Publishing a trimmed application results in duplicated warnings

[eerhardt]

Publish the following application with -p:PublishTrimmed=true

using System;
using System.Collections.Generic;
using System.Text.Json;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            var json = @"{""Name"":""Test"",""Sizes"":[0, 256, 256]}";

            var s = (Shape)JsonSerializer.Deserialize(json, typeof(Shape));
            Console.WriteLine(s.Sizes[0]);
            Console.WriteLine(s.Sizes[1]);
            Console.WriteLine(s.Sizes[2]);
        }
    }

    public class Shape
    {
        public string Name { get; set; }

        public List<int> Sizes { get; set; }
    }
}

Expected results

I only have 1 warning in my application, I should only see 1 warning in the output.

Actual results

❯ dotnet publish -r win-x64 -p:PublishTrimmed=true
Microsoft (R) Build Engine version 17.0.0-preview-21271-07+1560b6ce8 for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...
  All projects are up-to-date for restore.
  You are using a preview version of .NET. See: https://aka.ms/dotnet-core-preview
C:\DotNetTest\HelloWorld\Program.cs(13,28): warning IL2026: Using method 'System.Text.Json.JsonSerializer.Deserialize(string, System.Type, System.Text.Json.JsonSerializerOptions?)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. JSON serialization and deserialization might require types that cannot be statically analyzed. Use the overload that takes a JsonTypeInfo or JsonSerializerContext, or make sure all of the required types are preserved.. [C:\DotNetTest\HelloWorld\HelloWorld.csproj]
  HelloWorld -> C:\DotNetTest\HelloWorld\bin\Debug\net6.0\win-x64\HelloWorld.dll
C:\DotNetTest\HelloWorld\Program.cs(13,13): Trim analysis warning IL2026: ConsoleApp1.Program.Main(String[]): Using method 'System.Text.Json.JsonSerializer.Deserialize(String,Type,JsonSerializerOptions)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. JSON serialization and deserialization might require types that cannot be statically analyzed. Use the overload that takes a JsonTypeInfo or JsonSerializerContext, or make sure all of the required types are preserved.. [C:\DotNetTest\HelloWorld\HelloWorld.csproj]
  Optimizing assemblies for size, which may change the behavior of the app. Be sure to test after publishing. See: https://aka.ms/dotnet-illink
  HelloWorld -> C:\DotNetTest\HelloWorld\bin\Debug\net6.0\win-x64\publish\

Notice that I'm getting duplicated warnings:

C:\DotNetTest\HelloWorld\Program.cs(13,28): warning IL2026: Using method 'System.Text.Json.JsonSerializer.Deserialize...
and
C:\DotNetTest\HelloWorld\Program.cs(13,13): Trim analysis warning IL2026: ConsoleApp1.Program.Main(String[]): Using method 'System.Text.Json.JsonSerializer.Deserialize...

I assume the first warning comes from running the Roslyn analyzer, while the second warning comes from running the linker.

cc @sbomer @vitek-karas @agocke

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[agocke]

Interesting problem. Note that I expect this only happens if the publish forced a rebuild. If the build was cached I suspect you wouldn't see a build warning.