Incorrect results when coalescing expressions of different types

[ranma42]

Bug description

The ?? operator can return unexpected results when applied to operands with a different type (mapping).

In the attached code, the expected result for the null ?? 2.25 case would be 2.25, but EFCore actually returns 2.

Your code

// @nuget: Microsoft.EntityFrameworkCore.Sqlite -Version 9.0.1

using System;
using System.Data;
using System.Linq;
using Microsoft.EntityFrameworkCore;

using var db = new BloggingContext();

db.Database.EnsureDeleted();
db.Database.EnsureCreated();

var result = db
	.MyEntities
	.Select(x => x.Value ?? 2.25)
	.ToList();

foreach (var item in result) {
	Console.WriteLine($"{item.GetType()} {item}");
}

public class BloggingContext : DbContext
{
    public DbSet<MyEntity> MyEntities { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder options)
        => options
            .LogTo(Console.WriteLine, Microsoft.Extensions.Logging.LogLevel.Information)
            .EnableSensitiveDataLogging()
            .UseSqlite("Data Source=test.db");

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<MyEntity>().HasData(new MyEntity { Id = 1, Value = 5 });
        modelBuilder.Entity<MyEntity>().HasData(new MyEntity { Id = 2 });
    }
}

public class MyEntity
{
    public int Id { get; set; }
    public int? Value { get; set; }
}

Stack traces

Verbose output

info: 01/22/2025 23:16:55.864 RelationalEventId.CommandExecuted[20101] (Microsoft.EntityFrameworkCore.Database.Command) 
      Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT COALESCE("m"."Value", 2.25)
      FROM "MyEntities" AS "m"
System.Double 5
System.Double 2

EF Core version

9.0.1

Database provider

Microsoft.EntityFrameworkCore.Sqlite

Target framework

.NET 9.0

Operating system

Kali Linux

IDE

Visual Studio Code 1.96.4

[cincuranet]

Related to #15586.

[maumar]

InferTypeMapping goes through all arguments and takes first non-null mapping as a result, so we take the type mapping from the left, which is int. Dupe of #15586