From c0126939617dc86b0c5d29a712ce9e8fc67d2f0f Mon Sep 17 00:00:00 2001 From: Michael Howell Date: Tue, 4 Feb 2025 13:01:32 -0700 Subject: [PATCH] needless_collect: avoid warning if non-iterator methods are used It can make sense to `collect()` an iterator and then immediately iterate over it if the iterator has special methods that you need. For example, the Map iterator doesn't implement Clone, but the collection iterator might. Or the collection iterator might support slicing. --- clippy_lints/src/methods/needless_collect.rs | 71 ++++++++++++++++++-- tests/ui/needless_collect.fixed | 14 ++++ tests/ui/needless_collect.rs | 14 ++++ 3 files changed, 93 insertions(+), 6 deletions(-) diff --git a/clippy_lints/src/methods/needless_collect.rs b/clippy_lints/src/methods/needless_collect.rs index 2780c3f8af5c..6732aeeb4985 100644 --- a/clippy_lints/src/methods/needless_collect.rs +++ b/clippy_lints/src/methods/needless_collect.rs @@ -1,3 +1,5 @@ +use std::ops::ControlFlow; + use super::NEEDLESS_COLLECT; use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_hir_and_then}; use clippy_utils::source::{snippet, snippet_with_applicability}; @@ -9,9 +11,9 @@ use clippy_utils::{ }; use rustc_data_structures::fx::FxHashMap; use rustc_errors::{Applicability, MultiSpan}; -use rustc_hir::intravisit::{Visitor, walk_block, walk_expr}; +use rustc_hir::intravisit::{Visitor, walk_block, walk_expr, walk_stmt}; use rustc_hir::{ - BindingMode, Block, Expr, ExprKind, HirId, HirIdSet, LetStmt, Mutability, Node, PatKind, Stmt, StmtKind, + BindingMode, Block, Expr, ExprKind, HirId, HirIdSet, LetStmt, Mutability, Node, Pat, PatKind, Stmt, StmtKind, }; use rustc_lint::LateContext; use rustc_middle::hir::nested_filter; @@ -103,6 +105,12 @@ pub(super) fn check<'tcx>( return; } + if let IterFunctionKind::IntoIter(hir_id) = iter_call.func + && !check_iter_expr_used_only_as_iterator(cx, hir_id, block) + { + return; + } + // Suggest replacing iter_call with iter_replacement, and removing stmt let mut span = MultiSpan::from_span(name_span); span.push_span_label(iter_call.span, "the iterator could be used here instead"); @@ -253,7 +261,7 @@ struct IterFunction { impl IterFunction { fn get_iter_method(&self, cx: &LateContext<'_>) -> String { match &self.func { - IterFunctionKind::IntoIter => String::new(), + IterFunctionKind::IntoIter(_) => String::new(), IterFunctionKind::Len => String::from(".count()"), IterFunctionKind::IsEmpty => String::from(".next().is_none()"), IterFunctionKind::Contains(span) => { @@ -268,7 +276,7 @@ impl IterFunction { } fn get_suggestion_text(&self) -> &'static str { match &self.func { - IterFunctionKind::IntoIter => { + IterFunctionKind::IntoIter(_) => { "use the original Iterator instead of collecting it and then producing a new one" }, IterFunctionKind::Len => { @@ -284,7 +292,7 @@ impl IterFunction { } } enum IterFunctionKind { - IntoIter, + IntoIter(HirId), Len, IsEmpty, Contains(Span), @@ -343,7 +351,7 @@ impl<'tcx> Visitor<'tcx> for IterFunctionVisitor<'_, 'tcx> { } match method_name.ident.name.as_str() { "into_iter" => self.uses.push(Some(IterFunction { - func: IterFunctionKind::IntoIter, + func: IterFunctionKind::IntoIter(expr.hir_id), span: expr.span, })), "len" => self.uses.push(Some(IterFunction { @@ -520,3 +528,54 @@ fn get_captured_ids(cx: &LateContext<'_>, ty: Ty<'_>) -> HirIdSet { set } + +struct IteratorMethodCheckVisitor<'a, 'tcx> { + cx: &'a LateContext<'tcx>, + hir_id_of_expr: HirId, + hir_id_of_let_binding: Option, +} + +impl<'tcx> Visitor<'tcx> for IteratorMethodCheckVisitor<'_, 'tcx> { + type Result = ControlFlow<()>; + fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) -> ControlFlow<()> { + if let ExprKind::MethodCall(_method_name, recv, _args, _) = &expr.kind + && (recv.hir_id == self.hir_id_of_expr + || self + .hir_id_of_let_binding + .is_some_and(|hid| path_to_local_id(recv, hid))) + && !is_trait_method(self.cx, expr, sym::Iterator) + { + return ControlFlow::Break(()); + } + walk_expr(self, expr) + } + fn visit_stmt(&mut self, stmt: &'tcx Stmt<'tcx>) -> ControlFlow<()> { + if let StmtKind::Let(LetStmt { + init: Some(expr), + pat: + Pat { + kind: PatKind::Binding(BindingMode::NONE | BindingMode::MUT, id, _, None), + .. + }, + .. + }) = &stmt.kind + && expr.hir_id == self.hir_id_of_expr + { + self.hir_id_of_let_binding = Some(*id); + } + walk_stmt(self, stmt) + } +} + +fn check_iter_expr_used_only_as_iterator<'tcx>( + cx: &LateContext<'tcx>, + hir_id_of_expr: HirId, + block: &'tcx Block<'tcx>, +) -> bool { + let mut visitor = IteratorMethodCheckVisitor { + cx, + hir_id_of_expr, + hir_id_of_let_binding: None, + }; + visitor.visit_block(block).is_continue() +} diff --git a/tests/ui/needless_collect.fixed b/tests/ui/needless_collect.fixed index bd83581bdd97..e33b984a44b5 100644 --- a/tests/ui/needless_collect.fixed +++ b/tests/ui/needless_collect.fixed @@ -73,6 +73,20 @@ fn main() { let mut out = vec![]; values.iter().cloned().map(|x| out.push(x)).collect::>(); let _y = values.iter().cloned().map(|x| out.push(x)).collect::>(); // this is fine + + // Don't write a warning if we call `clone()` on the iterator + // https://github.com/rust-lang/rust-clippy/issues/13430 + let my_collection: Vec<()> = vec![()].into_iter().map(|()| {}).collect(); + let _cloned = my_collection.into_iter().clone(); + let my_collection: Vec<()> = vec![()].into_iter().map(|()| {}).collect(); + let my_iter = my_collection.into_iter(); + let _cloned = my_iter.clone(); + // Same for `as_slice()`, for same reason. + let my_collection: Vec<()> = vec![()].into_iter().map(|()| {}).collect(); + let _sliced = my_collection.into_iter().as_slice(); + let my_collection: Vec<()> = vec![()].into_iter().map(|()| {}).collect(); + let my_iter = my_collection.into_iter(); + let _sliced = my_iter.as_slice(); } fn foo(_: impl IntoIterator) {} diff --git a/tests/ui/needless_collect.rs b/tests/ui/needless_collect.rs index 6a81a767bbb6..fab00d67dbfd 100644 --- a/tests/ui/needless_collect.rs +++ b/tests/ui/needless_collect.rs @@ -73,6 +73,20 @@ fn main() { let mut out = vec![]; values.iter().cloned().map(|x| out.push(x)).collect::>(); let _y = values.iter().cloned().map(|x| out.push(x)).collect::>(); // this is fine + + // Don't write a warning if we call `clone()` on the iterator + // https://github.com/rust-lang/rust-clippy/issues/13430 + let my_collection: Vec<()> = vec![()].into_iter().map(|()| {}).collect(); + let _cloned = my_collection.into_iter().clone(); + let my_collection: Vec<()> = vec![()].into_iter().map(|()| {}).collect(); + let my_iter = my_collection.into_iter(); + let _cloned = my_iter.clone(); + // Same for `as_slice()`, for same reason. + let my_collection: Vec<()> = vec![()].into_iter().map(|()| {}).collect(); + let _sliced = my_collection.into_iter().as_slice(); + let my_collection: Vec<()> = vec![()].into_iter().map(|()| {}).collect(); + let my_iter = my_collection.into_iter(); + let _sliced = my_iter.as_slice(); } fn foo(_: impl IntoIterator) {}