Add check on redundant _ variables in structs

[GuillaumeGomez]

cc #479

This is just preview. I need help on some point:

• My code is called, but the lint is never displayed, why?
• Is the code correct? I'm not sure the way I search for the "_" pattern is the best.
• Is the comparison correct? I translate a type into a String, but isn't there another way?

Thanks in advance for your help. :)

[Manishearth]

You dont need pprust here; just check if its a PatWild

[Manishearth]

I would prefer if this were in its own file (pat.rs?) as an EarlyLintPass. Remember to register the pass in lib.rs!

[GuillaumeGomez]

I updated and added a more precise check. What do you think of it?

PS: it seems to break build because rut-clippy source code has issues like this in the code...

[llogiq]

A good idea would be to give a hint what the pattern would look like, which should be possible using utils::snippet(..) on the remaining pattern elements. Also we should follow our own advice and change the code to no longer trigger the lint.

[GuillaumeGomez]

@llogiq: This is a bit problematic because changing it seems to break. If we remove one field, it breaks because it says "[field] isn't bound".

[llogiq]

Have you added , ..? If that doesn't work, perhaps the lint is overzealous?

[llogiq]

Does that single space change anything about the code? Otherwise I think we may remove it from the change to reduce diff clutter. 😄

[GuillaumeGomez]

Oups. :p

[GuillaumeGomez]

@llogiq: I did, but I must have made a mistake somewhere else. Code updated.

[Manishearth]

Should be only one lint, unneeded_bindings. The actual message can be tweaked to handle plurals, but we don't want to create two lints for plurality.

[Manishearth]

dogfood failure

src/misc_early.rs:25:9: 51:10 error: you seem to be trying to use match for destructuring a single pattern. Consider using `if let` [-D single-match]
src/misc_early.rs:25         match pat.node {
src/misc_early.rs:26             PatStruct(_, ref pfields, _) => {
src/misc_early.rs:27                 let mut wilds = 0;
src/misc_early.rs:28 
src/misc_early.rs:29                 for field in pfields {
src/misc_early.rs:30                     if field.node.pat.node == PatWild {
                     ...
src/misc_early.rs:25:9: 51:10 help: try
if let PatStruct(_, ref pfields, _) = pat.node {
    let mut wilds = 0;

    for field in pfields {
        if field.node.pat.node == PatWild {
            wilds += 1;
        }
    }
    if pfields.len() > 0 && wilds == pfields.len() {
        span_lint(cx, UNNEEDED_BINDINGS, pat.span,
                  "All your fields are bound but not used. \
                   Consider replacing them with `..`");
        return;
    }
    if wilds > 0 {
        for field in pfields {
            if field.node.pat.node == PatWild {
                span_lint(cx, UNNEEDED_BINDING, field.span,
                          "You bound a field that's not being used. \
                           Consider using `..`");
            }
        }
    }
}
for further information visit https://github.com/Manishearth/rust-clippy/wiki#single_match
src/misc_early.rs:34:20: 34:37 error: consider replacing the len comparison with `!pfields.is_empty()` [-D len-zero]
src/misc_early.rs:34                 if pfields.len() > 0 && wilds == pfields.len() {
                                        ^~~~~~~~~~~~~~~~~
src/misc_early.rs:34:20: 34:37 help: for further information visit https://github.com/Manishearth/rust-clippy/wiki#len_zero
error: aborting due to 2 previous errors