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Auto merge of rust-lang#6706 - Y-Nak:excessive-for-each, r=camsteffen
New Lint: needless_for_each resolves: rust-lang#6543 changelog: Added pedantic lint: `needless_for_each`
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,167 @@ | ||
| use rustc_errors::Applicability; | ||
| use rustc_hir::{ | ||
| intravisit::{walk_expr, NestedVisitorMap, Visitor}, | ||
| Expr, ExprKind, Stmt, StmtKind, | ||
| }; | ||
| use rustc_lint::{LateContext, LateLintPass}; | ||
| use rustc_middle::hir::map::Map; | ||
| use rustc_session::{declare_lint_pass, declare_tool_lint}; | ||
| use rustc_span::{source_map::Span, sym, Symbol}; | ||
|
|
||
| use if_chain::if_chain; | ||
|
|
||
| use clippy_utils::diagnostics::span_lint_and_then; | ||
| use clippy_utils::is_trait_method; | ||
| use clippy_utils::source::snippet_with_applicability; | ||
| use clippy_utils::ty::has_iter_method; | ||
|
|
||
| declare_clippy_lint! { | ||
| /// **What it does:** Checks for usage of `for_each` that would be more simply written as a | ||
| /// `for` loop. | ||
| /// | ||
| /// **Why is this bad?** `for_each` may be used after applying iterator transformers like | ||
| /// `filter` for better readability and performance. It may also be used to fit a simple | ||
| /// operation on one line. | ||
| /// But when none of these apply, a simple `for` loop is more idiomatic. | ||
| /// | ||
| /// **Known problems:** None. | ||
| /// | ||
| /// **Example:** | ||
| /// | ||
| /// ```rust | ||
| /// let v = vec![0, 1, 2]; | ||
| /// v.iter().for_each(|elem| { | ||
| /// println!("{}", elem); | ||
| /// }) | ||
| /// ``` | ||
| /// Use instead: | ||
| /// ```rust | ||
| /// let v = vec![0, 1, 2]; | ||
| /// for elem in v.iter() { | ||
| /// println!("{}", elem); | ||
| /// } | ||
| /// ``` | ||
| pub NEEDLESS_FOR_EACH, | ||
| pedantic, | ||
| "using `for_each` where a `for` loop would be simpler" | ||
| } | ||
|
|
||
| declare_lint_pass!(NeedlessForEach => [NEEDLESS_FOR_EACH]); | ||
|
|
||
| impl LateLintPass<'_> for NeedlessForEach { | ||
| fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) { | ||
| let expr = match stmt.kind { | ||
| StmtKind::Expr(expr) | StmtKind::Semi(expr) => expr, | ||
| _ => return, | ||
| }; | ||
|
|
||
| if_chain! { | ||
| // Check the method name is `for_each`. | ||
| if let ExprKind::MethodCall(method_name, _, [for_each_recv, for_each_arg], _) = expr.kind; | ||
| if method_name.ident.name == Symbol::intern("for_each"); | ||
| // Check `for_each` is an associated function of `Iterator`. | ||
| if is_trait_method(cx, expr, sym::Iterator); | ||
| // Checks the receiver of `for_each` is also a method call. | ||
| if let ExprKind::MethodCall(_, _, [iter_recv], _) = for_each_recv.kind; | ||
| // Skip the lint if the call chain is too long. e.g. `v.field.iter().for_each()` or | ||
| // `v.foo().iter().for_each()` must be skipped. | ||
| if matches!( | ||
| iter_recv.kind, | ||
| ExprKind::Array(..) | ExprKind::Call(..) | ExprKind::Path(..) | ||
| ); | ||
| // Checks the type of the `iter` method receiver is NOT a user defined type. | ||
| if has_iter_method(cx, cx.typeck_results().expr_ty(&iter_recv)).is_some(); | ||
| // Skip the lint if the body is not block because this is simpler than `for` loop. | ||
| // e.g. `v.iter().for_each(f)` is simpler and clearer than using `for` loop. | ||
| if let ExprKind::Closure(_, _, body_id, ..) = for_each_arg.kind; | ||
| let body = cx.tcx.hir().body(body_id); | ||
| if let ExprKind::Block(..) = body.value.kind; | ||
| then { | ||
| let mut ret_collector = RetCollector::default(); | ||
| ret_collector.visit_expr(&body.value); | ||
|
|
||
| // Skip the lint if `return` is used in `Loop` in order not to suggest using `'label`. | ||
| if ret_collector.ret_in_loop { | ||
| return; | ||
| } | ||
|
|
||
| let (mut applicability, ret_suggs) = if ret_collector.spans.is_empty() { | ||
| (Applicability::MachineApplicable, None) | ||
| } else { | ||
| ( | ||
| Applicability::MaybeIncorrect, | ||
| Some( | ||
| ret_collector | ||
| .spans | ||
| .into_iter() | ||
| .map(|span| (span, "continue".to_string())) | ||
| .collect(), | ||
| ), | ||
| ) | ||
| }; | ||
|
|
||
| let sugg = format!( | ||
| "for {} in {} {}", | ||
| snippet_with_applicability(cx, body.params[0].pat.span, "..", &mut applicability), | ||
| snippet_with_applicability(cx, for_each_recv.span, "..", &mut applicability), | ||
| snippet_with_applicability(cx, body.value.span, "..", &mut applicability), | ||
| ); | ||
|
|
||
| span_lint_and_then(cx, NEEDLESS_FOR_EACH, stmt.span, "needless use of `for_each`", |diag| { | ||
| diag.span_suggestion(stmt.span, "try", sugg, applicability); | ||
| if let Some(ret_suggs) = ret_suggs { | ||
| diag.multipart_suggestion("...and replace `return` with `continue`", ret_suggs, applicability); | ||
| } | ||
| }) | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// This type plays two roles. | ||
| /// 1. Collect spans of `return` in the closure body. | ||
| /// 2. Detect use of `return` in `Loop` in the closure body. | ||
| /// | ||
| /// NOTE: The functionality of this type is similar to | ||
| /// [`crate::utilts::visitors::find_all_ret_expressions`], but we can't use | ||
| /// `find_all_ret_expressions` instead of this type. The reasons are: | ||
| /// 1. `find_all_ret_expressions` passes the argument of `ExprKind::Ret` to a callback, but what we | ||
| /// need here is `ExprKind::Ret` itself. | ||
| /// 2. We can't trace current loop depth with `find_all_ret_expressions`. | ||
| #[derive(Default)] | ||
| struct RetCollector { | ||
| spans: Vec<Span>, | ||
| ret_in_loop: bool, | ||
| loop_depth: u16, | ||
| } | ||
|
|
||
| impl<'tcx> Visitor<'tcx> for RetCollector { | ||
| type Map = Map<'tcx>; | ||
|
|
||
| fn visit_expr(&mut self, expr: &Expr<'_>) { | ||
| match expr.kind { | ||
| ExprKind::Ret(..) => { | ||
| if self.loop_depth > 0 && !self.ret_in_loop { | ||
| self.ret_in_loop = true | ||
| } | ||
|
|
||
| self.spans.push(expr.span) | ||
| }, | ||
|
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||
| ExprKind::Loop(..) => { | ||
| self.loop_depth += 1; | ||
| walk_expr(self, expr); | ||
| self.loop_depth -= 1; | ||
| return; | ||
| }, | ||
|
|
||
| _ => {}, | ||
| } | ||
|
|
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| walk_expr(self, expr); | ||
| } | ||
|
|
||
| fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { | ||
| NestedVisitorMap::None | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,113 @@ | ||
| // run-rustfix | ||
| #![warn(clippy::needless_for_each)] | ||
| #![allow(unused, clippy::needless_return, clippy::match_single_binding)] | ||
|
|
||
| use std::collections::HashMap; | ||
|
|
||
| fn should_lint() { | ||
| let v: Vec<i32> = Vec::new(); | ||
| let mut acc = 0; | ||
| for elem in v.iter() { | ||
| acc += elem; | ||
| } | ||
| for elem in v.into_iter() { | ||
| acc += elem; | ||
| } | ||
|
|
||
| for elem in [1, 2, 3].iter() { | ||
| acc += elem; | ||
| } | ||
|
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||
| let mut hash_map: HashMap<i32, i32> = HashMap::new(); | ||
| for (k, v) in hash_map.iter() { | ||
| acc += k + v; | ||
| } | ||
| for (k, v) in hash_map.iter_mut() { | ||
| acc += *k + *v; | ||
| } | ||
| for k in hash_map.keys() { | ||
| acc += k; | ||
| } | ||
| for v in hash_map.values() { | ||
| acc += v; | ||
| } | ||
|
|
||
| fn my_vec() -> Vec<i32> { | ||
| Vec::new() | ||
| } | ||
| for elem in my_vec().iter() { | ||
| acc += elem; | ||
| } | ||
| } | ||
|
|
||
| fn should_not_lint() { | ||
| let v: Vec<i32> = Vec::new(); | ||
| let mut acc = 0; | ||
|
|
||
| // `for_each` argument is not closure. | ||
| fn print(x: &i32) { | ||
| println!("{}", x); | ||
| } | ||
| v.iter().for_each(print); | ||
|
|
||
| // User defined type. | ||
| struct MyStruct { | ||
| v: Vec<i32>, | ||
| } | ||
| impl MyStruct { | ||
| fn iter(&self) -> impl Iterator<Item = &i32> { | ||
| self.v.iter() | ||
| } | ||
| } | ||
| let s = MyStruct { v: Vec::new() }; | ||
| s.iter().for_each(|elem| { | ||
| acc += elem; | ||
| }); | ||
|
|
||
| // `for_each` follows long iterator chain. | ||
| v.iter().chain(v.iter()).for_each(|v| { | ||
| acc += v; | ||
| }); | ||
| v.as_slice().iter().for_each(|v| { | ||
| acc += v; | ||
| }); | ||
| s.v.iter().for_each(|v| { | ||
| acc += v; | ||
| }); | ||
|
|
||
| // `return` is used in `Loop` of the closure. | ||
| v.iter().for_each(|v| { | ||
| for i in 0..*v { | ||
| if i == 10 { | ||
| return; | ||
| } else { | ||
| println!("{}", v); | ||
| } | ||
| } | ||
| if *v == 20 { | ||
| return; | ||
| } else { | ||
| println!("{}", v); | ||
| } | ||
| }); | ||
|
|
||
| // Previously transformed iterator variable. | ||
| let it = v.iter(); | ||
| it.chain(v.iter()).for_each(|elem| { | ||
| acc += elem; | ||
| }); | ||
|
|
||
| // `for_each` is not directly in a statement. | ||
| match 1 { | ||
| _ => v.iter().for_each(|elem| { | ||
| acc += elem; | ||
| }), | ||
| } | ||
|
|
||
| // `for_each` is in a let bingind. | ||
| let _ = v.iter().for_each(|elem| { | ||
| acc += elem; | ||
| }); | ||
| } | ||
|
|
||
| fn main() {} |
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