//! Checks for usage of `&Vec[_]` and `&String`. use std::borrow::Cow; use rustc::hir::*; use rustc::hir::map::NodeItem; use rustc::hir::QPath; use rustc::lint::*; use rustc::ty; use syntax::ast::NodeId; use syntax::codemap::Span; use syntax_pos::MultiSpan; use utils::{match_qpath, match_type, paths, snippet_opt, span_lint, span_lint_and_then, walk_ptrs_hir_ty}; use utils::ptr::get_spans; /// **What it does:** This lint checks for function arguments of type `&String` /// or `&Vec` unless the references are mutable. It will also suggest you /// replace `.clone()` calls with the appropriate `.to_owned()`/`to_string()` /// calls. /// /// **Why is this bad?** Requiring the argument to be of the specific size /// makes the function less useful for no benefit; slices in the form of `&[T]` /// or `&str` usually suffice and can be obtained from other types, too. /// /// **Known problems:** The lint does not follow data. So if you have an /// argument `x` and write `let y = x; y.clone()` the lint will not suggest /// changing that `.clone()` to `.to_owned()`. /// /// Other functions called from this function taking a `&String` or `&Vec` /// argument may also fail to compile if you change the argument. Applying /// this lint on them will fix the problem, but they may be in other crates. /// /// Also there may be `fn(&Vec)`-typed references pointing to your function. /// If you have them, you will get a compiler error after applying this lint's /// suggestions. You then have the choice to undo your changes or change the /// type of the reference. /// /// Note that if the function is part of your public interface, there may be /// other crates referencing it you may not be aware. Carefully deprecate the /// function before applying the lint suggestions in this case. /// /// **Example:** /// ```rust /// fn foo(&Vec) { .. } /// ``` declare_lint! { pub PTR_ARG, Warn, "fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` \ instead, respectively" } /// **What it does:** This lint checks for equality comparisons with `ptr::null` /// /// **Why is this bad?** It's easier and more readable to use the inherent /// `.is_null()` /// method instead /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// if x == ptr::null { .. } /// ``` declare_lint! { pub CMP_NULL, Warn, "comparing a pointer to a null pointer, suggesting to use `.is_null()` instead." } /// **What it does:** This lint checks for functions that take immutable /// references and return /// mutable ones. /// /// **Why is this bad?** This is trivially unsound, as one can create two /// mutable references /// from the same (immutable!) source. This /// [error](https://github.com/rust-lang/rust/issues/39465) /// actually lead to an interim Rust release 1.15.1. /// /// **Known problems:** To be on the conservative side, if there's at least one /// mutable reference /// with the output lifetime, this lint will not trigger. In practice, this /// case is unlikely anyway. /// /// **Example:** /// ```rust /// fn foo(&Foo) -> &mut Bar { .. } /// ``` declare_lint! { pub MUT_FROM_REF, Warn, "fns that create mutable refs from immutable ref args" } #[derive(Copy, Clone)] pub struct PointerPass; impl LintPass for PointerPass { fn get_lints(&self) -> LintArray { lint_array!(PTR_ARG, CMP_NULL, MUT_FROM_REF) } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for PointerPass { fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) { if let ItemFn(ref decl, _, _, _, _, body_id) = item.node { check_fn(cx, decl, item.id, Some(body_id)); } } fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) { if let ImplItemKind::Method(ref sig, body_id) = item.node { if let Some(NodeItem(it)) = cx.tcx.hir.find(cx.tcx.hir.get_parent(item.id)) { if let ItemImpl(_, _, _, _, Some(_), _, _) = it.node { return; // ignore trait impls } } check_fn(cx, &sig.decl, item.id, Some(body_id)); } } fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) { if let TraitItemKind::Method(ref sig, ref trait_method) = item.node { let body_id = if let TraitMethod::Provided(b) = *trait_method { Some(b) } else { None }; check_fn(cx, &sig.decl, item.id, body_id); } } fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { if let ExprBinary(ref op, ref l, ref r) = expr.node { if (op.node == BiEq || op.node == BiNe) && (is_null_path(l) || is_null_path(r)) { span_lint( cx, CMP_NULL, expr.span, "Comparing with null is better expressed by the .is_null() method", ); } } } } fn check_fn(cx: &LateContext, decl: &FnDecl, fn_id: NodeId, opt_body_id: Option) { let fn_def_id = cx.tcx.hir.local_def_id(fn_id); let sig = cx.tcx.fn_sig(fn_def_id); let fn_ty = sig.skip_binder(); for (idx, (arg, ty)) in decl.inputs.iter().zip(fn_ty.inputs()).enumerate() { if let ty::TyRef( _, ty::TypeAndMut { ty, mutbl: MutImmutable, }, ) = ty.sty { if match_type(cx, ty, &paths::VEC) { let mut ty_snippet = None; if_chain! { if let TyPath(QPath::Resolved(_, ref path)) = walk_ptrs_hir_ty(arg).node; if let Some(&PathSegment{parameters: Some(ref parameters), ..}) = path.segments.last(); if parameters.types.len() == 1; then { ty_snippet = snippet_opt(cx, parameters.types[0].span); } }; if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) { span_lint_and_then( cx, PTR_ARG, arg.span, "writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \ with non-Vec-based slices.", |db| { if let Some(ref snippet) = ty_snippet { db.span_suggestion(arg.span, "change this to", format!("&[{}]", snippet)); } for (clonespan, suggestion) in spans { db.span_suggestion( clonespan, &snippet_opt(cx, clonespan).map_or( "change the call to".into(), |x| Cow::Owned(format!("change `{}` to", x)), ), suggestion.into(), ); } }, ); } } else if match_type(cx, ty, &paths::STRING) { if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) { span_lint_and_then( cx, PTR_ARG, arg.span, "writing `&String` instead of `&str` involves a new object where a slice will do.", |db| { db.span_suggestion(arg.span, "change this to", "&str".into()); for (clonespan, suggestion) in spans { db.span_suggestion_short( clonespan, &snippet_opt(cx, clonespan).map_or( "change the call to".into(), |x| Cow::Owned(format!("change `{}` to", x)), ), suggestion.into(), ); } }, ); } } else if match_type(cx, ty, &paths::COW) { if_chain! { if let TyRptr(_, MutTy { ref ty, ..} ) = arg.node; if let TyPath(ref path) = ty.node; if let QPath::Resolved(None, ref pp) = *path; if let [ref bx] = *pp.segments; if let Some(ref params) = bx.parameters; if !params.parenthesized; if let [ref inner] = *params.types; then { let replacement = snippet_opt(cx, inner.span); if let Some(r) = replacement { span_lint_and_then( cx, PTR_ARG, arg.span, "using a reference to `Cow` is not recommended.", |db| { db.span_suggestion(arg.span, "change this to", "&".to_owned() + &r); }, ); } } } } } } if let FunctionRetTy::Return(ref ty) = decl.output { if let Some((out, MutMutable, _)) = get_rptr_lm(ty) { let mut immutables = vec![]; for (_, ref mutbl, ref argspan) in decl.inputs .iter() .filter_map(|ty| get_rptr_lm(ty)) .filter(|&(lt, _, _)| lt.name == out.name) { if *mutbl == MutMutable { return; } immutables.push(*argspan); } if immutables.is_empty() { return; } span_lint_and_then(cx, MUT_FROM_REF, ty.span, "mutable borrow from immutable input(s)", |db| { let ms = MultiSpan::from_spans(immutables); db.span_note(ms, "immutable borrow here"); }); } } } fn get_rptr_lm(ty: &Ty) -> Option<(&Lifetime, Mutability, Span)> { if let Ty_::TyRptr(ref lt, ref m) = ty.node { Some((lt, m.mutbl, ty.span)) } else { None } } fn is_null_path(expr: &Expr) -> bool { if let ExprCall(ref pathexp, ref args) = expr.node { if args.is_empty() { if let ExprPath(ref path) = pathexp.node { return match_qpath(path, &paths::PTR_NULL) || match_qpath(path, &paths::PTR_NULL_MUT); } } } false }