mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-13 06:42:46 +00:00
112 lines
3.5 KiB
Rust
112 lines
3.5 KiB
Rust
use crate::consts::constant;
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use crate::utils::{higher, is_copy, snippet_with_applicability, span_lint_and_sugg};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir::{BorrowKind, Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty::{self, Ty};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::Span;
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declare_clippy_lint! {
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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
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/// # fn foo(my_vec: &[u8]) {}
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///
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/// // Bad
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/// foo(&vec![1, 2]);
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///
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/// // Good
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/// foo(&[1, 2]);
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/// ```
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pub USELESS_VEC,
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perf,
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"useless `vec!`"
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}
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declare_lint_pass!(UselessVec => [USELESS_VEC]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UselessVec {
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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_chain! {
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if let ty::Ref(_, ty, _) = cx.tables.expr_ty_adjusted(expr).kind;
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if let ty::Slice(..) = ty.kind;
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if let ExprKind::AddrOf(BorrowKind::Ref, _, ref addressee) = expr.kind;
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if let Some(vec_args) = higher::vec_macro(cx, addressee);
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then {
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check_vec_macro(cx, &vec_args, expr.span);
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}
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}
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// search for `for _ in vec![…]`
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if_chain! {
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if let Some((_, arg, _)) = higher::for_loop(expr);
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if let Some(vec_args) = higher::vec_macro(cx, arg);
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if is_copy(cx, vec_type(cx.tables.expr_ty_adjusted(arg)));
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then {
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// report the error around the `vec!` not inside `<std macros>:`
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let span = arg.span
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.ctxt()
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.outer_expn_data()
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.call_site
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.ctxt()
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.outer_expn_data()
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.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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}
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fn check_vec_macro<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, vec_args: &higher::VecArgs<'tcx>, span: Span) {
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let mut applicability = Applicability::MachineApplicable;
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let snippet = match *vec_args {
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higher::VecArgs::Repeat(elem, len) => {
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if constant(cx, cx.tables, len).is_some() {
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format!(
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"&[{}; {}]",
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snippet_with_applicability(cx, elem.span, "elem", &mut applicability),
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snippet_with_applicability(cx, len.span, "len", &mut applicability)
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)
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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 = args[0].span.to(last.span);
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format!("&[{}]", snippet_with_applicability(cx, span, "..", &mut applicability))
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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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applicability,
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);
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}
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/// Returns the item type of the vector (i.e., the `T` in `Vec<T>`).
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fn vec_type(ty: Ty<'_>) -> Ty<'_> {
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if let ty::Adt(_, substs) = ty.kind {
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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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