3 use rustc::middle::const_val::ConstVal;
5 use rustc::hir::def::Def;
6 use rustc_const_eval::EvalHint::ExprTypeChecked;
7 use rustc_const_eval::eval_const_expr_partial;
10 use syntax::codemap::Span;
11 use utils::{get_trait_def_id, implements_trait, in_external_macro, in_macro, is_copy, match_path, match_trait_method,
12 match_type, method_chain_args, return_ty, same_tys, snippet, span_lint, span_lint_and_then,
13 span_note_and_lint, walk_ptrs_ty, walk_ptrs_ty_depth, last_path_segment, single_segment_path,
21 /// **What it does:** Checks for `.unwrap()` calls on `Option`s.
23 /// **Why is this bad?** Usually it is better to handle the `None` case, or to
24 /// at least call `.expect(_)` with a more helpful message. Still, for a lot of
25 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
26 /// `Allow` by default.
28 /// **Known problems:** None.
35 pub OPTION_UNWRAP_USED,
37 "using `Option.unwrap()`, which should at least get a better message using `expect()`"
40 /// **What it does:** Checks for `.unwrap()` calls on `Result`s.
42 /// **Why is this bad?** `result.unwrap()` will let the thread panic on `Err`
43 /// values. Normally, you want to implement more sophisticated error handling,
44 /// and propagate errors upwards with `try!`.
46 /// Even if you want to panic on errors, not all `Error`s implement good
47 /// messages on display. Therefore it may be beneficial to look at the places
48 /// where they may get displayed. Activate this lint to do just that.
50 /// **Known problems:** None.
57 pub RESULT_UNWRAP_USED,
59 "using `Result.unwrap()`, which might be better handled"
62 /// **What it does:** Checks for methods that should live in a trait
63 /// implementation of a `std` trait (see [llogiq's blog
64 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
65 /// information) instead of an inherent implementation.
67 /// **Why is this bad?** Implementing the traits improve ergonomics for users of
68 /// the code, often with very little cost. Also people seeing a `mul(...)` method
69 /// may expect `*` to work equally, so you should have good reason to disappoint
72 /// **Known problems:** None.
78 /// fn add(&self, other: &X) -> X { .. }
82 pub SHOULD_IMPLEMENT_TRAIT,
84 "defining a method that should be implementing a std trait"
87 /// **What it does:** Checks for methods with certain name prefixes and which
88 /// doesn't match how self is taken. The actual rules are:
90 /// |Prefix |`self` taken |
91 /// |-------|----------------------|
92 /// |`as_` |`&self` or `&mut self`|
95 /// |`is_` |`&self` or none |
98 /// **Why is this bad?** Consistency breeds readability. If you follow the
99 /// conventions, your users won't be surprised that they, e.g., need to supply a
100 /// mutable reference to a `as_..` function.
102 /// **Known problems:** None.
107 /// fn as_str(self) -> &str { .. }
111 pub WRONG_SELF_CONVENTION,
113 "defining a method named with an established prefix (like \"into_\") that takes \
114 `self` with the wrong convention"
117 /// **What it does:** This is the same as
118 /// [`wrong_self_convention`](#wrong_self_convention), but for public items.
120 /// **Why is this bad?** See [`wrong_self_convention`](#wrong_self_convention).
122 /// **Known problems:** Actually *renaming* the function may break clients if
123 /// the function is part of the public interface. In that case, be mindful of
124 /// the stability guarantees you've given your users.
129 /// pub fn as_str(self) -> &str { .. }
133 pub WRONG_PUB_SELF_CONVENTION,
135 "defining a public method named with an established prefix (like \"into_\") that takes \
136 `self` with the wrong convention"
139 /// **What it does:** Checks for usage of `ok().expect(..)`.
141 /// **Why is this bad?** Because you usually call `expect()` on the `Result`
142 /// directly to get a better error message.
144 /// **Known problems:** None.
148 /// x.ok().expect("why did I do this again?")
153 "using `ok().expect()`, which gives worse error messages than \
154 calling `expect` directly on the Result"
157 /// **What it does:** Checks for usage of `_.map(_).unwrap_or(_)`.
159 /// **Why is this bad?** Readability, this can be written more concisely as
160 /// `_.map_or(_, _)`.
162 /// **Known problems:** None.
166 /// x.map(|a| a + 1).unwrap_or(0)
169 pub OPTION_MAP_UNWRAP_OR,
171 "using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as \
175 /// **What it does:** Checks for usage of `_.map(_).unwrap_or_else(_)`.
177 /// **Why is this bad?** Readability, this can be written more concisely as
178 /// `_.map_or_else(_, _)`.
180 /// **Known problems:** None.
184 /// x.map(|a| a + 1).unwrap_or_else(some_function)
187 pub OPTION_MAP_UNWRAP_OR_ELSE,
189 "using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as \
193 /// **What it does:** Checks for usage of `_.filter(_).next()`.
195 /// **Why is this bad?** Readability, this can be written more concisely as
198 /// **Known problems:** None.
202 /// iter.filter(|x| x == 0).next()
207 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
210 /// **What it does:** Checks for usage of `_.filter(_).map(_)`,
211 /// `_.filter(_).flat_map(_)`, `_.filter_map(_).flat_map(_)` and similar.
213 /// **Why is this bad?** Readability, this can be written more concisely as a
214 /// single method call.
216 /// **Known problems:** Often requires a condition + Option/Iterator creation
217 /// inside the closure.
221 /// iter.filter(|x| x == 0).map(|x| x * 2)
226 "using combinations of `filter`, `map`, `filter_map` and `flat_map` which can \
227 usually be written as a single method call"
230 /// **What it does:** Checks for an iterator search (such as `find()`,
231 /// `position()`, or `rposition()`) followed by a call to `is_some()`.
233 /// **Why is this bad?** Readability, this can be written more concisely as
236 /// **Known problems:** None.
240 /// iter.find(|x| x == 0).is_some()
245 "using an iterator search followed by `is_some()`, which is more succinctly \
246 expressed as a call to `any()`"
249 /// **What it does:** Checks for usage of `.chars().next()` on a `str` to check
250 /// if it starts with a given char.
252 /// **Why is this bad?** Readability, this can be written more concisely as
253 /// `_.starts_with(_)`.
255 /// **Known problems:** None.
259 /// name.chars().next() == Some('_')
264 "using `.chars().next()` to check if a string starts with a char"
267 /// **What it does:** Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
268 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
269 /// `unwrap_or_default` instead.
271 /// **Why is this bad?** The function will always be called and potentially
272 /// allocate an object acting as the default.
274 /// **Known problems:** If the function has side-effects, not calling it will
275 /// change the semantic of the program, but you shouldn't rely on that anyway.
279 /// foo.unwrap_or(String::new())
281 /// this can instead be written:
283 /// foo.unwrap_or_else(String::new)
287 /// foo.unwrap_or_default()
292 "using any `*or` method with a function call, which suggests `*or_else`"
295 /// **What it does:** Checks for usage of `.extend(s)` on a `Vec` to extend the
296 /// vector by a slice.
298 /// **Why is this bad?** Since Rust 1.6, the `extend_from_slice(_)` method is
299 /// stable and at least for now faster.
301 /// **Known problems:** None.
305 /// my_vec.extend(&xs)
308 pub EXTEND_FROM_SLICE,
310 "`.extend_from_slice(_)` is a faster way to extend a Vec by a slice"
313 /// **What it does:** Checks for usage of `.clone()` on a `Copy` type.
315 /// **Why is this bad?** The only reason `Copy` types implement `Clone` is for
316 /// generics, not for using the `clone` method on a concrete type.
318 /// **Known problems:** None.
327 "using `clone` on a `Copy` type"
330 /// **What it does:** Checks for usage of `.clone()` on an `&&T`.
332 /// **Why is this bad?** Cloning an `&&T` copies the inner `&T`, instead of
333 /// cloning the underlying `T`.
335 /// **Known problems:** None.
342 /// let z = y.clone();
343 /// println!("{:p} {:p}",*y, z); // prints out the same pointer
347 pub CLONE_DOUBLE_REF,
349 "using `clone` on `&&T`"
352 /// **What it does:** Checks for `new` not returning `Self`.
354 /// **Why is this bad?** As a convention, `new` methods are used to make a new
355 /// instance of a type.
357 /// **Known problems:** None.
362 /// fn new(..) -> NotAFoo {
369 "not returning `Self` in a `new` method"
372 /// **What it does:** Checks for string methods that receive a single-character
373 /// `str` as an argument, e.g. `_.split("x")`.
375 /// **Why is this bad?** Performing these methods using a `char` is faster than
378 /// **Known problems:** Does not catch multi-byte unicode characters.
381 /// `_.split("x")` could be `_.split('x')
383 pub SINGLE_CHAR_PATTERN,
385 "using a single-character str where a char could be used, e.g. \
389 /// **What it does:** Checks for getting the inner pointer of a temporary `CString`.
391 /// **Why is this bad?** The inner pointer of a `CString` is only valid as long
392 /// as the `CString` is alive.
394 /// **Known problems:** None.
398 /// let c_str = CString::new("foo").unwrap().as_ptr();
400 /// call_some_ffi_func(c_str);
403 /// Here `c_str` point to a freed address. The correct use would be:
405 /// let c_str = CString::new("foo").unwrap();
407 /// call_some_ffi_func(c_str.as_ptr());
411 pub TEMPORARY_CSTRING_AS_PTR,
413 "getting the inner pointer of a temporary `CString`"
416 /// **What it does:** Checks for use of `.iter().nth()` (and the related
417 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
419 /// **Why is this bad?** `.get()` and `.get_mut()` are more efficient and more
422 /// **Known problems:** None.
426 /// let some_vec = vec![0, 1, 2, 3];
427 /// let bad_vec = some_vec.iter().nth(3);
428 /// let bad_slice = &some_vec[..].iter().nth(3);
430 /// The correct use would be:
432 /// let some_vec = vec![0, 1, 2, 3];
433 /// let bad_vec = some_vec.get(3);
434 /// let bad_slice = &some_vec[..].get(3);
439 "using `.iter().nth()` on a standard library type with O(1) element access"
442 /// **What it does:** Checks for use of `.skip(x).next()` on iterators.
444 /// **Why is this bad?** `.nth(x)` is cleaner
446 /// **Known problems:** None.
450 /// let some_vec = vec![0, 1, 2, 3];
451 /// let bad_vec = some_vec.iter().skip(3).next();
452 /// let bad_slice = &some_vec[..].iter().skip(3).next();
454 /// The correct use would be:
456 /// let some_vec = vec![0, 1, 2, 3];
457 /// let bad_vec = some_vec.iter().nth(3);
458 /// let bad_slice = &some_vec[..].iter().nth(3);
463 "using `.skip(x).next()` on an iterator"
466 /// **What it does:** Checks for use of `.get().unwrap()` (or
467 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
469 /// **Why is this bad?** Using the Index trait (`[]`) is more clear and more
472 /// **Known problems:** None.
476 /// let some_vec = vec![0, 1, 2, 3];
477 /// let last = some_vec.get(3).unwrap();
478 /// *some_vec.get_mut(0).unwrap() = 1;
480 /// The correct use would be:
482 /// let some_vec = vec![0, 1, 2, 3];
483 /// let last = some_vec[3];
489 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
492 /// **What it does:** Checks for the use of `.extend(s.chars())` where s is a
493 /// `&str` or `String`.
495 /// **Why is this bad?** `.push_str(s)` is clearer
497 /// **Known problems:** None.
502 /// let def = String::from("def");
503 /// let mut s = String::new();
504 /// s.extend(abc.chars());
505 /// s.extend(def.chars());
507 /// The correct use would be:
510 /// let def = String::from("def");
511 /// let mut s = String::new();
513 /// s.push_str(&def));
517 pub STRING_EXTEND_CHARS,
519 "using `x.extend(s.chars())` where s is a `&str` or `String`"
523 impl LintPass for Pass {
524 fn get_lints(&self) -> LintArray {
525 lint_array!(EXTEND_FROM_SLICE,
528 SHOULD_IMPLEMENT_TRAIT,
529 WRONG_SELF_CONVENTION,
530 WRONG_PUB_SELF_CONVENTION,
532 OPTION_MAP_UNWRAP_OR,
533 OPTION_MAP_UNWRAP_OR_ELSE,
541 TEMPORARY_CSTRING_AS_PTR,
551 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
552 #[allow(unused_attributes)]
553 // ^ required because `cyclomatic_complexity` attribute shows up as unused
554 #[cyclomatic_complexity = "30"]
555 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
556 if in_macro(cx, expr.span) {
561 hir::ExprMethodCall(name, _, ref args) => {
563 // GET_UNWRAP needs to be checked before general `UNWRAP` lints
564 if let Some(arglists) = method_chain_args(expr, &["get", "unwrap"]) {
565 lint_get_unwrap(cx, expr, arglists[0], false);
566 } else if let Some(arglists) = method_chain_args(expr, &["get_mut", "unwrap"]) {
567 lint_get_unwrap(cx, expr, arglists[0], true);
568 } else if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
569 lint_unwrap(cx, expr, arglists[0]);
570 } else if let Some(arglists) = method_chain_args(expr, &["ok", "expect"]) {
571 lint_ok_expect(cx, expr, arglists[0]);
572 } else if let Some(arglists) = method_chain_args(expr, &["map", "unwrap_or"]) {
573 lint_map_unwrap_or(cx, expr, arglists[0], arglists[1]);
574 } else if let Some(arglists) = method_chain_args(expr, &["map", "unwrap_or_else"]) {
575 lint_map_unwrap_or_else(cx, expr, arglists[0], arglists[1]);
576 } else if let Some(arglists) = method_chain_args(expr, &["filter", "next"]) {
577 lint_filter_next(cx, expr, arglists[0]);
578 } else if let Some(arglists) = method_chain_args(expr, &["filter", "map"]) {
579 lint_filter_map(cx, expr, arglists[0], arglists[1]);
580 } else if let Some(arglists) = method_chain_args(expr, &["filter_map", "map"]) {
581 lint_filter_map_map(cx, expr, arglists[0], arglists[1]);
582 } else if let Some(arglists) = method_chain_args(expr, &["filter", "flat_map"]) {
583 lint_filter_flat_map(cx, expr, arglists[0], arglists[1]);
584 } else if let Some(arglists) = method_chain_args(expr, &["filter_map", "flat_map"]) {
585 lint_filter_map_flat_map(cx, expr, arglists[0], arglists[1]);
586 } else if let Some(arglists) = method_chain_args(expr, &["find", "is_some"]) {
587 lint_search_is_some(cx, expr, "find", arglists[0], arglists[1]);
588 } else if let Some(arglists) = method_chain_args(expr, &["position", "is_some"]) {
589 lint_search_is_some(cx, expr, "position", arglists[0], arglists[1]);
590 } else if let Some(arglists) = method_chain_args(expr, &["rposition", "is_some"]) {
591 lint_search_is_some(cx, expr, "rposition", arglists[0], arglists[1]);
592 } else if let Some(arglists) = method_chain_args(expr, &["extend"]) {
593 lint_extend(cx, expr, arglists[0]);
594 } else if let Some(arglists) = method_chain_args(expr, &["unwrap", "as_ptr"]) {
595 lint_cstring_as_ptr(cx, expr, &arglists[0][0], &arglists[1][0]);
596 } else if let Some(arglists) = method_chain_args(expr, &["iter", "nth"]) {
597 lint_iter_nth(cx, expr, arglists[0], false);
598 } else if let Some(arglists) = method_chain_args(expr, &["iter_mut", "nth"]) {
599 lint_iter_nth(cx, expr, arglists[0], true);
600 } else if method_chain_args(expr, &["skip", "next"]).is_some() {
601 lint_iter_skip_next(cx, expr);
604 lint_or_fun_call(cx, expr, &name.node.as_str(), args);
606 let self_ty = cx.tcx.tables().expr_ty_adjusted(&args[0]);
607 if args.len() == 1 && &*name.node.as_str() == "clone" {
608 lint_clone_on_copy(cx, expr, &args[0], self_ty);
612 ty::TyRef(_, ty) if ty.ty.sty == ty::TyStr => {
613 for &(method, pos) in &PATTERN_METHODS {
614 if &*name.node.as_str() == method && args.len() > pos {
615 lint_single_char_pattern(cx, expr, &args[pos]);
622 hir::ExprBinary(op, ref lhs, ref rhs) if op.node == hir::BiEq || op.node == hir::BiNe => {
623 if !lint_chars_next(cx, expr, lhs, rhs, op.node == hir::BiEq) {
624 lint_chars_next(cx, expr, rhs, lhs, op.node == hir::BiEq);
631 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, implitem: &'tcx hir::ImplItem) {
632 if in_external_macro(cx, implitem.span) {
635 let name = implitem.name;
636 let parent = cx.tcx.map.get_parent(implitem.id);
637 let item = cx.tcx.map.expect_item(parent);
639 let hir::ImplItemKind::Method(ref sig, _) = implitem.node,
640 let Some(first_arg) = sig.decl.inputs.get(0),
641 let hir::ItemImpl(_, _, _, None, _, _) = item.node,
643 // check missing trait implementations
644 for &(method_name, n_args, self_kind, out_type, trait_name) in &TRAIT_METHODS {
645 if &*name.as_str() == method_name &&
646 sig.decl.inputs.len() == n_args &&
647 out_type.matches(&sig.decl.output) &&
648 self_kind.matches(&first_arg, false) {
649 span_lint(cx, SHOULD_IMPLEMENT_TRAIT, implitem.span, &format!(
650 "defining a method called `{}` on this type; consider implementing \
651 the `{}` trait or choosing a less ambiguous name", name, trait_name));
655 // check conventions w.r.t. conversion method names and predicates
656 let ty = cx.tcx.item_type(cx.tcx.map.local_def_id(item.id));
657 let is_copy = is_copy(cx, ty, item.id);
658 for &(ref conv, self_kinds) in &CONVENTIONS {
660 conv.check(&name.as_str()),
661 let Some(explicit_self) = sig.decl.inputs.get(0).and_then(hir::Arg::to_self),
662 !self_kinds.iter().any(|k| k.matches(&explicit_self, is_copy)),
664 let lint = if item.vis == hir::Visibility::Public {
665 WRONG_PUB_SELF_CONVENTION
667 WRONG_SELF_CONVENTION
672 &format!("methods called `{}` usually take {}; consider choosing a less \
676 .map(|k| k.description())
682 let ret_ty = return_ty(cx, implitem.id);
683 if &*name.as_str() == "new" &&
684 !ret_ty.walk().any(|t| same_tys(cx, t, ty, implitem.id)) {
688 "methods called `new` usually return `Self`");
694 /// Checks for the `OR_FUN_CALL` lint.
695 fn lint_or_fun_call(cx: &LateContext, expr: &hir::Expr, name: &str, args: &[hir::Expr]) {
696 /// Check for `unwrap_or(T::new())` or `unwrap_or(T::default())`.
697 fn check_unwrap_or_default(
701 self_expr: &hir::Expr,
710 if name == "unwrap_or" {
711 if let hir::ExprPath(ref qpath) = fun.node {
712 let path: &str = &*last_path_segment(qpath).name.as_str();
714 if ["default", "new"].contains(&path) {
715 let arg_ty = cx.tcx.tables().expr_ty(arg);
716 let default_trait_id = if let Some(default_trait_id) =
717 get_trait_def_id(cx, &paths::DEFAULT_TRAIT) {
723 if implements_trait(cx, arg_ty, default_trait_id, Vec::new()) {
724 span_lint_and_then(cx,
727 &format!("use of `{}` followed by a call to `{}`", name, path),
729 db.span_suggestion(span,
731 format!("{}.unwrap_or_default()", snippet(cx, self_expr.span, "_")));
742 /// Check for `*or(foo())`.
743 fn check_general_case(
747 self_expr: &hir::Expr,
752 // don't lint for constant values
753 // FIXME: can we `expect` here instead of match?
754 let promotable = cx.tcx().rvalue_promotable_to_static.borrow()
755 .get(&arg.id).cloned().unwrap_or(true);
760 // (path, fn_has_argument, methods, suffix)
761 let know_types: &[(&[_], _, &[_], _)] =
762 &[(&paths::BTREEMAP_ENTRY, false, &["or_insert"], "with"),
763 (&paths::HASHMAP_ENTRY, false, &["or_insert"], "with"),
764 (&paths::OPTION, false, &["map_or", "ok_or", "or", "unwrap_or"], "else"),
765 (&paths::RESULT, true, &["or", "unwrap_or"], "else")];
767 let self_ty = cx.tcx.tables().expr_ty(self_expr);
769 let (fn_has_arguments, poss, suffix) = if let Some(&(_, fn_has_arguments, poss, suffix)) =
770 know_types.iter().find(|&&i| match_type(cx, self_ty, i.0)) {
771 (fn_has_arguments, poss, suffix)
776 if !poss.contains(&name) {
780 let sugg: Cow<_> = match (fn_has_arguments, !or_has_args) {
781 (true, _) => format!("|_| {}", snippet(cx, arg.span, "..")).into(),
782 (false, false) => format!("|| {}", snippet(cx, arg.span, "..")).into(),
783 (false, true) => snippet(cx, fun.span, ".."),
786 span_lint_and_then(cx,
789 &format!("use of `{}` followed by a function call", name),
791 db.span_suggestion(span,
793 format!("{}.{}_{}({})", snippet(cx, self_expr.span, "_"), name, suffix, sugg));
798 if let hir::ExprCall(ref fun, ref or_args) = args[1].node {
799 let or_has_args = !or_args.is_empty();
800 if !check_unwrap_or_default(cx, name, fun, &args[0], &args[1], or_has_args, expr.span) {
801 check_general_case(cx, name, fun, &args[0], &args[1], or_has_args, expr.span);
807 /// Checks for the `CLONE_ON_COPY` lint.
808 fn lint_clone_on_copy(cx: &LateContext, expr: &hir::Expr, arg: &hir::Expr, arg_ty: ty::Ty) {
809 let ty = cx.tcx.tables().expr_ty(expr);
810 let parent = cx.tcx.map.get_parent(expr.id);
811 let parameter_environment = ty::ParameterEnvironment::for_item(cx.tcx, parent);
812 if let ty::TyRef(_, ty::TypeAndMut { ty: inner, .. }) = arg_ty.sty {
813 if let ty::TyRef(..) = inner.sty {
814 span_lint_and_then(cx,
817 "using `clone` on a double-reference; \
818 this will copy the reference instead of cloning the inner type",
819 |db| if let Some(snip) = sugg::Sugg::hir_opt(cx, arg) {
820 db.span_suggestion(expr.span,
821 "try dereferencing it",
822 format!("({}).clone()", snip.deref()));
824 return; // don't report clone_on_copy
828 if !ty.moves_by_default(cx.tcx.global_tcx(), ¶meter_environment, expr.span) {
829 span_lint_and_then(cx,
832 "using `clone` on a `Copy` type",
833 |db| if let Some(snip) = sugg::Sugg::hir_opt(cx, arg) {
834 if let ty::TyRef(..) = cx.tcx.tables().expr_ty(arg).sty {
835 db.span_suggestion(expr.span, "try dereferencing it", format!("{}", snip.deref()));
837 db.span_suggestion(expr.span, "try removing the `clone` call", format!("{}", snip));
843 fn lint_vec_extend(cx: &LateContext, expr: &hir::Expr, args: &[hir::Expr]) {
844 let arg_ty = cx.tcx.tables().expr_ty(&args[1]);
845 if let Some(slice) = derefs_to_slice(cx, &args[1], arg_ty) {
846 span_lint_and_then(cx,
849 "use of `extend` to extend a Vec by a slice",
851 db.span_suggestion(expr.span,
853 format!("{}.extend_from_slice({})", snippet(cx, args[0].span, "_"), slice));
858 fn lint_string_extend(cx: &LateContext, expr: &hir::Expr, args: &[hir::Expr]) {
860 if let Some(arglists) = method_chain_args(arg, &["chars"]) {
861 let target = &arglists[0][0];
862 let (self_ty, _) = walk_ptrs_ty_depth(cx.tcx.tables().expr_ty(target));
863 let ref_str = if self_ty.sty == ty::TyStr {
865 } else if match_type(cx, self_ty, &paths::STRING) {
871 span_lint_and_then(cx, STRING_EXTEND_CHARS, expr.span, "calling `.extend(_.chars())`", |db| {
872 db.span_suggestion(expr.span,
874 format!("{}.push_str({}{})",
875 snippet(cx, args[0].span, "_"),
877 snippet(cx, target.span, "_")));
882 fn lint_extend(cx: &LateContext, expr: &hir::Expr, args: &[hir::Expr]) {
883 let (obj_ty, _) = walk_ptrs_ty_depth(cx.tcx.tables().expr_ty(&args[0]));
884 if match_type(cx, obj_ty, &paths::VEC) {
885 lint_vec_extend(cx, expr, args);
886 } else if match_type(cx, obj_ty, &paths::STRING) {
887 lint_string_extend(cx, expr, args);
891 fn lint_cstring_as_ptr(cx: &LateContext, expr: &hir::Expr, new: &hir::Expr, unwrap: &hir::Expr) {
893 let hir::ExprCall(ref fun, ref args) = new.node,
895 let hir::ExprPath(ref path) = fun.node,
896 let Def::Method(did) = cx.tcx.tables().qpath_def(path, fun.id),
897 match_def_path(cx, did, &paths::CSTRING_NEW)
899 span_lint_and_then(cx, TEMPORARY_CSTRING_AS_PTR, expr.span,
900 "you are getting the inner pointer of a temporary `CString`",
902 db.note("that pointer will be invalid outside this expression");
903 db.span_help(unwrap.span, "assign the `CString` to a variable to extend its lifetime");
908 fn lint_iter_nth(cx: &LateContext, expr: &hir::Expr, iter_args: &[hir::Expr], is_mut: bool) {
909 let mut_str = if is_mut { "_mut" } else { "" };
910 let caller_type = if derefs_to_slice(cx, &iter_args[0], cx.tcx.tables().expr_ty(&iter_args[0])).is_some() {
912 } else if match_type(cx, cx.tcx.tables().expr_ty(&iter_args[0]), &paths::VEC) {
914 } else if match_type(cx, cx.tcx.tables().expr_ty(&iter_args[0]), &paths::VEC_DEQUE) {
917 return; // caller is not a type that we want to lint
923 &format!("called `.iter{0}().nth()` on a {1}. Calling `.get{0}()` is both faster and more readable",
928 fn lint_get_unwrap(cx: &LateContext, expr: &hir::Expr, get_args: &[hir::Expr], is_mut: bool) {
929 // Note: we don't want to lint `get_mut().unwrap` for HashMap or BTreeMap,
930 // because they do not implement `IndexMut`
931 let expr_ty = cx.tcx.tables().expr_ty(&get_args[0]);
932 let caller_type = if derefs_to_slice(cx, &get_args[0], expr_ty).is_some() {
934 } else if match_type(cx, expr_ty, &paths::VEC) {
936 } else if match_type(cx, expr_ty, &paths::VEC_DEQUE) {
938 } else if !is_mut && match_type(cx, expr_ty, &paths::HASHMAP) {
940 } else if !is_mut && match_type(cx, expr_ty, &paths::BTREEMAP) {
943 return; // caller is not a type that we want to lint
946 let mut_str = if is_mut { "_mut" } else { "" };
947 let borrow_str = if is_mut { "&mut " } else { "&" };
948 span_lint_and_then(cx,
951 &format!("called `.get{0}().unwrap()` on a {1}. Using `[]` is more clear and more concise",
955 db.span_suggestion(expr.span,
959 snippet(cx, get_args[0].span, "_"),
960 snippet(cx, get_args[1].span, "_")));
964 fn lint_iter_skip_next(cx: &LateContext, expr: &hir::Expr) {
965 // lint if caller of skip is an Iterator
966 if match_trait_method(cx, expr, &paths::ITERATOR) {
970 "called `skip(x).next()` on an iterator. This is more succinctly expressed by calling `nth(x)`");
974 fn derefs_to_slice(cx: &LateContext, expr: &hir::Expr, ty: ty::Ty) -> Option<sugg::Sugg<'static>> {
975 fn may_slice(cx: &LateContext, ty: ty::Ty) -> bool {
977 ty::TySlice(_) => true,
978 ty::TyAdt(..) => match_type(cx, ty, &paths::VEC),
979 ty::TyArray(_, size) => size < 32,
980 ty::TyRef(_, ty::TypeAndMut { ty: inner, .. }) |
981 ty::TyBox(inner) => may_slice(cx, inner),
986 if let hir::ExprMethodCall(name, _, ref args) = expr.node {
987 if &*name.node.as_str() == "iter" && may_slice(cx, cx.tcx.tables().expr_ty(&args[0])) {
988 sugg::Sugg::hir_opt(cx, &args[0]).map(|sugg| sugg.addr())
994 ty::TySlice(_) => sugg::Sugg::hir_opt(cx, expr),
995 ty::TyRef(_, ty::TypeAndMut { ty: inner, .. }) |
996 ty::TyBox(inner) => {
997 if may_slice(cx, inner) {
998 sugg::Sugg::hir_opt(cx, expr)
1008 /// lint use of `unwrap()` for `Option`s and `Result`s
1009 fn lint_unwrap(cx: &LateContext, expr: &hir::Expr, unwrap_args: &[hir::Expr]) {
1010 let (obj_ty, _) = walk_ptrs_ty_depth(cx.tcx.tables().expr_ty(&unwrap_args[0]));
1012 let mess = if match_type(cx, obj_ty, &paths::OPTION) {
1013 Some((OPTION_UNWRAP_USED, "an Option", "None"))
1014 } else if match_type(cx, obj_ty, &paths::RESULT) {
1015 Some((RESULT_UNWRAP_USED, "a Result", "Err"))
1020 if let Some((lint, kind, none_value)) = mess {
1024 &format!("used unwrap() on {} value. If you don't want to handle the {} case gracefully, consider \
1025 using expect() to provide a better panic
1032 /// lint use of `ok().expect()` for `Result`s
1033 fn lint_ok_expect(cx: &LateContext, expr: &hir::Expr, ok_args: &[hir::Expr]) {
1034 // lint if the caller of `ok()` is a `Result`
1035 if match_type(cx, cx.tcx.tables().expr_ty(&ok_args[0]), &paths::RESULT) {
1036 let result_type = cx.tcx.tables().expr_ty(&ok_args[0]);
1037 if let Some(error_type) = get_error_type(cx, result_type) {
1038 if has_debug_impl(error_type, cx) {
1042 "called `ok().expect()` on a Result value. You can call `expect` directly on the `Result`");
1048 /// lint use of `map().unwrap_or()` for `Option`s
1049 fn lint_map_unwrap_or(cx: &LateContext, expr: &hir::Expr, map_args: &[hir::Expr], unwrap_args: &[hir::Expr]) {
1050 // lint if the caller of `map()` is an `Option`
1051 if match_type(cx, cx.tcx.tables().expr_ty(&map_args[0]), &paths::OPTION) {
1053 let msg = "called `map(f).unwrap_or(a)` on an Option value. This can be done more directly by calling \
1054 `map_or(a, f)` instead";
1055 // get snippets for args to map() and unwrap_or()
1056 let map_snippet = snippet(cx, map_args[1].span, "..");
1057 let unwrap_snippet = snippet(cx, unwrap_args[1].span, "..");
1058 // lint, with note if neither arg is > 1 line and both map() and
1059 // unwrap_or() have the same span
1060 let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
1061 let same_span = map_args[1].span.expn_id == unwrap_args[1].span.expn_id;
1062 if same_span && !multiline {
1063 span_note_and_lint(cx,
1064 OPTION_MAP_UNWRAP_OR,
1068 &format!("replace `map({0}).unwrap_or({1})` with `map_or({1}, {0})`",
1071 } else if same_span && multiline {
1072 span_lint(cx, OPTION_MAP_UNWRAP_OR, expr.span, msg);
1077 /// lint use of `map().unwrap_or_else()` for `Option`s
1078 fn lint_map_unwrap_or_else(cx: &LateContext, expr: &hir::Expr, map_args: &[hir::Expr], unwrap_args: &[hir::Expr]) {
1079 // lint if the caller of `map()` is an `Option`
1080 if match_type(cx, cx.tcx.tables().expr_ty(&map_args[0]), &paths::OPTION) {
1082 let msg = "called `map(f).unwrap_or_else(g)` on an Option value. This can be done more directly by calling \
1083 `map_or_else(g, f)` instead";
1084 // get snippets for args to map() and unwrap_or_else()
1085 let map_snippet = snippet(cx, map_args[1].span, "..");
1086 let unwrap_snippet = snippet(cx, unwrap_args[1].span, "..");
1087 // lint, with note if neither arg is > 1 line and both map() and
1088 // unwrap_or_else() have the same span
1089 let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
1090 let same_span = map_args[1].span.expn_id == unwrap_args[1].span.expn_id;
1091 if same_span && !multiline {
1092 span_note_and_lint(cx,
1093 OPTION_MAP_UNWRAP_OR_ELSE,
1097 &format!("replace `map({0}).unwrap_or_else({1})` with `with map_or_else({1}, {0})`",
1100 } else if same_span && multiline {
1101 span_lint(cx, OPTION_MAP_UNWRAP_OR_ELSE, expr.span, msg);
1106 /// lint use of `filter().next()` for `Iterators`
1107 fn lint_filter_next(cx: &LateContext, expr: &hir::Expr, filter_args: &[hir::Expr]) {
1108 // lint if caller of `.filter().next()` is an Iterator
1109 if match_trait_method(cx, expr, &paths::ITERATOR) {
1110 let msg = "called `filter(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
1111 `.find(p)` instead.";
1112 let filter_snippet = snippet(cx, filter_args[1].span, "..");
1113 if filter_snippet.lines().count() <= 1 {
1114 // add note if not multi-line
1115 span_note_and_lint(cx,
1120 &format!("replace `filter({0}).next()` with `find({0})`", filter_snippet));
1122 span_lint(cx, FILTER_NEXT, expr.span, msg);
1127 /// lint use of `filter().map()` for `Iterators`
1128 fn lint_filter_map(cx: &LateContext, expr: &hir::Expr, _filter_args: &[hir::Expr], _map_args: &[hir::Expr]) {
1129 // lint if caller of `.filter().map()` is an Iterator
1130 if match_trait_method(cx, expr, &paths::ITERATOR) {
1131 let msg = "called `filter(p).map(q)` on an `Iterator`. \
1132 This is more succinctly expressed by calling `.filter_map(..)` instead.";
1133 span_lint(cx, FILTER_MAP, expr.span, msg);
1137 /// lint use of `filter().map()` for `Iterators`
1138 fn lint_filter_map_map(cx: &LateContext, expr: &hir::Expr, _filter_args: &[hir::Expr], _map_args: &[hir::Expr]) {
1139 // lint if caller of `.filter().map()` is an Iterator
1140 if match_trait_method(cx, expr, &paths::ITERATOR) {
1141 let msg = "called `filter_map(p).map(q)` on an `Iterator`. \
1142 This is more succinctly expressed by only calling `.filter_map(..)` instead.";
1143 span_lint(cx, FILTER_MAP, expr.span, msg);
1147 /// lint use of `filter().flat_map()` for `Iterators`
1148 fn lint_filter_flat_map(cx: &LateContext, expr: &hir::Expr, _filter_args: &[hir::Expr], _map_args: &[hir::Expr]) {
1149 // lint if caller of `.filter().flat_map()` is an Iterator
1150 if match_trait_method(cx, expr, &paths::ITERATOR) {
1151 let msg = "called `filter(p).flat_map(q)` on an `Iterator`. \
1152 This is more succinctly expressed by calling `.flat_map(..)` \
1153 and filtering by returning an empty Iterator.";
1154 span_lint(cx, FILTER_MAP, expr.span, msg);
1158 /// lint use of `filter_map().flat_map()` for `Iterators`
1159 fn lint_filter_map_flat_map(cx: &LateContext, expr: &hir::Expr, _filter_args: &[hir::Expr], _map_args: &[hir::Expr]) {
1160 // lint if caller of `.filter_map().flat_map()` is an Iterator
1161 if match_trait_method(cx, expr, &paths::ITERATOR) {
1162 let msg = "called `filter_map(p).flat_map(q)` on an `Iterator`. \
1163 This is more succinctly expressed by calling `.flat_map(..)` \
1164 and filtering by returning an empty Iterator.";
1165 span_lint(cx, FILTER_MAP, expr.span, msg);
1169 /// lint searching an Iterator followed by `is_some()`
1170 fn lint_search_is_some(
1173 search_method: &str,
1174 search_args: &[hir::Expr],
1175 is_some_args: &[hir::Expr]
1177 // lint if caller of search is an Iterator
1178 if match_trait_method(cx, &is_some_args[0], &paths::ITERATOR) {
1179 let msg = format!("called `is_some()` after searching an `Iterator` with {}. This is more succinctly \
1180 expressed by calling `any()`.",
1182 let search_snippet = snippet(cx, search_args[1].span, "..");
1183 if search_snippet.lines().count() <= 1 {
1184 // add note if not multi-line
1185 span_note_and_lint(cx,
1190 &format!("replace `{0}({1}).is_some()` with `any({1})`", search_method, search_snippet));
1192 span_lint(cx, SEARCH_IS_SOME, expr.span, &msg);
1197 /// Checks for the `CHARS_NEXT_CMP` lint.
1198 fn lint_chars_next(cx: &LateContext, expr: &hir::Expr, chain: &hir::Expr, other: &hir::Expr, eq: bool) -> bool {
1200 let Some(args) = method_chain_args(chain, &["chars", "next"]),
1201 let hir::ExprCall(ref fun, ref arg_char) = other.node,
1202 arg_char.len() == 1,
1203 let hir::ExprPath(ref qpath) = fun.node,
1204 let Some(segment) = single_segment_path(qpath),
1205 &*segment.name.as_str() == "Some"
1207 let self_ty = walk_ptrs_ty(cx.tcx.tables().expr_ty_adjusted(&args[0][0]));
1209 if self_ty.sty != ty::TyStr {
1213 span_lint_and_then(cx,
1216 "you should use the `starts_with` method",
1218 let sugg = format!("{}{}.starts_with({})",
1219 if eq { "" } else { "!" },
1220 snippet(cx, args[0][0].span, "_"),
1221 snippet(cx, arg_char[0].span, "_")
1224 db.span_suggestion(expr.span, "like this", sugg);
1233 /// lint for length-1 `str`s for methods in `PATTERN_METHODS`
1234 fn lint_single_char_pattern(cx: &LateContext, expr: &hir::Expr, arg: &hir::Expr) {
1235 if let Ok(ConstVal::Str(r)) = eval_const_expr_partial(cx.tcx, arg, ExprTypeChecked, None) {
1237 let hint = snippet(cx, expr.span, "..").replace(&format!("\"{}\"", r), &format!("'{}'", r));
1238 span_lint_and_then(cx,
1239 SINGLE_CHAR_PATTERN,
1241 "single-character string constant used as pattern",
1243 db.span_suggestion(expr.span, "try using a char instead:", hint);
1249 /// Given a `Result<T, E>` type, return its error type (`E`).
1250 fn get_error_type<'a>(cx: &LateContext, ty: ty::Ty<'a>) -> Option<ty::Ty<'a>> {
1251 if let ty::TyAdt(_, substs) = ty.sty {
1252 if match_type(cx, ty, &paths::RESULT) {
1253 substs.types().nth(1)
1262 /// This checks whether a given type is known to implement Debug.
1263 fn has_debug_impl<'a, 'b>(ty: ty::Ty<'a>, cx: &LateContext<'b, 'a>) -> bool {
1264 match cx.tcx.lang_items.debug_trait() {
1265 Some(debug) => implements_trait(cx, ty, debug, Vec::new()),
1272 StartsWith(&'static str),
1275 #[cfg_attr(rustfmt, rustfmt_skip)]
1276 const CONVENTIONS: [(Convention, &'static [SelfKind]); 6] = [
1277 (Convention::Eq("new"), &[SelfKind::No]),
1278 (Convention::StartsWith("as_"), &[SelfKind::Ref, SelfKind::RefMut]),
1279 (Convention::StartsWith("from_"), &[SelfKind::No]),
1280 (Convention::StartsWith("into_"), &[SelfKind::Value]),
1281 (Convention::StartsWith("is_"), &[SelfKind::Ref, SelfKind::No]),
1282 (Convention::StartsWith("to_"), &[SelfKind::Ref]),
1285 #[cfg_attr(rustfmt, rustfmt_skip)]
1286 const TRAIT_METHODS: [(&'static str, usize, SelfKind, OutType, &'static str); 30] = [
1287 ("add", 2, SelfKind::Value, OutType::Any, "std::ops::Add"),
1288 ("as_mut", 1, SelfKind::RefMut, OutType::Ref, "std::convert::AsMut"),
1289 ("as_ref", 1, SelfKind::Ref, OutType::Ref, "std::convert::AsRef"),
1290 ("bitand", 2, SelfKind::Value, OutType::Any, "std::ops::BitAnd"),
1291 ("bitor", 2, SelfKind::Value, OutType::Any, "std::ops::BitOr"),
1292 ("bitxor", 2, SelfKind::Value, OutType::Any, "std::ops::BitXor"),
1293 ("borrow", 1, SelfKind::Ref, OutType::Ref, "std::borrow::Borrow"),
1294 ("borrow_mut", 1, SelfKind::RefMut, OutType::Ref, "std::borrow::BorrowMut"),
1295 ("clone", 1, SelfKind::Ref, OutType::Any, "std::clone::Clone"),
1296 ("cmp", 2, SelfKind::Ref, OutType::Any, "std::cmp::Ord"),
1297 ("default", 0, SelfKind::No, OutType::Any, "std::default::Default"),
1298 ("deref", 1, SelfKind::Ref, OutType::Ref, "std::ops::Deref"),
1299 ("deref_mut", 1, SelfKind::RefMut, OutType::Ref, "std::ops::DerefMut"),
1300 ("div", 2, SelfKind::Value, OutType::Any, "std::ops::Div"),
1301 ("drop", 1, SelfKind::RefMut, OutType::Unit, "std::ops::Drop"),
1302 ("eq", 2, SelfKind::Ref, OutType::Bool, "std::cmp::PartialEq"),
1303 ("from_iter", 1, SelfKind::No, OutType::Any, "std::iter::FromIterator"),
1304 ("from_str", 1, SelfKind::No, OutType::Any, "std::str::FromStr"),
1305 ("hash", 2, SelfKind::Ref, OutType::Unit, "std::hash::Hash"),
1306 ("index", 2, SelfKind::Ref, OutType::Ref, "std::ops::Index"),
1307 ("index_mut", 2, SelfKind::RefMut, OutType::Ref, "std::ops::IndexMut"),
1308 ("into_iter", 1, SelfKind::Value, OutType::Any, "std::iter::IntoIterator"),
1309 ("mul", 2, SelfKind::Value, OutType::Any, "std::ops::Mul"),
1310 ("neg", 1, SelfKind::Value, OutType::Any, "std::ops::Neg"),
1311 ("next", 1, SelfKind::RefMut, OutType::Any, "std::iter::Iterator"),
1312 ("not", 1, SelfKind::Value, OutType::Any, "std::ops::Not"),
1313 ("rem", 2, SelfKind::Value, OutType::Any, "std::ops::Rem"),
1314 ("shl", 2, SelfKind::Value, OutType::Any, "std::ops::Shl"),
1315 ("shr", 2, SelfKind::Value, OutType::Any, "std::ops::Shr"),
1316 ("sub", 2, SelfKind::Value, OutType::Any, "std::ops::Sub"),
1319 #[cfg_attr(rustfmt, rustfmt_skip)]
1320 const PATTERN_METHODS: [(&'static str, usize); 17] = [
1328 ("split_terminator", 1),
1329 ("rsplit_terminator", 1),
1334 ("match_indices", 1),
1335 ("rmatch_indices", 1),
1336 ("trim_left_matches", 1),
1337 ("trim_right_matches", 1),
1341 #[derive(Clone, Copy)]
1350 fn matches(self, slf: &hir::Arg, allow_value_for_ref: bool) -> bool {
1351 if !slf.has_self() {
1354 match (self, &slf.node) {
1355 (SelfKind::Value, &hir::SelfKind::Value(_)) |
1356 (SelfKind::Ref, &hir::SelfKind::Region(_, hir::Mutability::MutImmutable)) |
1357 (SelfKind::RefMut, &hir::SelfKind::Region(_, hir::Mutability::MutMutable)) => true,
1358 (SelfKind::Ref, &hir::SelfKind::Value(_)) |
1359 (SelfKind::RefMut, &hir::SelfKind::Value(_)) => allow_value_for_ref,
1360 (_, &hir::SelfKind::Explicit(ref ty, _)) => self.matches_explicit_type(ty, allow_value_for_ref),
1366 fn matches_explicit_type(self, ty: &hir::Ty, allow_value_for_ref: bool) -> bool {
1367 match (self, &ty.node) {
1368 (SelfKind::Value, &hir::TyPath(..)) |
1369 (SelfKind::Ref, &hir::TyRptr(_, hir::MutTy { mutbl: hir::Mutability::MutImmutable, .. })) |
1370 (SelfKind::RefMut, &hir::TyRptr(_, hir::MutTy { mutbl: hir::Mutability::MutMutable, .. })) => true,
1371 (SelfKind::Ref, &hir::TyPath(..)) |
1372 (SelfKind::RefMut, &hir::TyPath(..)) => allow_value_for_ref,
1377 fn description(&self) -> &'static str {
1379 SelfKind::Value => "self by value",
1380 SelfKind::Ref => "self by reference",
1381 SelfKind::RefMut => "self by mutable reference",
1382 SelfKind::No => "no self",
1388 fn check(&self, other: &str) -> bool {
1390 Convention::Eq(this) => this == other,
1391 Convention::StartsWith(this) => other.starts_with(this) && this != other,
1396 impl fmt::Display for Convention {
1397 fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
1399 Convention::Eq(this) => this.fmt(f),
1400 Convention::StartsWith(this) => this.fmt(f).and_then(|_| '*'.fmt(f)),
1405 #[derive(Clone, Copy)]
1414 fn matches(&self, ty: &hir::FunctionRetTy) -> bool {
1416 (&OutType::Unit, &hir::DefaultReturn(_)) => true,
1417 (&OutType::Unit, &hir::Return(ref ty)) if ty.node == hir::TyTup(vec![].into()) => true,
1418 (&OutType::Bool, &hir::Return(ref ty)) if is_bool(ty) => true,
1419 (&OutType::Any, &hir::Return(ref ty)) if ty.node != hir::TyTup(vec![].into()) => true,
1420 (&OutType::Ref, &hir::Return(ref ty)) => matches!(ty.node, hir::TyRptr(_, _)),
1426 fn is_bool(ty: &hir::Ty) -> bool {
1427 if let hir::TyPath(ref p) = ty.node {
1428 match_path(p, &["bool"])