Fix .NET 10 AOT Publish `--no-build --no-restore` Errors

Introduction

Hey everyone! If you're diving into the exciting world of .NET 10 and leveraging its fantastic Ahead-of-Time (AOT) compilation features for leaner, faster applications, you might have hit a bit of a roadblock. Specifically, some of us have encountered a tricky issue when trying to publish our AOT-enabled apps using the dotnet publish command with the --no-build and --no-restore flags. What's the deal, you ask? Well, it turns out that a workflow that was perfectly smooth in .NET 9 seems to be failing in .NET 10, throwing a rather cryptic error about PrivateSdkAssemblies. This isn't just a minor inconvenience; for many developers and CI/CD pipelines, separating build, restore, and publish steps is a crucial best practice for efficiency and reliability. The idea is to build your project once, perhaps test it, and then simply package it for deployment without redundant compilation or dependency resolution. When this separation breaks down, it can really slow things down and complicate your automation. In this article, we're going to roll up our sleeves, get to the bottom of this .NET 10 AOT publish issue, understand exactly why it's happening, and, most importantly, explore the workarounds and best practices that will keep your development and deployment workflows running smoothly. We'll delve into the technical details, break down that error message, and even touch upon some peculiar local machine behavior that makes this problem even more interesting. So, buckle up, guys, and let's unravel this .NET 10 mystery together!

Understanding the Core Problem: AOT and dotnet publish

Alright, let's start by laying the groundwork, shall we? First up, what exactly is AOT (Ahead-of-Time) compilation in .NET? In a nutshell, AOT is a game-changer for many types of applications. Traditionally, .NET applications are compiled to Intermediate Language (IL), which is then Just-In-Time (JIT) compiled to native machine code when the application runs. AOT flips this by compiling your application directly into native code before it runs, often resulting in significantly faster startup times, reduced memory footprint, and smaller deployment packages. This is super beneficial for scenarios like serverless functions where cold starts are a big concern, containerized microservices needing minimal resource usage, or command-line tools where instant execution matters. It effectively removes the JIT overhead, making your applications feel snappier right from the get-go. With .NET continuously pushing the boundaries of performance, AOT is becoming an increasingly attractive option for modern applications.

Now, let's talk about the dotnet publish command and those two crucial flags: --no-build and --no-restore. The dotnet publish command is your go-to for packaging your application for deployment. By default, when you run dotnet publish, it first ensures all NuGet packages are restored (downloaded), then it builds your project (compiling your C# code into IL), and finally, it bundles everything up. However, in sophisticated build pipelines, especially in CI/CD environments, developers often want more granular control. This is where --no-build and --no-restore come in handy. The --no-restore flag tells dotnet publish to skip downloading dependencies, assuming they've already been restored in an earlier step. Similarly, --no-build instructs it to bypass the compilation phase, expecting that the project has already been built (e.g., via a preceding dotnet build command). This separation allows for faster, more efficient, and more deterministic builds. Imagine a multi-stage Dockerfile or a GitHub Actions workflow where you might restore and build once, cache the artifacts, and then simply publish. It's a fundamental pattern for keeping pipelines lean.

Here's where the regression in .NET 10 throws a wrench in the works. In .NET 9, this exact workflow – running dotnet build and then dotnet publish --no-build --no-restore for an AOT-enabled project – worked perfectly fine. Developers could confidently separate their build and publish steps. But with .NET 10, attempting this sequence for an AOT project results in an error: /home/runner/.nuget/packages/microsoft.dotnet.ilcompiler/10.0.0/build/Microsoft.NETCore.Native.Publish.targets(70,5): error : The PrivateSdkAssemblies ItemGroup is required for _ComputeAssembliesToCompileToNative. This isn't just a minor warning; it's a fatal error that halts the publish process. This cryptic message hints that something fundamental needed for the AOT compilation process is missing or not being correctly prepared when dotnet publish runs without its --build phase. The expectation that intermediate AOT-related artifacts would be present after a dotnet build step no longer holds true for AOT projects in .NET 10 when --no-build is used during publish, leading to a frustrating breaking change for many of us. Understanding this shift is key to finding a solution.

Diving Deep into the Error: Missing PrivateSdkAssemblies

Let's peel back the layers and really understand that intimidating error message, folks: