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use crate::consts::constant;
use crate::utils::{higher, is_copy, snippet_with_applicability, span_lint_and_sugg};
use if_chain::if_chain;
use rustc::ty::{self, Ty};
use rustc_errors::Applicability;
use rustc_hir::*;
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
declare_clippy_lint! {
/// **What it does:** Checks for usage of `&vec![..]` when using `&[..]` would
/// be possible.
///
/// **Why is this bad?** This is less efficient.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// foo(&vec![1, 2])
/// ```
pub USELESS_VEC,
perf,
"useless `vec!`"
}
declare_lint_pass!(UselessVec => [USELESS_VEC]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UselessVec {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
// search for `&vec![_]` expressions where the adjusted type is `&[_]`
if_chain! {
if let ty::Ref(_, ty, _) = cx.tables.expr_ty_adjusted(expr).kind;
if let ty::Slice(..) = ty.kind;
if let ExprKind::AddrOf(BorrowKind::Ref, _, ref addressee) = expr.kind;
if let Some(vec_args) = higher::vec_macro(cx, addressee);
then {
check_vec_macro(cx, &vec_args, expr.span);
}
}
// search for `for _ in vec![…]`
if_chain! {
if let Some((_, arg, _)) = higher::for_loop(expr);
if let Some(vec_args) = higher::vec_macro(cx, arg);
if is_copy(cx, vec_type(cx.tables.expr_ty_adjusted(arg)));
then {
// report the error around the `vec!` not inside `<std macros>:`
let span = arg.span
.ctxt()
.outer_expn_data()
.call_site
.ctxt()
.outer_expn_data()
.call_site;
check_vec_macro(cx, &vec_args, span);
}
}
}
}
fn check_vec_macro<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, vec_args: &higher::VecArgs<'tcx>, span: Span) {
let mut applicability = Applicability::MachineApplicable;
let snippet = match *vec_args {
higher::VecArgs::Repeat(elem, len) => {
if constant(cx, cx.tables, len).is_some() {
format!(
"&[{}; {}]",
snippet_with_applicability(cx, elem.span, "elem", &mut applicability),
snippet_with_applicability(cx, len.span, "len", &mut applicability)
)
} else {
return;
}
},
higher::VecArgs::Vec(args) => {
if let Some(last) = args.iter().last() {
let span = args[0].span.to(last.span);
format!("&[{}]", snippet_with_applicability(cx, span, "..", &mut applicability))
} else {
"&[]".into()
}
},
};
span_lint_and_sugg(
cx,
USELESS_VEC,
span,
"useless use of `vec!`",
"you can use a slice directly",
snippet,
applicability,
);
}
/// Returns the item type of the vector (i.e., the `T` in `Vec<T>`).
fn vec_type(ty: Ty<'_>) -> Ty<'_> {
if let ty::Adt(_, substs) = ty.kind {
substs.type_at(0)
} else {
panic!("The type of `vec!` is a not a struct?");
}
}
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