use crate::consts::{constant, Constant}; use crate::reexport::Name; use crate::utils::paths; use crate::utils::usage::{is_unused, mutated_variables}; use crate::utils::{ get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait, is_integer_const, is_no_std_crate, is_refutable, last_path_segment, match_trait_method, match_type, match_var, multispan_sugg, snippet, snippet_opt, snippet_with_applicability, span_lint, span_lint_and_help, span_lint_and_sugg, span_lint_and_then, SpanlessEq, }; use crate::utils::{is_type_diagnostic_item, qpath_res, same_tys, sext, sugg}; use if_chain::if_chain; use itertools::Itertools; use rustc::hir::map::Map; use rustc::lint::in_external_macro; use rustc::middle::region; use rustc::ty::{self, Ty}; use rustc_ast::ast; use rustc_data_structures::fx::{FxHashMap, FxHashSet}; use rustc_errors::Applicability; use rustc_hir::def::{DefKind, Res}; use rustc_hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor}; use rustc_hir::{ def_id, BinOpKind, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, GenericArg, HirId, LoopSource, MatchSource, Mutability, Node, Pat, PatKind, QPath, Stmt, StmtKind, }; use rustc_infer::infer::TyCtxtInferExt; use rustc_lint::{LateContext, LateLintPass, LintContext}; use rustc_session::{declare_lint_pass, declare_tool_lint}; use rustc_span::source_map::Span; use rustc_span::{BytePos, Symbol}; use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Place, PlaceBase}; use std::iter::{once, Iterator}; use std::mem; 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` values. /// /// **Why is this bad?** Readability. This is more clearly expressed as an `if /// let`. /// /// **Known problems:** None. /// /// **Example:** /// ```ignore /// for x in option { /// .. /// } /// ``` /// /// This should be /// ```ignore /// if let Some(x) = option { /// .. /// } /// ``` pub FOR_LOOP_OVER_OPTION, correctness, "for-looping over an `Option`, which is more clearly expressed as an `if let`" } declare_clippy_lint! { /// **What it does:** Checks for `for` loops over `Result` values. /// /// **Why is this bad?** Readability. This is more clearly expressed as an `if /// let`. /// /// **Known problems:** None. /// /// **Example:** /// ```ignore /// for x in result { /// .. /// } /// ``` /// /// This should be /// ```ignore /// if let Ok(x) = result { /// .. /// } /// ``` pub FOR_LOOP_OVER_RESULT, correctness, "for-looping over 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). /// /// **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::>().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 ranges `x..y` where both `x` and `y` /// are constant and `x` is greater or equal to `y`, unless the range is /// reversed or has a negative `.step_by(_)`. /// /// **Why is it bad?** Such loops will either be skipped or loop until /// wrap-around (in debug code, this may `panic!()`). Both options are probably /// not intended. /// /// **Known problems:** The lint cannot catch loops over dynamically defined /// ranges. Doing this would require simulating all possible inputs and code /// paths through the program, which would be complex and error-prone. /// /// **Example:** /// ```ignore /// for x in 5..10 - 5 { /// .. /// } // oops, stray `-` /// ``` pub REVERSE_RANGE_LOOP, correctness, "iteration over an empty range, such as `10..0` or `5..5`" } 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?** Those busy loops burn CPU cycles without doing /// anything. Think of the environment and either block on something or at least /// make the thread sleep for some microseconds. /// /// **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_lint_pass!(Loops => [ MANUAL_MEMCPY, NEEDLESS_RANGE_LOOP, EXPLICIT_ITER_LOOP, EXPLICIT_INTO_ITER_LOOP, ITER_NEXT_LOOP, FOR_LOOP_OVER_RESULT, FOR_LOOP_OVER_OPTION, WHILE_LET_LOOP, NEEDLESS_COLLECT, REVERSE_RANGE_LOOP, EXPLICIT_COUNTER_LOOP, EMPTY_LOOP, WHILE_LET_ON_ITERATOR, FOR_KV_MAP, NEVER_LOOP, MUT_RANGE_BOUND, WHILE_IMMUTABLE_CONDITION, ]); impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Loops { #[allow(clippy::too_many_lines)] fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) { if let Some((pat, arg, body)) = 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); } // we don't want to check expanded macros if expr.span.from_expansion() { return; } // check for never_loop 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 => (), } } // 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 if block.stmts.is_empty() && block.expr.is_none() && !is_no_std_crate(cx.tcx.hir().krate()) { span_lint( cx, EMPTY_LOOP, expr.span, "empty `loop {}` detected. You may want to either use `panic!()` or add \ `std::thread::sleep(..);` to the loop body.", ); } // extract the expression from the first statement (if any) in a block let inner_stmt_expr = extract_expr_from_first_stmt(block); // or extract the first expression (if any) from the block if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(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 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]; 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 iterator = snippet(cx, method_args[0].span, "_"); let loop_var = if pat_args.is_empty() { "_".to_string() } else { snippet(cx, pat_args[0].span, "_").into_owned() }; span_lint_and_sugg( cx, WHILE_LET_ON_ITERATOR, expr.span, "this loop could be written as a `for` loop", "try", format!("for {} in {} {{ .. }}", loop_var, iterator), Applicability::HasPlaceholders, ); } } } if let Some((cond, body)) = higher::while_loop(&expr) { check_infinite_loop(cx, cond, body); } check_needless_collect(expr, cx); } } 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_ref().map(|p| &**p)); let mut iter = stmts.chain(expr).filter_map(|e| e); never_loop_expr_seq(&mut iter, main_loop_id) } 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_ref().map(|p| &**p), _ => 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::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) => { if let Some(ref e) = *e { combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak) } else { NeverLoopResult::AlwaysBreak } }, ExprKind::Struct(_, _, None) | ExprKind::Yield(_, _) | ExprKind::Closure(_, _, _, _, _) | ExprKind::InlineAsm(_) | ExprKind::Path(_) | ExprKind::Lit(_) | ExprKind::Err => NeverLoopResult::Otherwise, } } fn never_loop_expr_seq<'a, T: Iterator>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult { es.map(|e| never_loop_expr(e, main_loop_id)) .fold(NeverLoopResult::Otherwise, combine_seq) } fn never_loop_expr_all<'a, T: Iterator>>(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>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult { e.map(|e| never_loop_expr(e, main_loop_id)) .fold(NeverLoopResult::AlwaysBreak, combine_branches) } fn check_for_loop<'a, 'tcx>( cx: &LateContext<'a, 'tcx>, pat: &'tcx Pat<'_>, arg: &'tcx Expr<'_>, body: &'tcx Expr<'_>, expr: &'tcx Expr<'_>, ) { check_for_loop_range(cx, pat, arg, body, expr); check_for_loop_reverse_range(cx, arg, expr); check_for_loop_arg(cx, pat, arg, expr); check_for_loop_explicit_counter(cx, pat, arg, body, expr); check_for_loop_over_map_kv(cx, pat, arg, body, expr); check_for_mut_range_bound(cx, arg, body); detect_manual_memcpy(cx, pat, arg, body, expr); } fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr<'_>, var: HirId) -> bool { if_chain! { if let ExprKind::Path(ref qpath) = expr.kind; if let QPath::Resolved(None, ref path) = *qpath; if path.segments.len() == 1; if let Res::Local(local_id) = qpath_res(cx, qpath, expr.hir_id); // our variable! if local_id == var; then { return true; } } false } struct Offset { value: String, negate: bool, } impl Offset { fn negative(s: String) -> Self { Self { value: s, negate: true } } fn positive(s: String) -> Self { Self { value: s, negate: false, } } } struct FixedOffsetVar { var_name: String, offset: Offset, } fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, '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, Symbol::intern("vec_type")) || match_type(cx, ty, &paths::VEC_DEQUE) } fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr<'_>, var: HirId) -> Option { fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr<'_>, var: HirId) -> Option { match e.kind { ExprKind::Lit(ref l) => match l.node { ast::LitKind::Int(x, _ty) => Some(x.to_string()), _ => None, }, ExprKind::Path(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())), _ => None, } } if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind { let ty = cx.tables.expr_ty(seqexpr); if !is_slice_like(cx, ty) { return None; } let offset = match idx.kind { ExprKind::Binary(op, ref lhs, ref rhs) => match op.node { BinOpKind::Add => { let offset_opt = if same_var(cx, lhs, var) { extract_offset(cx, rhs, var) } else if same_var(cx, rhs, var) { extract_offset(cx, lhs, var) } else { None }; offset_opt.map(Offset::positive) }, BinOpKind::Sub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative), _ => None, }, ExprKind::Path(..) => { if same_var(cx, idx, var) { Some(Offset::positive("0".into())) } else { None } }, _ => None, }; offset.map(|o| FixedOffsetVar { var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()), offset: o, }) } else { None } } fn fetch_cloned_fixed_offset_var<'a, 'tcx>( cx: &LateContext<'a, 'tcx>, expr: &Expr<'_>, var: HirId, ) -> Option { if_chain! { if let ExprKind::MethodCall(ref method, _, ref args) = expr.kind; if method.ident.name == sym!(clone); if args.len() == 1; if let Some(arg) = args.get(0); then { return get_fixed_offset_var(cx, arg, var); } } get_fixed_offset_var(cx, expr, var) } fn get_indexed_assignments<'a, 'tcx>( cx: &LateContext<'a, 'tcx>, body: &Expr<'_>, var: HirId, ) -> Vec<(FixedOffsetVar, FixedOffsetVar)> { fn get_assignment<'a, 'tcx>( cx: &LateContext<'a, 'tcx>, e: &Expr<'_>, var: HirId, ) -> Option<(FixedOffsetVar, FixedOffsetVar)> { if let ExprKind::Assign(ref lhs, ref rhs, _) = e.kind { match ( get_fixed_offset_var(cx, lhs, var), fetch_cloned_fixed_offset_var(cx, rhs, var), ) { (Some(offset_left), Some(offset_right)) => { // Source and destination must be different if offset_left.var_name == offset_right.var_name { None } else { Some((offset_left, offset_right)) } }, _ => None, } } else { None } } if let ExprKind::Block(ref b, _) = body.kind { let Block { ref stmts, ref expr, .. } = **b; stmts .iter() .map(|stmt| match stmt.kind { StmtKind::Local(..) | StmtKind::Item(..) => None, StmtKind::Expr(ref e) | StmtKind::Semi(ref e) => Some(get_assignment(cx, e, var)), }) .chain(expr.as_ref().into_iter().map(|e| Some(get_assignment(cx, &*e, var)))) .filter_map(|op| op) .collect::>>() .unwrap_or_else(|| vec![]) } else { get_assignment(cx, body, var).into_iter().collect() } } /// Checks for for loops that sequentially copy items from one slice-like /// object to another. fn detect_manual_memcpy<'a, 'tcx>( cx: &LateContext<'a, '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(cx, arg) { // the var must be a single name if let PatKind::Binding(_, canonical_id, _, _) = pat.kind { let print_sum = |arg1: &Offset, arg2: &Offset| -> String { match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) { ("0", _, "0", _) => "".into(), ("0", _, x, false) | (x, false, "0", false) => x.into(), ("0", _, x, true) | (x, false, "0", true) => format!("-{}", x), (x, false, y, false) => format!("({} + {})", x, y), (x, false, y, true) => { if x == y { "0".into() } else { format!("({} - {})", x, y) } }, (x, true, y, false) => { if x == y { "0".into() } else { format!("({} - {})", y, x) } }, (x, true, y, true) => format!("-({} + {})", x, y), } }; let print_limit = |end: &Option<&Expr<'_>>, offset: Offset, var_name: &str| { if let Some(end) = *end { if_chain! { if let ExprKind::MethodCall(ref method, _, ref len_args) = end.kind; if method.ident.name == sym!(len); if len_args.len() == 1; if let Some(arg) = len_args.get(0); if snippet(cx, arg.span, "??") == var_name; then { return if offset.negate { format!("({} - {})", snippet(cx, end.span, ".len()"), offset.value) } else { String::new() }; } } let end_str = match limits { ast::RangeLimits::Closed => { let end = sugg::Sugg::hir(cx, end, ""); format!("{}", end + sugg::ONE) }, ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")), }; print_sum(&Offset::positive(end_str), &offset) } else { "..".into() } }; // The only statements in the for loops can be indexed assignments from // indexed retrievals. let manual_copies = get_indexed_assignments(cx, body, canonical_id); let big_sugg = manual_copies .into_iter() .map(|(dst_var, src_var)| { let start_str = Offset::positive(snippet(cx, start.span, "").to_string()); let dst_offset = print_sum(&start_str, &dst_var.offset); let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name); let src_offset = print_sum(&start_str, &src_var.offset); let src_limit = print_limit(end, src_var.offset, &src_var.var_name); let dst = if dst_offset == "" && dst_limit == "" { dst_var.var_name } else { format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit) }; format!( "{}.clone_from_slice(&{}[{}..{}])", dst, src_var.var_name, src_offset, src_limit ) }) .join("\n "); if !big_sugg.is_empty() { span_lint_and_sugg( cx, MANUAL_MEMCPY, expr.span, "it looks like you're manually copying between slices", "try replacing the loop by", big_sugg, Applicability::Unspecified, ); } } } } /// 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)] fn check_for_loop_range<'a, 'tcx>( cx: &LateContext<'a, '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(cx, 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 { 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 { match limits { ast::RangeLimits::Closed => { let take_expr = sugg::Sugg::hir(cx, take_expr, ""); 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), |db| { multispan_sugg( db, "consider using an iterator".to_string(), vec![ (pat.span, format!("({}, )", 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 ), |db| { multispan_sugg( db, "consider using an iterator".to_string(), vec![(pat.span, "".to_string()), (arg.span, repl)], ); }, ); } } } } } fn is_len_call(expr: &Expr<'_>, var: Name) -> 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 } fn check_for_loop_reverse_range<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arg: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) { // if this for loop is iterating over a two-sided range... if let Some(higher::Range { start: Some(start), end: Some(end), limits, }) = higher::range(cx, arg) { // ...and both sides are compile-time constant integers... if let Some((start_idx, _)) = constant(cx, cx.tables, start) { if let Some((end_idx, _)) = constant(cx, cx.tables, end) { // ...and the start index is greater than the end index, // this loop will never run. This is often confusing for developers // who think that this will iterate from the larger value to the // smaller value. let ty = cx.tables.expr_ty(start); let (sup, eq) = match (start_idx, end_idx) { (Constant::Int(start_idx), Constant::Int(end_idx)) => ( match ty.kind { ty::Int(ity) => sext(cx.tcx, start_idx, ity) > sext(cx.tcx, end_idx, ity), ty::Uint(_) => start_idx > end_idx, _ => false, }, start_idx == end_idx, ), _ => (false, false), }; if sup { let start_snippet = snippet(cx, start.span, "_"); let end_snippet = snippet(cx, end.span, "_"); let dots = if limits == ast::RangeLimits::Closed { "..=" } else { ".." }; span_lint_and_then( cx, REVERSE_RANGE_LOOP, expr.span, "this range is empty so this for loop will never run", |db| { db.span_suggestion( arg.span, "consider using the following if you are attempting to iterate over this \ range in reverse", format!( "({end}{dots}{start}).rev()", end = end_snippet, dots = dots, start = start_snippet ), Applicability::MaybeIncorrect, ); }, ); } else if eq && limits != ast::RangeLimits::Closed { // if they are equal, it's also problematic - this loop // will never run. span_lint( cx, REVERSE_RANGE_LOOP, expr.span, "this range is empty so this for loop will never run", ); } } } } } fn lint_iter_method(cx: &LateContext<'_, '_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) { 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, ) } 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 if method_name == "iter" || method_name == "iter_mut" { if is_ref_iterable_type(cx, &args[0]) { lint_iter_method(cx, args, arg, method_name); } } else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) { let receiver_ty = cx.tables.expr_ty(&args[0]); let receiver_ty_adjusted = cx.tables.expr_ty_adjusted(&args[0]); if same_tys(cx, receiver_ty, receiver_ty_adjusted) { 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, ); } else { let ref_receiver_ty = cx.tcx.mk_ref( cx.tcx.lifetimes.re_erased, ty::TypeAndMut { ty: receiver_ty, mutbl: Mutability::Not, }, ); if same_tys(cx, receiver_ty_adjusted, ref_receiver_ty) { lint_iter_method(cx, args, arg, method_name) } } } else if method_name == "next" && 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", ); next_loop_linted = true; } } } if !next_loop_linted { check_arg_type(cx, pat, arg); } } /// Checks for `for` loops over `Option`s and `Result`s. fn check_arg_type(cx: &LateContext<'_, '_>, pat: &Pat<'_>, arg: &Expr<'_>) { let ty = cx.tables.expr_ty(arg); if match_type(cx, ty, &paths::OPTION) { span_lint_and_help( cx, FOR_LOOP_OVER_OPTION, 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, "_") ), &format!( "consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`", snippet(cx, pat.span, "_"), snippet(cx, arg.span, "_") ), ); } else if match_type(cx, ty, &paths::RESULT) { span_lint_and_help( cx, FOR_LOOP_OVER_RESULT, 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, "_") ), &format!( "consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`", snippet(cx, pat.span, "_"), snippet(cx, arg.span, "_") ), ); } } fn check_for_loop_explicit_counter<'a, 'tcx>( cx: &LateContext<'a, '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 visitor = IncrementVisitor { cx, states: FxHashMap::default(), depth: 0, done: false, }; walk_expr(&mut 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 visitor.states.iter().filter(|&(_, v)| *v == VarState::IncrOnce) { let mut visitor2 = InitializeVisitor { cx, end_expr: expr, var_id: *id, state: VarState::IncrOnce, name: None, depth: 0, past_loop: false, }; walk_block(&mut visitor2, block); if visitor2.state == VarState::Warn { if let Some(name) = visitor2.name { let mut applicability = Applicability::MachineApplicable; // for some reason this is the only way to get the `Span` // of the entire `for` loop let for_span = if let ExprKind::Match(_, arms, _) = &expr.kind { arms[0].body.span } else { unreachable!() }; 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, ); } } } } } /// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the /// actual `Iterator` that the loop uses. 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.tables.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.tables.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() ), } } } /// Checks for the `FOR_KV_MAP` lint. fn check_for_loop_over_map_kv<'a, 'tcx>( cx: &LateContext<'a, '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.tables.expr_ty(arg).kind { ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) { (key, _) if pat_is_wild(key, body) => (pat[1].span, "value", ty, mutbl), (_, value) if pat_is_wild(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 match_type(cx, ty, &paths::HASHMAP) || 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), |db| { let map = sugg::Sugg::hir(cx, arg, "map"); multispan_sugg( db, "use the corresponding method".into(), vec![ (pat_span, snippet(cx, new_pat_span, kind).into_owned()), (arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)), ], ); }, ); } } } } struct MutatePairDelegate { hir_id_low: Option, hir_id_high: Option, span_low: Option, span_high: Option, } impl<'tcx> Delegate<'tcx> for MutatePairDelegate { fn consume(&mut self, _: &Place<'tcx>, _: ConsumeMode) {} fn borrow(&mut self, cmt: &Place<'tcx>, bk: ty::BorrowKind) { if let ty::BorrowKind::MutBorrow = bk { if let PlaceBase::Local(id) = cmt.base { if Some(id) == self.hir_id_low { self.span_low = Some(cmt.span) } if Some(id) == self.hir_id_high { self.span_high = Some(cmt.span) } } } } fn mutate(&mut self, cmt: &Place<'tcx>) { if let PlaceBase::Local(id) = cmt.base { if Some(id) == self.hir_id_low { self.span_low = Some(cmt.span) } if Some(id) == self.hir_id_high { self.span_high = Some(cmt.span) } } } } impl<'tcx> MutatePairDelegate { fn mutation_span(&self) -> (Option, Option) { (self.span_low, self.span_high) } } fn check_for_mut_range_bound(cx: &LateContext<'_, '_>, arg: &Expr<'_>, body: &Expr<'_>) { if let Some(higher::Range { start: Some(start), end: Some(end), .. }) = higher::range(cx, 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) { 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 { if_chain! { if let ExprKind::Path(ref qpath) = bound.kind; if let QPath::Resolved(None, _) = *qpath; then { let res = qpath_res(cx, qpath, bound.hir_id); if let Res::Local(node_id) = res { let node_str = cx.tcx.hir().get(node_id); if_chain! { if let Node::Binding(pat) = node_str; if let PatKind::Binding(bind_ann, ..) = pat.kind; if let BindingAnnotation::Mutable = bind_ann; then { return Some(node_id); } } } } } None } fn check_for_mutation( cx: &LateContext<'_, '_>, body: &Expr<'_>, bound_ids: &[Option], ) -> (Option, Option) { let mut delegate = MutatePairDelegate { hir_id_low: bound_ids[0], hir_id_high: bound_ids[1], span_low: None, span_high: None, }; let def_id = def_id::DefId::local(body.hir_id.owner); cx.tcx.infer_ctxt().enter(|infcx| { ExprUseVisitor::new(&mut delegate, &infcx, def_id, cx.param_env, cx.tables).walk_expr(body); }); delegate.mutation_span() } /// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`. fn pat_is_wild<'tcx>(pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool { match *pat { PatKind::Wild => true, PatKind::Binding(.., ident, None) if ident.as_str().starts_with('_') => is_unused(&ident, body), _ => false, } } struct LocalUsedVisitor<'a, 'tcx> { cx: &'a LateContext<'a, 'tcx>, local: HirId, used: bool, } impl<'a, 'tcx> Visitor<'tcx> for LocalUsedVisitor<'a, 'tcx> { type Map = Map<'tcx>; fn visit_expr(&mut self, expr: &'tcx Expr<'_>) { if same_var(self.cx, expr, self.local) { self.used = true; } else { walk_expr(self, expr); } } fn nested_visit_map(&mut self) -> NestedVisitorMap { NestedVisitorMap::None } } struct VarVisitor<'a, 'tcx> { /// context reference cx: &'a LateContext<'a, 'tcx>, /// var name to look for as index var: HirId, /// indexed variables that are used mutably indexed_mut: FxHashSet, /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global indexed_indirectly: FxHashMap>, /// 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, 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, /// 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 = same_var(self.cx, idx, self.var); let indexed_indirectly = { let mut used_visitor = LocalUsedVisitor { cx: self.cx, local: self.var, used: false, }; 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 = qpath_res(self.cx, 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.tables.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.tables.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(ref qpath) = expr.kind; if let QPath::Resolved(None, ref path) = *qpath; if path.segments.len() == 1; then { if let Res::Local(local_id) = qpath_res(self.cx, qpath, expr.hir_id) { 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.tables.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.tables.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 { NestedVisitorMap::None } } fn is_used_inside<'a, 'tcx>(cx: &'a LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool { let def_id = match var_def_id(cx, 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<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr<'_>) -> bool { let def_id = match var_def_id(cx, iter_expr) { Some(id) => id, None => return false, }; let mut visitor = VarUsedAfterLoopVisitor { cx, 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 } struct VarUsedAfterLoopVisitor<'a, 'tcx> { cx: &'a LateContext<'a, 'tcx>, def_id: HirId, iter_expr_id: HirId, past_while_let: bool, var_used_after_while_let: bool, } impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> { type Map = Map<'tcx>; fn visit_expr(&mut self, expr: &'tcx Expr<'_>) { if self.past_while_let { if Some(self.def_id) == var_def_id(self.cx, expr) { 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 { NestedVisitorMap::None } } /// 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.tables.expr_ty(e); is_iterable_array(ty, cx) || is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) || match_type(cx, ty, &paths::LINKED_LIST) || match_type(cx, ty, &paths::HASHMAP) || match_type(cx, ty, &paths::HASHSET) || match_type(cx, ty, &paths::VEC_DEQUE) || 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) => { if let Some(val) = n.try_eval_usize(cx.tcx, cx.param_env) { (0..=32).contains(&val) } else { false } }, _ => false, } } /// 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 { if let Some(expr) = local.init { Some(expr) } else { None } } 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, } } // 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. #[derive(Debug, PartialEq)] enum VarState { Initial, // Not examined yet IncrOnce, // Incremented exactly once, may be a loop counter Declared, // Declared but not (yet) initialized to zero Warn, DontWarn, } /// Scan a for loop for variables that are incremented exactly once. struct IncrementVisitor<'a, 'tcx> { cx: &'a LateContext<'a, 'tcx>, // context reference states: FxHashMap, // incremented variables depth: u32, // depth of conditional expressions done: bool, } 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) = var_def_id(self.cx, expr) { if let Some(parent) = get_parent_expr(self.cx, expr) { let state = self.states.entry(def_id).or_insert(VarState::Initial); match parent.kind { ExprKind::AssignOp(op, ref lhs, ref rhs) => { if lhs.hir_id == expr.hir_id { if op.node == BinOpKind::Add && is_integer_const(self.cx, rhs, 1) { *state = match *state { VarState::Initial if self.depth == 0 => VarState::IncrOnce, _ => VarState::DontWarn, }; } else { // Assigned some other value *state = VarState::DontWarn; } } }, ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => *state = VarState::DontWarn, ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => { *state = VarState::DontWarn }, _ => (), } } } else if is_loop(expr) || is_conditional(expr) { self.depth += 1; walk_expr(self, expr); self.depth -= 1; return; } else if let ExprKind::Continue(_) = expr.kind { self.done = true; return; } walk_expr(self, expr); } fn nested_visit_map(&mut self) -> NestedVisitorMap { NestedVisitorMap::None } } /// Checks whether a variable is initialized to zero at the start of a loop. struct InitializeVisitor<'a, 'tcx> { cx: &'a LateContext<'a, 'tcx>, // context reference end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here. var_id: HirId, state: VarState, name: Option, depth: u32, // depth of conditional expressions past_loop: bool, } 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 let StmtKind::Local(ref local) = stmt.kind { if local.pat.hir_id == self.var_id { if let PatKind::Binding(.., ident, _) = local.pat.kind { self.name = Some(ident.name); self.state = if let Some(ref init) = local.init { if is_integer_const(&self.cx, init, 0) { VarState::Warn } else { VarState::Declared } } else { VarState::Declared } } } } walk_stmt(self, stmt); } fn visit_expr(&mut self, expr: &'tcx Expr<'_>) { if self.state == VarState::DontWarn { return; } if SpanlessEq::new(self.cx).eq_expr(&expr, self.end_expr) { self.past_loop = true; return; } // No need to visit expressions before the variable is // declared if self.state == VarState::IncrOnce { return; } // If node is the desired variable, see how it's used if var_def_id(self.cx, expr) == Some(self.var_id) { 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 = VarState::DontWarn; }, ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => { self.state = if is_integer_const(&self.cx, rhs, 0) && self.depth == 0 { VarState::Warn } else { VarState::DontWarn } }, ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => { self.state = VarState::DontWarn }, _ => (), } } if self.past_loop { self.state = VarState::DontWarn; return; } } else if !self.past_loop && is_loop(expr) { self.state = VarState::DontWarn; return; } else if is_conditional(expr) { self.depth += 1; walk_expr(self, expr); self.depth -= 1; return; } walk_expr(self, expr); } fn nested_visit_map(&mut self) -> NestedVisitorMap { NestedVisitorMap::OnlyBodies(self.cx.tcx.hir()) } } fn var_def_id(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> Option { if let ExprKind::Path(ref qpath) = expr.kind { let path_res = qpath_res(cx, qpath, expr.hir_id); if let Res::Local(node_id) = path_res { return Some(node_id); } } None } fn is_loop(expr: &Expr<'_>) -> bool { match expr.kind { ExprKind::Loop(..) => true, _ => false, } } fn is_conditional(expr: &Expr<'_>) -> bool { match expr.kind { ExprKind::Match(..) => true, _ => false, } } 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_name = if let Some(name) = path_name(iter_expr) { name } 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_name, nesting: Unknown, }; walk_block(&mut block_visitor, block); if block_visitor.nesting == RuledOut { return false; } }, Some(Node::Stmt(_)) => (), _ => { return false; }, } id = parent; } } #[derive(PartialEq, Eq)] 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}; struct LoopNestVisitor { hir_id: HirId, iterator: Name, 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 match_var(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(.., span_name, _) = pat.kind { if self.iterator == span_name.name { self.nesting = RuledOut; return; } } walk_pat(self, pat) } fn nested_visit_map(&mut self) -> NestedVisitorMap { NestedVisitorMap::None } } fn path_name(e: &Expr<'_>) -> Option { if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind { let segments = &path.segments; if segments.len() == 1 { return Some(segments[0].ident.name); } }; None } fn check_infinite_loop<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) { if constant(cx, cx.tables, 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", |db| { db.note("this may lead to an infinite or to a never running loop"); if has_break_or_return { db.note("this loop contains `return`s or `break`s"); db.help("rewrite it as `if cond { loop { } }`"); } }, ); } } struct HasBreakOrReturnVisitor { has_break_or_return: bool, } impl<'a, '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 { 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<'a, 'tcx>, ids: FxHashSet, def_ids: FxHashMap, 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 = qpath_res(self.cx, qpath, ex.hir_id); then { match res { Res::Local(node_id) => { self.ids.insert(node_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 { NestedVisitorMap::None } } const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed"; fn check_needless_collect<'a, 'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'a, '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.tables.node_type(ty.hir_id); if is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")) || match_type(cx, ty, &paths::VEC_DEQUE) || match_type(cx, ty, &paths::BTREEMAP) || match_type(cx, ty, &paths::HASHMAP) { if method.ident.name == sym!(len) { let span = shorten_needless_collect_span(expr); span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| { db.span_suggestion( span, "replace with", ".count()".to_string(), Applicability::MachineApplicable, ); }); } if method.ident.name == sym!(is_empty) { let span = shorten_needless_collect_span(expr); span_lint_and_then(cx, NEEDLESS_COLLECT, span, NEEDLESS_COLLECT_MSG, |db| { db.span_suggestion( span, "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, |db| { let (arg, pred) = if contains_arg.starts_with('&') { ("x", &contains_arg[1..]) } else { ("&x", &*contains_arg) }; db.span_suggestion( span, "replace with", format!( ".any(|{}| x == {})", arg, pred ), Applicability::MachineApplicable, ); }); } } } } } fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span { if_chain! { if let ExprKind::MethodCall(_, _, ref args) = expr.kind; if let ExprKind::MethodCall(_, ref span, _) = args[0].kind; then { return expr.span.with_lo(span.lo() - BytePos(1)); } } unreachable!() }