Export Swagger JSON files during compile time

MyWebApp.csproj

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

    ...

    <PropertyGroup>
        <ExportSwaggerDocs>true</ExportSwaggerDocs>
        <SwaggerExportPath>wwwroot/openapi</SwaggerExportPath>
    </PropertyGroup>

    <!-- this part is only needed for non-aot apps -->
    <Target Name="SwaggerExport" AfterTargets="Build" Condition="'$(Configuration)'=='Release'">
        <Exec WorkingDirectory="$(ProjectDir)" Command="dotnet '$(TargetPath)' --export-swagger-docs true"/>
    </Target>

    <ItemGroup>
        <PackageReference Include="FastEndpoints" Version="8.0.1"/>
        <PackageReference Include="FastEndpoints.Swagger" Version="8.0.1"/>
    </ItemGroup>

</Project>

Program.cs

var bld = WebApplication.CreateBuilder(args);
bld.Services
   .AddFastEndpoints()
   .SwaggerDocument(o => o.DocumentSettings = d => d.DocumentName = "v1"); //must match below

var app = bld.Build();
app.UseFastEndpoints();

await app.ExportSwaggerDocsAndExitAsync("v1"); //must match doc names above

app.UseSwaggerGen();
app.Run();

// run 'dotnet build -c Release' or do a "Release" build in the IDE for the swagger json docs to be exported.