340 lines
13 KiB
Rust
340 lines
13 KiB
Rust
use clippy_utils::diagnostics::{multispan_sugg, span_lint_and_then};
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use clippy_utils::ptr::get_spans;
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use clippy_utils::source::{snippet, snippet_opt};
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use clippy_utils::ty::{implements_trait, is_copy, is_type_diagnostic_item};
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use clippy_utils::{get_trait_def_id, is_self, paths};
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use if_chain::if_chain;
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use rustc_ast::ast::Attribute;
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use rustc_data_structures::fx::FxHashSet;
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use rustc_errors::{Applicability, DiagnosticBuilder};
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use rustc_hir::intravisit::FnKind;
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use rustc_hir::{BindingAnnotation, Body, FnDecl, GenericArg, HirId, Impl, ItemKind, Node, PatKind, QPath, TyKind};
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use rustc_hir::{HirIdMap, HirIdSet};
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use rustc_infer::infer::TyCtxtInferExt;
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::mir::FakeReadCause;
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use rustc_middle::ty::{self, TypeFoldable};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::symbol::kw;
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use rustc_span::{sym, Span};
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use rustc_target::spec::abi::Abi;
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use rustc_trait_selection::traits;
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use rustc_trait_selection::traits::misc::can_type_implement_copy;
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use rustc_typeck::expr_use_visitor as euv;
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use std::borrow::Cow;
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declare_clippy_lint! {
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/// ### What it does
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/// 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?
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/// 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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/// ```
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/// should be
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/// ```rust
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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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pub NEEDLESS_PASS_BY_VALUE,
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pedantic,
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"functions taking arguments by value, but not consuming them in its body"
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}
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declare_lint_pass!(NeedlessPassByValue => [NEEDLESS_PASS_BY_VALUE]);
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macro_rules! need {
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($e: expr) => {
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if let Some(x) = $e {
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x
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} else {
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return;
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}
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};
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}
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impl<'tcx> LateLintPass<'tcx> for NeedlessPassByValue {
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#[allow(clippy::too_many_lines)]
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fn check_fn(
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&mut self,
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cx: &LateContext<'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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hir_id: HirId,
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) {
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if span.from_expansion() {
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return;
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}
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match kind {
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FnKind::ItemFn(.., header, _) => {
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let attrs = cx.tcx.hir().attrs(hir_id);
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if header.abi != Abi::Rust || requires_exact_signature(attrs) {
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return;
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}
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},
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FnKind::Method(..) => (),
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FnKind::Closure => return,
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}
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// Exclude non-inherent impls
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if let Some(Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(hir_id)) {
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if matches!(
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item.kind,
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ItemKind::Impl(Impl { of_trait: Some(_), .. }) | 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 allowed_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(hir_id);
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let preds = traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds().iter())
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.filter(|p| !p.is_global(cx.tcx))
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.filter_map(|obligation| {
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// Note that we do not want to deal with qualified predicates here.
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match obligation.predicate.kind().no_bound_vars() {
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Some(ty::PredicateKind::Trait(pred)) if pred.def_id() != sized_trait => Some(pred),
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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::default();
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cx.tcx.infer_ctxt().enter(|infcx| {
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euv::ExprUseVisitor::new(&mut ctx, &infcx, fn_def_id, cx.param_env, cx.typeck_results())
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.consume_body(body);
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});
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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.iter().zip(fn_sig.inputs()).zip(body.params).enumerate() {
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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.kind {
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if ident.name == kw::SelfLower {
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continue;
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}
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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. (e.g., `std::convert::AsRef`,
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// `serde::Serialize`)
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let (implements_borrow_trait, all_borrowable_trait) = {
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let preds = preds.iter().filter(|t| t.self_ty() == ty).collect::<Vec<_>>();
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(
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preds.iter().any(|t| cx.tcx.is_diagnostic_item(sym::Borrow, t.def_id())),
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!preds.is_empty() && {
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let ty_empty_region = cx.tcx.mk_imm_ref(cx.tcx.lifetimes.re_root_empty, ty);
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preds.iter().all(|t| {
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let ty_params = t.trait_ref.substs.iter().skip(1).collect::<Vec<_>>();
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implements_trait(cx, ty_empty_region, t.def_id(), &ty_params)
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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_ptr();
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if !is_copy(cx, ty);
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if !allowed_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.kind;
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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 = |diag: &mut DiagnosticBuilder<'_>| {
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if let ty::Adt(def, ..) = ty.kind() {
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if let Some(span) = cx.tcx.hir().span_if_local(def.did) {
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if can_type_implement_copy(cx.tcx, cx.param_env, ty).is_ok() {
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diag.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 is_type_diagnostic_item(cx, ty, sym::vec_type);
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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(_, path)) = input.kind;
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if let Some(elem_ty) = path.segments.iter()
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.find(|seg| seg.ident.name == sym::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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_ => 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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diag.span_suggestion(
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input.span,
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"consider changing the type to",
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slice_ty,
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Applicability::Unspecified,
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);
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for (span, suggestion) in clone_spans {
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diag.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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Applicability::Unspecified,
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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 is_type_diagnostic_item(cx, ty, sym::string_type) {
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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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diag.span_suggestion(
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input.span,
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"consider changing the type to",
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"&str".to_string(),
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Applicability::Unspecified,
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);
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for (span, suggestion) in clone_spans {
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diag.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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Applicability::Unspecified,
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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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.copied()
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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(diag, "consider taking a reference instead", 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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/// Functions marked with these attributes must have the exact signature.
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fn requires_exact_signature(attrs: &[Attribute]) -> bool {
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attrs.iter().any(|attr| {
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[sym::proc_macro, sym::proc_macro_attribute, sym::proc_macro_derive]
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.iter()
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.any(|&allow| attr.has_name(allow))
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})
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}
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#[derive(Default)]
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struct MovedVariablesCtxt {
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moved_vars: HirIdSet,
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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: HirIdMap<FxHashSet<Span>>,
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}
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impl MovedVariablesCtxt {
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fn move_common(&mut self, cmt: &euv::PlaceWithHirId<'_>) {
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if let euv::PlaceBase::Local(vid) = cmt.place.base {
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self.moved_vars.insert(vid);
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}
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}
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}
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impl<'tcx> euv::Delegate<'tcx> for MovedVariablesCtxt {
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fn consume(&mut self, cmt: &euv::PlaceWithHirId<'tcx>, _: HirId) {
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self.move_common(cmt);
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}
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fn borrow(&mut self, _: &euv::PlaceWithHirId<'tcx>, _: HirId, _: ty::BorrowKind) {}
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fn mutate(&mut self, _: &euv::PlaceWithHirId<'tcx>, _: HirId) {}
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fn fake_read(&mut self, _: rustc_typeck::expr_use_visitor::Place<'tcx>, _: FakeReadCause, _: HirId) {}
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}
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