Add lint for 'field_reassign_with_default` #568

[hegza]

changelog: Add lint for field_reassign_with_default that checks if mutable object + field modification is used to edit a binding initialized with Default::default() instead of struct constructor.

Fixes #568

Notes:

• Checks for immediate reassignment of fields of a binding initialized with Default::default().
• Implemented using EarlyLintPass, might be future proofed better with LateLintPass.
• Does not trigger if Default::default() is used via another type implementing Default.

[bors]

☔ The latest upstream changes (presumably #4788) made this pull request unmergeable. Please resolve the merge conflicts.

[flip1995]

Thanks for implementing this and sorry for not replying. This went under my radar.

Do you think, you could enhance this lint, to also catch more than one assignment. So that

let a = Default::default();
a.i = 42;
a.j = 43;

suggests

let a = A { i: 42, j: 43, ..Default::default() };

[hegza]

Ah, yes, sure, doesn't look too difficult. I'm sure I intended it that way but forgot about it somehow.

[bors]

☔ The latest upstream changes (presumably #5202) made this pull request unmergeable. Please resolve the merge conflicts.

[phansch]

Hi @hegza, are you still interested in continuing the PR? As far as I can tell the last suggestion isn't implemented yet; or there's no test case for it at least.

Let us know if you need any help =)

[hegza]

Yeah, sorry, trying to get papers out at work and really having to push it down on the priority list. I'm interested, just busy.

[flip1995]

Thanks for contributing to Clippy! Sadly this PR was not updated in quite some time. If you waited on input from a reviewer, we're sorry that this fell under the radar. If you want to continue to work on this, just reopen the PR and/or ping a reviewer.

[HKalbasi]

finished in #5911
@rustbot label -S-inactive-closed