Use SwiftSyntax itself to generate SwiftSyntax’s source code

[ahoppen (Alex Hoppen)]

@vrjuliao

There is no way to generate files like the gyb ones. I mean, I could not find any way to format a file, and also comment it. So, maybe, we could provide ways to do that. I can see that there is an auto-indentation tool, but we cannot generate a file like SwiftSyntaxBuilder/gyb_generated/Tokens.swift since it splits the chain of member calls SyntaxFactory.makeSpacedBinaryOperator(text).withLeadingTrivia(.spaces(1)).withTrailingTrivia(.spaces(1)) in multiple lines. I propose to add a TrailingNewLine attribute in some calls and declaraions in order to improve that formatting. For example: in a Chain of member calls, in an ArgumentList, or ArrayDecl for example.

I wouldn’t worry about formatting too much at this point. Formatting is a non-trivial problem to solve and I would suggest running a formatter like swift-format on the code generated by SwiftSyntaxBuilder but that would be a follow-up step after generating the actual code.

@vrjuliao

Furthermore, we don't have an way to provide comments (neither blocks or inline).

Yes, that’s a known limitation at the moment. @iMostfa has some ideas how to fix this in [GSoC 2022] Use SwiftSyntax itself to generate SwiftSyntax’s source code instead of GYB - #9 by iMostfa

@vrjuliao

To create an expression like:

static var `enum`: TokenSyntax{ ... }

We have to nest: VariableDecl -> PatternBinding.accessor -> CodeBlock. Actually, I'm not sure if the expression inside the braces is an accessor (in the Tokens.swift file). It seems like an initialization. So, perhaps we could improve the InitializationClause in order to comply with it.

The code is an accessor and not an initializer because every time you access the enum variable, the code in the braces gets executed to generate TokenSyntax representing the enum keyword. You can see this behavior if you e.g. put a print statement in the accessor. An initializer would be static var `enum`: TokenSyntax = SyntaxFactory.makeEnumKeyword().withTrailingTrivia(.spaces(1))

I agree that the syntax to generate variables is a little verbose at the moment. IMHO adding convenience initializers like the one you added in Tokens.gen.swift is the way forward here.