rust/clippy_lints/src/vec.rs

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use rustc::hir::*;
use rustc::lint::*;
use rustc::ty::{self, Ty};
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use rustc::ty::subst::Substs;
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use rustc_const_eval::ConstContext;
use syntax::codemap::Span;
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use utils::{higher, is_copy, snippet, span_lint_and_sugg};
/// **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:**
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/// ```rust,ignore
/// foo(&vec![1, 2])
/// ```
declare_lint! {
pub USELESS_VEC,
Warn,
"useless `vec!`"
}
#[derive(Copy, Clone, Debug)]
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pub struct Pass;
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impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array!(USELESS_VEC)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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// search for `&vec![_]` expressions where the adjusted type is `&[_]`
if_let_chain!{[
let ty::TyRef(_, ref ty) = cx.tables.expr_ty_adjusted(expr).sty,
let ty::TySlice(..) = ty.ty.sty,
let ExprAddrOf(_, ref addressee) = expr.node,
let Some(vec_args) = higher::vec_macro(cx, addressee),
], {
check_vec_macro(cx, &vec_args, expr.span);
}}
// search for `for _ in vec![…]`
if_let_chain!{[
let Some((_, arg, _)) = higher::for_loop(expr),
let Some(vec_args) = higher::vec_macro(cx, arg),
is_copy(cx, vec_type(cx.tables.expr_ty_adjusted(arg))),
], {
// report the error around the `vec!` not inside `<std macros>:`
let span = arg.span.ctxt().outer().expn_info().map(|info| info.call_site).expect("unable to get call_site");
check_vec_macro(cx, &vec_args, span);
}}
}
}
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fn check_vec_macro<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, vec_args: &higher::VecArgs<'tcx>, span: Span) {
let snippet = match *vec_args {
higher::VecArgs::Repeat(elem, len) => {
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let parent_item = cx.tcx.hir.get_parent(len.id);
let parent_def_id = cx.tcx.hir.local_def_id(parent_item);
let substs = Substs::identity_for_item(cx.tcx, parent_def_id);
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if ConstContext::new(cx.tcx, cx.param_env.and(substs), cx.tables)
.eval(len)
.is_ok()
{
format!("&[{}; {}]", snippet(cx, elem.span, "elem"), snippet(cx, len.span, "len")).into()
} else {
return;
}
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},
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higher::VecArgs::Vec(args) => if let Some(last) = args.iter().last() {
let span = args[0].span.to(last.span);
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format!("&[{}]", snippet(cx, span, "..")).into()
} else {
"&[]".into()
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},
};
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span_lint_and_sugg(
cx,
USELESS_VEC,
span,
"useless use of `vec!`",
"you can use a slice directly",
snippet,
);
}
/// Return the item type of the vector (ie. the `T` in `Vec<T>`).
fn vec_type(ty: Ty) -> Ty {
if let ty::TyAdt(_, substs) = ty.sty {
substs.type_at(0)
} else {
panic!("The type of `vec!` is a not a struct?");
}
}