Document some internal constructors

Part of #16708

src/EFCore.Cosmos/Query/Internal/SqlParameterExpression.cs

@@ -16,12 +16,17 @@ namespace Microsoft.EntityFrameworkCore.Cosmos.Query.Internal
     ///     any release. You should only use it directly in your code with extreme caution and knowing that
     ///     doing so can result in application failures when updating to a new Entity Framework Core release.
     /// </summary>
-    // Class is sealed because there are no public/protected constructors. Can be unsealed if this is changed.
     public sealed class SqlParameterExpression : SqlExpression
     {
         private readonly ParameterExpression _parameterExpression;
 
-        internal SqlParameterExpression(ParameterExpression parameterExpression, CoreTypeMapping typeMapping)
+        /// <summary>
+        ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+        ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+        ///     any release. You should only use it directly in your code with extreme caution and knowing that
+        ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+        /// </summary>
+        public SqlParameterExpression([NotNull] ParameterExpression parameterExpression, [CanBeNull] CoreTypeMapping typeMapping)
             : base(parameterExpression.Type, typeMapping)
         {
             _parameterExpression = parameterExpression;
@@ -78,13 +83,13 @@ protected override void Print(ExpressionPrinter expressionPrinter)
         /// </summary>
         public override bool Equals(object obj)
             => obj != null
-               && (ReferenceEquals(this, obj)
-                   || obj is SqlParameterExpression sqlParameterExpression
-                   && Equals(sqlParameterExpression));
+                && (ReferenceEquals(this, obj)
+                    || obj is SqlParameterExpression sqlParameterExpression
+                    && Equals(sqlParameterExpression));
 
         private bool Equals(SqlParameterExpression sqlParameterExpression)
             => base.Equals(sqlParameterExpression)
-               && string.Equals(Name, sqlParameterExpression.Name);
+                && string.Equals(Name, sqlParameterExpression.Name);
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to

src/EFCore.Relational/Query/RelationalSqlTranslatingExpressionVisitor.cs

@@ -11,7 +11,6 @@
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.EntityFrameworkCore.Infrastructure;
-using Microsoft.EntityFrameworkCore.Internal;
 using Microsoft.EntityFrameworkCore.Metadata;
 using Microsoft.EntityFrameworkCore.Query.SqlExpressions;
 using Microsoft.EntityFrameworkCore.Utilities;

src/EFCore.Relational/Query/SqlExpressions/ColumnExpression.cs

@@ -6,7 +6,6 @@
 using System.Linq;
 using System.Linq.Expressions;
 using Microsoft.EntityFrameworkCore.Metadata;
-using Microsoft.EntityFrameworkCore.Metadata.Internal;
 using Microsoft.EntityFrameworkCore.Storage;
 using Microsoft.EntityFrameworkCore.Utilities;
 

src/EFCore.Relational/Query/SqlExpressions/ProjectionExpression.cs

@@ -13,11 +13,11 @@ namespace Microsoft.EntityFrameworkCore.Query.SqlExpressions
     ///         An expression that represents a projection in <see cref="SelectExpression"/>.
     ///     </para>
     ///     <para>
-    ///         This type is typically used by database providers (and other extensions). It is generally
-    ///         not used in application code.
+    ///         This is a simple wrapper around a <see cref="SqlExpression"/> and an alias.
+    ///         Instances of this type cannot be constructed by application or database provider code. If this is a problem for your
+    ///         application or provider, then please file an issue at https://github.com/dotnet/efcore.
     ///     </para>
     /// </summary>
-    // Class is sealed because there are no public/protected constructors. Can be unsealed if this is changed.
     public sealed class ProjectionExpression : Expression, IPrintableExpression
     {
         internal ProjectionExpression([NotNull] SqlExpression expression, [NotNull] string alias)
@@ -41,7 +41,7 @@ internal ProjectionExpression([NotNull] SqlExpression expression, [NotNull] stri
         /// <inheritdoc />
         public override Type Type => Expression.Type;
         /// <inheritdoc />
-        public sealed override ExpressionType NodeType => ExpressionType.Extension;
+        public override ExpressionType NodeType => ExpressionType.Extension;
 
         /// <inheritdoc />
         protected override Expression VisitChildren(ExpressionVisitor visitor)

src/EFCore.Relational/Query/SqlExpressions/SqlParameterExpression.cs

@@ -14,11 +14,11 @@ namespace Microsoft.EntityFrameworkCore.Query.SqlExpressions
     ///         An expression that represents a parameter in a SQL tree.
     ///     </para>
     ///     <para>
-    ///         This type is typically used by database providers (and other extensions). It is generally
-    ///         not used in application code.
+    ///         This is a simple wrapper around a <see cref="ParameterExpression"/> in the SQL tree.
+    ///         Instances of this type cannot be constructed by application or database provider code. If this is a problem for your
+    ///         application or provider, then please file an issue at https://github.com/dotnet/efcore.
     ///     </para>
     /// </summary>
-    // Class is sealed because there are no public/protected constructors. Can be unsealed if this is changed.
     public sealed class SqlParameterExpression : SqlExpression
     {
         private readonly ParameterExpression _parameterExpression;

src/EFCore.Relational/Query/SqlExpressions/TableExpression.cs

@@ -13,11 +13,11 @@ namespace Microsoft.EntityFrameworkCore.Query.SqlExpressions
     ///         An expression that represents a table or view in a SQL tree.
     ///     </para>
     ///     <para>
-    ///         This type is typically used by database providers (and other extensions). It is generally
-    ///         not used in application code.
+    ///         This is a simple wrapper around a table and schema name. Instances of this type cannot be constructed by
+    ///         application or database provider code. If this is a problem for your application or provider, then please file
+    ///         an issue at https://github.com/dotnet/efcore.
     ///     </para>
     /// </summary>
-    // Class is sealed because there are no public/protected constructors. Can be unsealed if this is changed.
     public sealed class TableExpression : TableExpressionBase
     {
         internal TableExpression([NotNull] ITableBase table)
@@ -44,6 +44,7 @@ protected override void Print(ExpressionPrinter expressionPrinter)
         ///     The name of the table or view.
         /// </summary>
         public string Name { get; }
+
         /// <summary>
         ///     The schema of the table or view.
         /// </summary>

src/EFCore/DbFunctions.cs

@@ -9,13 +9,14 @@ namespace Microsoft.EntityFrameworkCore
     ///     Provides CLR methods that get translated to database functions when used in LINQ to Entities queries.
     ///     The methods on this class are accessed via <see cref="EF.Functions" />.
     /// </summary>
-    // Class is sealed because there are no public/protected constructors. Can be unsealed if this is changed.
     public sealed class DbFunctions
     {
-        internal DbFunctions()
+        private DbFunctions()
         {
         }
 
+        internal static DbFunctions Instance { get; } = new DbFunctions();
+
         #region Hidden System.Object members
 
         /// <summary>

src/EFCore/EF.cs

@@ -46,6 +46,7 @@ public static TProperty Property<TProperty>(
         ///     Provides CLR methods that get translated to database functions when used in LINQ to Entities queries.
         ///     Calling these methods in other contexts (e.g. LINQ to Objects) will throw a <see cref="NotSupportedException" />.
         /// </summary>
-        public static DbFunctions Functions { get; } = new DbFunctions();
+        public static DbFunctions Functions
+            => DbFunctions.Instance;
     }
 }

test/EFCore.Tests/DbFunctionsTest.cs

@@ -18,7 +18,7 @@ public void Like_on_client_throws()
             Assert.Equal(
                 CoreStrings.FunctionOnClient(nameof(DbFunctionsExtensions.Like)),
                 Assert.Throws<InvalidOperationException>(
-                    () => new DbFunctions().Like("abc", "abc")).Message);
+                    () => EF.Functions.Like("abc", "abc")).Message);
         }
     }
 }