diff options
Diffstat (limited to 'clippy_lints/src/loops')
20 files changed, 3387 insertions, 0 deletions
diff --git a/clippy_lints/src/loops/empty_loop.rs b/clippy_lints/src/loops/empty_loop.rs new file mode 100644 index 00000000000..43e85538f28 --- /dev/null +++ b/clippy_lints/src/loops/empty_loop.rs @@ -0,0 +1,17 @@ +use super::EMPTY_LOOP; +use crate::utils::{is_in_panic_handler, is_no_std_crate, span_lint_and_help}; + +use rustc_hir::{Block, Expr}; +use rustc_lint::LateContext; + +pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, loop_block: &'tcx Block<'_>) { + if loop_block.stmts.is_empty() && loop_block.expr.is_none() && !is_in_panic_handler(cx, expr) { + let msg = "empty `loop {}` wastes CPU cycles"; + let help = if is_no_std_crate(cx) { + "you should either use `panic!()` or add a call pausing or sleeping the thread to the loop body" + } else { + "you should either use `panic!()` or add `std::thread::sleep(..);` to the loop body" + }; + span_lint_and_help(cx, EMPTY_LOOP, expr.span, msg, None, help); + } +} diff --git a/clippy_lints/src/loops/explicit_counter_loop.rs b/clippy_lints/src/loops/explicit_counter_loop.rs new file mode 100644 index 00000000000..8d98b940c66 --- /dev/null +++ b/clippy_lints/src/loops/explicit_counter_loop.rs @@ -0,0 +1,58 @@ +use super::{ + get_span_of_entire_for_loop, make_iterator_snippet, IncrementVisitor, InitializeVisitor, EXPLICIT_COUNTER_LOOP, +}; +use crate::utils::{get_enclosing_block, is_integer_const, snippet_with_applicability, span_lint_and_sugg}; +use if_chain::if_chain; +use rustc_errors::Applicability; +use rustc_hir::intravisit::{walk_block, walk_expr}; +use rustc_hir::{Expr, Pat}; +use rustc_lint::LateContext; + +// To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be +// incremented exactly once in the loop body, and initialized to zero +// at the start of the loop. +pub(super) fn check<'tcx>( + cx: &LateContext<'tcx>, + pat: &'tcx Pat<'_>, + arg: &'tcx Expr<'_>, + body: &'tcx Expr<'_>, + expr: &'tcx Expr<'_>, +) { + // Look for variables that are incremented once per loop iteration. + let mut increment_visitor = IncrementVisitor::new(cx); + walk_expr(&mut increment_visitor, body); + + // For each candidate, check the parent block to see if + // it's initialized to zero at the start of the loop. + if let Some(block) = get_enclosing_block(&cx, expr.hir_id) { + for id in increment_visitor.into_results() { + let mut initialize_visitor = InitializeVisitor::new(cx, expr, id); + walk_block(&mut initialize_visitor, block); + + if_chain! { + if let Some((name, initializer)) = initialize_visitor.get_result(); + if is_integer_const(cx, initializer, 0); + then { + let mut applicability = Applicability::MachineApplicable; + + let for_span = get_span_of_entire_for_loop(expr); + + span_lint_and_sugg( + cx, + EXPLICIT_COUNTER_LOOP, + for_span.with_hi(arg.span.hi()), + &format!("the variable `{}` is used as a loop counter", name), + "consider using", + format!( + "for ({}, {}) in {}.enumerate()", + name, + snippet_with_applicability(cx, pat.span, "item", &mut applicability), + make_iterator_snippet(cx, arg, &mut applicability), + ), + applicability, + ); + } + } + } + } +} diff --git a/clippy_lints/src/loops/explicit_into_iter_loop.rs b/clippy_lints/src/loops/explicit_into_iter_loop.rs new file mode 100644 index 00000000000..1d778205a2a --- /dev/null +++ b/clippy_lints/src/loops/explicit_into_iter_loop.rs @@ -0,0 +1,27 @@ +use super::EXPLICIT_INTO_ITER_LOOP; +use crate::utils::{snippet_with_applicability, span_lint_and_sugg}; +use rustc_errors::Applicability; +use rustc_hir::Expr; +use rustc_lint::LateContext; +use rustc_middle::ty::TyS; + +pub(super) fn check(cx: &LateContext<'_>, args: &'hir [Expr<'hir>], arg: &Expr<'_>) { + let receiver_ty = cx.typeck_results().expr_ty(&args[0]); + let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]); + if !TyS::same_type(receiver_ty, receiver_ty_adjusted) { + return; + } + + let mut applicability = Applicability::MachineApplicable; + let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability); + span_lint_and_sugg( + cx, + EXPLICIT_INTO_ITER_LOOP, + arg.span, + "it is more concise to loop over containers instead of using explicit \ + iteration methods", + "to write this more concisely, try", + object.to_string(), + applicability, + ); +} diff --git a/clippy_lints/src/loops/explicit_iter_loop.rs b/clippy_lints/src/loops/explicit_iter_loop.rs new file mode 100644 index 00000000000..9683e59a396 --- /dev/null +++ b/clippy_lints/src/loops/explicit_iter_loop.rs @@ -0,0 +1,74 @@ +use super::EXPLICIT_ITER_LOOP; +use crate::utils::{match_trait_method, snippet_with_applicability, span_lint_and_sugg}; +use rustc_errors::Applicability; +use rustc_hir::{Expr, Mutability}; +use rustc_lint::LateContext; +use rustc_middle::ty::{self, Ty, TyS}; +use rustc_span::sym; + +use crate::utils::{is_type_diagnostic_item, match_type, paths}; + +pub(super) fn check(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) { + let should_lint = match method_name { + "iter" | "iter_mut" => is_ref_iterable_type(cx, &args[0]), + "into_iter" if match_trait_method(cx, arg, &paths::INTO_ITERATOR) => { + let receiver_ty = cx.typeck_results().expr_ty(&args[0]); + let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]); + let ref_receiver_ty = cx.tcx.mk_ref( + cx.tcx.lifetimes.re_erased, + ty::TypeAndMut { + ty: receiver_ty, + mutbl: Mutability::Not, + }, + ); + TyS::same_type(receiver_ty_adjusted, ref_receiver_ty) + }, + _ => false, + }; + + if !should_lint { + return; + } + + let mut applicability = Applicability::MachineApplicable; + let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability); + let muta = if method_name == "iter_mut" { "mut " } else { "" }; + span_lint_and_sugg( + cx, + EXPLICIT_ITER_LOOP, + arg.span, + "it is more concise to loop over references to containers instead of using explicit \ + iteration methods", + "to write this more concisely, try", + format!("&{}{}", muta, object), + applicability, + ) +} + +/// Returns `true` if the type of expr is one that provides `IntoIterator` impls +/// for `&T` and `&mut T`, such as `Vec`. +#[rustfmt::skip] +fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool { + // no walk_ptrs_ty: calling iter() on a reference can make sense because it + // will allow further borrows afterwards + let ty = cx.typeck_results().expr_ty(e); + is_iterable_array(ty, cx) || + is_type_diagnostic_item(cx, ty, sym::vec_type) || + match_type(cx, ty, &paths::LINKED_LIST) || + is_type_diagnostic_item(cx, ty, sym::hashmap_type) || + is_type_diagnostic_item(cx, ty, sym::hashset_type) || + is_type_diagnostic_item(cx, ty, sym::vecdeque_type) || + match_type(cx, ty, &paths::BINARY_HEAP) || + match_type(cx, ty, &paths::BTREEMAP) || + match_type(cx, ty, &paths::BTREESET) +} + +fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool { + // IntoIterator is currently only implemented for array sizes <= 32 in rustc + match ty.kind() { + ty::Array(_, n) => n + .try_eval_usize(cx.tcx, cx.param_env) + .map_or(false, |val| (0..=32).contains(&val)), + _ => false, + } +} diff --git a/clippy_lints/src/loops/for_kv_map.rs b/clippy_lints/src/loops/for_kv_map.rs new file mode 100644 index 00000000000..6ee9b95a3b6 --- /dev/null +++ b/clippy_lints/src/loops/for_kv_map.rs @@ -0,0 +1,71 @@ +use super::FOR_KV_MAP; +use crate::utils::visitors::LocalUsedVisitor; +use crate::utils::{is_type_diagnostic_item, match_type, multispan_sugg, paths, snippet, span_lint_and_then, sugg}; +use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability, Pat, PatKind}; +use rustc_lint::LateContext; +use rustc_middle::ty; +use rustc_span::sym; + +/// Checks for the `FOR_KV_MAP` lint. +pub(super) fn check<'tcx>( + cx: &LateContext<'tcx>, + pat: &'tcx Pat<'_>, + arg: &'tcx Expr<'_>, + body: &'tcx Expr<'_>, + expr: &'tcx Expr<'_>, +) { + let pat_span = pat.span; + + if let PatKind::Tuple(ref pat, _) = pat.kind { + if pat.len() == 2 { + let arg_span = arg.span; + let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() { + ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) { + (key, _) if pat_is_wild(cx, key, body) => (pat[1].span, "value", ty, mutbl), + (_, value) if pat_is_wild(cx, value, body) => (pat[0].span, "key", ty, Mutability::Not), + _ => return, + }, + _ => return, + }; + let mutbl = match mutbl { + Mutability::Not => "", + Mutability::Mut => "_mut", + }; + let arg = match arg.kind { + ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr, + _ => arg, + }; + + if is_type_diagnostic_item(cx, ty, sym::hashmap_type) || match_type(cx, ty, &paths::BTREEMAP) { + span_lint_and_then( + cx, + FOR_KV_MAP, + expr.span, + &format!("you seem to want to iterate on a map's {}s", kind), + |diag| { + let map = sugg::Sugg::hir(cx, arg, "map"); + multispan_sugg( + diag, + "use the corresponding method", + vec![ + (pat_span, snippet(cx, new_pat_span, kind).into_owned()), + (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)), + ], + ); + }, + ); + } + } + } +} + +/// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`. +fn pat_is_wild<'tcx>(cx: &LateContext<'tcx>, pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool { + match *pat { + PatKind::Wild => true, + PatKind::Binding(_, id, ident, None) if ident.as_str().starts_with('_') => { + !LocalUsedVisitor::new(cx, id).check_expr(body) + }, + _ => false, + } +} diff --git a/clippy_lints/src/loops/for_loops_over_fallibles.rs b/clippy_lints/src/loops/for_loops_over_fallibles.rs new file mode 100644 index 00000000000..db22d90a304 --- /dev/null +++ b/clippy_lints/src/loops/for_loops_over_fallibles.rs @@ -0,0 +1,45 @@ +use super::FOR_LOOPS_OVER_FALLIBLES; +use crate::utils::{is_type_diagnostic_item, snippet, span_lint_and_help}; +use rustc_hir::{Expr, Pat}; +use rustc_lint::LateContext; +use rustc_span::symbol::sym; + +/// Checks for `for` loops over `Option`s and `Result`s. +pub(super) fn check(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) { + let ty = cx.typeck_results().expr_ty(arg); + if is_type_diagnostic_item(cx, ty, sym::option_type) { + span_lint_and_help( + cx, + FOR_LOOPS_OVER_FALLIBLES, + arg.span, + &format!( + "for loop over `{0}`, which is an `Option`. This is more readably written as an \ + `if let` statement", + snippet(cx, arg.span, "_") + ), + None, + &format!( + "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`", + snippet(cx, pat.span, "_"), + snippet(cx, arg.span, "_") + ), + ); + } else if is_type_diagnostic_item(cx, ty, sym::result_type) { + span_lint_and_help( + cx, + FOR_LOOPS_OVER_FALLIBLES, + arg.span, + &format!( + "for loop over `{0}`, which is a `Result`. This is more readably written as an \ + `if let` statement", + snippet(cx, arg.span, "_") + ), + None, + &format!( + "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`", + snippet(cx, pat.span, "_"), + snippet(cx, arg.span, "_") + ), + ); + } +} diff --git a/clippy_lints/src/loops/iter_next_loop.rs b/clippy_lints/src/loops/iter_next_loop.rs new file mode 100644 index 00000000000..cf78bbc49a3 --- /dev/null +++ b/clippy_lints/src/loops/iter_next_loop.rs @@ -0,0 +1,19 @@ +use super::ITER_NEXT_LOOP; +use crate::utils::{match_trait_method, paths, span_lint}; +use rustc_hir::Expr; +use rustc_lint::LateContext; + +pub(super) fn check(cx: &LateContext<'_>, arg: &Expr<'_>, expr: &Expr<'_>) -> bool { + if match_trait_method(cx, arg, &paths::ITERATOR) { + span_lint( + cx, + ITER_NEXT_LOOP, + expr.span, + "you are iterating over `Iterator::next()` which is an Option; this will compile but is \ + probably not what you want", + ); + true + } else { + false + } +} diff --git a/clippy_lints/src/loops/manual_flatten.rs b/clippy_lints/src/loops/manual_flatten.rs new file mode 100644 index 00000000000..3d3ae6f3152 --- /dev/null +++ b/clippy_lints/src/loops/manual_flatten.rs @@ -0,0 +1,79 @@ +use super::utils::make_iterator_snippet; +use super::MANUAL_FLATTEN; +use crate::utils::{is_ok_ctor, is_some_ctor, path_to_local_id, span_lint_and_then}; +use if_chain::if_chain; +use rustc_errors::Applicability; +use rustc_hir::{Expr, ExprKind, MatchSource, Pat, PatKind, QPath, StmtKind}; +use rustc_lint::LateContext; +use rustc_span::source_map::Span; + +/// Check for unnecessary `if let` usage in a for loop where only the `Some` or `Ok` variant of the +/// iterator element is used. +pub(super) fn check<'tcx>( + cx: &LateContext<'tcx>, + pat: &'tcx Pat<'_>, + arg: &'tcx Expr<'_>, + body: &'tcx Expr<'_>, + span: Span, +) { + if let ExprKind::Block(ref block, _) = body.kind { + // Ensure the `if let` statement is the only expression or statement in the for-loop + let inner_expr = if block.stmts.len() == 1 && block.expr.is_none() { + let match_stmt = &block.stmts[0]; + if let StmtKind::Semi(inner_expr) = match_stmt.kind { + Some(inner_expr) + } else { + None + } + } else if block.stmts.is_empty() { + block.expr + } else { + None + }; + + if_chain! { + if let Some(inner_expr) = inner_expr; + if let ExprKind::Match( + ref match_expr, ref match_arms, MatchSource::IfLetDesugar{ contains_else_clause: false } + ) = inner_expr.kind; + // Ensure match_expr in `if let` statement is the same as the pat from the for-loop + if let PatKind::Binding(_, pat_hir_id, _, _) = pat.kind; + if path_to_local_id(match_expr, pat_hir_id); + // Ensure the `if let` statement is for the `Some` variant of `Option` or the `Ok` variant of `Result` + if let PatKind::TupleStruct(QPath::Resolved(None, path), _, _) = match_arms[0].pat.kind; + let some_ctor = is_some_ctor(cx, path.res); + let ok_ctor = is_ok_ctor(cx, path.res); + if some_ctor || ok_ctor; + let if_let_type = if some_ctor { "Some" } else { "Ok" }; + + then { + // Prepare the error message + let msg = format!("unnecessary `if let` since only the `{}` variant of the iterator element is used", if_let_type); + + // Prepare the help message + let mut applicability = Applicability::MaybeIncorrect; + let arg_snippet = make_iterator_snippet(cx, arg, &mut applicability); + + span_lint_and_then( + cx, + MANUAL_FLATTEN, + span, + &msg, + |diag| { + let sugg = format!("{}.flatten()", arg_snippet); + diag.span_suggestion( + arg.span, + "try", + sugg, + Applicability::MaybeIncorrect, + ); + diag.span_help( + inner_expr.span, + "...and remove the `if let` statement in the for loop", + ); + } + ); + } + } + } +} diff --git a/clippy_lints/src/loops/manual_memcpy.rs b/clippy_lints/src/loops/manual_memcpy.rs new file mode 100644 index 00000000000..fad96c2d5c0 --- /dev/null +++ b/clippy_lints/src/loops/manual_memcpy.rs @@ -0,0 +1,451 @@ +use super::{get_span_of_entire_for_loop, IncrementVisitor, InitializeVisitor, MANUAL_MEMCPY}; +use crate::utils::sugg::Sugg; +use crate::utils::{ + get_enclosing_block, higher, is_type_diagnostic_item, path_to_local, snippet, span_lint_and_sugg, sugg, +}; +use if_chain::if_chain; +use rustc_ast::ast; +use rustc_errors::Applicability; +use rustc_hir::intravisit::walk_block; +use rustc_hir::{BinOpKind, Block, Expr, ExprKind, HirId, Pat, PatKind, StmtKind}; +use rustc_lint::LateContext; +use rustc_middle::ty::{self, Ty}; +use rustc_span::symbol::sym; +use std::iter::Iterator; + +/// Checks for for loops that sequentially copy items from one slice-like +/// object to another. +pub(super) fn check<'tcx>( + cx: &LateContext<'tcx>, + pat: &'tcx Pat<'_>, + arg: &'tcx Expr<'_>, + body: &'tcx Expr<'_>, + expr: &'tcx Expr<'_>, +) -> bool { + if let Some(higher::Range { + start: Some(start), + end: Some(end), + limits, + }) = higher::range(arg) + { + // the var must be a single name + if let PatKind::Binding(_, canonical_id, _, _) = pat.kind { + let mut starts = vec![Start { + id: canonical_id, + kind: StartKind::Range, + }]; + + // This is one of few ways to return different iterators + // derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434 + let mut iter_a = None; + let mut iter_b = None; + + if let ExprKind::Block(block, _) = body.kind { + if let Some(loop_counters) = get_loop_counters(cx, block, expr) { + starts.extend(loop_counters); + } + iter_a = Some(get_assignments(block, &starts)); + } else { + iter_b = Some(get_assignment(body)); + } + + let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter()); + + let big_sugg = assignments + // The only statements in the for loops can be indexed assignments from + // indexed retrievals (except increments of loop counters). + .map(|o| { + o.and_then(|(lhs, rhs)| { + let rhs = fetch_cloned_expr(rhs); + if_chain! { + if let ExprKind::Index(base_left, idx_left) = lhs.kind; + if let ExprKind::Index(base_right, idx_right) = rhs.kind; + if is_slice_like(cx, cx.typeck_results().expr_ty(base_left)) + && is_slice_like(cx, cx.typeck_results().expr_ty(base_right)); + if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts); + if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts); + + // Source and destination must be different + if path_to_local(base_left) != path_to_local(base_right); + then { + Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left }, + IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right })) + } else { + None + } + } + }) + }) + .map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src))) + .collect::<Option<Vec<_>>>() + .filter(|v| !v.is_empty()) + .map(|v| v.join("\n ")); + + if let Some(big_sugg) = big_sugg { + span_lint_and_sugg( + cx, + MANUAL_MEMCPY, + get_span_of_entire_for_loop(expr), + "it looks like you're manually copying between slices", + "try replacing the loop by", + big_sugg, + Applicability::Unspecified, + ); + return true; + } + } + } + false +} + +fn build_manual_memcpy_suggestion<'tcx>( + cx: &LateContext<'tcx>, + start: &Expr<'_>, + end: &Expr<'_>, + limits: ast::RangeLimits, + dst: &IndexExpr<'_>, + src: &IndexExpr<'_>, +) -> String { + fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> { + if offset.as_str() == "0" { + sugg::EMPTY.into() + } else { + offset + } + } + + let print_limit = |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| { + if_chain! { + if let ExprKind::MethodCall(method, _, len_args, _) = end.kind; + if method.ident.name == sym!(len); + if len_args.len() == 1; + if let Some(arg) = len_args.get(0); + if path_to_local(arg) == path_to_local(base); + then { + if sugg.as_str() == end_str { + sugg::EMPTY.into() + } else { + sugg + } + } else { + match limits { + ast::RangeLimits::Closed => { + sugg + &sugg::ONE.into() + }, + ast::RangeLimits::HalfOpen => sugg, + } + } + } + }; + + let start_str = Sugg::hir(cx, start, "").into(); + let end_str: MinifyingSugg<'_> = Sugg::hir(cx, end, "").into(); + + let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx { + StartKind::Range => ( + print_offset(apply_offset(&start_str, &idx_expr.idx_offset)).into_sugg(), + print_limit( + end, + end_str.as_str(), + idx_expr.base, + apply_offset(&end_str, &idx_expr.idx_offset), + ) + .into_sugg(), + ), + StartKind::Counter { initializer } => { + let counter_start = Sugg::hir(cx, initializer, "").into(); + ( + print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)).into_sugg(), + print_limit( + end, + end_str.as_str(), + idx_expr.base, + apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str, + ) + .into_sugg(), + ) + }, + }; + + let (dst_offset, dst_limit) = print_offset_and_limit(&dst); + let (src_offset, src_limit) = print_offset_and_limit(&src); + + let dst_base_str = snippet(cx, dst.base.span, "???"); + let src_base_str = snippet(cx, src.base.span, "???"); + + let dst = if dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY { + dst_base_str + } else { + format!( + "{}[{}..{}]", + dst_base_str, + dst_offset.maybe_par(), + dst_limit.maybe_par() + ) + .into() + }; + + format!( + "{}.clone_from_slice(&{}[{}..{}]);", + dst, + src_base_str, + src_offset.maybe_par(), + src_limit.maybe_par() + ) +} + +/// a wrapper of `Sugg`. Besides what `Sugg` do, this removes unnecessary `0`; +/// and also, it avoids subtracting a variable from the same one by replacing it with `0`. +/// it exists for the convenience of the overloaded operators while normal functions can do the +/// same. +#[derive(Clone)] +struct MinifyingSugg<'a>(Sugg<'a>); + +impl<'a> MinifyingSugg<'a> { + fn as_str(&self) -> &str { + let (Sugg::NonParen(s) | Sugg::MaybeParen(s) | Sugg::BinOp(_, s)) = &self.0; + s.as_ref() + } + + fn into_sugg(self) -> Sugg<'a> { + self.0 + } +} + +impl<'a> From<Sugg<'a>> for MinifyingSugg<'a> { + fn from(sugg: Sugg<'a>) -> Self { + Self(sugg) + } +} + +impl std::ops::Add for &MinifyingSugg<'static> { + type Output = MinifyingSugg<'static>; + fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> { + match (self.as_str(), rhs.as_str()) { + ("0", _) => rhs.clone(), + (_, "0") => self.clone(), + (_, _) => (&self.0 + &rhs.0).into(), + } + } +} + +impl std::ops::Sub for &MinifyingSugg<'static> { + type Output = MinifyingSugg<'static>; + fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> { + match (self.as_str(), rhs.as_str()) { + (_, "0") => self.clone(), + ("0", _) => (-rhs.0.clone()).into(), + (x, y) if x == y => sugg::ZERO.into(), + (_, _) => (&self.0 - &rhs.0).into(), + } + } +} + +impl std::ops::Add<&MinifyingSugg<'static>> for MinifyingSugg<'static> { + type Output = MinifyingSugg<'static>; + fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> { + match (self.as_str(), rhs.as_str()) { + ("0", _) => rhs.clone(), + (_, "0") => self, + (_, _) => (self.0 + &rhs.0).into(), + } + } +} + +impl std::ops::Sub<&MinifyingSugg<'static>> for MinifyingSugg<'static> { + type Output = MinifyingSugg<'static>; + fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> { + match (self.as_str(), rhs.as_str()) { + (_, "0") => self, + ("0", _) => (-rhs.0.clone()).into(), + (x, y) if x == y => sugg::ZERO.into(), + (_, _) => (self.0 - &rhs.0).into(), + } + } +} + +/// a wrapper around `MinifyingSugg`, which carries a operator like currying +/// so that the suggested code become more efficient (e.g. `foo + -bar` `foo - bar`). +struct Offset { + value: MinifyingSugg<'static>, + sign: OffsetSign, +} + +#[derive(Clone, Copy)] +enum OffsetSign { + Positive, + Negative, +} + +impl Offset { + fn negative(value: Sugg<'static>) -> Self { + Self { + value: value.into(), + sign: OffsetSign::Negative, + } + } + + fn positive(value: Sugg<'static>) -> Self { + Self { + value: value.into(), + sign: OffsetSign::Positive, + } + } + + fn empty() -> Self { + Self::positive(sugg::ZERO) + } +} + +fn apply_offset(lhs: &MinifyingSugg<'static>, rhs: &Offset) -> MinifyingSugg<'static> { + match rhs.sign { + OffsetSign::Positive => lhs + &rhs.value, + OffsetSign::Negative => lhs - &rhs.value, + } +} + +#[derive(Debug, Clone, Copy)] +enum StartKind<'hir> { + Range, + Counter { initializer: &'hir Expr<'hir> }, +} + +struct IndexExpr<'hir> { + base: &'hir Expr<'hir>, + idx: StartKind<'hir>, + idx_offset: Offset, +} + +struct Start<'hir> { + id: HirId, + kind: StartKind<'hir>, +} + +fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool { + let is_slice = match ty.kind() { + ty::Ref(_, subty, _) => is_slice_like(cx, subty), + ty::Slice(..) | ty::Array(..) => true, + _ => false, + }; + + is_slice || is_type_diagnostic_item(cx, ty, sym::vec_type) || is_type_diagnostic_item(cx, ty, sym::vecdeque_type) +} + +fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> { + if_chain! { + if let ExprKind::MethodCall(method, _, args, _) = expr.kind; + if method.ident.name == sym::clone; + if args.len() == 1; + if let Some(arg) = args.get(0); + then { arg } else { expr } + } +} + +fn get_details_from_idx<'tcx>( + cx: &LateContext<'tcx>, + idx: &Expr<'_>, + starts: &[Start<'tcx>], +) -> Option<(StartKind<'tcx>, Offset)> { + fn get_start<'tcx>(e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<StartKind<'tcx>> { + let id = path_to_local(e)?; + starts.iter().find(|start| start.id == id).map(|start| start.kind) + } + + fn get_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<Sugg<'static>> { + match &e.kind { + ExprKind::Lit(l) => match l.node { + ast::LitKind::Int(x, _ty) => Some(Sugg::NonParen(x.to_string().into())), + _ => None, + }, + ExprKind::Path(..) if get_start(e, starts).is_none() => Some(Sugg::hir(cx, e, "???")), + _ => None, + } + } + + match idx.kind { + ExprKind::Binary(op, lhs, rhs) => match op.node { + BinOpKind::Add => { + let offset_opt = get_start(lhs, starts) + .and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, o))) + .or_else(|| get_start(rhs, starts).and_then(|s| get_offset(cx, lhs, starts).map(|o| (s, o)))); + + offset_opt.map(|(s, o)| (s, Offset::positive(o))) + }, + BinOpKind::Sub => { + get_start(lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o)))) + }, + _ => None, + }, + ExprKind::Path(..) => get_start(idx, starts).map(|s| (s, Offset::empty())), + _ => None, + } +} + +fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> { + if let ExprKind::Assign(lhs, rhs, _) = e.kind { + Some((lhs, rhs)) + } else { + None + } +} + +/// Get assignments from the given block. +/// The returned iterator yields `None` if no assignment expressions are there, +/// filtering out the increments of the given whitelisted loop counters; +/// because its job is to make sure there's nothing other than assignments and the increments. +fn get_assignments<'a, 'tcx>( + Block { stmts, expr, .. }: &'tcx Block<'tcx>, + loop_counters: &'a [Start<'tcx>], +) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'a { + // As the `filter` and `map` below do different things, I think putting together + // just increases complexity. (cc #3188 and #4193) + stmts + .iter() + .filter_map(move |stmt| match stmt.kind { + StmtKind::Local(..) | StmtKind::Item(..) => None, + StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e), + }) + .chain((*expr).into_iter()) + .filter(move |e| { + if let ExprKind::AssignOp(_, place, _) = e.kind { + path_to_local(place).map_or(false, |id| { + !loop_counters + .iter() + // skip the first item which should be `StartKind::Range` + // this makes it possible to use the slice with `StartKind::Range` in the same iterator loop. + .skip(1) + .any(|counter| counter.id == id) + }) + } else { + true + } + }) + .map(get_assignment) +} + +fn get_loop_counters<'a, 'tcx>( + cx: &'a LateContext<'tcx>, + body: &'tcx Block<'tcx>, + expr: &'tcx Expr<'_>, +) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> { + // Look for variables that are incremented once per loop iteration. + let mut increment_visitor = IncrementVisitor::new(cx); + walk_block(&mut increment_visitor, body); + + // For each candidate, check the parent block to see if + // it's initialized to zero at the start of the loop. + get_enclosing_block(&cx, expr.hir_id).and_then(|block| { + increment_visitor + .into_results() + .filter_map(move |var_id| { + let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id); + walk_block(&mut initialize_visitor, block); + + initialize_visitor.get_result().map(|(_, initializer)| Start { + id: var_id, + kind: StartKind::Counter { initializer }, + }) + }) + .into() + }) +} diff --git a/clippy_lints/src/loops/mod.rs b/clippy_lints/src/loops/mod.rs new file mode 100644 index 00000000000..2a372c6307e --- /dev/null +++ b/clippy_lints/src/loops/mod.rs @@ -0,0 +1,627 @@ +mod empty_loop; +mod explicit_counter_loop; +mod explicit_into_iter_loop; +mod explicit_iter_loop; +mod for_kv_map; +mod for_loops_over_fallibles; +mod iter_next_loop; +mod manual_flatten; +mod manual_memcpy; +mod mut_range_bound; +mod needless_collect; +mod needless_range_loop; +mod never_loop; +mod same_item_push; +mod single_element_loop; +mod utils; +mod while_immutable_condition; +mod while_let_loop; +mod while_let_on_iterator; + +use crate::utils::higher; +use rustc_hir::{Expr, ExprKind, LoopSource, Pat}; +use rustc_lint::{LateContext, LateLintPass}; +use rustc_session::{declare_lint_pass, declare_tool_lint}; +use rustc_span::source_map::Span; +use utils::{get_span_of_entire_for_loop, make_iterator_snippet, IncrementVisitor, InitializeVisitor}; + +declare_clippy_lint! { + /// **What it does:** Checks for for-loops that manually copy items between + /// slices that could be optimized by having a memcpy. + /// + /// **Why is this bad?** It is not as fast as a memcpy. + /// + /// **Known problems:** None. + /// + /// **Example:** + /// ```rust + /// # let src = vec![1]; + /// # let mut dst = vec![0; 65]; + /// for i in 0..src.len() { + /// dst[i + 64] = src[i]; + /// } + /// ``` + /// Could be written as: + /// ```rust + /// # let src = vec![1]; + /// # let mut dst = vec![0; 65]; + /// dst[64..(src.len() + 64)].clone_from_slice(&src[..]); + /// ``` + pub MANUAL_MEMCPY, + perf, + "manually copying items between slices" +} + +declare_clippy_lint! { + /// **What it does:** Checks for looping over the range of `0..len` of some + /// collection just to get the values by index. + /// + /// **Why is this bad?** Just iterating the collection itself makes the intent + /// more clear and is probably faster. + /// + /// **Known problems:** None. + /// + /// **Example:** + /// ```rust + /// let vec = vec!['a', 'b', 'c']; + /// for i in 0..vec.len() { + /// println!("{}", vec[i]); + /// } + /// ``` + /// Could be written as: + /// ```rust + /// let vec = vec!['a', 'b', 'c']; + /// for i in vec { + /// println!("{}", i); + /// } + /// ``` + pub NEEDLESS_RANGE_LOOP, + style, + "for-looping over a range of indices where an iterator over items would do" +} + +declare_clippy_lint! { + /// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and + /// suggests the latter. + /// + /// **Why is this bad?** Readability. + /// + /// **Known problems:** False negatives. We currently only warn on some known + /// types. + /// + /// **Example:** + /// ```rust + /// // with `y` a `Vec` or slice: + /// # let y = vec![1]; + /// for x in y.iter() { + /// // .. + /// } + /// ``` + /// can be rewritten to + /// ```rust + /// # let y = vec![1]; + /// for x in &y { + /// // .. + /// } + /// ``` + pub EXPLICIT_ITER_LOOP, + pedantic, + "for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do" +} + +declare_clippy_lint! { + /// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and + /// suggests the latter. + /// + /// **Why is this bad?** Readability. + /// + /// **Known problems:** None + /// + /// **Example:** + /// ```rust + /// # let y = vec![1]; + /// // with `y` a `Vec` or slice: + /// for x in y.into_iter() { + /// // .. + /// } + /// ``` + /// can be rewritten to + /// ```rust + /// # let y = vec![1]; + /// for x in y { + /// // .. + /// } + /// ``` + pub EXPLICIT_INTO_ITER_LOOP, + pedantic, + "for-looping over `_.into_iter()` when `_` would do" +} + +declare_clippy_lint! { + /// **What it does:** Checks for loops on `x.next()`. + /// + /// **Why is this bad?** `next()` returns either `Some(value)` if there was a + /// value, or `None` otherwise. The insidious thing is that `Option<_>` + /// implements `IntoIterator`, so that possibly one value will be iterated, + /// leading to some hard to find bugs. No one will want to write such code + /// [except to win an Underhanded Rust + /// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr). + /// + /// **Known problems:** None. + /// + /// **Example:** + /// ```ignore + /// for x in y.next() { + /// .. + /// } + /// ``` + pub ITER_NEXT_LOOP, + correctness, + "for-looping over `_.next()` which is probably not intended" +} + +declare_clippy_lint! { + /// **What it does:** Checks for `for` loops over `Option` or `Result` values. + /// + /// **Why is this bad?** Readability. This is more clearly expressed as an `if + /// let`. + /// + /// **Known problems:** None. + /// + /// **Example:** + /// ```rust + /// # let opt = Some(1); + /// + /// // Bad + /// for x in opt { + /// // .. + /// } + /// + /// // Good + /// if let Some(x) = opt { + /// // .. + /// } + /// ``` + /// + /// // or + /// + /// ```rust + /// # let res: Result<i32, std::io::Error> = Ok(1); + /// + /// // Bad + /// for x in &res { + /// // .. + /// } + /// + /// // Good + /// if let Ok(x) = res { + /// // .. + /// } + /// ``` + pub FOR_LOOPS_OVER_FALLIBLES, + correctness, + "for-looping over an `Option` or a `Result`, which is more clearly expressed as an `if let`" +} + +declare_clippy_lint! { + /// **What it does:** Detects `loop + match` combinations that are easier + /// written as a `while let` loop. + /// + /// **Why is this bad?** The `while let` loop is usually shorter and more + /// readable. + /// + /// **Known problems:** Sometimes the wrong binding is displayed ([#383](https://github.com/rust-lang/rust-clippy/issues/383)). + /// + /// **Example:** + /// ```rust,no_run + /// # let y = Some(1); + /// loop { + /// let x = match y { + /// Some(x) => x, + /// None => break, + /// }; + /// // .. do something with x + /// } + /// // is easier written as + /// while let Some(x) = y { + /// // .. do something with x + /// }; + /// ``` + pub WHILE_LET_LOOP, + complexity, + "`loop { if let { ... } else break }`, which can be written as a `while let` loop" +} + +declare_clippy_lint! { + /// **What it does:** Checks for functions collecting an iterator when collect + /// is not needed. + /// + /// **Why is this bad?** `collect` causes the allocation of a new data structure, + /// when this allocation may not be needed. + /// + /// **Known problems:** + /// None + /// + /// **Example:** + /// ```rust + /// # let iterator = vec![1].into_iter(); + /// let len = iterator.clone().collect::<Vec<_>>().len(); + /// // should be + /// let len = iterator.count(); + /// ``` + pub NEEDLESS_COLLECT, + perf, + "collecting an iterator when collect is not needed" +} + +declare_clippy_lint! { + /// **What it does:** Checks `for` loops over slices with an explicit counter + /// and suggests the use of `.enumerate()`. + /// + /// **Why is it bad?** Using `.enumerate()` makes the intent more clear, + /// declutters the code and may be faster in some instances. + /// + /// **Known problems:** None. + /// + /// **Example:** + /// ```rust + /// # let v = vec![1]; + /// # fn bar(bar: usize, baz: usize) {} + /// let mut i = 0; + /// for item in &v { + /// bar(i, *item); + /// i += 1; + /// } + /// ``` + /// Could be written as + /// ```rust + /// # let v = vec![1]; + /// # fn bar(bar: usize, baz: usize) {} + /// for (i, item) in v.iter().enumerate() { bar(i, *item); } + /// ``` + pub EXPLICIT_COUNTER_LOOP, + complexity, + "for-looping with an explicit counter when `_.enumerate()` would do" +} + +declare_clippy_lint! { + /// **What it does:** Checks for empty `loop` expressions. + /// + /// **Why is this bad?** These busy loops burn CPU cycles without doing + /// anything. It is _almost always_ a better idea to `panic!` than to have + /// a busy loop. + /// + /// If panicking isn't possible, think of the environment and either: + /// - block on something + /// - sleep the thread for some microseconds + /// - yield or pause the thread + /// + /// For `std` targets, this can be done with + /// [`std::thread::sleep`](https://doc.rust-lang.org/std/thread/fn.sleep.html) + /// or [`std::thread::yield_now`](https://doc.rust-lang.org/std/thread/fn.yield_now.html). + /// + /// For `no_std` targets, doing this is more complicated, especially because + /// `#[panic_handler]`s can't panic. To stop/pause the thread, you will + /// probably need to invoke some target-specific intrinsic. Examples include: + /// - [`x86_64::instructions::hlt`](https://docs.rs/x86_64/0.12.2/x86_64/instructions/fn.hlt.html) + /// - [`cortex_m::asm::wfi`](https://docs.rs/cortex-m/0.6.3/cortex_m/asm/fn.wfi.html) + /// + /// **Known problems:** None. + /// + /// **Example:** + /// ```no_run + /// loop {} + /// ``` + pub EMPTY_LOOP, + style, + "empty `loop {}`, which should block or sleep" +} + +declare_clippy_lint! { + /// **What it does:** Checks for `while let` expressions on iterators. + /// + /// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys + /// the intent better. + /// + /// **Known problems:** None. + /// + /// **Example:** + /// ```ignore + /// while let Some(val) = iter() { + /// .. + /// } + /// ``` + pub WHILE_LET_ON_ITERATOR, + style, + "using a `while let` loop instead of a for loop on an iterator" +} + +declare_clippy_lint! { + /// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and + /// ignoring either the keys or values. + /// + /// **Why is this bad?** Readability. There are `keys` and `values` methods that + /// can be used to express that don't need the values or keys. + /// + /// **Known problems:** None. + /// + /// **Example:** + /// ```ignore + /// for (k, _) in &map { + /// .. + /// } + /// ``` + /// + /// could be replaced by + /// + /// ```ignore + /// for k in map.keys() { + /// .. + /// } + /// ``` + pub FOR_KV_MAP, + style, + "looping on a map using `iter` when `keys` or `values` would do" +} + +declare_clippy_lint! { + /// **What it does:** Checks for loops that will always `break`, `return` or + /// `continue` an outer loop. + /// + /// **Why is this bad?** This loop never loops, all it does is obfuscating the + /// code. + /// + /// **Known problems:** None + /// + /// **Example:** + /// ```rust + /// loop { + /// ..; + /// break; + /// } + /// ``` + pub NEVER_LOOP, + correctness, + "any loop that will always `break` or `return`" +} + +declare_clippy_lint! { + /// **What it does:** Checks for loops which have a range bound that is a mutable variable + /// + /// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds + /// + /// **Known problems:** None + /// + /// **Example:** + /// ```rust + /// let mut foo = 42; + /// for i in 0..foo { + /// foo -= 1; + /// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21 + /// } + /// ``` + pub MUT_RANGE_BOUND, + complexity, + "for loop over a range where one of the bounds is a mutable variable" +} + +declare_clippy_lint! { + /// **What it does:** Checks whether variables used within while loop condition + /// can be (and are) mutated in the body. + /// + /// **Why is this bad?** If the condition is unchanged, entering the body of the loop + /// will lead to an infinite loop. + /// + /// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the + /// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is + /// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger. + /// + /// **Example:** + /// ```rust + /// let i = 0; + /// while i > 10 { + /// println!("let me loop forever!"); + /// } + /// ``` + pub WHILE_IMMUTABLE_CONDITION, + correctness, + "variables used within while expression are not mutated in the body" +} + +declare_clippy_lint! { + /// **What it does:** Checks whether a for loop is being used to push a constant + /// value into a Vec. + /// + /// **Why is this bad?** This kind of operation can be expressed more succinctly with + /// `vec![item;SIZE]` or `vec.resize(NEW_SIZE, item)` and using these alternatives may also + /// have better performance. + /// **Known problems:** None + /// + /// **Example:** + /// ```rust + /// let item1 = 2; + /// let item2 = 3; + /// let mut vec: Vec<u8> = Vec::new(); + /// for _ in 0..20 { + /// vec.push(item1); + /// } + /// for _ in 0..30 { + /// vec.push(item2); + /// } + /// ``` + /// could be written as + /// ```rust + /// let item1 = 2; + /// let item2 = 3; + /// let mut vec: Vec<u8> = vec![item1; 20]; + /// vec.resize(20 + 30, item2); + /// ``` + pub SAME_ITEM_PUSH, + style, + "the same item is pushed inside of a for loop" +} + +declare_clippy_lint! { + /// **What it does:** Checks whether a for loop has a single element. + /// + /// **Why is this bad?** There is no reason to have a loop of a + /// single element. + /// **Known problems:** None + /// + /// **Example:** + /// ```rust + /// let item1 = 2; + /// for item in &[item1] { + /// println!("{}", item); + /// } + /// ``` + /// could be written as + /// ```rust + /// let item1 = 2; + /// let item = &item1; + /// println!("{}", item); + /// ``` + pub SINGLE_ELEMENT_LOOP, + complexity, + "there is no reason to have a single element loop" +} + +declare_clippy_lint! { + /// **What it does:** Check for unnecessary `if let` usage in a for loop + /// where only the `Some` or `Ok` variant of the iterator element is used. + /// + /// **Why is this bad?** It is verbose and can be simplified + /// by first calling the `flatten` method on the `Iterator`. + /// + /// **Known problems:** None. + /// + /// **Example:** + /// + /// ```rust + /// let x = vec![Some(1), Some(2), Some(3)]; + /// for n in x { + /// if let Some(n) = n { + /// println!("{}", n); + /// } + /// } + /// ``` + /// Use instead: + /// ```rust + /// let x = vec![Some(1), Some(2), Some(3)]; + /// for n in x.into_iter().flatten() { + /// println!("{}", n); + /// } + /// ``` + pub MANUAL_FLATTEN, + complexity, + "for loops over `Option`s or `Result`s with a single expression can be simplified" +} + +declare_lint_pass!(Loops => [ + MANUAL_MEMCPY, + MANUAL_FLATTEN, + NEEDLESS_RANGE_LOOP, + EXPLICIT_ITER_LOOP, + EXPLICIT_INTO_ITER_LOOP, + ITER_NEXT_LOOP, + FOR_LOOPS_OVER_FALLIBLES, + WHILE_LET_LOOP, + NEEDLESS_COLLECT, + EXPLICIT_COUNTER_LOOP, + EMPTY_LOOP, + WHILE_LET_ON_ITERATOR, + FOR_KV_MAP, + NEVER_LOOP, + MUT_RANGE_BOUND, + WHILE_IMMUTABLE_CONDITION, + SAME_ITEM_PUSH, + SINGLE_ELEMENT_LOOP, +]); + +impl<'tcx> LateLintPass<'tcx> for Loops { + #[allow(clippy::too_many_lines)] + fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { + if let Some((pat, arg, body, span)) = higher::for_loop(expr) { + // we don't want to check expanded macros + // this check is not at the top of the function + // since higher::for_loop expressions are marked as expansions + if body.span.from_expansion() { + return; + } + check_for_loop(cx, pat, arg, body, expr, span); + } + + // we don't want to check expanded macros + if expr.span.from_expansion() { + return; + } + + // check for never_loop + never_loop::check(cx, expr); + + // check for `loop { if let {} else break }` that could be `while let` + // (also matches an explicit "match" instead of "if let") + // (even if the "match" or "if let" is used for declaration) + if let ExprKind::Loop(ref block, _, LoopSource::Loop, _) = expr.kind { + // also check for empty `loop {}` statements, skipping those in #[panic_handler] + empty_loop::check(cx, expr, block); + while_let_loop::check(cx, expr, block); + } + + while_let_on_iterator::check(cx, expr); + + if let Some((cond, body)) = higher::while_loop(&expr) { + while_immutable_condition::check(cx, cond, body); + } + + needless_collect::check(expr, cx); + } +} + +fn check_for_loop<'tcx>( + cx: &LateContext<'tcx>, + pat: &'tcx Pat<'_>, + arg: &'tcx Expr<'_>, + body: &'tcx Expr<'_>, + expr: &'tcx Expr<'_>, + span: Span, +) { + let is_manual_memcpy_triggered = manual_memcpy::check(cx, pat, arg, body, expr); + if !is_manual_memcpy_triggered { + needless_range_loop::check(cx, pat, arg, body, expr); + explicit_counter_loop::check(cx, pat, arg, body, expr); + } + check_for_loop_arg(cx, pat, arg, expr); + for_kv_map::check(cx, pat, arg, body, expr); + mut_range_bound::check(cx, arg, body); + single_element_loop::check(cx, pat, arg, body, expr); + same_item_push::check(cx, pat, arg, body, expr); + manual_flatten::check(cx, pat, arg, body, span); +} + +fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) { + let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used + + if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind { + // just the receiver, no arguments + if args.len() == 1 { + let method_name = &*method.ident.as_str(); + // check for looping over x.iter() or x.iter_mut(), could use &x or &mut x + match method_name { + "iter" | "iter_mut" => explicit_iter_loop::check(cx, args, arg, method_name), + "into_iter" => { + explicit_iter_loop::check(cx, args, arg, method_name); + explicit_into_iter_loop::check(cx, args, arg); + }, + "next" => { + next_loop_linted = iter_next_loop::check(cx, arg, expr); + }, + _ => {}, + } + } + } + + if !next_loop_linted { + for_loops_over_fallibles::check(cx, pat, arg); + } +} diff --git a/clippy_lints/src/loops/mut_range_bound.rs b/clippy_lints/src/loops/mut_range_bound.rs new file mode 100644 index 00000000000..3ae592950f1 --- /dev/null +++ b/clippy_lints/src/loops/mut_range_bound.rs @@ -0,0 +1,115 @@ +use super::MUT_RANGE_BOUND; +use crate::utils::{higher, path_to_local, span_lint}; +use if_chain::if_chain; +use rustc_hir::{BindingAnnotation, Expr, HirId, Node, PatKind}; +use rustc_infer::infer::TyCtxtInferExt; +use rustc_lint::LateContext; +use rustc_middle::ty; +use rustc_span::source_map::Span; +use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId}; + +pub(super) fn check(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) { + if let Some(higher::Range { + start: Some(start), + end: Some(end), + .. + }) = higher::range(arg) + { + let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)]; + if mut_ids[0].is_some() || mut_ids[1].is_some() { + let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids); + mut_warn_with_span(cx, span_low); + mut_warn_with_span(cx, span_high); + } + } +} + +fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) { + if let Some(sp) = span { + span_lint( + cx, + MUT_RANGE_BOUND, + sp, + "attempt to mutate range bound within loop; note that the range of the loop is unchanged", + ); + } +} + +fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> { + if_chain! { + if let Some(hir_id) = path_to_local(bound); + if let Node::Binding(pat) = cx.tcx.hir().get(hir_id); + if let PatKind::Binding(BindingAnnotation::Mutable, ..) = pat.kind; + then { + return Some(hir_id); + } + } + None +} + +fn check_for_mutation<'tcx>( + cx: &LateContext<'tcx>, + body: &Expr<'_>, + bound_ids: &[Option<HirId>], +) -> (Option<Span>, Option<Span>) { + let mut delegate = MutatePairDelegate { + cx, + hir_id_low: bound_ids[0], + hir_id_high: bound_ids[1], + span_low: None, + span_high: None, + }; + cx.tcx.infer_ctxt().enter(|infcx| { + ExprUseVisitor::new( + &mut delegate, + &infcx, + body.hir_id.owner, + cx.param_env, + cx.typeck_results(), + ) + .walk_expr(body); + }); + delegate.mutation_span() +} + +struct MutatePairDelegate<'a, 'tcx> { + cx: &'a LateContext<'tcx>, + hir_id_low: Option<HirId>, + hir_id_high: Option<HirId>, + span_low: Option<Span>, + span_high: Option<Span>, +} + +impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> { + fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: HirId, _: ConsumeMode) {} + + fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId, bk: ty::BorrowKind) { + if let ty::BorrowKind::MutBorrow = bk { + if let PlaceBase::Local(id) = cmt.place.base { + if Some(id) == self.hir_id_low { + self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id)) + } + if Some(id) == self.hir_id_high { + self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id)) + } + } + } + } + + fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId) { + if let PlaceBase::Local(id) = cmt.place.base { + if Some(id) == self.hir_id_low { + self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id)) + } + if Some(id) == self.hir_id_high { + self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id)) + } + } + } +} + +impl MutatePairDelegate<'_, '_> { + fn mutation_span(&self) -> (Option<Span>, Option<Span>) { + (self.span_low, self.span_high) + } +} diff --git a/clippy_lints/src/loops/needless_collect.rs b/clippy_lints/src/loops/needless_collect.rs new file mode 100644 index 00000000000..92560c80629 --- /dev/null +++ b/clippy_lints/src/loops/needless_collect.rs @@ -0,0 +1,283 @@ +use super::NEEDLESS_COLLECT; +use crate::utils::sugg::Sugg; +use crate::utils::{ + is_type_diagnostic_item, match_trait_method, match_type, path_to_local_id, paths, snippet, span_lint_and_sugg, + span_lint_and_then, +}; +use if_chain::if_chain; +use rustc_errors::Applicability; +use rustc_hir::intravisit::{walk_block, walk_expr, NestedVisitorMap, Visitor}; +use rustc_hir::{Block, Expr, ExprKind, GenericArg, HirId, Local, Pat, PatKind, QPath, StmtKind}; +use rustc_lint::LateContext; +use rustc_middle::hir::map::Map; +use rustc_span::source_map::Span; +use rustc_span::symbol::{sym, Ident}; + +const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed"; + +pub(super) fn check<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) { + check_needless_collect_direct_usage(expr, cx); + check_needless_collect_indirect_usage(expr, cx); +} +fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) { + if_chain! { + if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind; + if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind; + if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR); + if let Some(ref generic_args) = chain_method.args; + if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0); + then { + let ty = cx.typeck_results().node_type(ty.hir_id); + if is_type_diagnostic_item(cx, ty, sym::vec_type) || + is_type_diagnostic_item(cx, ty, sym::vecdeque_type) || + match_type(cx, ty, &paths::BTREEMAP) || + is_type_diagnostic_item(cx, ty, sym::hashmap_type) { + if method.ident.name == sym!(len) { + let span = shorten_needless_collect_span(expr); + span_lint_and_sugg( + cx, + NEEDLESS_COLLECT, + span, + NEEDLESS_COLLECT_MSG, + "replace with", + "count()".to_string(), + Applicability::MachineApplicable, + ); + } + if method.ident.name == sym!(is_empty) { + let span = shorten_needless_collect_span(expr); + span_lint_and_sugg( + cx, + NEEDLESS_COLLECT, + span, + NEEDLESS_COLLECT_MSG, + "replace with", + "next().is_none()".to_string(), + Applicability::MachineApplicable, + ); + } + if method.ident.name == sym!(contains) { + let contains_arg = snippet(cx, args[1].span, "??"); + let span = shorten_needless_collect_span(expr); + span_lint_and_then( + cx, + NEEDLESS_COLLECT, + span, + NEEDLESS_COLLECT_MSG, + |diag| { + let (arg, pred) = contains_arg + .strip_prefix('&') + .map_or(("&x", &*contains_arg), |s| ("x", s)); + diag.span_suggestion( + span, + "replace with", + format!( + "any(|{}| x == {})", + arg, pred + ), + Applicability::MachineApplicable, + ); + } + ); + } + } + } + } +} + +fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) { + if let ExprKind::Block(ref block, _) = expr.kind { + for ref stmt in block.stmts { + if_chain! { + if let StmtKind::Local( + Local { pat: Pat { hir_id: pat_id, kind: PatKind::Binding(_, _, ident, .. ), .. }, + init: Some(ref init_expr), .. } + ) = stmt.kind; + if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind; + if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR); + if let Some(ref generic_args) = method_name.args; + if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0); + if let ty = cx.typeck_results().node_type(ty.hir_id); + if is_type_diagnostic_item(cx, ty, sym::vec_type) || + is_type_diagnostic_item(cx, ty, sym::vecdeque_type) || + match_type(cx, ty, &paths::LINKED_LIST); + if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident); + if iter_calls.len() == 1; + then { + let mut used_count_visitor = UsedCountVisitor { + cx, + id: *pat_id, + count: 0, + }; + walk_block(&mut used_count_visitor, block); + if used_count_visitor.count > 1 { + return; + } + + // Suggest replacing iter_call with iter_replacement, and removing stmt + let iter_call = &iter_calls[0]; + span_lint_and_then( + cx, + super::NEEDLESS_COLLECT, + stmt.span.until(iter_call.span), + NEEDLESS_COLLECT_MSG, + |diag| { + let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx)); + diag.multipart_suggestion( + iter_call.get_suggestion_text(), + vec![ + (stmt.span, String::new()), + (iter_call.span, iter_replacement) + ], + Applicability::MachineApplicable,// MaybeIncorrect, + ).emit(); + }, + ); + } + } + } + } +} + +struct IterFunction { + func: IterFunctionKind, + span: Span, +} +impl IterFunction { + fn get_iter_method(&self, cx: &LateContext<'_>) -> String { + match &self.func { + IterFunctionKind::IntoIter => String::new(), + IterFunctionKind::Len => String::from(".count()"), + IterFunctionKind::IsEmpty => String::from(".next().is_none()"), + IterFunctionKind::Contains(span) => { + let s = snippet(cx, *span, ".."); + if let Some(stripped) = s.strip_prefix('&') { + format!(".any(|x| x == {})", stripped) + } else { + format!(".any(|x| x == *{})", s) + } + }, + } + } + fn get_suggestion_text(&self) -> &'static str { + match &self.func { + IterFunctionKind::IntoIter => { + "use the original Iterator instead of collecting it and then producing a new one" + }, + IterFunctionKind::Len => { + "take the original Iterator's count instead of collecting it and finding the length" + }, + IterFunctionKind::IsEmpty => { + "check if the original Iterator has anything instead of collecting it and seeing if it's empty" + }, + IterFunctionKind::Contains(_) => { + "check if the original Iterator contains an element instead of collecting then checking" + }, + } + } +} +enum IterFunctionKind { + IntoIter, + Len, + IsEmpty, + Contains(Span), +} + +struct IterFunctionVisitor { + uses: Vec<IterFunction>, + seen_other: bool, + target: Ident, +} +impl<'tcx> Visitor<'tcx> for IterFunctionVisitor { + fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) { + // Check function calls on our collection + if_chain! { + if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind; + if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0); + if let &[name] = &path.segments; + if name.ident == self.target; + then { + let len = sym!(len); + let is_empty = sym!(is_empty); + let contains = sym!(contains); + match method_name.ident.name { + sym::into_iter => self.uses.push( + IterFunction { func: IterFunctionKind::IntoIter, span: expr.span } + ), + name if name == len => self.uses.push( + IterFunction { func: IterFunctionKind::Len, span: expr.span } + ), + name if name == is_empty => self.uses.push( + IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span } + ), + name if name == contains => self.uses.push( + IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span } + ), + _ => self.seen_other = true, + } + return + } + } + // Check if the collection is used for anything else + if_chain! { + if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr; + if let &[name] = &path.segments; + if name.ident == self.target; + then { + self.seen_other = true; + } else { + walk_expr(self, expr); + } + } + } + + type Map = Map<'tcx>; + fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { + NestedVisitorMap::None + } +} + +struct UsedCountVisitor<'a, 'tcx> { + cx: &'a LateContext<'tcx>, + id: HirId, + count: usize, +} + +impl<'a, 'tcx> Visitor<'tcx> for UsedCountVisitor<'a, 'tcx> { + type Map = Map<'tcx>; + + fn visit_expr(&mut self, expr: &'tcx Expr<'_>) { + if path_to_local_id(expr, self.id) { + self.count += 1; + } else { + walk_expr(self, expr); + } + } + + fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { + NestedVisitorMap::OnlyBodies(self.cx.tcx.hir()) + } +} + +/// Detect the occurrences of calls to `iter` or `into_iter` for the +/// given identifier +fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> { + let mut visitor = IterFunctionVisitor { + uses: Vec::new(), + target: identifier, + seen_other: false, + }; + visitor.visit_block(block); + if visitor.seen_other { None } else { Some(visitor.uses) } +} + +fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span { + if_chain! { + if let ExprKind::MethodCall(.., args, _) = &expr.kind; + if let ExprKind::MethodCall(_, span, ..) = &args[0].kind; + then { + return expr.span.with_lo(span.lo()); + } + } + unreachable!(); +} diff --git a/clippy_lints/src/loops/needless_range_loop.rs b/clippy_lints/src/loops/needless_range_loop.rs new file mode 100644 index 00000000000..5f02e4b9d87 --- /dev/null +++ b/clippy_lints/src/loops/needless_range_loop.rs @@ -0,0 +1,391 @@ +use super::NEEDLESS_RANGE_LOOP; +use crate::utils::visitors::LocalUsedVisitor; +use crate::utils::{ + contains_name, has_iter_method, higher, is_integer_const, match_trait_method, multispan_sugg, path_to_local_id, + paths, snippet, span_lint_and_then, sugg, SpanlessEq, +}; +use if_chain::if_chain; +use rustc_ast::ast; +use rustc_data_structures::fx::{FxHashMap, FxHashSet}; +use rustc_hir::def::{DefKind, Res}; +use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor}; +use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, HirId, Mutability, Pat, PatKind, QPath}; +use rustc_lint::LateContext; +use rustc_middle::hir::map::Map; +use rustc_middle::middle::region; +use rustc_middle::ty::{self, Ty}; +use rustc_span::symbol::{sym, Symbol}; +use std::iter::Iterator; +use std::mem; + +/// Checks for looping over a range and then indexing a sequence with it. +/// The iteratee must be a range literal. +#[allow(clippy::too_many_lines)] +pub(super) fn check<'tcx>( + cx: &LateContext<'tcx>, + pat: &'tcx Pat<'_>, + arg: &'tcx Expr<'_>, + body: &'tcx Expr<'_>, + expr: &'tcx Expr<'_>, +) { + if let Some(higher::Range { + start: Some(start), + ref end, + limits, + }) = higher::range(arg) + { + // the var must be a single name + if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind { + let mut visitor = VarVisitor { + cx, + var: canonical_id, + indexed_mut: FxHashSet::default(), + indexed_indirectly: FxHashMap::default(), + indexed_directly: FxHashMap::default(), + referenced: FxHashSet::default(), + nonindex: false, + prefer_mutable: false, + }; + walk_expr(&mut visitor, body); + + // linting condition: we only indexed one variable, and indexed it directly + if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 { + let (indexed, (indexed_extent, indexed_ty)) = visitor + .indexed_directly + .into_iter() + .next() + .expect("already checked that we have exactly 1 element"); + + // ensure that the indexed variable was declared before the loop, see #601 + if let Some(indexed_extent) = indexed_extent { + let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id); + let parent_def_id = cx.tcx.hir().local_def_id(parent_id); + let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id); + let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id); + if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) { + return; + } + } + + // don't lint if the container that is indexed does not have .iter() method + let has_iter = has_iter_method(cx, indexed_ty); + if has_iter.is_none() { + return; + } + + // don't lint if the container that is indexed into is also used without + // indexing + if visitor.referenced.contains(&indexed) { + return; + } + + let starts_at_zero = is_integer_const(cx, start, 0); + + let skip = if starts_at_zero { + String::new() + } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, start) { + return; + } else { + format!(".skip({})", snippet(cx, start.span, "..")) + }; + + let mut end_is_start_plus_val = false; + + let take = if let Some(end) = *end { + let mut take_expr = end; + + if let ExprKind::Binary(ref op, ref left, ref right) = end.kind { + if let BinOpKind::Add = op.node { + let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left); + let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right); + + if start_equal_left { + take_expr = right; + } else if start_equal_right { + take_expr = left; + } + + end_is_start_plus_val = start_equal_left | start_equal_right; + } + } + + if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) { + String::new() + } else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, take_expr) { + return; + } else { + match limits { + ast::RangeLimits::Closed => { + let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>"); + format!(".take({})", take_expr + sugg::ONE) + }, + ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")), + } + } + } else { + String::new() + }; + + let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) { + ("mut ", "iter_mut") + } else { + ("", "iter") + }; + + let take_is_empty = take.is_empty(); + let mut method_1 = take; + let mut method_2 = skip; + + if end_is_start_plus_val { + mem::swap(&mut method_1, &mut method_2); + } + + if visitor.nonindex { + span_lint_and_then( + cx, + NEEDLESS_RANGE_LOOP, + expr.span, + &format!("the loop variable `{}` is used to index `{}`", ident.name, indexed), + |diag| { + multispan_sugg( + diag, + "consider using an iterator", + vec![ + (pat.span, format!("({}, <item>)", ident.name)), + ( + arg.span, + format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2), + ), + ], + ); + }, + ); + } else { + let repl = if starts_at_zero && take_is_empty { + format!("&{}{}", ref_mut, indexed) + } else { + format!("{}.{}(){}{}", indexed, method, method_1, method_2) + }; + + span_lint_and_then( + cx, + NEEDLESS_RANGE_LOOP, + expr.span, + &format!("the loop variable `{}` is only used to index `{}`", ident.name, indexed), + |diag| { + multispan_sugg( + diag, + "consider using an iterator", + vec![(pat.span, "<item>".to_string()), (arg.span, repl)], + ); + }, + ); + } + } + } + } +} + +fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool { + if_chain! { + if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind; + if len_args.len() == 1; + if method.ident.name == sym!(len); + if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind; + if path.segments.len() == 1; + if path.segments[0].ident.name == var; + then { + return true; + } + } + + false +} + +fn is_end_eq_array_len<'tcx>( + cx: &LateContext<'tcx>, + end: &Expr<'_>, + limits: ast::RangeLimits, + indexed_ty: Ty<'tcx>, +) -> bool { + if_chain! { + if let ExprKind::Lit(ref lit) = end.kind; + if let ast::LitKind::Int(end_int, _) = lit.node; + if let ty::Array(_, arr_len_const) = indexed_ty.kind(); + if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env); + then { + return match limits { + ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(), + ast::RangeLimits::HalfOpen => end_int >= arr_len.into(), + }; + } + } + + false +} + +struct VarVisitor<'a, 'tcx> { + /// context reference + cx: &'a LateContext<'tcx>, + /// var name to look for as index + var: HirId, + /// indexed variables that are used mutably + indexed_mut: FxHashSet<Symbol>, + /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global + indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>, + /// subset of `indexed` of vars that are indexed directly: `v[i]` + /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]` + indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>, + /// Any names that are used outside an index operation. + /// Used to detect things like `&mut vec` used together with `vec[i]` + referenced: FxHashSet<Symbol>, + /// has the loop variable been used in expressions other than the index of + /// an index op? + nonindex: bool, + /// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar + /// takes `&mut self` + prefer_mutable: bool, +} + +impl<'a, 'tcx> VarVisitor<'a, 'tcx> { + fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool { + if_chain! { + // the indexed container is referenced by a name + if let ExprKind::Path(ref seqpath) = seqexpr.kind; + if let QPath::Resolved(None, ref seqvar) = *seqpath; + if seqvar.segments.len() == 1; + then { + let index_used_directly = path_to_local_id(idx, self.var); + let indexed_indirectly = { + let mut used_visitor = LocalUsedVisitor::new(self.cx, self.var); + walk_expr(&mut used_visitor, idx); + used_visitor.used + }; + + if indexed_indirectly || index_used_directly { + if self.prefer_mutable { + self.indexed_mut.insert(seqvar.segments[0].ident.name); + } + let res = self.cx.qpath_res(seqpath, seqexpr.hir_id); + match res { + Res::Local(hir_id) => { + let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id); + let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id); + let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id); + if indexed_indirectly { + self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent)); + } + if index_used_directly { + self.indexed_directly.insert( + seqvar.segments[0].ident.name, + (Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)), + ); + } + return false; // no need to walk further *on the variable* + } + Res::Def(DefKind::Static | DefKind::Const, ..) => { + if indexed_indirectly { + self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None); + } + if index_used_directly { + self.indexed_directly.insert( + seqvar.segments[0].ident.name, + (None, self.cx.typeck_results().node_type(seqexpr.hir_id)), + ); + } + return false; // no need to walk further *on the variable* + } + _ => (), + } + } + } + } + true + } +} + +impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> { + type Map = Map<'tcx>; + + fn visit_expr(&mut self, expr: &'tcx Expr<'_>) { + if_chain! { + // a range index op + if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind; + if (meth.ident.name == sym::index && match_trait_method(self.cx, expr, &paths::INDEX)) + || (meth.ident.name == sym::index_mut && match_trait_method(self.cx, expr, &paths::INDEX_MUT)); + if !self.check(&args[1], &args[0], expr); + then { return } + } + + if_chain! { + // an index op + if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind; + if !self.check(idx, seqexpr, expr); + then { return } + } + + if_chain! { + // directly using a variable + if let ExprKind::Path(QPath::Resolved(None, path)) = expr.kind; + if let Res::Local(local_id) = path.res; + then { + if local_id == self.var { + self.nonindex = true; + } else { + // not the correct variable, but still a variable + self.referenced.insert(path.segments[0].ident.name); + } + } + } + + let old = self.prefer_mutable; + match expr.kind { + ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => { + self.prefer_mutable = true; + self.visit_expr(lhs); + self.prefer_mutable = false; + self.visit_expr(rhs); + }, + ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => { + if mutbl == Mutability::Mut { + self.prefer_mutable = true; + } + self.visit_expr(expr); + }, + ExprKind::Call(ref f, args) => { + self.visit_expr(f); + for expr in args { + let ty = self.cx.typeck_results().expr_ty_adjusted(expr); + self.prefer_mutable = false; + if let ty::Ref(_, _, mutbl) = *ty.kind() { + if mutbl == Mutability::Mut { + self.prefer_mutable = true; + } + } + self.visit_expr(expr); + } + }, + ExprKind::MethodCall(_, _, args, _) => { + let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap(); + for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) { + self.prefer_mutable = false; + if let ty::Ref(_, _, mutbl) = *ty.kind() { + if mutbl == Mutability::Mut { + self.prefer_mutable = true; + } + } + self.visit_expr(expr); + } + }, + ExprKind::Closure(_, _, body_id, ..) => { + let body = self.cx.tcx.hir().body(body_id); + self.visit_expr(&body.value); + }, + _ => walk_expr(self, expr), + } + self.prefer_mutable = old; + } + fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { + NestedVisitorMap::None + } +} diff --git a/clippy_lints/src/loops/never_loop.rs b/clippy_lints/src/loops/never_loop.rs new file mode 100644 index 00000000000..45e1001d755 --- /dev/null +++ b/clippy_lints/src/loops/never_loop.rs @@ -0,0 +1,172 @@ +use super::NEVER_LOOP; +use crate::utils::span_lint; +use rustc_hir::{Block, Expr, ExprKind, HirId, InlineAsmOperand, Stmt, StmtKind}; +use rustc_lint::LateContext; +use std::iter::{once, Iterator}; + +pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { + if let ExprKind::Loop(ref block, _, _, _) = expr.kind { + match never_loop_block(block, expr.hir_id) { + NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"), + NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (), + } + } +} + +enum NeverLoopResult { + // A break/return always get triggered but not necessarily for the main loop. + AlwaysBreak, + // A continue may occur for the main loop. + MayContinueMainLoop, + Otherwise, +} + +#[must_use] +fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult { + match *arg { + NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise, + NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop, + } +} + +// Combine two results for parts that are called in order. +#[must_use] +fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult { + match first { + NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first, + NeverLoopResult::Otherwise => second, + } +} + +// Combine two results where both parts are called but not necessarily in order. +#[must_use] +fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult { + match (left, right) { + (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => { + NeverLoopResult::MayContinueMainLoop + }, + (NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak, + (NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise, + } +} + +// Combine two results where only one of the part may have been executed. +#[must_use] +fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult { + match (b1, b2) { + (NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak, + (NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => { + NeverLoopResult::MayContinueMainLoop + }, + (NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise, + } +} + +fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult { + let stmts = block.stmts.iter().map(stmt_to_expr); + let expr = once(block.expr.as_deref()); + let mut iter = stmts.chain(expr).flatten(); + never_loop_expr_seq(&mut iter, main_loop_id) +} + +fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult { + es.map(|e| never_loop_expr(e, main_loop_id)) + .fold(NeverLoopResult::Otherwise, combine_seq) +} + +fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> { + match stmt.kind { + StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e), + StmtKind::Local(ref local) => local.init.as_deref(), + _ => None, + } +} + +fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult { + match expr.kind { + ExprKind::Box(ref e) + | ExprKind::Unary(_, ref e) + | ExprKind::Cast(ref e, _) + | ExprKind::Type(ref e, _) + | ExprKind::Field(ref e, _) + | ExprKind::AddrOf(_, _, ref e) + | ExprKind::Struct(_, _, Some(ref e)) + | ExprKind::Repeat(ref e, _) + | ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id), + ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es, _) | ExprKind::Tup(ref es) => { + never_loop_expr_all(&mut es.iter(), main_loop_id) + }, + ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id), + ExprKind::Binary(_, ref e1, ref e2) + | ExprKind::Assign(ref e1, ref e2, _) + | ExprKind::AssignOp(_, ref e1, ref e2) + | ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id), + ExprKind::Loop(ref b, _, _, _) => { + // Break can come from the inner loop so remove them. + absorb_break(&never_loop_block(b, main_loop_id)) + }, + ExprKind::If(ref e, ref e2, ref e3) => { + let e1 = never_loop_expr(e, main_loop_id); + let e2 = never_loop_expr(e2, main_loop_id); + let e3 = e3 + .as_ref() + .map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id)); + combine_seq(e1, combine_branches(e2, e3)) + }, + ExprKind::Match(ref e, ref arms, _) => { + let e = never_loop_expr(e, main_loop_id); + if arms.is_empty() { + e + } else { + let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id); + combine_seq(e, arms) + } + }, + ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id), + ExprKind::Continue(d) => { + let id = d + .target_id + .expect("target ID can only be missing in the presence of compilation errors"); + if id == main_loop_id { + NeverLoopResult::MayContinueMainLoop + } else { + NeverLoopResult::AlwaysBreak + } + }, + ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| { + combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak) + }), + ExprKind::InlineAsm(ref asm) => asm + .operands + .iter() + .map(|(o, _)| match o { + InlineAsmOperand::In { expr, .. } + | InlineAsmOperand::InOut { expr, .. } + | InlineAsmOperand::Const { expr } + | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id), + InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id), + InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => { + never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id) + }, + }) + .fold(NeverLoopResult::Otherwise, combine_both), + ExprKind::Struct(_, _, None) + | ExprKind::Yield(_, _) + | ExprKind::Closure(_, _, _, _, _) + | ExprKind::LlvmInlineAsm(_) + | ExprKind::Path(_) + | ExprKind::ConstBlock(_) + | ExprKind::Lit(_) + | ExprKind::Err => NeverLoopResult::Otherwise, + } +} + +fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult { + es.map(|e| never_loop_expr(e, main_loop_id)) + .fold(NeverLoopResult::Otherwise, combine_both) +} + +fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult { + e.map(|e| never_loop_expr(e, main_loop_id)) + .fold(NeverLoopResult::AlwaysBreak, combine_branches) +} diff --git a/clippy_lints/src/loops/same_item_push.rs b/clippy_lints/src/loops/same_item_push.rs new file mode 100644 index 00000000000..f3585830e4a --- /dev/null +++ b/clippy_lints/src/loops/same_item_push.rs @@ -0,0 +1,169 @@ +use super::SAME_ITEM_PUSH; +use crate::utils::{implements_trait, is_type_diagnostic_item, snippet_with_macro_callsite, span_lint_and_help}; +use if_chain::if_chain; +use rustc_hir::def::{DefKind, Res}; +use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor}; +use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, Node, Pat, PatKind, Stmt, StmtKind}; +use rustc_lint::LateContext; +use rustc_middle::hir::map::Map; +use rustc_span::symbol::sym; +use std::iter::Iterator; + +/// Detects for loop pushing the same item into a Vec +pub(super) fn check<'tcx>( + cx: &LateContext<'tcx>, + pat: &'tcx Pat<'_>, + _: &'tcx Expr<'_>, + body: &'tcx Expr<'_>, + _: &'tcx Expr<'_>, +) { + fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) { + let vec_str = snippet_with_macro_callsite(cx, vec.span, ""); + let item_str = snippet_with_macro_callsite(cx, pushed_item.span, ""); + + span_lint_and_help( + cx, + SAME_ITEM_PUSH, + vec.span, + "it looks like the same item is being pushed into this Vec", + None, + &format!( + "try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})", + item_str, vec_str, item_str + ), + ) + } + + if !matches!(pat.kind, PatKind::Wild) { + return; + } + + // Determine whether it is safe to lint the body + let mut same_item_push_visitor = SameItemPushVisitor { + should_lint: true, + vec_push: None, + cx, + }; + walk_expr(&mut same_item_push_visitor, body); + if same_item_push_visitor.should_lint { + if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push { + let vec_ty = cx.typeck_results().expr_ty(vec); + let ty = vec_ty.walk().nth(1).unwrap().expect_ty(); + if cx + .tcx + .lang_items() + .clone_trait() + .map_or(false, |id| implements_trait(cx, ty, id, &[])) + { + // Make sure that the push does not involve possibly mutating values + match pushed_item.kind { + ExprKind::Path(ref qpath) => { + match cx.qpath_res(qpath, pushed_item.hir_id) { + // immutable bindings that are initialized with literal or constant + Res::Local(hir_id) => { + if_chain! { + let node = cx.tcx.hir().get(hir_id); + if let Node::Binding(pat) = node; + if let PatKind::Binding(bind_ann, ..) = pat.kind; + if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable); + let parent_node = cx.tcx.hir().get_parent_node(hir_id); + if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node); + if let Some(init) = parent_let_expr.init; + then { + match init.kind { + // immutable bindings that are initialized with literal + ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item), + // immutable bindings that are initialized with constant + ExprKind::Path(ref path) => { + if let Res::Def(DefKind::Const, ..) = cx.qpath_res(path, init.hir_id) { + emit_lint(cx, vec, pushed_item); + } + } + _ => {}, + } + } + } + }, + // constant + Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item), + _ => {}, + } + }, + ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item), + _ => {}, + } + } + } + } +} + +// Scans the body of the for loop and determines whether lint should be given +struct SameItemPushVisitor<'a, 'tcx> { + should_lint: bool, + // this field holds the last vec push operation visited, which should be the only push seen + vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>, + cx: &'a LateContext<'tcx>, +} + +impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> { + type Map = Map<'tcx>; + + fn visit_expr(&mut self, expr: &'tcx Expr<'_>) { + match &expr.kind { + // Non-determinism may occur ... don't give a lint + ExprKind::Loop(..) | ExprKind::Match(..) => self.should_lint = false, + ExprKind::Block(block, _) => self.visit_block(block), + _ => {}, + } + } + + fn visit_block(&mut self, b: &'tcx Block<'_>) { + for stmt in b.stmts.iter() { + self.visit_stmt(stmt); + } + } + + fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) { + let vec_push_option = get_vec_push(self.cx, s); + if vec_push_option.is_none() { + // Current statement is not a push so visit inside + match &s.kind { + StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr), + _ => {}, + } + } else { + // Current statement is a push ...check whether another + // push had been previously done + if self.vec_push.is_none() { + self.vec_push = vec_push_option; + } else { + // There are multiple pushes ... don't lint + self.should_lint = false; + } + } + } + + fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { + NestedVisitorMap::None + } +} + +// Given some statement, determine if that statement is a push on a Vec. If it is, return +// the Vec being pushed into and the item being pushed +fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> { + if_chain! { + // Extract method being called + if let StmtKind::Semi(semi_stmt) = &stmt.kind; + if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind; + // Figure out the parameters for the method call + if let Some(self_expr) = args.get(0); + if let Some(pushed_item) = args.get(1); + // Check that the method being called is push() on a Vec + if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym::vec_type); + if path.ident.name.as_str() == "push"; + then { + return Some((self_expr, pushed_item)) + } + } + None +} diff --git a/clippy_lints/src/loops/single_element_loop.rs b/clippy_lints/src/loops/single_element_loop.rs new file mode 100644 index 00000000000..38400c93c9a --- /dev/null +++ b/clippy_lints/src/loops/single_element_loop.rs @@ -0,0 +1,42 @@ +use super::{get_span_of_entire_for_loop, SINGLE_ELEMENT_LOOP}; +use crate::utils::{indent_of, single_segment_path, snippet, span_lint_and_sugg}; +use if_chain::if_chain; +use rustc_errors::Applicability; +use rustc_hir::{BorrowKind, Expr, ExprKind, Pat, PatKind}; +use rustc_lint::LateContext; + +pub(super) fn check<'tcx>( + cx: &LateContext<'tcx>, + pat: &'tcx Pat<'_>, + arg: &'tcx Expr<'_>, + body: &'tcx Expr<'_>, + expr: &'tcx Expr<'_>, +) { + if_chain! { + if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg_expr) = arg.kind; + if let PatKind::Binding(.., target, _) = pat.kind; + if let ExprKind::Array([arg_expression]) = arg_expr.kind; + if let ExprKind::Path(ref list_item) = arg_expression.kind; + if let Some(list_item_name) = single_segment_path(list_item).map(|ps| ps.ident.name); + if let ExprKind::Block(ref block, _) = body.kind; + if !block.stmts.is_empty(); + + then { + let for_span = get_span_of_entire_for_loop(expr); + let mut block_str = snippet(cx, block.span, "..").into_owned(); + block_str.remove(0); + block_str.pop(); + + + span_lint_and_sugg( + cx, + SINGLE_ELEMENT_LOOP, + for_span, + "for loop over a single element", + "try", + format!("{{\n{}let {} = &{};{}}}", " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0)), target.name, list_item_name, block_str), + Applicability::MachineApplicable + ) + } + } +} diff --git a/clippy_lints/src/loops/utils.rs b/clippy_lints/src/loops/utils.rs new file mode 100644 index 00000000000..9e38e17719a --- /dev/null +++ b/clippy_lints/src/loops/utils.rs @@ -0,0 +1,350 @@ +use crate::utils::{ + get_parent_expr, get_trait_def_id, has_iter_method, implements_trait, is_integer_const, path_to_local, + path_to_local_id, paths, sugg, +}; +use if_chain::if_chain; +use rustc_data_structures::fx::FxHashMap; +use rustc_errors::Applicability; +use rustc_hir::intravisit::{walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor}; +use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, HirId, Mutability, Pat, PatKind, Stmt, StmtKind}; +use rustc_lint::LateContext; +use rustc_middle::hir::map::Map; +use rustc_span::source_map::Span; +use rustc_span::symbol::Symbol; +use std::iter::Iterator; + +#[derive(Debug, PartialEq)] +enum IncrementVisitorVarState { + Initial, // Not examined yet + IncrOnce, // Incremented exactly once, may be a loop counter + DontWarn, +} + +/// Scan a for loop for variables that are incremented exactly once and not used after that. +pub(super) struct IncrementVisitor<'a, 'tcx> { + cx: &'a LateContext<'tcx>, // context reference + states: FxHashMap<HirId, IncrementVisitorVarState>, // incremented variables + depth: u32, // depth of conditional expressions + done: bool, +} + +impl<'a, 'tcx> IncrementVisitor<'a, 'tcx> { + pub(super) fn new(cx: &'a LateContext<'tcx>) -> Self { + Self { + cx, + states: FxHashMap::default(), + depth: 0, + done: false, + } + } + + pub(super) fn into_results(self) -> impl Iterator<Item = HirId> { + self.states.into_iter().filter_map(|(id, state)| { + if state == IncrementVisitorVarState::IncrOnce { + Some(id) + } else { + None + } + }) + } +} + +impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> { + type Map = Map<'tcx>; + + fn visit_expr(&mut self, expr: &'tcx Expr<'_>) { + if self.done { + return; + } + + // If node is a variable + if let Some(def_id) = path_to_local(expr) { + if let Some(parent) = get_parent_expr(self.cx, expr) { + let state = self.states.entry(def_id).or_insert(IncrementVisitorVarState::Initial); + if *state == IncrementVisitorVarState::IncrOnce { + *state = IncrementVisitorVarState::DontWarn; + return; + } + + match parent.kind { + ExprKind::AssignOp(op, ref lhs, ref rhs) => { + if lhs.hir_id == expr.hir_id { + *state = if op.node == BinOpKind::Add + && is_integer_const(self.cx, rhs, 1) + && *state == IncrementVisitorVarState::Initial + && self.depth == 0 + { + IncrementVisitorVarState::IncrOnce + } else { + // Assigned some other value or assigned multiple times + IncrementVisitorVarState::DontWarn + }; + } + }, + ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => { + *state = IncrementVisitorVarState::DontWarn + }, + ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => { + *state = IncrementVisitorVarState::DontWarn + }, + _ => (), + } + } + + walk_expr(self, expr); + } else if is_loop(expr) || is_conditional(expr) { + self.depth += 1; + walk_expr(self, expr); + self.depth -= 1; + } else if let ExprKind::Continue(_) = expr.kind { + self.done = true; + } else { + walk_expr(self, expr); + } + } + fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { + NestedVisitorMap::None + } +} + +enum InitializeVisitorState<'hir> { + Initial, // Not examined yet + Declared(Symbol), // Declared but not (yet) initialized + Initialized { + name: Symbol, + initializer: &'hir Expr<'hir>, + }, + DontWarn, +} + +/// Checks whether a variable is initialized at the start of a loop and not modified +/// and used after the loop. +pub(super) struct InitializeVisitor<'a, 'tcx> { + cx: &'a LateContext<'tcx>, // context reference + end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here. + var_id: HirId, + state: InitializeVisitorState<'tcx>, + depth: u32, // depth of conditional expressions + past_loop: bool, +} + +impl<'a, 'tcx> InitializeVisitor<'a, 'tcx> { + pub(super) fn new(cx: &'a LateContext<'tcx>, end_expr: &'tcx Expr<'tcx>, var_id: HirId) -> Self { + Self { + cx, + end_expr, + var_id, + state: InitializeVisitorState::Initial, + depth: 0, + past_loop: false, + } + } + + pub(super) fn get_result(&self) -> Option<(Symbol, &'tcx Expr<'tcx>)> { + if let InitializeVisitorState::Initialized { name, initializer } = self.state { + Some((name, initializer)) + } else { + None + } + } +} + +impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> { + type Map = Map<'tcx>; + + fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) { + // Look for declarations of the variable + if_chain! { + if let StmtKind::Local(ref local) = stmt.kind; + if local.pat.hir_id == self.var_id; + if let PatKind::Binding(.., ident, _) = local.pat.kind; + then { + self.state = local.init.map_or(InitializeVisitorState::Declared(ident.name), |init| { + InitializeVisitorState::Initialized { + initializer: init, + name: ident.name, + } + }) + } + } + walk_stmt(self, stmt); + } + + fn visit_expr(&mut self, expr: &'tcx Expr<'_>) { + if matches!(self.state, InitializeVisitorState::DontWarn) { + return; + } + if expr.hir_id == self.end_expr.hir_id { + self.past_loop = true; + return; + } + // No need to visit expressions before the variable is + // declared + if matches!(self.state, InitializeVisitorState::Initial) { + return; + } + + // If node is the desired variable, see how it's used + if path_to_local_id(expr, self.var_id) { + if self.past_loop { + self.state = InitializeVisitorState::DontWarn; + return; + } + + if let Some(parent) = get_parent_expr(self.cx, expr) { + match parent.kind { + ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => { + self.state = InitializeVisitorState::DontWarn; + }, + ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => { + self.state = if_chain! { + if self.depth == 0; + if let InitializeVisitorState::Declared(name) + | InitializeVisitorState::Initialized { name, ..} = self.state; + then { + InitializeVisitorState::Initialized { initializer: rhs, name } + } else { + InitializeVisitorState::DontWarn + } + } + }, + ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => { + self.state = InitializeVisitorState::DontWarn + }, + _ => (), + } + } + + walk_expr(self, expr); + } else if !self.past_loop && is_loop(expr) { + self.state = InitializeVisitorState::DontWarn; + } else if is_conditional(expr) { + self.depth += 1; + walk_expr(self, expr); + self.depth -= 1; + } else { + walk_expr(self, expr); + } + } + + fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { + NestedVisitorMap::OnlyBodies(self.cx.tcx.hir()) + } +} + +fn is_loop(expr: &Expr<'_>) -> bool { + matches!(expr.kind, ExprKind::Loop(..)) +} + +fn is_conditional(expr: &Expr<'_>) -> bool { + matches!(expr.kind, ExprKind::If(..) | ExprKind::Match(..)) +} + +#[derive(PartialEq, Eq)] +pub(super) enum Nesting { + Unknown, // no nesting detected yet + RuledOut, // the iterator is initialized or assigned within scope + LookFurther, // no nesting detected, no further walk required +} + +use self::Nesting::{LookFurther, RuledOut, Unknown}; + +pub(super) struct LoopNestVisitor { + pub(super) hir_id: HirId, + pub(super) iterator: HirId, + pub(super) nesting: Nesting, +} + +impl<'tcx> Visitor<'tcx> for LoopNestVisitor { + type Map = Map<'tcx>; + + fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) { + if stmt.hir_id == self.hir_id { + self.nesting = LookFurther; + } else if self.nesting == Unknown { + walk_stmt(self, stmt); + } + } + + fn visit_expr(&mut self, expr: &'tcx Expr<'_>) { + if self.nesting != Unknown { + return; + } + if expr.hir_id == self.hir_id { + self.nesting = LookFurther; + return; + } + match expr.kind { + ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => { + if path_to_local_id(path, self.iterator) { + self.nesting = RuledOut; + } + }, + _ => walk_expr(self, expr), + } + } + + fn visit_pat(&mut self, pat: &'tcx Pat<'_>) { + if self.nesting != Unknown { + return; + } + if let PatKind::Binding(_, id, ..) = pat.kind { + if id == self.iterator { + self.nesting = RuledOut; + return; + } + } + walk_pat(self, pat) + } + + fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { + NestedVisitorMap::None + } +} + +// this function assumes the given expression is a `for` loop. +pub(super) fn get_span_of_entire_for_loop(expr: &Expr<'_>) -> Span { + // for some reason this is the only way to get the `Span` + // of the entire `for` loop + if let ExprKind::Match(_, arms, _) = &expr.kind { + arms[0].body.span + } else { + unreachable!() + } +} + +/// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the +/// actual `Iterator` that the loop uses. +pub(super) fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String { + let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| { + implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[]) + }); + if impls_iterator { + format!( + "{}", + sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par() + ) + } else { + // (&x).into_iter() ==> x.iter() + // (&mut x).into_iter() ==> x.iter_mut() + match &arg.kind { + ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner) + if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() => + { + let meth_name = match mutability { + Mutability::Mut => "iter_mut", + Mutability::Not => "iter", + }; + format!( + "{}.{}()", + sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(), + meth_name, + ) + } + _ => format!( + "{}.into_iter()", + sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par() + ), + } + } +} diff --git a/clippy_lints/src/loops/while_immutable_condition.rs b/clippy_lints/src/loops/while_immutable_condition.rs new file mode 100644 index 00000000000..05e0a722563 --- /dev/null +++ b/clippy_lints/src/loops/while_immutable_condition.rs @@ -0,0 +1,139 @@ +use super::WHILE_IMMUTABLE_CONDITION; +use crate::consts::constant; +use crate::utils::span_lint_and_then; +use crate::utils::usage::mutated_variables; +use if_chain::if_chain; +use rustc_data_structures::fx::{FxHashMap, FxHashSet}; +use rustc_hir::def::{DefKind, Res}; +use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor}; +use rustc_hir::{def_id, Expr, ExprKind, HirId, QPath}; +use rustc_lint::LateContext; +use rustc_middle::hir::map::Map; +use std::iter::Iterator; + +pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) { + if constant(cx, cx.typeck_results(), cond).is_some() { + // A pure constant condition (e.g., `while false`) is not linted. + return; + } + + let mut var_visitor = VarCollectorVisitor { + cx, + ids: FxHashSet::default(), + def_ids: FxHashMap::default(), + skip: false, + }; + var_visitor.visit_expr(cond); + if var_visitor.skip { + return; + } + let used_in_condition = &var_visitor.ids; + let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) { + used_in_condition.is_disjoint(&used_mutably) + } else { + return; + }; + let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v); + + let mut has_break_or_return_visitor = HasBreakOrReturnVisitor { + has_break_or_return: false, + }; + has_break_or_return_visitor.visit_expr(expr); + let has_break_or_return = has_break_or_return_visitor.has_break_or_return; + + if no_cond_variable_mutated && !mutable_static_in_cond { + span_lint_and_then( + cx, + WHILE_IMMUTABLE_CONDITION, + cond.span, + "variables in the condition are not mutated in the loop body", + |diag| { + diag.note("this may lead to an infinite or to a never running loop"); + + if has_break_or_return { + diag.note("this loop contains `return`s or `break`s"); + diag.help("rewrite it as `if cond { loop { } }`"); + } + }, + ); + } +} + +struct HasBreakOrReturnVisitor { + has_break_or_return: bool, +} + +impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor { + type Map = Map<'tcx>; + + fn visit_expr(&mut self, expr: &'tcx Expr<'_>) { + if self.has_break_or_return { + return; + } + + match expr.kind { + ExprKind::Ret(_) | ExprKind::Break(_, _) => { + self.has_break_or_return = true; + return; + }, + _ => {}, + } + + walk_expr(self, expr); + } + + fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { + NestedVisitorMap::None + } +} + +/// Collects the set of variables in an expression +/// Stops analysis if a function call is found +/// Note: In some cases such as `self`, there are no mutable annotation, +/// All variables definition IDs are collected +struct VarCollectorVisitor<'a, 'tcx> { + cx: &'a LateContext<'tcx>, + ids: FxHashSet<HirId>, + def_ids: FxHashMap<def_id::DefId, bool>, + skip: bool, +} + +impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> { + fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) { + if_chain! { + if let ExprKind::Path(ref qpath) = ex.kind; + if let QPath::Resolved(None, _) = *qpath; + let res = self.cx.qpath_res(qpath, ex.hir_id); + then { + match res { + Res::Local(hir_id) => { + self.ids.insert(hir_id); + }, + Res::Def(DefKind::Static, def_id) => { + let mutable = self.cx.tcx.is_mutable_static(def_id); + self.def_ids.insert(def_id, mutable); + }, + _ => {}, + } + } + } + } +} + +impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> { + type Map = Map<'tcx>; + + fn visit_expr(&mut self, ex: &'tcx Expr<'_>) { + match ex.kind { + ExprKind::Path(_) => self.insert_def_id(ex), + // If there is any function/method call… we just stop analysis + ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true, + + _ => walk_expr(self, ex), + } + } + + fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { + NestedVisitorMap::None + } +} diff --git a/clippy_lints/src/loops/while_let_loop.rs b/clippy_lints/src/loops/while_let_loop.rs new file mode 100644 index 00000000000..65d8f2f1111 --- /dev/null +++ b/clippy_lints/src/loops/while_let_loop.rs @@ -0,0 +1,87 @@ +use super::WHILE_LET_LOOP; +use crate::utils::{snippet_with_applicability, span_lint_and_sugg}; +use rustc_errors::Applicability; +use rustc_hir::{Block, Expr, ExprKind, MatchSource, StmtKind}; +use rustc_lint::{LateContext, LintContext}; +use rustc_middle::lint::in_external_macro; + +pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, loop_block: &'tcx Block<'_>) { + // extract the expression from the first statement (if any) in a block + let inner_stmt_expr = extract_expr_from_first_stmt(loop_block); + // or extract the first expression (if any) from the block + if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(loop_block)) { + if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind { + // ensure "if let" compatible match structure + match *source { + MatchSource::Normal | MatchSource::IfLetDesugar { .. } => { + if arms.len() == 2 + && arms[0].guard.is_none() + && arms[1].guard.is_none() + && is_simple_break_expr(&arms[1].body) + { + if in_external_macro(cx.sess(), expr.span) { + return; + } + + // NOTE: we used to build a body here instead of using + // ellipsis, this was removed because: + // 1) it was ugly with big bodies; + // 2) it was not indented properly; + // 3) it wasn’t very smart (see #675). + let mut applicability = Applicability::HasPlaceholders; + span_lint_and_sugg( + cx, + WHILE_LET_LOOP, + expr.span, + "this loop could be written as a `while let` loop", + "try", + format!( + "while let {} = {} {{ .. }}", + snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability), + snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability), + ), + applicability, + ); + } + }, + _ => (), + } + } + } +} + +/// If a block begins with a statement (possibly a `let` binding) and has an +/// expression, return it. +fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> { + if block.stmts.is_empty() { + return None; + } + if let StmtKind::Local(ref local) = block.stmts[0].kind { + local.init //.map(|expr| expr) + } else { + None + } +} + +/// If a block begins with an expression (with or without semicolon), return it. +fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> { + match block.expr { + Some(ref expr) if block.stmts.is_empty() => Some(expr), + None if !block.stmts.is_empty() => match block.stmts[0].kind { + StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr), + StmtKind::Local(..) | StmtKind::Item(..) => None, + }, + _ => None, + } +} + +/// Returns `true` if expr contains a single break expr without destination label +/// and +/// passed expression. The expression may be within a block. +fn is_simple_break_expr(expr: &Expr<'_>) -> bool { + match expr.kind { + ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true, + ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)), + _ => false, + } +} diff --git a/clippy_lints/src/loops/while_let_on_iterator.rs b/clippy_lints/src/loops/while_let_on_iterator.rs new file mode 100644 index 00000000000..e5a47694faa --- /dev/null +++ b/clippy_lints/src/loops/while_let_on_iterator.rs @@ -0,0 +1,171 @@ +use super::utils::{LoopNestVisitor, Nesting}; +use super::WHILE_LET_ON_ITERATOR; +use crate::utils::usage::mutated_variables; +use crate::utils::{ + get_enclosing_block, get_trait_def_id, implements_trait, is_refutable, last_path_segment, match_trait_method, + path_to_local, path_to_local_id, paths, snippet_with_applicability, span_lint_and_sugg, +}; +use if_chain::if_chain; +use rustc_errors::Applicability; +use rustc_hir::intravisit::{walk_block, walk_expr, NestedVisitorMap, Visitor}; +use rustc_hir::{Expr, ExprKind, HirId, MatchSource, Node, PatKind}; +use rustc_lint::LateContext; +use rustc_middle::hir::map::Map; + +use rustc_span::symbol::sym; + +pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { + if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind { + let pat = &arms[0].pat.kind; + if let ( + &PatKind::TupleStruct(ref qpath, ref pat_args, _), + &ExprKind::MethodCall(ref method_path, _, ref method_args, _), + ) = (pat, &match_expr.kind) + { + let iter_expr = &method_args[0]; + + // Don't lint when the iterator is recreated on every iteration + if_chain! { + if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind; + if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR); + if implements_trait(cx, cx.typeck_results().expr_ty(iter_expr), iter_def_id, &[]); + then { + return; + } + } + + let lhs_constructor = last_path_segment(qpath); + if method_path.ident.name == sym::next + && match_trait_method(cx, match_expr, &paths::ITERATOR) + && lhs_constructor.ident.name == sym::Some + && (pat_args.is_empty() + || !is_refutable(cx, &pat_args[0]) + && !is_used_inside(cx, iter_expr, &arms[0].body) + && !is_iterator_used_after_while_let(cx, iter_expr) + && !is_nested(cx, expr, &method_args[0])) + { + let mut applicability = Applicability::MachineApplicable; + let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability); + let loop_var = if pat_args.is_empty() { + "_".to_string() + } else { + snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned() + }; + span_lint_and_sugg( + cx, + WHILE_LET_ON_ITERATOR, + expr.span.with_hi(match_expr.span.hi()), + "this loop could be written as a `for` loop", + "try", + format!("for {} in {}", loop_var, iterator), + applicability, + ); + } + } + } +} + +fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool { + let def_id = match path_to_local(expr) { + Some(id) => id, + None => return false, + }; + if let Some(used_mutably) = mutated_variables(container, cx) { + if used_mutably.contains(&def_id) { + return true; + } + } + false +} + +fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool { + let def_id = match path_to_local(iter_expr) { + Some(id) => id, + None => return false, + }; + let mut visitor = VarUsedAfterLoopVisitor { + def_id, + iter_expr_id: iter_expr.hir_id, + past_while_let: false, + var_used_after_while_let: false, + }; + if let Some(enclosing_block) = get_enclosing_block(cx, def_id) { + walk_block(&mut visitor, enclosing_block); + } + visitor.var_used_after_while_let +} + +fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool { + if_chain! { + if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id); + let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id); + if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node); + then { + return is_loop_nested(cx, loop_expr, iter_expr) + } + } + false +} + +fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool { + let mut id = loop_expr.hir_id; + let iter_id = if let Some(id) = path_to_local(iter_expr) { + id + } else { + return true; + }; + loop { + let parent = cx.tcx.hir().get_parent_node(id); + if parent == id { + return false; + } + match cx.tcx.hir().find(parent) { + Some(Node::Expr(expr)) => { + if let ExprKind::Loop(..) = expr.kind { + return true; + }; + }, + Some(Node::Block(block)) => { + let mut block_visitor = LoopNestVisitor { + hir_id: id, + iterator: iter_id, + nesting: Nesting::Unknown, + }; + walk_block(&mut block_visitor, block); + if block_visitor.nesting == Nesting::RuledOut { + return false; + } + }, + Some(Node::Stmt(_)) => (), + _ => { + return false; + }, + } + id = parent; + } +} + +struct VarUsedAfterLoopVisitor { + def_id: HirId, + iter_expr_id: HirId, + past_while_let: bool, + var_used_after_while_let: bool, +} + +impl<'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor { + type Map = Map<'tcx>; + + fn visit_expr(&mut self, expr: &'tcx Expr<'_>) { + if self.past_while_let { + if path_to_local_id(expr, self.def_id) { + self.var_used_after_while_let = true; + } + } else if self.iter_expr_id == expr.hir_id { + self.past_while_let = true; + } + walk_expr(self, expr); + } + fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { + NestedVisitorMap::None + } +} |