Equivalent to AssemblyInfo in dotnet core/csproj

Since dotnet core moved back to the .csproj format, there is a new autogenerated MyProject.AssemblyInfo.cs which contains, among others:

[assembly: AssemblyCompany("MyProject")]
[assembly: AssemblyVersion("1.0.0.0")]

Note that this is automatically regenerated every build. Previously, the file was found in the /obj/ directory, now it appears to be only in memory as the file can't be found on disk and clicking the error message does not open any file.

This is the error message:

Since they are defined there, I can't define them myself in the classical AssemblyInfo.cs.

Where/how can I define the Company and Version of a project?

As you've already noticed, you can control most of these settings in .csproj.

If you'd rather keep these in AssemblyInfo.cs, you can turn off auto-generated assembly attributes.

<PropertyGroup>
   <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
</PropertyGroup> 

If you want to see what's going on under the hood, checkout Microsoft.NET.GenerateAssemblyInfo.targets inside of Microsoft.NET.Sdk.

Those settings has moved into the .csproj file.

By default they don't show up but you can discover them from Visual Studio 2017 in the project properties Package tab.

Once saved those values can be found in MyProject.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net461</TargetFramework>
    <Version>1.2.3.4</Version>
    <Authors>Author 1</Authors>
    <Company>Company XYZ</Company>
    <Product>Product 2</Product>
    <PackageId>MyApp</PackageId>
    <AssemblyVersion>2.0.0.0</AssemblyVersion>
    <FileVersion>3.0.0.0</FileVersion>
    <NeutralLanguage>en</NeutralLanguage>
    <Description>Description here</Description>
    <Copyright>Copyright</Copyright>
    <PackageLicenseUrl>License URL</PackageLicenseUrl>
    <PackageProjectUrl>Project URL</PackageProjectUrl>
    <PackageIconUrl>Icon URL</PackageIconUrl>
    <RepositoryUrl>Repo URL</RepositoryUrl>
    <RepositoryType>Repo type</RepositoryType>
    <PackageTags>Tags</PackageTags>
    <PackageReleaseNotes>Release</PackageReleaseNotes>
  </PropertyGroup>

In the file explorer properties information tab, FileVersion is shown as "File Version" and Version is shown as "Product version"

I do the following for my .NET Standard 2.0 projects.

Create a Directory.Build.props file (e.g. in the root of your repo) and move the properties to be shared from the .csproj file to this file.

MSBuild will pick it up automatically and apply them to the autogenerated AssemblyInfo.cs.

They also get applied to the nuget package when building one with dotnet pack or via the UI in Visual Studio 2017.

See https://docs.microsoft.com/en-us/visualstudio/msbuild/customize-your-build

Example:

<Project>
    <PropertyGroup>
        <Company>Some company</Company>
        <Copyright>Copyright © 2020</Copyright>
        <AssemblyVersion>1.0.0.1</AssemblyVersion>
        <FileVersion>1.0.0.1</FileVersion>
        <Version>1.0.0.1</Version>
        <!-- ... -->
    </PropertyGroup>
</Project>