Un-xfail working test #7346
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Un-xfail working test #7346
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Taking this on my incoming branch. |
flip1995
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Jul 15, 2021
fix 5707 changelog: ``[`redundant_clone`]``, fix rust-lang#5707 # Root problem of rust-lang#5707 : ``` &2:&mut HashMap = &mut _4; &3:&str = & _5; _1 = HashMap::insert(move _2,move _3, _); ``` generate PossibleBorrower(_2,_1) and PossibleBorrower(_3,_1). However, it misses PossibleBorrower(_3,_2). # My solution to rust-lang#5707 : When meet a function call, we should: 1. build PossibleBorrower between borrow parameters and return value (currently) 2. build PossibleBorrower between immutable borrow parameters and mutable borrow parameters (*add*) 3. build PossibleBorrower inside mutable borrow parameters (*add*) For example: ``` _2: &mut _22; _3: &mut _; _4: & _; _5: & _; _1 = call(move _2, move _3, move _4, move _5); ``` we need to build 1. return value with parameter(current implementataion) PossibleBorrower(_2,_1) PossibleBorrower(_3,_1) PossibleBorrower(_4,_1) PossibleBorrower(_5,_1) 2. between mutable borrow and immutable borrow PossibleBorrower(_4,_2) PossibleBorrower(_5,_2) PossibleBorrower(_4,_3) PossibleBorrower(_5,_3) 3. between mutable borrow and mutable borrow PossibleBorrower(_3,_2) PossibleBorrower(_2,_3) But that's not enough. Modification to _2 actually apply to _22. So I write a `PossibleBorrowed` visitor, which tracks (borrower => possible borrowed) relation. For example (_2 => _22). However, a lot of problems exist here. ## Known Problems: 1. not sure all `&mut`'s origin are collected. I'm not sure how to deal with `&mut` when meet a function call, so I didn't do it currently. Also, my implement is not flow sensitive, so it's not accurate. ``` foo(_2:&mut _, _3: &_) ``` This pr doesn't count _3 as origin of _2. 2. introduce false negative `foo(_2, _3)` will emit PossibleBorrower(_3,_2) in this pr, but _3 and _2 may not have relation. Clippy may feel that _3 is still in use because of _2, but actually, _3 is on longer needed and can be moved. ## Insight The key problem is determine where every `&mut` come from accurately. I think Polonius is an elegant solution to it. Polonius is flow sensitive and accurate. But I'm uncertain about whether we can import Polonius in rust-clippy currently. This pr actually is part of Polonius' functionality, I think. # TODO 1. `cargo test` can't pass yet due to similar variable name
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