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Auto merge of #11895 - ericwu2003:useless_vec-FP, r=blyxyas

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Useless vec false positive

changelog: [`useless_vec`]: fix false positive in macros.

fixes #11861

We delay the emission of `useless_vec` lints to the check_crate_post stage, which allows us to effectively undo lints if we find that a `vec![]` expression is being used multiple times after macro expansion.
This commit is contained in:
bors 2023-12-12 22:57:24 +00:00
commit c19508b356
5 changed files with 163 additions and 71 deletions
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3
clippy_lints/src/lib.rs
View File

@ -50,6 +50,8 @@
#[macro_use]
extern crate declare_clippy_lint;
use std::collections::BTreeMap;
use rustc_data_structures::fx::FxHashSet;
use rustc_lint::{Lint, LintId};
@ -725,6 +727,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
Box::new(vec::UselessVec {
too_large_for_stack,
msrv: msrv(),
span_to_lint_map: BTreeMap::new(),
})
});
store.register_late_pass(|_| Box::new(panic_unimplemented::PanicUnimplemented));

115
clippy_lints/src/vec.rs
View File

@ -1,25 +1,27 @@
use std::collections::BTreeMap;
use std::ops::ControlFlow;
use clippy_config::msrvs::{self, Msrv};
use clippy_utils::consts::{constant, Constant};
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::diagnostics::span_lint_hir_and_then;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::ty::is_copy;
use clippy_utils::visitors::for_each_local_use_after_expr;
use clippy_utils::{get_parent_expr, higher, is_trait_method};
use rustc_errors::Applicability;
use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability, Node, PatKind};
use rustc_hir::{BorrowKind, Expr, ExprKind, HirId, Mutability, Node, PatKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::layout::LayoutOf;
use rustc_middle::ty::{self, Ty};
use rustc_session::impl_lint_pass;
use rustc_span::{sym, Span};
use rustc_span::{sym, DesugaringKind, Span};
#[expect(clippy::module_name_repetitions)]
#[derive(Clone)]
pub struct UselessVec {
pub too_large_for_stack: u64,
pub msrv: Msrv,
pub span_to_lint_map: BTreeMap<Span, Option<(HirId, SuggestedType, String, Applicability)>>,
}
declare_clippy_lint! {
@ -69,31 +71,15 @@ pub fn is_allowed_vec_method(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
impl<'tcx> LateLintPass<'tcx> for UselessVec {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
// search for `&vec![_]` or `vec![_]` expressions where the adjusted type is `&[_]`
if adjusts_to_slice(cx, expr)
&& let Some(vec_args) = higher::VecArgs::hir(cx, expr.peel_borrows())
{
let (suggest_slice, span) = if let ExprKind::AddrOf(BorrowKind::Ref, mutability, _) = expr.kind {
// `expr` is `&vec![_]`, so suggest `&[_]` (or `&mut[_]` resp.)
(SuggestedType::SliceRef(mutability), expr.span)
} else {
// `expr` is the `vec![_]` expansion, so suggest `[_]`
// and also use the span of the actual `vec![_]` expression
(SuggestedType::Array, expr.span.ctxt().outer_expn_data().call_site)
};
self.check_vec_macro(cx, &vec_args, span, suggest_slice);
}
if let Some(vec_args) = higher::VecArgs::hir(cx, expr.peel_borrows()) {
// search for `let foo = vec![_]` expressions where all uses of `foo`
// adjust to slices or call a method that exist on slices (e.g. len)
if let Some(vec_args) = higher::VecArgs::hir(cx, expr)
&& let Node::Local(local) = cx.tcx.hir().get_parent(expr.hir_id)
if let Node::Local(local) = cx.tcx.hir().get_parent(expr.hir_id)
// for now ignore locals with type annotations.
// this is to avoid compile errors when doing the suggestion here: let _: Vec<_> = vec![..];
&& local.ty.is_none()
&& let PatKind::Binding(_, id, ..) = local.pat.kind
&& is_copy(cx, vec_type(cx.typeck_results().expr_ty_adjusted(expr)))
&& is_copy(cx, vec_type(cx.typeck_results().expr_ty_adjusted(expr.peel_borrows())))
{
let only_slice_uses = for_each_local_use_after_expr(cx, id, expr.hir_id, |expr| {
// allow indexing into a vec and some set of allowed method calls that exist on slices, too
@ -109,24 +95,64 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
})
.is_continue();
let span = expr.span.ctxt().outer_expn_data().call_site;
if only_slice_uses {
self.check_vec_macro(
cx,
&vec_args,
expr.span.ctxt().outer_expn_data().call_site,
SuggestedType::Array,
);
self.check_vec_macro(cx, &vec_args, span, expr.hir_id, SuggestedType::Array);
} else {
self.span_to_lint_map.insert(span, None);
}
}
// search for `for _ in vec![…]`
if let Some(higher::ForLoop { arg, .. }) = higher::ForLoop::hir(expr)
&& let Some(vec_args) = higher::VecArgs::hir(cx, arg)
// if the local pattern has a specified type, do not lint.
else if let Some(_) = higher::VecArgs::hir(cx, expr)
&& let Node::Local(local) = cx.tcx.hir().get_parent(expr.hir_id)
&& local.ty.is_some()
{
let span = expr.span.ctxt().outer_expn_data().call_site;
self.span_to_lint_map.insert(span, None);
}
// search for `for _ in vec![...]`
else if let Some(parent) = get_parent_expr(cx, expr)
&& parent.span.is_desugaring(DesugaringKind::ForLoop)
&& self.msrv.meets(msrvs::ARRAY_INTO_ITERATOR)
{
// report the error around the `vec!` not inside `<std macros>:`
let span = arg.span.ctxt().outer_expn_data().call_site;
self.check_vec_macro(cx, &vec_args, span, SuggestedType::Array);
let span = expr.span.ctxt().outer_expn_data().call_site;
self.check_vec_macro(cx, &vec_args, span, expr.hir_id, SuggestedType::Array);
}
// search for `&vec![_]` or `vec![_]` expressions where the adjusted type is `&[_]`
else {
let (suggest_slice, span) = if let ExprKind::AddrOf(BorrowKind::Ref, mutability, _) = expr.kind {
// `expr` is `&vec![_]`, so suggest `&[_]` (or `&mut[_]` resp.)
(SuggestedType::SliceRef(mutability), expr.span)
} else {
// `expr` is the `vec![_]` expansion, so suggest `[_]`
// and also use the span of the actual `vec![_]` expression
(SuggestedType::Array, expr.span.ctxt().outer_expn_data().call_site)
};
if adjusts_to_slice(cx, expr) {
self.check_vec_macro(cx, &vec_args, span, expr.hir_id, suggest_slice);
} else {
self.span_to_lint_map.insert(span, None);
}
}
}
}
fn check_crate_post(&mut self, cx: &LateContext<'tcx>) {
for (span, lint_opt) in &self.span_to_lint_map {
if let Some((hir_id, suggest_slice, snippet, applicability)) = lint_opt {
let help_msg = format!(
"you can use {} directly",
match suggest_slice {
SuggestedType::SliceRef(_) => "a slice",
SuggestedType::Array => "an array",
}
);
span_lint_hir_and_then(cx, USELESS_VEC, *hir_id, *span, "useless use of `vec!`", |diag| {
diag.span_suggestion(*span, help_msg, snippet, *applicability);
});
}
}
}
@ -134,7 +160,7 @@ fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
}
#[derive(Copy, Clone)]
enum SuggestedType {
pub(crate) enum SuggestedType {
/// Suggest using a slice `&[..]` / `&mut [..]`
SliceRef(Mutability),
/// Suggest using an array: `[..]`
@ -147,6 +173,7 @@ fn check_vec_macro<'tcx>(
cx: &LateContext<'tcx>,
vec_args: &higher::VecArgs<'tcx>,
span: Span,
hir_id: HirId,
suggest_slice: SuggestedType,
) {
if span.from_expansion() {
@ -204,21 +231,9 @@ fn check_vec_macro<'tcx>(
},
};
span_lint_and_sugg(
cx,
USELESS_VEC,
span,
"useless use of `vec!`",
&format!(
"you can use {} directly",
match suggest_slice {
SuggestedType::SliceRef(_) => "a slice",
SuggestedType::Array => "an array",
}
),
snippet,
applicability,
);
self.span_to_lint_map
.entry(span)
.or_insert(Some((hir_id, suggest_slice, snippet, applicability)));
}
}

34
tests/ui/vec.fixed
View File

@ -176,3 +176,37 @@ fn below() {
let _: String = a;
}
}
fn func_needing_vec(_bar: usize, _baz: Vec<usize>) {}
fn func_not_needing_vec(_bar: usize, _baz: usize) {}
fn issue11861() {
macro_rules! this_macro_needs_vec {
($x:expr) => {{
func_needing_vec($x.iter().sum(), $x);
for _ in $x {}
}};
}
macro_rules! this_macro_doesnt_need_vec {
($x:expr) => {{ func_not_needing_vec($x.iter().sum(), $x.iter().sum()) }};
}
// Do not lint the next line
this_macro_needs_vec!(vec![1]);
this_macro_doesnt_need_vec!([1]); //~ ERROR: useless use of `vec!`
macro_rules! m {
($x:expr) => {
fn f2() {
let _x: Vec<i32> = $x;
}
fn f() {
let _x = $x;
$x.starts_with(&[]);
}
};
}
// should not lint
m!(vec![1]);
}

34
tests/ui/vec.rs
View File

@ -176,3 +176,37 @@ fn below() {
let _: String = a;
}
}
fn func_needing_vec(_bar: usize, _baz: Vec<usize>) {}
fn func_not_needing_vec(_bar: usize, _baz: usize) {}
fn issue11861() {
macro_rules! this_macro_needs_vec {
($x:expr) => {{
func_needing_vec($x.iter().sum(), $x);
for _ in $x {}
}};
}
macro_rules! this_macro_doesnt_need_vec {
($x:expr) => {{ func_not_needing_vec($x.iter().sum(), $x.iter().sum()) }};
}
// Do not lint the next line
this_macro_needs_vec!(vec![1]);
this_macro_doesnt_need_vec!(vec![1]); //~ ERROR: useless use of `vec!`
macro_rules! m {
($x:expr) => {
fn f2() {
let _x: Vec<i32> = $x;
}
fn f() {
let _x = $x;
$x.starts_with(&[]);
}
};
}
// should not lint
m!(vec![1]);
}

8
tests/ui/vec.stderr
View File

@ -115,5 +115,11 @@ error: useless use of `vec!`
LL | for a in vec![String::new(), String::new()] {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: you can use an array directly: `[String::new(), String::new()]`
error: aborting due to 19 previous errors
error: useless use of `vec!`
--> $DIR/vec.rs:196:33
|
LL | this_macro_doesnt_need_vec!(vec![1]);
| ^^^^^^^ help: you can use an array directly: `[1]`
error: aborting due to 20 previous errors