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|
use crate::consts::{constant, Constant};
use crate::rustc_target::abi::LayoutOf;
use crate::utils::{higher, snippet_with_applicability, span_lint_and_sugg};
use clippy_utils::ty::is_copy;
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{BorrowKind, Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::{self, Ty};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::source_map::Span;
#[allow(clippy::module_name_repetitions)]
#[derive(Copy, Clone)]
pub struct UselessVec {
pub too_large_for_stack: u64,
}
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
/// # fn foo(my_vec: &[u8]) {}
///
/// // Bad
/// foo(&vec![1, 2]);
///
/// // Good
/// foo(&[1, 2]);
/// ```
pub USELESS_VEC,
perf,
"useless `vec!`"
}
impl_lint_pass!(UselessVec => [USELESS_VEC]);
impl<'tcx> LateLintPass<'tcx> for UselessVec {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
// search for `&vec![_]` expressions where the adjusted type is `&[_]`
if_chain! {
if let ty::Ref(_, ty, _) = cx.typeck_results().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 {
self.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.typeck_results().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;
self.check_vec_macro(cx, &vec_args, span);
}
}
}
}
impl UselessVec {
fn check_vec_macro<'tcx>(self, cx: &LateContext<'tcx>, vec_args: &higher::VecArgs<'tcx>, span: Span) {
let mut applicability = Applicability::MachineApplicable;
let snippet = match *vec_args {
higher::VecArgs::Repeat(elem, len) => {
if let Some((Constant::Int(len_constant), _)) = constant(cx, cx.typeck_results(), len) {
#[allow(clippy::cast_possible_truncation)]
if len_constant as u64 * size_of(cx, elem) > self.too_large_for_stack {
return;
}
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() {
#[allow(clippy::cast_possible_truncation)]
if args.len() as u64 * size_of(cx, last) > self.too_large_for_stack {
return;
}
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,
);
}
}
fn size_of(cx: &LateContext<'_>, expr: &Expr<'_>) -> u64 {
let ty = cx.typeck_results().expr_ty_adjusted(expr);
cx.layout_of(ty).map_or(0, |l| l.size.bytes())
}
/// 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?");
}
}
|
