Inconcistent definition of implicit framework defines when using /p:DefineConstants.

[teo-tsirpanis]

Describe the bug

When building a project by setting DefineConstants from the command line, the NET***_OR_GREATER symbols are defined, but NET***, NET, and NETCOREAPP are not.

To Reproduce

Build a .NET 9 library with the following file with dotnet build -f net9.0 /p:DefineConstants=HELLOWORLD:

public class MyClass
{
#if NET
    public string _myString;
#endif

#if NET9_0_OR_GREATER
    public string MyString => _myString;
#endif
}

Exceptions (if any)

  net-sdk-repro failed with 1 error(s) (2,9s)
    C:\Users\teo\code\ephemeral\net-sdk-repro\Class1.cs(8,31): error CS0103: The name '_myString' does not exist in the current context

Build failed with 1 error(s) in 3,9s

Further technical details

I'm using .NET SDK 9.0.101.

After some investigation, the NET*** constants are defined here, and the NET***_OR_GREATER constants here. The former has no effect because because we are reassigning a global property, but the latter succeeds because we can reassign global properties inside a Target?

One way of fixing this is to update the NET*** constant definition to use the _ImplicitDefineConstant item, and move it to BeforeCommon.targets, which will also deduplicate the logic from C#, F# and VB. If that sounds good I can open a PR.

[baronfel]

Good observation - this is one of a category of problems that we have due to the duplicate use of global properties. Your proposal sounds good to me, but there are a number of other places that the Roslyn compiler especially is called (Razor and WPF are the main ones I'm thinking of) so we'd need to coordinate/sequence the change.