What's new in .NET 7 Preview 1 [WIP]

[leecow]

What's new in .NET 7 Preview 1

This issue is for teams to highlight work for the community that will release .NET 7 Preview 1

To add content, use a new conversation entry. The entry should include the team name and feature title as the first line as shown in the template below.

## Team Name: Feature title

[link to the tracking issue or epic item for the work]

Tell the story of the feature and anything the community should pay particular attention 
to be successful using the feature.

Preview 1: #7106
Preview 2: #7107
Preview 3: #7108
Preview 4: #7378
Preview 5: #7441
Preview 6: #7454
Preview 7: #7455

[danmoseley]

@stephentoub reasonable to blog about regex SG in preview 1? If so, we'll need some content - either from @joperezr or yourself, what do you prefer? It's probably worth its own blog post, but for Preview 1, we'll just need a paragraph/screenshot for the release post.

[stephentoub]

reasonable to blog about regex SG in preview 1?

We can if you think now's a good time.

[AaronRobinsonMSFT]

Now that the DllImport generator is in the product too, perhaps we that also deserves a post or at least a mention? @elinor-fung interested in writing up something? I'd imagine it mentions that is what we did and the plan is to make it available to everyone in the future.

[eerhardt]

.NET Libraries: Nullable annotations for Microsoft.Extensions

dotnet/runtime#43605

We have been making progress on annotating the Microsoft.Extensions.* libraries for nullability. In .NET 7 Preview 1, the following libraries have been annotated for nullability:

• Microsoft.Extensions.DependencyInjection.Abstractions
• Microsoft.Extensions.Logging.Abstractions
• Microsoft.Extensions.Primitives
• Microsoft.Extensions.FileSystemGlobbing
• Microsoft.Extensions.DependencyModel
• Microsoft.Extensions.Configuration.Abstractions
• Microsoft.Extensions.FileProviders.Abstractions
• Microsoft.Extensions.FileProviders.Physical
• Microsoft.Extensions.Configuration
• Microsoft.Extensions.Configuration.Binder
• Microsoft.Extensions.Configuration.CommandLine
• Microsoft.Extensions.Configuration.EnvironmentVariables
• Microsoft.Extensions.Configuration.FileExtensions
• Microsoft.Extensions.Configuration.Ini
• Microsoft.Extensions.Configuration.Json

You can see the remaining libraries, and follow the progress at dotnet/runtime#43605.

By the time .NET 7 is released, we plan on annotating all the Microsoft.Extensions.* libraries for nullability.

A huge thank you to @maxkoshevoi who has been contributing the bulk of this effort. Without @maxkoshevoi's help, we would not be nearly as far as we are.

[tarekgh]

Observability

Continue improving the tracing APIs:

• Adding the overload to ActivityContext.TryParse allows parsing and creating an ActivityContext object including if the activity context was propagated from a remote parent. ActivityContext.TryParse should support IsRemote runtime#42575
• Adding the method Activity.IsStopped() to indicates whether the Activity object is stopped. [API Proposal]: Activity.IsStopped (functionality required to conform to OpenTelemetry specification) runtime#63353

[JulieLeeMSFT]

CodeGen

Community PRs (Many thanks to JIT community contributors!!)

From @am11

• Convert some old style intrinsics to NamedIntrinsic runtime#62271

From @anthonycanino

• Add additional binary operations into the RangeCheck analysis. runtime#61662

From @SeanWoo

• [JIT] [Issue: 61620] Optimizing ARM64 for *x = dblCns; runtime#61847

From @SingleAccretion

• Tune floating-point CSEs live across a call better runtime#63903
• Update hash of the new CSE when resizing runtime#61984
• Rewrite selection for fields and always normalize SIMD types in VN runtime#61370
• Add documentation on how VN numbers memory runtime#60476
• Improve value numbering for casts runtime#59841
• Address-expose locals under complex local addresses in block morphing runtime#63100
• Handle embedded assignments in copy propagation runtime#63447
• Exception sets: debug checker & fixes runtime#63539
• Implement the "moffset" encoding size optimization in emitOutputAM runtime#62896
• Compress operand kinds array and optimize OperIsLocal runtime#63253
• Make gtHasRef pay attention to LCL_FLD nodes runtime#62568
• Enable global constant propagation for GT_LCL_FLD runtime#61209
• Enable global constant propagation for small types runtime#57726
• Properly type primary selectors in fgMemoryVNForLoopSideEffects runtime#60505

From @RalfKornmannEnvision

• CoreRT support for ARM64&Unix runtime#41023

From @weilinwa

• Optimize FMA codegen base on the overwritten runtime#58196

Dynamic PGO

• OSR support for Arm64 runtime#62831
• JIT: support OSR for synchronized methods runtime#61712
• JIT: handle interaction of OSR, PGO, and tail calls runtime#62263
• Add 2009 Jit Architecture Plan (excerpts) runtime#60939
• JIT: limited version of forward substitution for some relops runtime#61023
• JIT: save generics context for late devirtualization runtime#63420

Arm64

• Arm64: Memory barrier improvements runtime#62895
  
• Use SIMD operations in InitBlkUnroll/CopyBlkUnroll and increase unroll limit up to 128 bytes runtime#61030
  -- 61030 and 63422: SIMDfying MemCopy and MemSet instructions sequences and allowing the JIT to unroll such sequences (instead of using a helper call) up to 128 bytes on Arm64 (it was 64 bytes before the change)
• [Arm64] Keep unrolling InitBlock and CopyBlock up to 128 bytes runtime#63422
• 'cmeq' and 'fcmeq' Vector64<T>.Zero/Vector128<T>.Zero ARM64 containment optimizations runtime#62933
• [arm64] JIT: X % 2 == 0 -> X & 1 == 0 runtime#62399
• [arm64] JIT: Add with sign/zero extend runtime#61549
• [arm64] JIT: Enable CSE/hoisting for "arrayBase + elementOffset" runtime#61293
• [arm64] JIT: Fold "A * B + C" to MADD/MSUB runtime#61037

Loop Optimizations

• Generalize loop pre-header creation and loop hoisting runtime#62560
• Loop refactoring and commenting improvements runtime#61496

General Optimizations

• Accelerate additional cross platform hardware intrinsics runtime#61649
• Implement Narrow and Widen using SIMDAsHWIntrinsic runtime#60094
• Add IsKnownConstant jit helper and optimize 'str == ""' with str.StartsWith('c') runtime#63734
• Allow JIT to keep HFA/HVA in the registers when passing them as argument/returning values runtime#62623
• Enable support for nint/nuint for Vector64/128/256<T> runtime#63329
• Adding support for X86Base.Pause() and ArmBase.Yield() runtime#61065
• Use preferred region from PAL for JIT reloc hints runtime#60747
• Support fast tailcalls in R2R runtime#56669
• Allow contained indirections in tailcalls on x64 runtime#58686
• Optimize indirection cell call sequences more generally runtime#59602
• Avoid additional local created for delegate invocations runtime#63796

[elinor-fung]

Interop: P/Invoke source generation

dotnet/runtime#60212
dotnet/runtime#60595

We integrated the p/invoke source generator that was prototyped in .NET 6 into dotnet/runtime and have been converting the runtime libraries to use it. This means the converted p/invokes are AOT-compatible and no longer require an IL stub to be generated at runtime.

We intend to make the p/invoke source generator available for use outside the runtime in the future. You can follow our remaining work in dotnet/runtime#60595.

[eiriktsarpalis]

New APIs in System.Text.Json

System.Text.Json ships with a couple of minor quality-of-life enhancements:

• Add JsonSerializerOptions.Default runtime#61434: developers now have access to the default JsonSerializerOptions singleton used internally by System.Text.Json.
• Add a JsonWriterOptions.MaxDepth property runtime#61608: add a JsonWriterOptions.MaxDepth property and ensure this value flows from the equivalent JsonSerializerOptions.MaxDepth property on serialization.
• [API Proposal]: HttpClient.PatchAsJsonAsync() runtime#60531 Add Patch methods to System.Net.Http.Json.

[lambdageek]

Mono: Hot Reload

Tracking issue: dotnet/runtime#57365

• [mono] Hot Reload: initial push to support adding lambdas runtime#63513 The following edits are now allowed in C# hot reload for Blazor WebAssembly and .NET for iOS and Android:
  • Adding static lambdas to existing methods
  • Adding lambdas that capture this to existing methods that already have at least one lambda that captures this
  • Adding new static or non-virtual instance methods to existing classes
  • Adding new static fields to existing classes
  • Adding new classes
  • Known issues:
    • instance fields in newly added classes are not supported
    • newly added methods and fields in existing or new classes are not visible to reflection

[safern]

System.Drawing.Common: Unix support dropped

Based on the .NET 6 announcement made in: https://docs.microsoft.com/en-us/dotnet/core/compatibility/core-libraries/6.0/system-drawing-common-windows-only

In addition, we may completely remove support for non-Windows platforms in a future release, even if you enable it using the runtime configuration switch.

We removed support for that switch in 7.0-preview1: dotnet/runtime#64084

[mthalman]

Reverted Console Formatter Change in ASP.NET Core Container Images

In .NET 6, the Logging__Console__FormatterName environment variable was explicitly set to Json in the aspnet container images. Based on usability issues and your feedback, we've reverted this change in .NET 7.

This is a breaking change. If you relied on this environment variable being set to Json for your application, you'll need to explicitly set it yourself in your Dockerfile:

ENV Logging__Console__FormatterName=Json