108 lines
3.2 KiB
Rust
108 lines
3.2 KiB
Rust
use rustc::hir::*;
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use rustc::lint::*;
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use rustc::ty::{self, Ty};
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use rustc::ty::subst::Substs;
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use rustc_const_eval::ConstContext;
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use syntax::codemap::Span;
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use utils::{higher, is_copy, snippet, span_lint_and_sugg};
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/// **What it does:** Checks for usage of `&vec![..]` when using `&[..]` would
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/// be possible.
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///
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/// **Why is this bad?** This is less efficient.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust,ignore
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/// foo(&vec![1, 2])
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/// ```
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declare_lint! {
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pub USELESS_VEC,
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Warn,
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"useless `vec!`"
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}
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#[derive(Copy, Clone, Debug)]
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pub struct Pass;
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array!(USELESS_VEC)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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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 `&[_]`
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if_let_chain!{[
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let ty::TyRef(_, ref ty) = cx.tables.expr_ty_adjusted(expr).sty,
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let ty::TySlice(..) = ty.ty.sty,
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let ExprAddrOf(_, ref addressee) = expr.node,
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let Some(vec_args) = higher::vec_macro(cx, addressee),
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], {
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check_vec_macro(cx, &vec_args, expr.span);
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}}
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// search for `for _ in vec![…]`
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if_let_chain!{[
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let Some((_, arg, _)) = higher::for_loop(expr),
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let Some(vec_args) = higher::vec_macro(cx, arg),
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is_copy(cx, vec_type(cx.tables.expr_ty_adjusted(arg))),
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], {
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// report the error around the `vec!` not inside `<std macros>:`
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let span = arg.span.ctxt.outer().expn_info().map(|info| info.call_site).expect("unable to get call_site");
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check_vec_macro(cx, &vec_args, span);
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}}
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}
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}
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fn check_vec_macro(cx: &LateContext, vec_args: &higher::VecArgs, span: Span) {
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let snippet = match *vec_args {
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higher::VecArgs::Repeat(elem, len) => {
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let parent_item = cx.tcx.hir.get_parent(len.id);
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let parent_def_id = cx.tcx.hir.local_def_id(parent_item);
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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)
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.eval(len)
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.is_ok()
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{
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format!("&[{}; {}]", snippet(cx, elem.span, "elem"), snippet(cx, len.span, "len")).into()
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} else {
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return;
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}
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},
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higher::VecArgs::Vec(args) => {
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if let Some(last) = args.iter().last() {
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let span = Span {
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lo: args[0].span.lo,
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hi: last.span.hi,
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ctxt: args[0].span.ctxt,
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};
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format!("&[{}]", snippet(cx, span, "..")).into()
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} else {
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"&[]".into()
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}
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},
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};
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span_lint_and_sugg(
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cx,
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USELESS_VEC,
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span,
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"useless use of `vec!`",
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"you can use a slice directly",
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snippet,
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);
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}
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/// Return the item type of the vector (ie. the `T` in `Vec<T>`).
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fn vec_type(ty: Ty) -> Ty {
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if let ty::TyAdt(_, substs) = ty.sty {
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substs.type_at(0)
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} else {
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panic!("The type of `vec!` is a not a struct?");
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}
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}
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