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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::higher::{get_vec_init_kind, VecInitKind};
use clippy_utils::source::snippet;
use clippy_utils::visitors::for_each_local_use_after_expr;
use clippy_utils::{get_parent_expr, path_to_local_id};
use core::ops::ControlFlow;
use rustc_errors::Applicability;
use rustc_hir::def::Res;
use rustc_hir::{
BindingAnnotation, Block, Expr, ExprKind, HirId, Local, Mutability, PatKind, QPath, Stmt, StmtKind, UnOp,
};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::{Span, Symbol};
declare_clippy_lint! {
/// ### What it does
/// Checks for calls to `push` immediately after creating a new `Vec`.
///
/// If the `Vec` is created using `with_capacity` this will only lint if the capacity is a
/// constant and the number of pushes is greater than or equal to the initial capacity.
///
/// If the `Vec` is extended after the initial sequence of pushes and it was default initialized
/// then this will only lint after there were at least four pushes. This number may change in
/// the future.
///
/// ### Why is this bad?
/// The `vec![]` macro is both more performant and easier to read than
/// multiple `push` calls.
///
/// ### Example
/// ```rust
/// let mut v = Vec::new();
/// v.push(0);
/// ```
/// Use instead:
/// ```rust
/// let v = vec![0];
/// ```
#[clippy::version = "1.51.0"]
pub VEC_INIT_THEN_PUSH,
perf,
"`push` immediately after `Vec` creation"
}
impl_lint_pass!(VecInitThenPush => [VEC_INIT_THEN_PUSH]);
#[derive(Default)]
pub struct VecInitThenPush {
searcher: Option<VecPushSearcher>,
}
struct VecPushSearcher {
local_id: HirId,
init: VecInitKind,
lhs_is_let: bool,
let_ty_span: Option<Span>,
name: Symbol,
err_span: Span,
found: u128,
last_push_expr: HirId,
}
impl VecPushSearcher {
fn display_err(&self, cx: &LateContext<'_>) {
let required_pushes_before_extension = match self.init {
_ if self.found == 0 => return,
VecInitKind::WithConstCapacity(x) if x > self.found => return,
VecInitKind::WithConstCapacity(x) => x,
VecInitKind::WithExprCapacity(_) => return,
_ => 3,
};
let mut needs_mut = false;
let res = for_each_local_use_after_expr(cx, self.local_id, self.last_push_expr, |e| {
let Some(parent) = get_parent_expr(cx, e) else {
return ControlFlow::Continue(())
};
let adjusted_ty = cx.typeck_results().expr_ty_adjusted(e);
let adjusted_mut = adjusted_ty.ref_mutability().unwrap_or(Mutability::Not);
needs_mut |= adjusted_mut == Mutability::Mut;
match parent.kind {
ExprKind::AddrOf(_, Mutability::Mut, _) => {
needs_mut = true;
return ControlFlow::Break(true);
},
ExprKind::Unary(UnOp::Deref, _) | ExprKind::Index(..) if !needs_mut => {
let mut last_place = parent;
while let Some(parent) = get_parent_expr(cx, last_place) {
if matches!(parent.kind, ExprKind::Unary(UnOp::Deref, _) | ExprKind::Field(..))
|| matches!(parent.kind, ExprKind::Index(e, _) if e.hir_id == last_place.hir_id)
{
last_place = parent;
} else {
break;
}
}
needs_mut |= cx.typeck_results().expr_ty_adjusted(last_place).ref_mutability()
== Some(Mutability::Mut)
|| get_parent_expr(cx, last_place)
.map_or(false, |e| matches!(e.kind, ExprKind::AddrOf(_, Mutability::Mut, _)));
},
ExprKind::MethodCall(_, recv, ..)
if recv.hir_id == e.hir_id
&& adjusted_mut == Mutability::Mut
&& !adjusted_ty.peel_refs().is_slice() =>
{
// No need to set `needs_mut` to true. The receiver will be either explicitly borrowed, or it will
// be implicitly borrowed via an adjustment. Both of these cases are already handled by this point.
return ControlFlow::Break(true);
},
ExprKind::Assign(lhs, ..) if e.hir_id == lhs.hir_id => {
needs_mut = true;
return ControlFlow::Break(false);
},
_ => (),
}
ControlFlow::Continue(())
});
// Avoid allocating small `Vec`s when they'll be extended right after.
if res == ControlFlow::Break(true) && self.found <= required_pushes_before_extension {
return;
}
let mut s = if self.lhs_is_let {
String::from("let ")
} else {
String::new()
};
if needs_mut {
s.push_str("mut ");
}
s.push_str(self.name.as_str());
if let Some(span) = self.let_ty_span {
s.push_str(": ");
s.push_str(&snippet(cx, span, "_"));
}
s.push_str(" = vec![..];");
span_lint_and_sugg(
cx,
VEC_INIT_THEN_PUSH,
self.err_span,
"calls to `push` immediately after creation",
"consider using the `vec![]` macro",
s,
Applicability::HasPlaceholders,
);
}
}
impl<'tcx> LateLintPass<'tcx> for VecInitThenPush {
fn check_block(&mut self, _: &LateContext<'tcx>, _: &'tcx Block<'tcx>) {
self.searcher = None;
}
fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'tcx>) {
if let Some(init_expr) = local.init
&& let PatKind::Binding(BindingAnnotation::MUT, id, name, None) = local.pat.kind
&& !in_external_macro(cx.sess(), local.span)
&& let Some(init) = get_vec_init_kind(cx, init_expr)
&& !matches!(init, VecInitKind::WithExprCapacity(_))
{
self.searcher = Some(VecPushSearcher {
local_id: id,
init,
lhs_is_let: true,
name: name.name,
let_ty_span: local.ty.map(|ty| ty.span),
err_span: local.span,
found: 0,
last_push_expr: init_expr.hir_id,
});
}
}
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if self.searcher.is_none()
&& let ExprKind::Assign(left, right, _) = expr.kind
&& let ExprKind::Path(QPath::Resolved(None, path)) = left.kind
&& let [name] = &path.segments
&& let Res::Local(id) = path.res
&& !in_external_macro(cx.sess(), expr.span)
&& let Some(init) = get_vec_init_kind(cx, right)
&& !matches!(init, VecInitKind::WithExprCapacity(_))
{
self.searcher = Some(VecPushSearcher {
local_id: id,
init,
lhs_is_let: false,
let_ty_span: None,
name: name.ident.name,
err_span: expr.span,
found: 0,
last_push_expr: expr.hir_id,
});
}
}
fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
if let Some(searcher) = self.searcher.take() {
if let StmtKind::Expr(expr) | StmtKind::Semi(expr) = stmt.kind
&& let ExprKind::MethodCall(name, self_arg, [_], _) = expr.kind
&& path_to_local_id(self_arg, searcher.local_id)
&& name.ident.as_str() == "push"
{
self.searcher = Some(VecPushSearcher {
found: searcher.found + 1,
err_span: searcher.err_span.to(stmt.span),
last_push_expr: expr.hir_id,
.. searcher
});
} else {
searcher.display_err(cx);
}
}
}
fn check_block_post(&mut self, cx: &LateContext<'tcx>, _: &'tcx Block<'tcx>) {
if let Some(searcher) = self.searcher.take() {
searcher.display_err(cx);
}
}
}
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