mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-15 15:52:46 +00:00
416 lines
16 KiB
Rust
416 lines
16 KiB
Rust
use matches::matches;
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use rustc::hir::*;
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use rustc::hir::map::*;
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use rustc::hir::intravisit::FnKind;
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use rustc::lint::*;
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use rustc::{declare_lint, lint_array};
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use if_chain::if_chain;
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use rustc::ty::{self, RegionKind, TypeFoldable};
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use rustc::traits;
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use rustc::middle::expr_use_visitor as euv;
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use rustc::middle::mem_categorization as mc;
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use rustc_target::spec::abi::Abi;
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use syntax::ast::NodeId;
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use syntax_pos::Span;
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use syntax::errors::DiagnosticBuilder;
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use crate::utils::{get_trait_def_id, implements_trait, in_macro, is_copy, is_self, match_type, multispan_sugg, paths,
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snippet, snippet_opt, span_lint_and_then};
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use crate::utils::ptr::get_spans;
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use std::collections::{HashMap, HashSet};
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use std::borrow::Cow;
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/// **What it does:** Checks for functions taking arguments by value, but not
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/// consuming them in its
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/// body.
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///
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/// **Why is this bad?** Taking arguments by reference is more flexible and can
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/// sometimes avoid
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/// unnecessary allocations.
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///
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/// **Known problems:**
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/// * This lint suggests taking an argument by reference,
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/// however sometimes it is better to let users decide the argument type
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/// (by using `Borrow` trait, for example), depending on how the function is used.
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///
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/// **Example:**
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/// ```rust
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/// fn foo(v: Vec<i32>) {
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/// assert_eq!(v.len(), 42);
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/// }
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/// // should be
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/// fn foo(v: &[i32]) {
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/// assert_eq!(v.len(), 42);
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/// }
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/// ```
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declare_clippy_lint! {
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pub NEEDLESS_PASS_BY_VALUE,
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style,
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"functions taking arguments by value, but not consuming them in its body"
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}
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pub struct NeedlessPassByValue;
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impl LintPass for NeedlessPassByValue {
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fn get_lints(&self) -> LintArray {
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lint_array![NEEDLESS_PASS_BY_VALUE]
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}
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}
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macro_rules! need {
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($e: expr) => { if let Some(x) = $e { x } else { return; } };
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
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fn check_fn(
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&mut self,
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cx: &LateContext<'a, 'tcx>,
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kind: FnKind<'tcx>,
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decl: &'tcx FnDecl,
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body: &'tcx Body,
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span: Span,
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node_id: NodeId,
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) {
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if in_macro(span) {
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return;
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}
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match kind {
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FnKind::ItemFn(.., header, _, attrs) => {
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if header.abi != Abi::Rust {
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return;
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}
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for a in attrs {
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if a.meta_item_list().is_some() && a.name() == "proc_macro_derive" {
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return;
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}
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}
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},
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FnKind::Method(..) => (),
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_ => return,
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}
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// Exclude non-inherent impls
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if let Some(NodeItem(item)) = cx.tcx.hir.find(cx.tcx.hir.get_parent_node(node_id)) {
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if matches!(item.node, ItemKind::Impl(_, _, _, _, Some(_), _, _) |
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ItemKind::Trait(..))
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{
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return;
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}
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}
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// Allow `Borrow` or functions to be taken by value
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let borrow_trait = need!(get_trait_def_id(cx, &paths::BORROW_TRAIT));
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let whitelisted_traits = [
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need!(cx.tcx.lang_items().fn_trait()),
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need!(cx.tcx.lang_items().fn_once_trait()),
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need!(cx.tcx.lang_items().fn_mut_trait()),
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need!(get_trait_def_id(cx, &paths::RANGE_ARGUMENT_TRAIT))
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];
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let sized_trait = need!(cx.tcx.lang_items().sized_trait());
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let fn_def_id = cx.tcx.hir.local_def_id(node_id);
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let preds = traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds.to_vec())
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.filter(|p| !p.is_global())
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.filter_map(|pred| {
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if let ty::Predicate::Trait(poly_trait_ref) = pred {
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if poly_trait_ref.def_id() == sized_trait || poly_trait_ref.skip_binder().has_escaping_regions() {
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return None;
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}
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Some(poly_trait_ref)
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} else {
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None
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}
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})
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.collect::<Vec<_>>();
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// Collect moved variables and spans which will need dereferencings from the
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// function body.
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let MovedVariablesCtxt {
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moved_vars,
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spans_need_deref,
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..
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} = {
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let mut ctx = MovedVariablesCtxt::new(cx);
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let region_scope_tree = &cx.tcx.region_scope_tree(fn_def_id);
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euv::ExprUseVisitor::new(&mut ctx, cx.tcx, cx.param_env, region_scope_tree, cx.tables, None)
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.consume_body(body);
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ctx
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};
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let fn_sig = cx.tcx.fn_sig(fn_def_id);
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let fn_sig = cx.tcx.erase_late_bound_regions(&fn_sig);
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for (idx, ((input, &ty), arg)) in decl.inputs
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.iter()
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.zip(fn_sig.inputs())
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.zip(&body.arguments)
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.enumerate()
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{
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// All spans generated from a proc-macro invocation are the same...
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if span == input.span {
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return;
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}
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// Ignore `self`s.
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if idx == 0 {
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if let PatKind::Binding(_, _, ident, ..) = arg.pat.node {
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if ident.as_str() == "self" {
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continue;
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}
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}
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}
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// * Exclude a type that is specifically bounded by `Borrow`.
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// * Exclude a type whose reference also fulfills its bound.
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// (e.g. `std::convert::AsRef`, `serde::Serialize`)
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let (implements_borrow_trait, all_borrowable_trait) = {
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let preds = preds
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.iter()
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.filter(|t| t.skip_binder().self_ty() == ty)
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.collect::<Vec<_>>();
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(
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preds.iter().any(|t| t.def_id() == borrow_trait),
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!preds.is_empty() && preds.iter().all(|t| {
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implements_trait(
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cx,
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cx.tcx.mk_imm_ref(&RegionKind::ReErased, ty),
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t.def_id(),
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&t.skip_binder()
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.input_types()
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.skip(1)
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.map(|ty| ty.into())
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.collect::<Vec<_>>(),
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)
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}),
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)
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};
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if_chain! {
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if !is_self(arg);
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if !ty.is_mutable_pointer();
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if !is_copy(cx, ty);
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if !whitelisted_traits.iter().any(|&t| implements_trait(cx, ty, t, &[]));
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if !implements_borrow_trait;
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if !all_borrowable_trait;
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if let PatKind::Binding(mode, canonical_id, ..) = arg.pat.node;
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if !moved_vars.contains(&canonical_id);
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then {
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if mode == BindingAnnotation::Mutable || mode == BindingAnnotation::RefMut {
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continue;
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}
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// Dereference suggestion
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let sugg = |db: &mut DiagnosticBuilder<'_>| {
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if let ty::TypeVariants::TyAdt(def, ..) = ty.sty {
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if let Some(span) = cx.tcx.hir.span_if_local(def.did) {
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if cx.param_env.can_type_implement_copy(cx.tcx, ty).is_ok() {
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db.span_help(span, "consider marking this type as Copy");
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}
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}
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}
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let deref_span = spans_need_deref.get(&canonical_id);
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if_chain! {
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if match_type(cx, ty, &paths::VEC);
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if let Some(clone_spans) =
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get_spans(cx, Some(body.id()), idx, &[("clone", ".to_owned()")]);
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if let TyKind::Path(QPath::Resolved(_, ref path)) = input.node;
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if let Some(elem_ty) = path.segments.iter()
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.find(|seg| seg.ident.name == "Vec")
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.and_then(|ps| ps.args.as_ref())
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.map(|params| params.args.iter().find_map(|arg| match arg {
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GenericArg::Type(ty) => Some(ty),
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GenericArg::Lifetime(_) => None,
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}).unwrap());
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then {
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let slice_ty = format!("&[{}]", snippet(cx, elem_ty.span, "_"));
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db.span_suggestion(input.span,
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"consider changing the type to",
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slice_ty);
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for (span, suggestion) in clone_spans {
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db.span_suggestion(
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span,
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&snippet_opt(cx, span)
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.map_or(
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"change the call to".into(),
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|x| Cow::from(format!("change `{}` to", x)),
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),
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suggestion.into()
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);
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}
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// cannot be destructured, no need for `*` suggestion
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assert!(deref_span.is_none());
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return;
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}
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}
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if match_type(cx, ty, &paths::STRING) {
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if let Some(clone_spans) =
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get_spans(cx, Some(body.id()), idx, &[("clone", ".to_string()"), ("as_str", "")]) {
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db.span_suggestion(input.span, "consider changing the type to", "&str".to_string());
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for (span, suggestion) in clone_spans {
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db.span_suggestion(
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span,
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&snippet_opt(cx, span)
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.map_or(
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"change the call to".into(),
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|x| Cow::from(format!("change `{}` to", x))
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),
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suggestion.into(),
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);
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}
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assert!(deref_span.is_none());
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return;
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}
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}
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let mut spans = vec![(input.span, format!("&{}", snippet(cx, input.span, "_")))];
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// Suggests adding `*` to dereference the added reference.
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if let Some(deref_span) = deref_span {
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spans.extend(
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deref_span
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.iter()
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.cloned()
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.map(|span| (span, format!("*{}", snippet(cx, span, "<expr>")))),
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);
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spans.sort_by_key(|&(span, _)| span);
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}
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multispan_sugg(db, "consider taking a reference instead".to_string(), spans);
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};
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span_lint_and_then(
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cx,
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NEEDLESS_PASS_BY_VALUE,
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input.span,
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"this argument is passed by value, but not consumed in the function body",
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sugg,
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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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struct MovedVariablesCtxt<'a, 'tcx: 'a> {
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cx: &'a LateContext<'a, 'tcx>,
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moved_vars: HashSet<NodeId>,
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/// Spans which need to be prefixed with `*` for dereferencing the
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/// suggested additional reference.
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spans_need_deref: HashMap<NodeId, HashSet<Span>>,
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}
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impl<'a, 'tcx> MovedVariablesCtxt<'a, 'tcx> {
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fn new(cx: &'a LateContext<'a, 'tcx>) -> Self {
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Self {
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cx,
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moved_vars: HashSet::new(),
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spans_need_deref: HashMap::new(),
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}
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}
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fn move_common(&mut self, _consume_id: NodeId, _span: Span, cmt: &mc::cmt_<'tcx>) {
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let cmt = unwrap_downcast_or_interior(cmt);
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if let mc::Categorization::Local(vid) = cmt.cat {
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self.moved_vars.insert(vid);
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}
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}
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fn non_moving_pat(&mut self, matched_pat: &Pat, cmt: &mc::cmt_<'tcx>) {
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let cmt = unwrap_downcast_or_interior(cmt);
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if let mc::Categorization::Local(vid) = cmt.cat {
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let mut id = matched_pat.id;
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loop {
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let parent = self.cx.tcx.hir.get_parent_node(id);
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if id == parent {
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// no parent
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return;
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}
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id = parent;
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if let Some(node) = self.cx.tcx.hir.find(id) {
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match node {
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map::Node::NodeExpr(e) => {
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// `match` and `if let`
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if let ExprKind::Match(ref c, ..) = e.node {
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self.spans_need_deref
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.entry(vid)
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.or_insert_with(HashSet::new)
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.insert(c.span);
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}
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},
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map::Node::NodeStmt(s) => {
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// `let <pat> = x;`
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if_chain! {
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if let StmtKind::Decl(ref decl, _) = s.node;
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if let DeclKind::Local(ref local) = decl.node;
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then {
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self.spans_need_deref
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.entry(vid)
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.or_insert_with(HashSet::new)
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.insert(local.init
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.as_ref()
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.map(|e| e.span)
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.expect("`let` stmt without init aren't caught by match_pat"));
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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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}
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}
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}
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impl<'a, 'tcx> euv::Delegate<'tcx> for MovedVariablesCtxt<'a, 'tcx> {
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fn consume(&mut self, consume_id: NodeId, consume_span: Span, cmt: &mc::cmt_<'tcx>, mode: euv::ConsumeMode) {
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if let euv::ConsumeMode::Move(_) = mode {
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self.move_common(consume_id, consume_span, cmt);
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}
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}
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fn matched_pat(&mut self, matched_pat: &Pat, cmt: &mc::cmt_<'tcx>, mode: euv::MatchMode) {
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if let euv::MatchMode::MovingMatch = mode {
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self.move_common(matched_pat.id, matched_pat.span, cmt);
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} else {
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self.non_moving_pat(matched_pat, cmt);
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}
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}
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fn consume_pat(&mut self, consume_pat: &Pat, cmt: &mc::cmt_<'tcx>, mode: euv::ConsumeMode) {
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if let euv::ConsumeMode::Move(_) = mode {
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self.move_common(consume_pat.id, consume_pat.span, cmt);
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}
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}
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fn borrow(&mut self, _: NodeId, _: Span, _: &mc::cmt_<'tcx>, _: ty::Region<'_>, _: ty::BorrowKind, _: euv::LoanCause) {}
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fn mutate(&mut self, _: NodeId, _: Span, _: &mc::cmt_<'tcx>, _: euv::MutateMode) {}
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fn decl_without_init(&mut self, _: NodeId, _: Span) {}
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}
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fn unwrap_downcast_or_interior<'a, 'tcx>(mut cmt: &'a mc::cmt_<'tcx>) -> mc::cmt_<'tcx> {
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loop {
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match cmt.cat {
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mc::Categorization::Downcast(ref c, _) | mc::Categorization::Interior(ref c, _) => {
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cmt = c;
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},
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_ => return (*cmt).clone(),
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}
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};
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}
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