Build failing on .net Core app due to missing definition

Question

I'm trying to build my .NET Core app from the CLI using dotnet build, but every single time I get this error:

'IConfigurationBuilder' does not contain a definition for 'AddEnvironmentVariables' and no extension method 'AddEnvironmentVariables' accepting a first argument of type 'IConfigurationBuilder' could be found (are you missing a using directive or an assembly reference?)

This is my ConfigureServices method in Startup.cs where the problem is happening:

    public void ConfigureServices(IServiceCollection services)     {         var builder = new ConfigurationBuilder()             .AddJsonFile("config.json")             .AddEnvironmentVariables()             .Build();          services.AddEntityFrameworkSqlServer()              .AddDbContext<MyContext>(options =>                  options.UseSqlServer(builder["Data:MyContext:ConnectionString"]));          services.AddIdentity<ApplicationUser, ApplicationRole>()             .AddEntityFrameworkStores<MyContext>()             .AddDefaultTokenProviders()             .AddOpenIddictCore<Application>(config => config.UseEntityFramework());          services.AddMvc();          services.AddScoped<OpenIddictManager<ApplicationUser, Application>, CustomOpenIddictManager>();     } 

Looking at this example I see nothing obviously wrong with my Startup.cs.

Update My project.json file:

{   "compilationOptions": {     "debugType": "portable",     "emitEntryPoint": true,     "preserveCompilationContext": true   },    "dependencies": {     "AspNet.Security.OAuth.Validation": "1.0.0-alpha1-*",     "Microsoft.AspNetCore.Authentication.Cookies": "1.0.0-rc2-*",     "Microsoft.AspNetCore.Authentication.JwtBearer": "1.0.0-rc2-*",     "Microsoft.AspNetCore.Diagnostics": "1.0.0-rc2-*",     "Microsoft.AspNetCore.Hosting": "1.0.0-rc2-*",     "Microsoft.AspNetCore.Identity.EntityFrameworkCore": "1.0.0-rc2-*",     "Microsoft.AspNetCore.IISPlatformHandler": "1.0.0-rc2-*",     "Microsoft.AspNetCore.Mvc": "1.0.0-rc2-*",     "Microsoft.AspNetCore.Server.Kestrel": "1.0.0-rc2-*",     "Microsoft.AspNetCore.StaticFiles": "1.0.0-rc2-*",     "Microsoft.EntityFrameworkCore.SqlServer": "1.0.0-rc2-*",     "Microsoft.Extensions.Configuration.Json": "1.0.0-rc2-*",     "Microsoft.Extensions.Logging.Console": "1.0.0-rc2-*",     "Microsoft.Extensions.Logging.Debug": "1.0.0-rc2-*",     "OpenIddict.Core": "1.0.0-*",     "OpenIddict.EF": "1.0.0-*"   },    "frameworks": {     "net451": {       "frameworkAssemblies": {         "System.ComponentModel": { "type": "build" }       }     },      "netcoreapp1.0": {       "dependencies": {         "Microsoft.NETCore.App": {           "type": "platform",           "version": "1.0.0-rc2-*"         }       },        "imports": [         "dnxcore50",         "portable-net451+win8"       ]     }   },    "tools": {     "Microsoft.AspNetCore.Server.IISIntegration.Tools": {       "version": "1.0.0-rc2-*",       "imports": "portable-net45+wp80+win8+wpa81+dnxcore50"     }   },    "scripts": {     "postpublish": "dotnet publish-iis --publish-folder %publish:OutputPath% --framework %publish:FullTargetFramework%"   },    "content": [     "wwwroot",     "Views",     "config.json",     "web.config"   ],    "exclude": [     "wwwroot",     "node_modules"   ],    "publishExclude": [     "**.user",     "**.vspscc"   ] } 

Oct 2018 Update: This problem does not occur when creating a new .NET Core 2.1 app in the latest build of VS 2017. Everything is now at a long-stable version since I asked this question.

Answer 1

You need the Microsoft.Extensions.Configuration namespace in scope to get that extension method. Either fully qualify it, or add this to the top of your file:

using Microsoft.Extensions.Configuration; 

You also will need the NuGet reference Microsoft.Extensions.Configuration.EnvironmentVariables.