Auto-generated program for F# breaks compilation

[rojepp]

Description

In #1664, @saul added automatic generation of a main method. This breaks compilation for <OutputType>Exe</OutputType>, as it is generated even if there is already a main method. Compiling then gives the error

error FS0433: A function labeled with the 'EntryPointAttribute' attribute must be the last declaration in the last file in the compilation sequence.

I ran into this using MiniScaffold template. There, the Test app has a Main.fs, not a Program.fs .
Checking for a hard-coded filename seems like a too weak of a check, and I'd rather have no generation at all (and not have to find out about an obscure switch to turn this magic off.

Because of this magic, this took a really long time to find. Users can be expected to know that there should be a main method in exe programs.

[saul]

@rojepp what are you proposing as the solution?

The MiniScaffold template be setting the property to not autogenerate a program, as other templates did when this change was rolled out.

[rojepp]

Reading the background issue more thoroughly, I don't have a better option. For reference, the property to set is GenerateProgramFile.

[saul]

@rojepp at a minimum I think the compiler error should be improved (although that will be an issue for Microsoft/visualfsharp). The compiler error should log the file that is the last compile item - that would at least show you where to look.

It may also help if the auto-generated Program.fs had a comment explaining how to disable its generation.