Lint to suggest clone_from and clone_into

[clarfonthey]

Basically, we'd suggest the following replacements:

a = b.clone() => a.clone_from(&b)
a = b.to_owned() => b.clone_into(&mut a)

[luisbg]

Is anybody working on this one? If not, I am happy to do it.

Looks like a good new contributor issue 😄

[oli-obk]

@luisbg it's all yours! Feel free to ask questions here or open a prototype PR in any level of completeness if you have questions.

[oli-obk]

Note that this should not lint in case a has never been assigned before:

let a = b.clone();

/// or

let a;

....

a = b.clone();

[luisbg]

Great! Will start working on it and share progress soon

[llogiq]

Fantastic! Feel free to push early if you like to discuss. It's easier to discuss a WIP PR if it actually exists. 😄

[luisbg]

I have created some boilerplate code in the following commit:
luisbg@38c59c2

Wanted to be sure I am going in the right direction and not sure how to proceed with checking the expression.

I have been following @llogiq 's blogpost [0], but not clear how to do the check_item() since lints seem to use rustc::hir now instead of syntax::ast.

Any advice? Thanks! 😃

[0] https://llogiq.github.io/2015/06/04/workflows.html

[Manishearth]

hir is basically a different AST.

http://manishearth.github.io/rust-internals-docs/rustc/hir/enum.Expr_.html may help with figuring out how the HIR works.