使用Microsoft.Build NuGet包解析解决方案时触发内部MSBuild错误求助

尝试使用Microsoft.Build NuGet包实现以下操作：打开解决方案、枚举项目、定位生成的DLL，排查多个问题后遇到Internal MSBuild Error。

测试解决方案仅含一个net8.0项目，项目文件如下：

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Build" Version="17.9.5" />
    <PackageReference Include="Microsoft.Build.Utilities.Core" Version="17.9.5" />
  </ItemGroup>

</Project>

测试项目的唯一源文件代码：

namespace ConsoleApp1;

using System;
using System.IO;
using System.Collections.Generic;
using Microsoft.Build.Construction;
using Microsoft.Build.Definition;
using Microsoft.Build.Evaluation;
using Microsoft.Build.Evaluation.Context;

class Program
{
    static void Main( string[] args )
    {
        Directory.SetCurrentDirectory( @"C:\" ); // 确保后续错误不是当前目录导致
        msBuildApiTest( @"D:\Personal\MyVisualStudioSolution\Solution.sln" ); // 执行失败
        msBuildApiTest( @"D:\Personal\scratch\scratch.sln" ); // 同样失败
    }

    static void msBuildApiTest( string solutionFilePath )
    {
        string msBuildExtensionsPath = @"C:\Program Files\dotnet\sdk\8.0.102";
        string msBuildSdksPath = Path.Combine( msBuildExtensionsPath, "Sdks" );

        Environment.SetEnvironmentVariable( "MSBuildSDKsPath", msBuildSdksPath ); // 解决"The SDK 'Microsoft.NET.Sdk' specified could not be found"错误
        Environment.SetEnvironmentVariable( "MSBuildEnableWorkloadResolver", "false" ); // 解决"The SDK 'Microsoft.NET.SDK.WorkloadAutoImportPropsLocator' specified could not be found"错误

        ProjectOptions projectOptions = new();
        projectOptions.EvaluationContext = EvaluationContext.Create( EvaluationContext.SharingPolicy.Shared );
        projectOptions.LoadSettings = ProjectLoadSettings.DoNotEvaluateElementsWithFalseCondition;
        projectOptions.GlobalProperties = new Dictionary<string, string>();
        projectOptions.GlobalProperties.Add( "SolutionDir", Path.GetDirectoryName( solutionFilePath ) + "\\" ); // 末尾反斜杠必须存在
        projectOptions.GlobalProperties.Add( "MSBuildExtensionsPath", msBuildExtensionsPath ); // 解决"imported project ... was not found"错误
        ProjectCollection projectCollection = new( ToolsetDefinitionLocations.Default );
        
        SolutionFile solutionFile = SolutionFile.Parse( solutionFilePath );
        foreach( ProjectInSolution projectInSolution in solutionFile.ProjectsInOrder )
        {
            if( projectInSolution.ProjectType is SolutionProjectType.SolutionFolder or SolutionProjectType.SharedProject )
                continue;
            Console.WriteLine( $"{projectInSolution.ProjectType}\t{projectInSolution.ProjectName}\t{projectInSolution.RelativePath}" );

            Project project1 = Project.FromFile( projectInSolution.AbsolutePath, projectOptions ); // 此处失败
            Project project2 = new( projectInSolution.AbsolutePath, projectOptions.GlobalProperties, "Current", projectCollection ); // 同样失败
        }
    }
}

执行后抛出Microsoft.Build.Exceptions.InvalidProjectFileException，错误信息：

The expression "[MSBuild]::GetTargetFrameworkIdentifier(net8.0)" cannot be evaluated.
MSB0001: Internal MSBuild Error: A required NuGet assembly was not found.
Expected Path: D:\Personal\scratch\ConsoleApp1\bin\Debug\net8.0
C:\Program Files\dotnet\sdk\8.0.102\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.TargetFrameworkInference.targets

备注：

• "Expected Path"指向测试项目输出目录，与待解析解决方案无关，且已切换当前目录至C:\
• 本地msBuildExtensionsPath为C:\Program Files\dotnet\sdk\8.0.102，可按需修改
• 待解析解决方案包含多个net8.0项目和一个net472项目，解析测试项目自身也会触发相同错误

核心原因是缺少MSBuild处理.NET SDK项目所需的NuGet相关依赖组件：

• [MSBuild]::GetTargetFrameworkIdentifier这类函数依赖NuGet的核心组件（如NuGet.Frameworks.dll）解析目标框架信息，但当前项目仅引用了Microsoft.Build和Microsoft.Build.Utilities.Core，未包含必要的NuGet相关包。
• MSBuild默认从当前应用程序的输出目录检索依赖组件，错误中的"Expected Path"即测试项目的输出目录，该目录下缺少所需NuGet组件，导致表达式无法评估。

1. 添加必要的NuGet包引用 #

更新测试项目的ItemGroup，补充以下包引用：

<ItemGroup>
  <PackageReference Include="Microsoft.Build" Version="17.9.5" />
  <PackageReference Include="Microsoft.Build.Utilities.Core" Version="17.9.5" />
  <!-- 新增NuGet相关依赖包 -->
  <PackageReference Include="NuGet.Frameworks" Version="6.8.1" />
  <PackageReference Include="Microsoft.Build.NuGetSdkResolver" Version="17.9.5" />
</ItemGroup>

• NuGet.Frameworks提供目标框架解析的核心能力，是GetTargetFrameworkIdentifier函数的底层依赖。
• Microsoft.Build.NuGetSdkResolver帮助MSBuild正确识别和加载.NET SDK项目的依赖结构。

2. 调整项目加载逻辑，避免环境变量冲突 #

将环境变量的设置替换为全局属性传递，减少上下文冲突：

static void msBuildApiTest( string solutionFilePath )
{
    string msBuildExtensionsPath = @"C:\Program Files\dotnet\sdk\8.0.102";
    string msBuildSdksPath = Path.Combine( msBuildExtensionsPath, "Sdks" );

    ProjectOptions projectOptions = new();
    projectOptions.EvaluationContext = EvaluationContext.Create( EvaluationContext.SharingPolicy.Shared );
    projectOptions.LoadSettings = ProjectLoadSettings.DoNotEvaluateElementsWithFalseCondition;
    projectOptions.GlobalProperties = new Dictionary<string, string>
    {
        { "SolutionDir", Path.GetDirectoryName( solutionFilePath ) + "\\" },
        { "MSBuildExtensionsPath", msBuildExtensionsPath },
        { "MSBuildSDKsPath", msBuildSdksPath }, // 通过全局属性传递，替代环境变量
        { "MSBuildEnableWorkloadResolver", "false" } // 全局属性传递配置，避免环境变量污染
    };

    // 初始化ProjectCollection时绑定全局属性，确保上下文一致
    var projectCollection = new ProjectCollection( projectOptions.GlobalProperties );
    
    SolutionFile solutionFile = SolutionFile.Parse( solutionFilePath );
    foreach( ProjectInSolution projectInSolution in solutionFile.ProjectsInOrder )
    {
        if( projectInSolution.ProjectType is SolutionProjectType.SolutionFolder or SolutionProjectType.SharedProject )
            continue;
        Console.WriteLine( $"{projectInSolution.ProjectType}\t{projectInSolution.ProjectName}\t{projectInSolution.RelativePath}" );

        // 通过ProjectCollection加载项目，保证配置上下文统一
        var project = projectCollection.LoadProject( projectInSolution.AbsolutePath, projectOptions.GlobalProperties, "Current" );
        // 可通过以下代码获取生成的DLL路径
        Console.WriteLine( $"输出DLL路径：{project.GetPropertyValue("TargetPath")}" );
    }
}

3. 验证依赖组件是否存在 #

构建测试项目后，检查输出目录（如bin\Debug\net8.0）下是否存在NuGet.Frameworks.dll和Microsoft.Build.NuGetSdkResolver.dll。若不存在，清理项目后重新构建，确保NuGet包正确恢复。

内容的提问来源于stack exchange，提问作者Mike Nakis