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Suggest using Vec::extend() in same_item_push (#13987)

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Using `Vec::extend(std::iter::repeat_n(item, N))` allows to use the more
natural number of elements to add `N`, as is probably done in the
original loop, instead of computing the difference between the existing
number of elements and the wanted one.

Before MSRV 1.82, the older suggestion to use `Vec::resize()` is still
issued.

Inspired by #6156 (which predates `repeat_n()`).

changelog: [`same_item_push`]: recommend using `Vec::extend()` to extend
a vector
This commit is contained in:
Fridtjof Stoldt 2025-01-22 14:41:13 +00:00 • committed by GitHub
commit 67e6bf33fe
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GPG key ID: B5690EEEBB952194
6 changed files with 66 additions and 28 deletions
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2
clippy_lints/src/loops/mod.rs
View file

@ -830,7 +830,7 @@ impl Loops {
for_kv_map::check(cx, pat, arg, body);
mut_range_bound::check(cx, arg, body);
single_element_loop::check(cx, pat, arg, body, expr);
same_item_push::check(cx, pat, arg, body, expr);
same_item_push::check(cx, pat, arg, body, expr, &self.msrv);
manual_flatten::check(cx, pat, arg, body, span);
manual_find::check(cx, pat, arg, body, span, expr);
unused_enumerate_index::check(cx, pat, arg, body);

34
clippy_lints/src/loops/same_item_push.rs
View file

@ -1,8 +1,9 @@
use super::SAME_ITEM_PUSH;
use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::path_to_local;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::msrvs::Msrv;
use clippy_utils::source::snippet_with_context;
use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
use clippy_utils::{msrvs, path_to_local, std_or_core};
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::Applicability;
use rustc_hir::def::{DefKind, Res};
@ -19,19 +20,30 @@ pub(super) fn check<'tcx>(
_: &'tcx Expr<'_>,
body: &'tcx Expr<'_>,
_: &'tcx Expr<'_>,
msrv: &Msrv,
) {
fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>, ctxt: SyntaxContext) {
fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>, ctxt: SyntaxContext, msrv: &Msrv) {
let mut app = Applicability::Unspecified;
let vec_str = snippet_with_context(cx, vec.span, ctxt, "", &mut app).0;
let item_str = snippet_with_context(cx, pushed_item.span, ctxt, "", &mut app).0;
span_lint_and_help(
let secondary_help = if msrv.meets(msrvs::REPEAT_N)
&& let Some(std_or_core) = std_or_core(cx)
{
format!("or `{vec_str}.extend({std_or_core}::iter::repeat_n({item_str}, SIZE))`")
} else {
format!("or `{vec_str}.resize(NEW_SIZE, {item_str})`")
};
span_lint_and_then(
cx,
SAME_ITEM_PUSH,
vec.span,
"it looks like the same item is being pushed into this Vec",
None,
format!("consider using vec![{item_str};SIZE] or {vec_str}.resize(NEW_SIZE, {item_str})"),
"it looks like the same item is being pushed into this `Vec`",
|diag| {
diag.help(format!("consider using `vec![{item_str};SIZE]`"))
.help(secondary_help);
},
);
}
@ -67,11 +79,11 @@ pub(super) fn check<'tcx>(
{
match init.kind {
// immutable bindings that are initialized with literal
ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item, ctxt),
ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item, ctxt, msrv),
// immutable bindings that are initialized with constant
ExprKind::Path(ref path) => {
if let Res::Def(DefKind::Const, ..) = cx.qpath_res(path, init.hir_id) {
emit_lint(cx, vec, pushed_item, ctxt);
emit_lint(cx, vec, pushed_item, ctxt, msrv);
}
},
_ => {},
@ -79,11 +91,11 @@ pub(super) fn check<'tcx>(
}
},
// constant
Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item, ctxt),
Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item, ctxt, msrv),
_ => {},
}
},
ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item, ctxt),
ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item, ctxt, msrv),
_ => {},
}
}