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7535: Extract function assist r=cpud36 a=cpud36 This PR adds `extract function/method` assist. closes #5409. # Supported features Assist should support extracting from expressions(`1`, `2 + 2`, `loop { }`) and from a series of statements, e.g.: ```rust foo(); $0bar(); baz();$0 quix(); ``` Assist also supports extracting parameters, like: ```rust fn foo() -> i32 { let n = 1; $0n + 1$0 } // - fn foo() -> i32 { let n = 1; fun_name(n) } fn fun_name(n: i32) -> i32 { n + 1 } ``` Extracting methods also generally works. Assist allows referencing outer variables, both mutably and immutably, and handles handles access to variables local to extracted function: ```rust fn foo() { let mut n = 1; let mut m = 2; let mut moved_v = Vec::new(); let mut ref_mut_v = Vec::new(); $0 n += 1; let k = 1; moved_v.push(n); let r = &mut m; ref_mut_v.push(*r); let h = 3; $0 n = ref_mut_v.len() + k; n -= h + m; } // - fn foo() { let mut n = 1; let mut m = 2; let mut moved_v = Vec::new(); let mut ref_mut_v = Vec::new(); let (k, h) = fun_name(&mut n, moved_v, &mut m, &mut ref_mut_v); n = ref_mut_v.len() + k; n -= h + m; } fn fun_name(n: &mut i32, mut moved_v: Vec<i32>, m: &mut i32, ref_mut_v: &mut Vec<i32>) -> (i32, i32) { *n += 1; let k = 1; moved_v.push(*n); let r = m; ref_mut_v.push(*r); let h = 3; (k, h) } ``` So we handle both input and output paramters # Showcase     # Working with non-`Copy` types Consider the following example: ```rust fn foo() { let v = Vec::new(); $0 let n = v.len(); $0 let is_empty = v.is_empty(); } ``` `v` must be a parameter to extracted function. The question is, what type should it have. It could be `v: Vec<i32>`, or `v: &Vec<i32>`. The former is incorrect for `Vec<i32>`, but the later is silly for `i32`. To resolve this we need to know if the type implements `Copy` trait. I didn't find any api available from assists to query this. `hir_ty::method_resolution::implements` seems relevant, but is isn't publicly re-exported from `hir`. # Star(`*`) token and pointer dereference If I understand correctly, in order to create expression like `*p`, one should use `ast::make::expr_prefix(T![*], ...)`, which in turn calls `token(T![*])`. `token` does not have star in `tokens::SOURCE_FILE`, so this panics. I had to add `*` to `SOURCE_FILE` to make it work. Correct me if this is not intended way to do this. # Lowering access `value -> mut ref -> shared ref` Consider the following example: ```rust fn foo() { let v = Vec::new(); $0 let n = v.len(); $0 } ``` `v` is not used after extracted function body, so both `v: &Vec<i32>` and `v: Vec<i32>` would work. Currently the later would be chosen. We can however check the body of extracted function and conclude that `v: &Vec<i32>` is sufficient. Using `v: &Vec<i32>`(that is a minimal required access level) might be a better default. I am unsure. # Cleanup The assist seems to be reasonably handling most of common cases. If there are no concerns with code it produces(i.e. with test cases), I will start cleaning up [edit] added showcase Co-authored-by: Vladyslav Katasonov <cpud47@gmail.com> |
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rust-analyzer is an experimental modular compiler frontend for the Rust language. It is a part of a larger rls-2.0 effort to create excellent IDE support for Rust.
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