Make some of the ast_util functions into methods

[Manishearth]

https://github.com/rust-lang/rust/blob/master/src/libsyntax/ast_util.rs

Things like

pub fn stmt_id(s: &Stmt) -> Option<NodeId>

should instead be

impl Stmt {
    pub fn id(s: &Stmt) -> Option<NodeId> {..}
}

The same goes for many other functions that take their first argument as an AST type (BinOp, Stmt, IntTy, Path, Ident, etc. Similarly, functions like these could be Generics::empty() instead.

(Feel free to keep it in the same file or move it to ast.rs)

[faineance]

Is this up for grabs? I'd like to start contributing to Rust.

[faineance]

I presume I'd need to update all usage across the codebase.

[faineance]

I've just noticed a bunch of the extremely similar functions declared in here what's up with that?

[jonas-schievink]

@faineance These are part of the HIR, they should probably be made into methods as well

[faineance]

What do you think about refactoring them into traits?

[jonas-schievink]

I'd prefer plain methods, since that allows to change the HIR without changing the trait or AST - which is basically the point of the HIR. It would also have exactly 2 implementors - AST and HIR - and probably never gain more than that, which makes it a bit useless.

[faineance]

Good point, thanks.

[Manishearth]

Yes, this is up for grabs. Feel free to work on it!

The HIR and AST should stay separate as they will slowly diverge over time.

[Manishearth]

#30105