warning for assignment to temporary #4497

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1. sanxiyn commented on Sep 4, 2019

   

   sanxiyn

   on Sep 4, 2019

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   FYI, this is temporary_assignment lint. rust-lang/rust#53224 is the general issue for upstreaming Clippy lints. (temporary_assignment is not included in that issue, but it probably should be?)
2. flip1995 commented on Sep 4, 2019

   

   flip1995

   on Sep 4, 2019

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   The rust issue only looks at correctness lints. temporary_assignment is a complexity lint. Doing something like this cannot result in wrong code, since you can't use the structure you temporary assigned a value to (The assignment operator = always returns () in Rust, so a = b = 1, will result in a = () and b = 1*).

   So this is valid rust code, that does not have any influence on the correctness of your program. So this doesn't qualify for a rustc lint, because for such cases Clippy exists.

   ---

   * This seems that it may cause errors, but if you would try to use a = () as an integer somewhere in your program, this would be caught by the rust type system, so we're good here.
3. flip1995

   closed this as completedon Sep 4, 2019
4. sanxiyn commented on Sep 4, 2019

   

   sanxiyn

   on Sep 4, 2019

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   I very much disagree in that Rust's standard unused_variables lint is not a correctness issue either. It does make sense to prioritize correctness lints though.
5. flip1995 commented on Sep 4, 2019

   

   flip1995

   on Sep 4, 2019

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   I agree, that rust has lints, that aren't really correctness concerns (most of them are allow-by-default though). But on the other hand, the rust compiler still has a pretty strict "no new lints" rule, except, there are really good reasons to add a new lint. That's why Clippy exists.

   ---

   As a site note: unused_variables can lead to errors:

   let similar_name1 = 10;
   let similar_nameI = 11; // unused_variable
   
   assert_eq!(similar_name1, 11); // panic

   That is a very constructed example, but it does happen in actual code. (BTW, Clippy has a lint for this: https://rust-lang.github.io/rust-clippy/master/index.html#similar_names)