source.SelectMany(item =>
-                selector(item)?.Apply(result => new[] { result })
-                ?? Enumerable.Empty<TResult>());
-
-        /// <summary>
-        /// Projects each element of a sequence into a new form and discards null values.
-        /// </summary>
-        /// <remarks>Overload for value types.</remarks>
-        internal static IEnumerable<TResult> SelectNotNull<TSource, TResult>(
-            this IEnumerable<TSource> source, Func<TSource, TResult?> selector)
-            where TResult : struct =>
-            source.SelectMany(item =>
-                selector(item)?.Apply(result => new[] { result })
-                ?? Enumerable.Empty<TResult>());
-
         /// <summary>
         /// Returns true if the given lock is either ReadLockHeld, or is UpgradeableReadLockHeld, or isWriteLockHeld.
         /// Throws an ArgumentNullException if the given lock is null.

src/QsCompiler/DocumentationParser/DocCallable.cs

@@ -18,7 +18,7 @@ internal class DocCallable : DocItem
     {
         private readonly string syntax;
         private readonly string inputContent;
-        private readonly string outputType;
+        private readonly string? outputType;
         private readonly List<string> functors = new List<string>();
         private readonly QsCallable callable;
 

src/QsCompiler/DocumentationParser/Utils.cs

@@ -55,11 +55,11 @@ internal static class Utils
         internal static readonly string YamlExtension = ".yml";
         internal static readonly string LogExtension = ".log";
 
-        internal static YamlNode BuildStringNode(string item)
+        internal static YamlNode BuildStringNode(string? item)
         {
             var node = new YamlScalarNode(item);
             // Set the style to literal (YAML |-) if the string is multi-line
-            if (item.IndexOfAny(new char[] { '\n', '\r' }) >= 0)
+            if (item?.IndexOfAny(new char[] { '\n', '\r' }) >= 0)
             {
                 node.Style = YamlDotNet.Core.ScalarStyle.Literal;
             }
@@ -69,7 +69,7 @@ internal static YamlNode BuildStringNode(string item)
         internal static void AddString(this YamlSequenceNode root, string item) => root.Add(BuildStringNode(item));
 
         // We don't need to set the key to literal because all of our keys are simple one-line strings.
-        internal static void AddStringMapping(this YamlMappingNode root, string key, string item)
+        internal static void AddStringMapping(this YamlMappingNode root, string key, string? item)
         {
             root.Children[new YamlScalarNode(key)] = BuildStringNode(item);
         }
@@ -129,7 +129,7 @@ internal static YamlNode BuildSequenceMappingNode(Dictionary<string, string> pai
         /// </summary>
         /// <param name="t">The resolved type</param>
         /// <returns>A string containing the source representation of the type</returns>
-        internal static string ResolvedTypeToString(ResolvedType t) =>
+        internal static string? ResolvedTypeToString(ResolvedType t) =>
             SyntaxTreeToQsharp.Default.ToCode(t);
 
         /// <summary>

src/QsCompiler/Transformations/Attributes.cs

@@ -53,46 +53,46 @@ public static TypedExpression StringArguments(params string[] items) =>
         /// - if the predicate is specified and not null.
         /// Throws an ArgumentNullException if the given attribute or compilation is null.
         /// </summary>
-        public static QsCompilation AddToCallables(QsCompilation compilation, QsDeclarationAttribute attribute, CallablePredicate predicate = null) =>
+        public static QsCompilation AddToCallables(QsCompilation compilation, QsDeclarationAttribute attribute, CallablePredicate? predicate = null) =>
             new AddAttributes(new[] { (attribute, predicate) }).OnCompilation(compilation);
 
         /// <summary>
         /// Adds the given attribute(s) to all callables in the given compilation that satisfy the given predicate
         /// - if the predicate is specified and not null.
         /// Throws an ArgumentNullException if one of the given attributes or the compilation is null.
         /// </summary>
-        public static QsCompilation AddToCallables(QsCompilation compilation, params (QsDeclarationAttribute, CallablePredicate)[] attributes) =>
+        public static QsCompilation AddToCallables(QsCompilation compilation, params (QsDeclarationAttribute, CallablePredicate?)[] attributes) =>
             new AddAttributes(attributes).OnCompilation(compilation);
 
         /// <summary>
         /// Adds the given attribute(s) to all callables in the given compilation.
         /// Throws an ArgumentNullException if one of the given attributes or the compilation is null.
         /// </summary>
         public static QsCompilation AddToCallables(QsCompilation compilation, params QsDeclarationAttribute[] attributes) =>
-            new AddAttributes(attributes.Select(att => (att, (CallablePredicate)null))).OnCompilation(compilation);
+            new AddAttributes(attributes.Select(att => (att, (CallablePredicate?)null))).OnCompilation(compilation);
 
         /// <summary>
         /// Adds the given attribute to all callables in the given namespace that satisfy the given predicate
         /// - if the predicate is specified and not null.
         /// Throws an ArgumentNullException if the given attribute or namespace is null.
         /// </summary>
-        public static QsNamespace AddToCallables(QsNamespace ns, QsDeclarationAttribute attribute, CallablePredicate predicate = null) =>
+        public static QsNamespace AddToCallables(QsNamespace ns, QsDeclarationAttribute attribute, CallablePredicate? predicate = null) =>
             new AddAttributes(new[] { (attribute, predicate) }).Namespaces.OnNamespace(ns);
 
         /// <summary>
         /// Adds the given attribute(s) to all callables in the given namespace that satisfy the given predicate
         /// - if the predicate is specified and not null.
         /// Throws an ArgumentNullException if one of the given attributes or the namespace is null.
         /// </summary>
-        public static QsNamespace AddToCallables(QsNamespace ns, params (QsDeclarationAttribute, CallablePredicate)[] attributes) =>
+        public static QsNamespace AddToCallables(QsNamespace ns, params (QsDeclarationAttribute, CallablePredicate?)[] attributes) =>
             new AddAttributes(attributes).Namespaces.OnNamespace(ns);
 
         /// <summary>
         /// Adds the given attribute(s) to all callables in the given namespace.
         /// Throws an ArgumentNullException if one of the given attributes or the namespace is null.
         /// </summary>
         public static QsNamespace AddToCallables(QsNamespace ns, params QsDeclarationAttribute[] attributes) =>
-            new AddAttributes(attributes.Select(att => (att, (CallablePredicate)null))).Namespaces.OnNamespace(ns);
+            new AddAttributes(attributes.Select(att => (att, (CallablePredicate?)null))).Namespaces.OnNamespace(ns);
 
         // private transformation class(es)
 
@@ -104,14 +104,14 @@ private class AddAttributes
         {
             internal class TransformationState
             {
-                internal readonly ImmutableArray<(QsDeclarationAttribute, Func<QsCallable, bool>)> AttributeSelection;
+                internal readonly ImmutableArray<(QsDeclarationAttribute, CallablePredicate)> AttributeSelection;
 
                 /// <exception cref="ArgumentNullException">Thrown when the given selection is null.</exception>
-                internal TransformationState(IEnumerable<(QsDeclarationAttribute, Func<QsCallable, bool>)> selections) =>
+                internal TransformationState(IEnumerable<(QsDeclarationAttribute, CallablePredicate)>? selections) =>
                     this.AttributeSelection = selections?.ToImmutableArray() ?? throw new ArgumentNullException(nameof(selections));
             }
 
-            internal AddAttributes(IEnumerable<(QsDeclarationAttribute, CallablePredicate)> attributes)
+            internal AddAttributes(IEnumerable<(QsDeclarationAttribute, CallablePredicate?)> attributes)
             : base(new TransformationState(attributes?.Select(entry => (entry.Item1, entry.Item2 ?? (_ => true)))))
             {
                 if (attributes == null || attributes.Any(entry => entry.Item1 == null))

src/QsCompiler/Transformations/BasicTransformations.cs

@@ -37,7 +37,7 @@ private GetSourceFiles()
         /// </summary>
         public static ImmutableHashSet<NonNullable<string>> Apply(IEnumerable<QsNamespace> namespaces)
         {
-            if (namespaces == null || namespaces.Contains(null))
+            if (namespaces == null || namespaces.Contains(null!))
             {
                 throw new ArgumentNullException(nameof(namespaces));
             }
@@ -235,7 +235,7 @@ public SelectByFoldingOverExpressions(Func<TypedExpression, bool> condition, Fun
         public class StatementTransformation<TSelector>
         : Core.StatementTransformation<TransformationState> where TSelector : SelectByFoldingOverExpressions
         {
-            protected TSelector SubSelector;
+            protected TSelector? SubSelector;
             protected readonly Func<TransformationState, TSelector> CreateSelector;
 
             /// <summary>
@@ -267,7 +267,7 @@ public override QsScope OnScope(QsScope scope)
                     // StatementKind.Transform sets a new Subselector that walks all expressions contained in statement,
                     // and sets its satisfiesCondition to true if one of them satisfies the condition given on initialization
                     var transformed = this.OnStatement(statement);
-                    if (this.SubSelector.SharedState.SatisfiesCondition)
+                    if (this.SubSelector?.SharedState.SatisfiesCondition ?? false)
                     {
                         statements.Add(transformed);
                     }