349 lines
14 KiB
Rust
349 lines
14 KiB
Rust
use crate::utils::ptr::get_spans;
|
|
use crate::utils::{
|
|
get_trait_def_id, implements_trait, is_copy, is_self, is_type_diagnostic_item, multispan_sugg, paths, snippet,
|
|
snippet_opt, span_lint_and_then,
|
|
};
|
|
use if_chain::if_chain;
|
|
use rustc_ast::ast::Attribute;
|
|
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
|
|
use rustc_errors::{Applicability, DiagnosticBuilder};
|
|
use rustc_hir::intravisit::FnKind;
|
|
use rustc_hir::{BindingAnnotation, Body, FnDecl, GenericArg, HirId, ItemKind, Node, PatKind, QPath, TyKind};
|
|
use rustc_infer::infer::TyCtxtInferExt;
|
|
use rustc_lint::{LateContext, LateLintPass};
|
|
use rustc_middle::ty::{self, TypeFoldable};
|
|
use rustc_session::{declare_lint_pass, declare_tool_lint};
|
|
use rustc_span::Span;
|
|
use rustc_target::spec::abi::Abi;
|
|
use rustc_trait_selection::traits;
|
|
use rustc_trait_selection::traits::misc::can_type_implement_copy;
|
|
use rustc_typeck::expr_use_visitor as euv;
|
|
use std::borrow::Cow;
|
|
|
|
declare_clippy_lint! {
|
|
/// **What it does:** Checks for functions taking arguments by value, but not
|
|
/// consuming them in its
|
|
/// body.
|
|
///
|
|
/// **Why is this bad?** Taking arguments by reference is more flexible and can
|
|
/// sometimes avoid
|
|
/// unnecessary allocations.
|
|
///
|
|
/// **Known problems:**
|
|
/// * This lint suggests taking an argument by reference,
|
|
/// however sometimes it is better to let users decide the argument type
|
|
/// (by using `Borrow` trait, for example), depending on how the function is used.
|
|
///
|
|
/// **Example:**
|
|
/// ```rust
|
|
/// fn foo(v: Vec<i32>) {
|
|
/// assert_eq!(v.len(), 42);
|
|
/// }
|
|
/// ```
|
|
///
|
|
/// ```rust
|
|
/// // should be
|
|
/// fn foo(v: &[i32]) {
|
|
/// assert_eq!(v.len(), 42);
|
|
/// }
|
|
/// ```
|
|
pub NEEDLESS_PASS_BY_VALUE,
|
|
pedantic,
|
|
"functions taking arguments by value, but not consuming them in its body"
|
|
}
|
|
|
|
declare_lint_pass!(NeedlessPassByValue => [NEEDLESS_PASS_BY_VALUE]);
|
|
|
|
macro_rules! need {
|
|
($e: expr) => {
|
|
if let Some(x) = $e {
|
|
x
|
|
} else {
|
|
return;
|
|
}
|
|
};
|
|
}
|
|
|
|
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessPassByValue {
|
|
#[allow(clippy::too_many_lines)]
|
|
fn check_fn(
|
|
&mut self,
|
|
cx: &LateContext<'a, 'tcx>,
|
|
kind: FnKind<'tcx>,
|
|
decl: &'tcx FnDecl<'_>,
|
|
body: &'tcx Body<'_>,
|
|
span: Span,
|
|
hir_id: HirId,
|
|
) {
|
|
if span.from_expansion() {
|
|
return;
|
|
}
|
|
|
|
match kind {
|
|
FnKind::ItemFn(.., header, _, attrs) => {
|
|
if header.abi != Abi::Rust || requires_exact_signature(attrs) {
|
|
return;
|
|
}
|
|
},
|
|
FnKind::Method(..) => (),
|
|
_ => return,
|
|
}
|
|
|
|
// Exclude non-inherent impls
|
|
if let Some(Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(hir_id)) {
|
|
if matches!(item.kind, ItemKind::Impl{ of_trait: Some(_), .. } |
|
|
ItemKind::Trait(..))
|
|
{
|
|
return;
|
|
}
|
|
}
|
|
|
|
// Allow `Borrow` or functions to be taken by value
|
|
let borrow_trait = need!(get_trait_def_id(cx, &paths::BORROW_TRAIT));
|
|
let whitelisted_traits = [
|
|
need!(cx.tcx.lang_items().fn_trait()),
|
|
need!(cx.tcx.lang_items().fn_once_trait()),
|
|
need!(cx.tcx.lang_items().fn_mut_trait()),
|
|
need!(get_trait_def_id(cx, &paths::RANGE_ARGUMENT_TRAIT)),
|
|
];
|
|
|
|
let sized_trait = need!(cx.tcx.lang_items().sized_trait());
|
|
|
|
let fn_def_id = cx.tcx.hir().local_def_id(hir_id);
|
|
|
|
let preds = traits::elaborate_predicates(cx.tcx, cx.param_env.caller_bounds.to_vec())
|
|
.filter(|p| !p.is_global())
|
|
.filter_map(|obligation| {
|
|
if let ty::Predicate::Trait(poly_trait_ref, _) = obligation.predicate {
|
|
if poly_trait_ref.def_id() == sized_trait || poly_trait_ref.skip_binder().has_escaping_bound_vars()
|
|
{
|
|
return None;
|
|
}
|
|
Some(poly_trait_ref)
|
|
} else {
|
|
None
|
|
}
|
|
})
|
|
.collect::<Vec<_>>();
|
|
|
|
// Collect moved variables and spans which will need dereferencings from the
|
|
// function body.
|
|
let MovedVariablesCtxt {
|
|
moved_vars,
|
|
spans_need_deref,
|
|
..
|
|
} = {
|
|
let mut ctx = MovedVariablesCtxt::default();
|
|
cx.tcx.infer_ctxt().enter(|infcx| {
|
|
euv::ExprUseVisitor::new(&mut ctx, &infcx, fn_def_id.to_def_id(), cx.param_env, cx.tables)
|
|
.consume_body(body);
|
|
});
|
|
ctx
|
|
};
|
|
|
|
let fn_sig = cx.tcx.fn_sig(fn_def_id);
|
|
let fn_sig = cx.tcx.erase_late_bound_regions(&fn_sig);
|
|
|
|
for (idx, ((input, &ty), arg)) in decl.inputs.iter().zip(fn_sig.inputs()).zip(body.params).enumerate() {
|
|
// All spans generated from a proc-macro invocation are the same...
|
|
if span == input.span {
|
|
return;
|
|
}
|
|
|
|
// Ignore `self`s.
|
|
if idx == 0 {
|
|
if let PatKind::Binding(.., ident, _) = arg.pat.kind {
|
|
if ident.as_str() == "self" {
|
|
continue;
|
|
}
|
|
}
|
|
}
|
|
|
|
//
|
|
// * Exclude a type that is specifically bounded by `Borrow`.
|
|
// * Exclude a type whose reference also fulfills its bound. (e.g., `std::convert::AsRef`,
|
|
// `serde::Serialize`)
|
|
let (implements_borrow_trait, all_borrowable_trait) = {
|
|
let preds = preds
|
|
.iter()
|
|
.filter(|t| t.skip_binder().self_ty() == ty)
|
|
.collect::<Vec<_>>();
|
|
|
|
(
|
|
preds.iter().any(|t| t.def_id() == borrow_trait),
|
|
!preds.is_empty() && {
|
|
let ty_empty_region = cx.tcx.mk_imm_ref(cx.tcx.lifetimes.re_root_empty, ty);
|
|
preds.iter().all(|t| {
|
|
let ty_params = &t
|
|
.skip_binder()
|
|
.trait_ref
|
|
.substs
|
|
.iter()
|
|
.skip(1)
|
|
.cloned()
|
|
.collect::<Vec<_>>();
|
|
implements_trait(cx, ty_empty_region, t.def_id(), ty_params)
|
|
})
|
|
},
|
|
)
|
|
};
|
|
|
|
if_chain! {
|
|
if !is_self(arg);
|
|
if !ty.is_mutable_ptr();
|
|
if !is_copy(cx, ty);
|
|
if !whitelisted_traits.iter().any(|&t| implements_trait(cx, ty, t, &[]));
|
|
if !implements_borrow_trait;
|
|
if !all_borrowable_trait;
|
|
|
|
if let PatKind::Binding(mode, canonical_id, ..) = arg.pat.kind;
|
|
if !moved_vars.contains(&canonical_id);
|
|
then {
|
|
if mode == BindingAnnotation::Mutable || mode == BindingAnnotation::RefMut {
|
|
continue;
|
|
}
|
|
|
|
// Dereference suggestion
|
|
let sugg = |diag: &mut DiagnosticBuilder<'_>| {
|
|
if let ty::Adt(def, ..) = ty.kind {
|
|
if let Some(span) = cx.tcx.hir().span_if_local(def.did) {
|
|
if can_type_implement_copy(cx.tcx, cx.param_env, ty).is_ok() {
|
|
diag.span_help(span, "consider marking this type as `Copy`");
|
|
}
|
|
}
|
|
}
|
|
|
|
let deref_span = spans_need_deref.get(&canonical_id);
|
|
if_chain! {
|
|
if is_type_diagnostic_item(cx, ty, sym!(vec_type));
|
|
if let Some(clone_spans) =
|
|
get_spans(cx, Some(body.id()), idx, &[("clone", ".to_owned()")]);
|
|
if let TyKind::Path(QPath::Resolved(_, ref path)) = input.kind;
|
|
if let Some(elem_ty) = path.segments.iter()
|
|
.find(|seg| seg.ident.name == sym!(Vec))
|
|
.and_then(|ps| ps.args.as_ref())
|
|
.map(|params| params.args.iter().find_map(|arg| match arg {
|
|
GenericArg::Type(ty) => Some(ty),
|
|
_ => None,
|
|
}).unwrap());
|
|
then {
|
|
let slice_ty = format!("&[{}]", snippet(cx, elem_ty.span, "_"));
|
|
diag.span_suggestion(
|
|
input.span,
|
|
"consider changing the type to",
|
|
slice_ty,
|
|
Applicability::Unspecified,
|
|
);
|
|
|
|
for (span, suggestion) in clone_spans {
|
|
diag.span_suggestion(
|
|
span,
|
|
&snippet_opt(cx, span)
|
|
.map_or(
|
|
"change the call to".into(),
|
|
|x| Cow::from(format!("change `{}` to", x)),
|
|
),
|
|
suggestion.into(),
|
|
Applicability::Unspecified,
|
|
);
|
|
}
|
|
|
|
// cannot be destructured, no need for `*` suggestion
|
|
assert!(deref_span.is_none());
|
|
return;
|
|
}
|
|
}
|
|
|
|
if is_type_diagnostic_item(cx, ty, sym!(string_type)) {
|
|
if let Some(clone_spans) =
|
|
get_spans(cx, Some(body.id()), idx, &[("clone", ".to_string()"), ("as_str", "")]) {
|
|
diag.span_suggestion(
|
|
input.span,
|
|
"consider changing the type to",
|
|
"&str".to_string(),
|
|
Applicability::Unspecified,
|
|
);
|
|
|
|
for (span, suggestion) in clone_spans {
|
|
diag.span_suggestion(
|
|
span,
|
|
&snippet_opt(cx, span)
|
|
.map_or(
|
|
"change the call to".into(),
|
|
|x| Cow::from(format!("change `{}` to", x))
|
|
),
|
|
suggestion.into(),
|
|
Applicability::Unspecified,
|
|
);
|
|
}
|
|
|
|
assert!(deref_span.is_none());
|
|
return;
|
|
}
|
|
}
|
|
|
|
let mut spans = vec![(input.span, format!("&{}", snippet(cx, input.span, "_")))];
|
|
|
|
// Suggests adding `*` to dereference the added reference.
|
|
if let Some(deref_span) = deref_span {
|
|
spans.extend(
|
|
deref_span
|
|
.iter()
|
|
.cloned()
|
|
.map(|span| (span, format!("*{}", snippet(cx, span, "<expr>")))),
|
|
);
|
|
spans.sort_by_key(|&(span, _)| span);
|
|
}
|
|
multispan_sugg(diag, "consider taking a reference instead".to_string(), spans);
|
|
};
|
|
|
|
span_lint_and_then(
|
|
cx,
|
|
NEEDLESS_PASS_BY_VALUE,
|
|
input.span,
|
|
"this argument is passed by value, but not consumed in the function body",
|
|
sugg,
|
|
);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Functions marked with these attributes must have the exact signature.
|
|
fn requires_exact_signature(attrs: &[Attribute]) -> bool {
|
|
attrs.iter().any(|attr| {
|
|
[sym!(proc_macro), sym!(proc_macro_attribute), sym!(proc_macro_derive)]
|
|
.iter()
|
|
.any(|&allow| attr.check_name(allow))
|
|
})
|
|
}
|
|
|
|
#[derive(Default)]
|
|
struct MovedVariablesCtxt {
|
|
moved_vars: FxHashSet<HirId>,
|
|
/// Spans which need to be prefixed with `*` for dereferencing the
|
|
/// suggested additional reference.
|
|
spans_need_deref: FxHashMap<HirId, FxHashSet<Span>>,
|
|
}
|
|
|
|
impl MovedVariablesCtxt {
|
|
fn move_common(&mut self, cmt: &euv::Place<'_>) {
|
|
if let euv::PlaceBase::Local(vid) = cmt.base {
|
|
self.moved_vars.insert(vid);
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'tcx> euv::Delegate<'tcx> for MovedVariablesCtxt {
|
|
fn consume(&mut self, cmt: &euv::Place<'tcx>, mode: euv::ConsumeMode) {
|
|
if let euv::ConsumeMode::Move = mode {
|
|
self.move_common(cmt);
|
|
}
|
|
}
|
|
|
|
fn borrow(&mut self, _: &euv::Place<'tcx>, _: ty::BorrowKind) {}
|
|
|
|
fn mutate(&mut self, _: &euv::Place<'tcx>) {}
|
|
}
|