Implement constant expression handling for enum members and private const fields

src/ExpressiveSharp.Generator/Emitter/ExpressionTreeEmitter.cs

@@ -666,6 +666,11 @@ private string EmitFieldReference(IFieldReferenceOperation fieldRef)
             return resultVar;
         }
 
+        // Enum members and const fields are inlined as constants, matching the C# compiler. A reflected
+        // field access would be funcletized by query providers into a parameter instead.
+        if (fieldRef.Field.HasConstantValue)
+            return EmitConstantField(fieldRef.Field);
+
         var fieldResultVar = NextVar();
         var fieldName = _fieldCache.EnsureFieldInfo(fieldRef.Field);
 
@@ -682,6 +687,30 @@ private string EmitFieldReference(IFieldReferenceOperation fieldRef)
         return fieldResultVar;
     }
 
+    private string EmitConstantField(IFieldSymbol field)
+    {
+        var resultVar = NextVar();
+        var typeFqn = field.Type.ToDisplayString(_fqnFormat);
+
+        string valueLiteral;
+        if (field.ContainingType.TypeKind == TypeKind.Enum)
+        {
+            valueLiteral = $"{typeFqn}.{EscapeIdentifier(field.Name)}";
+        }
+        else if (field.Type.TypeKind == TypeKind.Enum)
+        {
+            // The const itself may be inaccessible from the generated class, so emit its value rather than its name.
+            valueLiteral = $"({typeFqn})({FormatConstantValue(field.ConstantValue, field.Type)})";
+        }
+        else
+        {
+            valueLiteral = FormatConstantValue(field.ConstantValue, field.Type);
+        }
+
+        AppendLine($"var {resultVar} = {Expr}.Constant({valueLiteral}, typeof({typeFqn}));");
+        return resultVar;
+    }
+
     private bool TryEmitEnumMethodExpansion(IInvocationOperation invocation, out string resultVar)
     {
         resultVar = "";
@@ -793,7 +822,7 @@ string BuildCall(string operandVar)
         foreach (var member in enumMembers.AsEnumerable().Reverse())
         {
             var enumValueVar = NextVar();
-            AppendLine($"var {enumValueVar} = {Expr}.Constant({enumTypeFqn}.{member.Name}, typeof({enumTypeFqn}));");
+            AppendLine($"var {enumValueVar} = {Expr}.Constant({enumTypeFqn}.{EscapeIdentifier(member.Name)}, typeof({enumTypeFqn}));");
 
             // The MethodInfo is bound on the original receiver type — for an instance method on
             // Nullable<TEnum> or an extension whose first param is Nullable<TEnum>, the per-arm
@@ -3573,6 +3602,10 @@ private static string SanitizeIdentifier(string name)
         return name.Replace("@", "_").Replace(".", "_").Replace("<", "_").Replace(">", "_");
     }
 
+    // Symbol display's EscapeKeywordIdentifiers does not cover enum members, so escape by hand.
+    private static string EscapeIdentifier(string name) =>
+        SyntaxFacts.GetKeywordKind(name) != SyntaxKind.None ? "@" + name : name;
+
     private static string FormatConstantValue(object? value, ITypeSymbol? type)
     {
         if (value is null)

tests/ExpressiveSharp.EntityFrameworkCore.IntegrationTests/Tests/Sqlite/CommonScenarioTests.cs

@@ -1,4 +1,6 @@
+using System.Linq.Expressions;
 using ExpressiveSharp.EntityFrameworkCore.IntegrationTests.Infrastructure;
+using ExpressiveSharp.IntegrationTests.Scenarios.Store.Models;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 
@@ -13,4 +15,16 @@ protected override IAsyncDisposable CreateContextHandle(out DbContext context)
         context = handle.Context;
         return handle;
     }
+
+    [TestMethod]
+    public void Select_EnumSwitch_InlinesEnumConstantsIntoSql()
+    {
+        Expression<Func<Order, string>> expr = o => o.GetStatusLabelSwitchStatement();
+        var expanded = (Expression<Func<Order, string>>)expr.ExpandExpressives();
+
+        var sql = Context.Set<Order>().Select(expanded).ToQueryString();
+
+        StringAssert.Contains(sql, "CASE");
+        Assert.IsFalse(sql.Contains('@'));
+    }
 }

tests/ExpressiveSharp.Generator.Tests/ExpressiveGenerator/ConstructorTests.ProjectableConstructor_ReferencingStaticConstMember.verified.txt

@@ -17,7 +17,7 @@ namespace ExpressiveSharp.Generated
             var p_first = global::System.Linq.Expressions.Expression.Parameter(typeof(string), "first");
             var p_last = global::System.Linq.Expressions.Expression.Parameter(typeof(string), "last");
             var expr_0 = global::System.Linq.Expressions.Expression.New(typeof(global::Foo.PersonDto).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null));
-            var expr_3 = global::System.Linq.Expressions.Expression.Field(null, typeof(global::Foo.PersonDto).GetField("Separator", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static)); // Separator
+            var expr_3 = global::System.Linq.Expressions.Expression.Constant(" - ", typeof(string)); // Separator
             var expr_2 = global::System.Linq.Expressions.Expression.Call(typeof(string).GetMethod("Concat", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static, null, new global::System.Type[] { typeof(string), typeof(string) }, null), p_first, expr_3);
             var expr_1 = global::System.Linq.Expressions.Expression.Call(typeof(string).GetMethod("Concat", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static, null, new global::System.Type[] { typeof(string), typeof(string) }, null), expr_2, p_last);
             var expr_4 = global::System.Linq.Expressions.Expression.Bind(typeof(global::Foo.PersonDto).GetProperty("FullName", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance), expr_1);

tests/ExpressiveSharp.Generator.Tests/ExpressiveGenerator/EnumTests.EnumRelationalComparison.verified.txt

@@ -13,13 +13,13 @@ namespace ExpressiveSharp.Generated
         {
             var p__this = global::System.Linq.Expressions.Expression.Parameter(typeof(global::Foo.Entity), "@this");
             var expr_2 = global::System.Linq.Expressions.Expression.Property(p__this, typeof(global::Foo.Entity).GetProperty("Value", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // Value
-            var expr_3 = global::System.Linq.Expressions.Expression.Field(null, typeof(global::Foo.Bucket).GetField("Low", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static)); // Bucket.Low
+            var expr_3 = global::System.Linq.Expressions.Expression.Constant(global::Foo.Bucket.Low, typeof(global::Foo.Bucket)); // Bucket.Low
             var expr_4 = global::System.Linq.Expressions.Expression.Convert(expr_2, typeof(int));
             var expr_5 = global::System.Linq.Expressions.Expression.Convert(expr_3, typeof(int));
             var expr_1 = global::System.Linq.Expressions.Expression.MakeBinary(global::System.Linq.Expressions.ExpressionType.LessThanOrEqual, expr_4, expr_5);
             var expr_6 = global::System.Linq.Expressions.Expression.Constant("low", typeof(string)); // "low"
             var expr_9 = global::System.Linq.Expressions.Expression.Property(p__this, typeof(global::Foo.Entity).GetProperty("Value", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // Value
-            var expr_10 = global::System.Linq.Expressions.Expression.Field(null, typeof(global::Foo.Bucket).GetField("Mid", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static)); // Bucket.Mid
+            var expr_10 = global::System.Linq.Expressions.Expression.Constant(global::Foo.Bucket.Mid, typeof(global::Foo.Bucket)); // Bucket.Mid
             var expr_11 = global::System.Linq.Expressions.Expression.Convert(expr_9, typeof(int));
             var expr_12 = global::System.Linq.Expressions.Expression.Convert(expr_10, typeof(int));
             var expr_8 = global::System.Linq.Expressions.Expression.MakeBinary(global::System.Linq.Expressions.ExpressionType.LessThanOrEqual, expr_11, expr_12);

tests/ExpressiveSharp.Generator.Tests/ExpressiveGenerator/EnumTests.EnumRelationalComparisonWithNullableEnum.verified.txt

@@ -13,7 +13,7 @@ namespace ExpressiveSharp.Generated
         {
             var p__this = global::System.Linq.Expressions.Expression.Parameter(typeof(global::Foo.Entity), "@this");
             var expr_1 = global::System.Linq.Expressions.Expression.Property(p__this, typeof(global::Foo.Entity).GetProperty("Value", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // Value
-            var expr_3 = global::System.Linq.Expressions.Expression.Field(null, typeof(global::Foo.Bucket).GetField("Mid", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static)); // Bucket.Mid
+            var expr_3 = global::System.Linq.Expressions.Expression.Constant(global::Foo.Bucket.Mid, typeof(global::Foo.Bucket)); // Bucket.Mid
             var expr_2 = global::System.Linq.Expressions.Expression.Convert(expr_3, typeof(global::Foo.Bucket?));
             var expr_4 = global::System.Linq.Expressions.Expression.Convert(expr_1, typeof(global::System.Nullable<int>));
             var expr_5 = global::System.Linq.Expressions.Expression.Convert(expr_2, typeof(global::System.Nullable<int>));

tests/ExpressiveSharp.Generator.Tests/ExpressiveGenerator/EnumTests.EnumRelationalPattern.verified.txt

@@ -13,7 +13,7 @@ namespace ExpressiveSharp.Generated
         {
             var p__this = global::System.Linq.Expressions.Expression.Parameter(typeof(global::Foo.Entity), "@this");
             var expr_0 = global::System.Linq.Expressions.Expression.Property(p__this, typeof(global::Foo.Entity).GetProperty("Value", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // Value
-            var expr_2 = global::System.Linq.Expressions.Expression.Field(null, typeof(global::Foo.Bucket).GetField("Mid", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static)); // Bucket.Mid
+            var expr_2 = global::System.Linq.Expressions.Expression.Constant(global::Foo.Bucket.Mid, typeof(global::Foo.Bucket)); // Bucket.Mid
             var expr_3 = global::System.Linq.Expressions.Expression.Convert(expr_0, typeof(int));
             var expr_4 = global::System.Linq.Expressions.Expression.Convert(expr_2, typeof(int));
             var expr_1 = global::System.Linq.Expressions.Expression.MakeBinary(global::System.Linq.Expressions.ExpressionType.LessThanOrEqual, expr_3, expr_4);

tests/ExpressiveSharp.Generator.Tests/ExpressiveGenerator/EnumTests.EnumToEnumSwitchMapping.verified.txt

@@ -0,0 +1,38 @@
+// <auto-generated/>
+#nullable disable
+
+using Foo;
+
+namespace ExpressiveSharp.Generated
+{
+    static partial class Foo_Entity 
+    {
+        // [Expressive]
+        // public GeneralStatus General => Status switch
+        // {
+        //     ActualStatus.New => GeneralStatus.Defined,
+        //     ActualStatus.InProgress => GeneralStatus.PartiallyProcessed,
+        //     ActualStatus.Archived => GeneralStatus.Annulled,
+        //     _ => throw new System.NotImplementedException()};
+        static global::System.Linq.Expressions.Expression<global::System.Func<global::Foo.Entity, global::Foo.GeneralStatus>> General_Expression() 
+        {
+            var p__this = global::System.Linq.Expressions.Expression.Parameter(typeof(global::Foo.Entity), "@this");
+            var expr_0 = global::System.Linq.Expressions.Expression.Property(p__this, typeof(global::Foo.Entity).GetProperty("Status", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // Status
+            var expr_2 = global::System.Linq.Expressions.Expression.New(typeof(global::System.NotImplementedException).GetConstructor(global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance, null, new global::System.Type[] {  }, null)); // new System.NotImplementedException()
+            var expr_1 = global::System.Linq.Expressions.Expression.Throw(expr_2, typeof(global::Foo.GeneralStatus));
+            var expr_4 = global::System.Linq.Expressions.Expression.Constant(global::Foo.ActualStatus.Archived, typeof(global::Foo.ActualStatus)); // ActualStatus.Archived
+            var expr_3 = global::System.Linq.Expressions.Expression.Equal(expr_0, expr_4);
+            var expr_5 = global::System.Linq.Expressions.Expression.Constant(global::Foo.GeneralStatus.Annulled, typeof(global::Foo.GeneralStatus)); // GeneralStatus.Annulled
+            var expr_6 = global::System.Linq.Expressions.Expression.Condition(expr_3, expr_5, expr_1, typeof(global::Foo.GeneralStatus));
+            var expr_8 = global::System.Linq.Expressions.Expression.Constant(global::Foo.ActualStatus.InProgress, typeof(global::Foo.ActualStatus)); // ActualStatus.InProgress
+            var expr_7 = global::System.Linq.Expressions.Expression.Equal(expr_0, expr_8);
+            var expr_9 = global::System.Linq.Expressions.Expression.Constant(global::Foo.GeneralStatus.PartiallyProcessed, typeof(global::Foo.GeneralStatus)); // GeneralStatus.PartiallyProcessed
+            var expr_10 = global::System.Linq.Expressions.Expression.Condition(expr_7, expr_9, expr_6, typeof(global::Foo.GeneralStatus));
+            var expr_12 = global::System.Linq.Expressions.Expression.Constant(global::Foo.ActualStatus.New, typeof(global::Foo.ActualStatus)); // ActualStatus.New
+            var expr_11 = global::System.Linq.Expressions.Expression.Equal(expr_0, expr_12);
+            var expr_13 = global::System.Linq.Expressions.Expression.Constant(global::Foo.GeneralStatus.Defined, typeof(global::Foo.GeneralStatus)); // GeneralStatus.Defined
+            var expr_14 = global::System.Linq.Expressions.Expression.Condition(expr_11, expr_13, expr_10, typeof(global::Foo.GeneralStatus));
+            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::Foo.Entity, global::Foo.GeneralStatus>>(expr_14, p__this);
+        }
+    }
+}

tests/ExpressiveSharp.Generator.Tests/ExpressiveGenerator/EnumTests.KeywordNamedEnumMembers.verified.txt

@@ -0,0 +1,50 @@
+// <auto-generated/>
+#nullable disable
+
+using Foo;
+
+namespace ExpressiveSharp.Generated
+{
+    static partial class Foo_Entity 
+    {
+        // [Expressive]
+        // public bool IsClass => Value == Kind.@class;
+        static global::System.Linq.Expressions.Expression<global::System.Func<global::Foo.Entity, bool>> IsClass_Expression() 
+        {
+            var p__this = global::System.Linq.Expressions.Expression.Parameter(typeof(global::Foo.Entity), "@this");
+            var expr_1 = global::System.Linq.Expressions.Expression.Property(p__this, typeof(global::Foo.Entity).GetProperty("Value", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // Value
+            var expr_2 = global::System.Linq.Expressions.Expression.Constant(global::Foo.Kind.@class, typeof(global::Foo.Kind)); // Kind.@class
+            var expr_0 = global::System.Linq.Expressions.Expression.MakeBinary(global::System.Linq.Expressions.ExpressionType.Equal, expr_1, expr_2);
+            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::Foo.Entity, bool>>(expr_0, p__this);
+        }
+    }
+}
+
+// <auto-generated/>
+#nullable disable
+
+using Foo;
+
+namespace ExpressiveSharp.Generated
+{
+    static partial class Foo_Entity 
+    {
+        // [Expressive]
+        // public string Description => Value.Describe();
+        static global::System.Linq.Expressions.Expression<global::System.Func<global::Foo.Entity, string>> Description_Expression() 
+        {
+            var p__this = global::System.Linq.Expressions.Expression.Parameter(typeof(global::Foo.Entity), "@this");
+            var expr_0 = global::System.Linq.Expressions.Expression.Property(p__this, typeof(global::Foo.Entity).GetProperty("Value", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Instance)); // Value
+            var expr_1 = global::System.Linq.Expressions.Expression.Constant(null, typeof(string));
+            var expr_2 = global::System.Linq.Expressions.Expression.Constant(global::Foo.Kind.@default, typeof(global::Foo.Kind));
+            var expr_3 = global::System.Linq.Expressions.Expression.Call(typeof(global::Foo.KindExtensions).GetMethod("Describe", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static, null, new global::System.Type[] { typeof(global::Foo.Kind) }, null), new global::System.Linq.Expressions.Expression[] { expr_2 });
+            var expr_4 = global::System.Linq.Expressions.Expression.Equal(expr_0, expr_2);
+            var expr_5 = global::System.Linq.Expressions.Expression.Condition(expr_4, expr_3, expr_1, typeof(string));
+            var expr_6 = global::System.Linq.Expressions.Expression.Constant(global::Foo.Kind.@class, typeof(global::Foo.Kind));
+            var expr_7 = global::System.Linq.Expressions.Expression.Call(typeof(global::Foo.KindExtensions).GetMethod("Describe", global::System.Reflection.BindingFlags.Public | global::System.Reflection.BindingFlags.NonPublic | global::System.Reflection.BindingFlags.Static, null, new global::System.Type[] { typeof(global::Foo.Kind) }, null), new global::System.Linq.Expressions.Expression[] { expr_6 });
+            var expr_8 = global::System.Linq.Expressions.Expression.Equal(expr_0, expr_6);
+            var expr_9 = global::System.Linq.Expressions.Expression.Condition(expr_8, expr_7, expr_5, typeof(string));
+            return global::System.Linq.Expressions.Expression.Lambda<global::System.Func<global::Foo.Entity, string>>(expr_9, p__this);
+        }
+    }
+}