[release/6.0-rc1] Make JsonGenerator be an incremental generator (#57088)

[eerhardt]

Backport of #57088 to release/6.0-rc1

Contributes to #56702

Customer Impact

Customers are reporting sluggish IDE behavior when targeting net6.0 in large solutions.

VS typing performance quickly degrades (hangs, up to several seconds pauses between characters typing, etc.) after working with several cs files for like 20 minutes or more in the context of a medium-sized DotNet 6 Preview 6 solution with maybe 70 projects, each with ~ 10 to 500 files.

This change is converting the System.Text.Json source generator to use the new IIncrementalGenerator Roslyn API. This allows for the source generator to do considerably less work in the background of the IDE, especially when no code in the solution uses the source generator.

Testing

All automated tests continue to pass.

I also tested manually using VS 2022 that the source generator still works after converting to the new Roslyn API.

The responsiveness of VS 2022 in a large solution on my Standard_D8as_v4 Azure VM went from ~2 seconds to open the Intellisense window to almost instantaneous.

Risk

Since the IIncrementalGenerator Roslyn API is new in Roslyn v4.0, it doesn't work in VS 2019. This means a customer using the 6.0-rc1 NuGet package in VS 2019 will get a warning:

Warning CS8032 An instance of analyzer System.Text.Json.SourceGeneration.JsonSourceGenerator cannot be created from C:\Users\eerhardt\.nuget\packages\system.text.json\7.0.0-dev\analyzers\dotnet\cs\System.Text.Json.SourceGeneration.dll : Could not load file or assembly 'Microsoft.CodeAnalysis, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

The plan is to enable "multi-targeting" different Roslyn versions in 6.0-rc2. This will allow us to ship 2 versions of the source generator in the NuGet package - one targeting the 3.x Roslyn APIs and one targeting the 4.0 Roslyn APIs, with the performance of the 4.0 Roslyn version being much better.

cc @chsienki @ericstj @jaredpar @sharwell

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Issue Details

---

Backport of #57088 to release/6.0-rc1

Contributes to #56702

Customer Impact

Customers are reporting sluggish IDE behavior when targeting net6.0 in large solutions.

VS typing performance quickly degrades (hangs, up to several seconds pauses between characters typing, etc.) after working with several cs files for like 20 minutes or more in the context of a medium-sized DotNet 6 Preview 6 solution with maybe 70 projects, each with ~ 10 to 500 files.

This change is converting the System.Text.Json source generator to use the new IIncrementalGenerator Roslyn API. This allows for the source generator to do considerably less work in the background of the IDE, especially when no code in the solution uses the source generator.

Testing

All automated tests continue to pass.

I also tested manually using VS 2022 that the source generator still works after converting to the new Roslyn API.

Risk

Since the IIncrementalGenerator Roslyn API is new in Roslyn v4.0, it doesn't work in VS 2019. This means a customer using the 6.0-rc1 NuGet package in VS 2019 will get a warning:

Warning CS8032 An instance of analyzer System.Text.Json.SourceGeneration.JsonSourceGenerator cannot be created from C:\Users\eerhardt\.nuget\packages\system.text.json\7.0.0-dev\analyzers\dotnet\cs\System.Text.Json.SourceGeneration.dll : Could not load file or assembly 'Microsoft.CodeAnalysis, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

The plan is to enable "multi-targeting" different Roslyn versions in 6.0-rc2. This will allow us to ship 2 versions of the source generator in the NuGet package - one targeting the 3.x Roslyn APIs and one targeting the 4.0 Roslyn APIs, with the performance of the 4.0 Roslyn version being much better.

cc @chsienki @ericstj @jaredpar @sharwell

Author:	eerhardt
Assignees:	-
Labels:	area-System.Text.Json
Milestone:	-

[Anipik]

approved offline