Projection of constant owned entity with implicit conversion throws

[Xriuk]

Bug description

When I project an owned entity which has an implicit conversion from string I get:

The client projection contains a reference to a constant expression of '[...].Currency'. This could potentially cause a memory leak; consider assigning this constant to a local variable and using the variable in the query instead. See https://go.microsoft.com/fwlink/?linkid=2103067 for more information and examples.

But I don't get where the memory leak is in this case.

Your code

I have an owned entity for validation purposes:

[Owned]
public class Currency{
  public string CurrencyCode { get; set; }


  public static implicit operator string(Currency value) {
    return value.CurrencyCode;
  }

  public static implicit operator Currency(string value) {
    // Various validation ...

    return new Currency { CurrencyCode = value };
  }
}

I project it like this (the actual query is more complex, this is just to create a projection):

db.Set<MyEntity>()
  .Select(e => (Currency)"EUR")
  .First();

Stack traces

at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.ConstantVerifyingExpressionVisitor.VisitConstant(ConstantExpression constantExpression)
   at System.Linq.Expressions.ExpressionVisitor.VisitConditional(ConditionalExpression node)
   at System.Linq.Expressions.ExpressionVisitor.VisitMemberAssignment(MemberAssignment node)
   at System.Linq.Expressions.ExpressionVisitor.VisitMemberBinding(MemberBinding node)
   at System.Linq.Expressions.ExpressionVisitor.Visit[T](ReadOnlyCollection`1 nodes, Func`2 elementVisitor)
   at System.Linq.Expressions.ExpressionVisitor.VisitMemberInit(MemberInitExpression node)
   at System.Linq.Expressions.ExpressionVisitor.VisitMemberAssignment(MemberAssignment node)
   at System.Linq.Expressions.ExpressionVisitor.VisitMemberBinding(MemberBinding node)
   at System.Linq.Expressions.ExpressionVisitor.Visit[T](ReadOnlyCollection`1 nodes, Func`2 elementVisitor)
   at System.Linq.Expressions.ExpressionVisitor.VisitMemberInit(MemberInitExpression node)
   at System.Linq.Expressions.ExpressionVisitor.VisitMemberAssignment(MemberAssignment node)
   at System.Linq.Expressions.ExpressionVisitor.VisitMemberBinding(MemberBinding node)
   at System.Linq.Expressions.ExpressionVisitor.Visit[T](ReadOnlyCollection`1 nodes, Func`2 elementVisitor)
   at System.Linq.Expressions.ExpressionVisitor.VisitMemberInit(MemberInitExpression node)
   at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.VerifyNoClientConstant(Expression expression)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.VisitShapedQuery(ShapedQueryExpression shapedQueryExpression)
   at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.VisitExtension(Expression extensionExpression)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.VisitExtension(Expression extensionExpression)
   at Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](IDatabase database, Expression query, IModel model, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass9_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
   at EntityFrameworkCore.Projectables.Infrastructure.Internal.CustomQueryCompiler.Execute[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1.GetEnumerator()
  ...

EF Core version

8.0.16

Database provider

Microsoft.EntityFrameworkCore.SqlServer

Target framework

.NET 8.0

[Xriuk]

Also this does not work (static readonly variable):

public class Currency {
  public static readonly Currency EUR = "EUR";

  ...
}

...

db.Set<MyEntity>()
  .Select(e => Currency.EUR)
  .First();

While if I make the static variable non-readonly it does work, also a local variable does work:

Currency currency = "EUR";
db.Set<MyEntity>()
  .Select(e => currency)
  .First();

Is there a reason for this? What's the difference?