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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::{path_to_local, path_to_local_id};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, HirId, Local, PatKind, Stmt, StmtKind};
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;
declare_clippy_lint! {
/// ### What it does
/// Checks for calls to `push` immediately after creating a new `Vec`.
///
/// ### 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_local: bool,
lhs_span: Span,
err_span: Span,
found: u64,
}
impl VecPushSearcher {
fn display_err(&self, cx: &LateContext<'_>) {
match self.init {
_ if self.found == 0 => return,
VecInitKind::WithLiteralCapacity(x) if x > self.found => return,
VecInitKind::WithExprCapacity(_) => return,
_ => (),
};
let mut s = if self.lhs_is_local {
String::from("let ")
} else {
String::new()
};
s.push_str(&snippet(cx, self.lhs_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_chain! {
if !in_external_macro(cx.sess(), local.span);
if let Some(init) = local.init;
if let PatKind::Binding(BindingAnnotation::Mutable, id, _, None) = local.pat.kind;
if let Some(init_kind) = get_vec_init_kind(cx, init);
then {
self.searcher = Some(VecPushSearcher {
local_id: id,
init: init_kind,
lhs_is_local: true,
lhs_span: local.ty.map_or(local.pat.span, |t| local.pat.span.to(t.span)),
err_span: local.span,
found: 0,
});
}
}
}
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if_chain! {
if self.searcher.is_none();
if !in_external_macro(cx.sess(), expr.span);
if let ExprKind::Assign(left, right, _) = expr.kind;
if let Some(id) = path_to_local(left);
if let Some(init_kind) = get_vec_init_kind(cx, right);
then {
self.searcher = Some(VecPushSearcher {
local_id: id,
init: init_kind,
lhs_is_local: false,
lhs_span: left.span,
err_span: expr.span,
found: 0,
});
}
}
}
fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
if let Some(searcher) = self.searcher.take() {
if_chain! {
if let StmtKind::Expr(expr) | StmtKind::Semi(expr) = stmt.kind;
if let ExprKind::MethodCall(path, _, [self_arg, _], _) = expr.kind;
if path_to_local_id(self_arg, searcher.local_id);
if path.ident.name.as_str() == "push";
then {
self.searcher = Some(VecPushSearcher {
found: searcher.found + 1,
err_span: searcher.err_span.to(stmt.span),
.. 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);
}
}
}
|
