330 lines
13 KiB
Rust
330 lines
13 KiB
Rust
//! Checks for usage of `&Vec[_]` and `&String`.
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use crate::utils::ptr::get_spans;
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use crate::utils::{
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is_allowed, is_type_diagnostic_item, match_qpath, match_type, paths, snippet_opt, span_lint, span_lint_and_sugg,
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span_lint_and_then, walk_ptrs_hir_ty,
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};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir::{
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BinOpKind, BodyId, Expr, ExprKind, FnDecl, FnRetTy, GenericArg, HirId, ImplItem, ImplItemKind, Item, ItemKind,
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Lifetime, MutTy, Mutability, Node, PathSegment, QPath, TraitFn, TraitItem, TraitItemKind, Ty, TyKind,
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};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::Span;
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use rustc_span::MultiSpan;
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use std::borrow::Cow;
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declare_clippy_lint! {
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/// **What it does:** This lint checks for function arguments of type `&String`
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/// or `&Vec` unless the references are mutable. It will also suggest you
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/// replace `.clone()` calls with the appropriate `.to_owned()`/`to_string()`
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/// calls.
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///
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/// **Why is this bad?** Requiring the argument to be of the specific size
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/// makes the function less useful for no benefit; slices in the form of `&[T]`
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/// or `&str` usually suffice and can be obtained from other types, too.
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///
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/// **Known problems:** The lint does not follow data. So if you have an
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/// argument `x` and write `let y = x; y.clone()` the lint will not suggest
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/// changing that `.clone()` to `.to_owned()`.
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///
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/// Other functions called from this function taking a `&String` or `&Vec`
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/// argument may also fail to compile if you change the argument. Applying
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/// this lint on them will fix the problem, but they may be in other crates.
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///
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/// One notable example of a function that may cause issues, and which cannot
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/// easily be changed due to being in the standard library is `Vec::contains`.
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/// when called on a `Vec<Vec<T>>`. If a `&Vec` is passed to that method then
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/// it will compile, but if a `&[T]` is passed then it will not compile.
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///
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/// ```ignore
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/// fn cannot_take_a_slice(v: &Vec<u8>) -> bool {
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/// let vec_of_vecs: Vec<Vec<u8>> = some_other_fn();
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///
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/// vec_of_vecs.contains(v)
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/// }
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/// ```
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///
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/// Also there may be `fn(&Vec)`-typed references pointing to your function.
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/// If you have them, you will get a compiler error after applying this lint's
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/// suggestions. You then have the choice to undo your changes or change the
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/// type of the reference.
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///
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/// Note that if the function is part of your public interface, there may be
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/// other crates referencing it, of which you may not be aware. Carefully
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/// deprecate the function before applying the lint suggestions in this case.
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///
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/// **Example:**
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/// ```ignore
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/// // Bad
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/// fn foo(&Vec<u32>) { .. }
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///
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/// // Good
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/// fn foo(&[u32]) { .. }
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/// ```
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pub PTR_ARG,
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style,
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"fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively"
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}
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declare_clippy_lint! {
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/// **What it does:** This lint checks for equality comparisons with `ptr::null`
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///
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/// **Why is this bad?** It's easier and more readable to use the inherent
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/// `.is_null()`
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/// method instead
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```ignore
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/// // Bad
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/// if x == ptr::null {
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/// ..
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/// }
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///
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/// // Good
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/// if x.is_null() {
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/// ..
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/// }
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/// ```
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pub CMP_NULL,
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style,
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"comparing a pointer to a null pointer, suggesting to use `.is_null()` instead."
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}
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declare_clippy_lint! {
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/// **What it does:** This lint checks for functions that take immutable
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/// references and return mutable ones.
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///
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/// **Why is this bad?** This is trivially unsound, as one can create two
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/// mutable references from the same (immutable!) source.
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/// This [error](https://github.com/rust-lang/rust/issues/39465)
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/// actually lead to an interim Rust release 1.15.1.
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///
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/// **Known problems:** To be on the conservative side, if there's at least one
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/// mutable reference with the output lifetime, this lint will not trigger.
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/// In practice, this case is unlikely anyway.
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///
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/// **Example:**
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/// ```ignore
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/// fn foo(&Foo) -> &mut Bar { .. }
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/// ```
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pub MUT_FROM_REF,
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correctness,
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"fns that create mutable refs from immutable ref args"
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}
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declare_lint_pass!(Ptr => [PTR_ARG, CMP_NULL, MUT_FROM_REF]);
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impl<'tcx> LateLintPass<'tcx> for Ptr {
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fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
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if let ItemKind::Fn(ref sig, _, body_id) = item.kind {
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check_fn(cx, &sig.decl, item.hir_id, Some(body_id));
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}
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}
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fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
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if let ImplItemKind::Fn(ref sig, body_id) = item.kind {
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let parent_item = cx.tcx.hir().get_parent_item(item.hir_id);
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if let Some(Node::Item(it)) = cx.tcx.hir().find(parent_item) {
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if let ItemKind::Impl { of_trait: Some(_), .. } = it.kind {
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return; // ignore trait impls
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}
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}
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check_fn(cx, &sig.decl, item.hir_id, Some(body_id));
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}
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}
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fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
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if let TraitItemKind::Fn(ref sig, ref trait_method) = item.kind {
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let body_id = if let TraitFn::Provided(b) = *trait_method {
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Some(b)
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} else {
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None
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};
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check_fn(cx, &sig.decl, item.hir_id, body_id);
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}
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}
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if let ExprKind::Binary(ref op, ref l, ref r) = expr.kind {
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if (op.node == BinOpKind::Eq || op.node == BinOpKind::Ne) && (is_null_path(l) || is_null_path(r)) {
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span_lint(
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cx,
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CMP_NULL,
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expr.span,
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"comparing with null is better expressed by the `.is_null()` method",
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);
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}
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}
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}
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}
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#[allow(clippy::too_many_lines)]
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fn check_fn(cx: &LateContext<'_>, decl: &FnDecl<'_>, fn_id: HirId, opt_body_id: Option<BodyId>) {
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let fn_def_id = cx.tcx.hir().local_def_id(fn_id);
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let sig = cx.tcx.fn_sig(fn_def_id);
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let fn_ty = sig.skip_binder();
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let body = opt_body_id.map(|id| cx.tcx.hir().body(id));
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for (idx, (arg, ty)) in decl.inputs.iter().zip(fn_ty.inputs()).enumerate() {
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// Honor the allow attribute on parameters. See issue 5644.
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if let Some(body) = &body {
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if is_allowed(cx, PTR_ARG, body.params[idx].hir_id) {
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continue;
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}
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}
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if let ty::Ref(_, ty, Mutability::Not) = ty.kind {
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if is_type_diagnostic_item(cx, ty, sym!(vec_type)) {
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let mut ty_snippet = None;
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if_chain! {
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if let TyKind::Path(QPath::Resolved(_, ref path)) = walk_ptrs_hir_ty(arg).kind;
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if let Some(&PathSegment{args: Some(ref parameters), ..}) = path.segments.last();
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then {
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let types: Vec<_> = parameters.args.iter().filter_map(|arg| match arg {
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GenericArg::Type(ty) => Some(ty),
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_ => None,
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}).collect();
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if types.len() == 1 {
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ty_snippet = snippet_opt(cx, types[0].span);
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}
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}
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};
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if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_owned()")]) {
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span_lint_and_then(
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cx,
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PTR_ARG,
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arg.span,
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"writing `&Vec<_>` instead of `&[_]` involves one more reference and cannot be used \
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with non-Vec-based slices.",
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|diag| {
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if let Some(ref snippet) = ty_snippet {
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diag.span_suggestion(
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arg.span,
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"change this to",
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format!("&[{}]", snippet),
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Applicability::Unspecified,
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);
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}
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for (clonespan, suggestion) in spans {
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diag.span_suggestion(
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clonespan,
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&snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
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Cow::Owned(format!("change `{}` to", x))
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}),
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suggestion.into(),
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Applicability::Unspecified,
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);
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}
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},
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);
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}
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} else if is_type_diagnostic_item(cx, ty, sym!(string_type)) {
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if let Some(spans) = get_spans(cx, opt_body_id, idx, &[("clone", ".to_string()"), ("as_str", "")]) {
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span_lint_and_then(
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cx,
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PTR_ARG,
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arg.span,
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"writing `&String` instead of `&str` involves a new object where a slice will do.",
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|diag| {
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diag.span_suggestion(arg.span, "change this to", "&str".into(), Applicability::Unspecified);
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for (clonespan, suggestion) in spans {
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diag.span_suggestion_short(
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clonespan,
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&snippet_opt(cx, clonespan).map_or("change the call to".into(), |x| {
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Cow::Owned(format!("change `{}` to", x))
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}),
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suggestion.into(),
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Applicability::Unspecified,
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);
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}
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},
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);
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}
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} else if match_type(cx, ty, &paths::COW) {
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if_chain! {
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if let TyKind::Rptr(_, MutTy { ref ty, ..} ) = arg.kind;
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if let TyKind::Path(ref path) = ty.kind;
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if let QPath::Resolved(None, ref pp) = *path;
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if let [ref bx] = *pp.segments;
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if let Some(ref params) = bx.args;
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if !params.parenthesized;
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if let Some(inner) = params.args.iter().find_map(|arg| match arg {
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GenericArg::Type(ty) => Some(ty),
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_ => None,
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});
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then {
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let replacement = snippet_opt(cx, inner.span);
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if let Some(r) = replacement {
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span_lint_and_sugg(
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cx,
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PTR_ARG,
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arg.span,
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"using a reference to `Cow` is not recommended.",
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"change this to",
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"&".to_owned() + &r,
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Applicability::Unspecified,
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);
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}
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}
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}
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}
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}
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}
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if let FnRetTy::Return(ref ty) = decl.output {
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if let Some((out, Mutability::Mut, _)) = get_rptr_lm(ty) {
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let mut immutables = vec![];
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for (_, ref mutbl, ref argspan) in decl
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.inputs
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.iter()
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.filter_map(|ty| get_rptr_lm(ty))
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.filter(|&(lt, _, _)| lt.name == out.name)
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{
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if *mutbl == Mutability::Mut {
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return;
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}
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immutables.push(*argspan);
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}
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if immutables.is_empty() {
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return;
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}
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span_lint_and_then(
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cx,
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MUT_FROM_REF,
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ty.span,
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"mutable borrow from immutable input(s)",
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|diag| {
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let ms = MultiSpan::from_spans(immutables);
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diag.span_note(ms, "immutable borrow here");
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},
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);
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}
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}
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}
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fn get_rptr_lm<'tcx>(ty: &'tcx Ty<'tcx>) -> Option<(&'tcx Lifetime, Mutability, Span)> {
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if let TyKind::Rptr(ref lt, ref m) = ty.kind {
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Some((lt, m.mutbl, ty.span))
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} else {
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None
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}
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}
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fn is_null_path(expr: &Expr<'_>) -> bool {
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if let ExprKind::Call(ref pathexp, ref args) = expr.kind {
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if args.is_empty() {
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if let ExprKind::Path(ref path) = pathexp.kind {
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return match_qpath(path, &paths::PTR_NULL) || match_qpath(path, &paths::PTR_NULL_MUT);
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}
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}
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}
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false
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}
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