rust/clippy_lints/src/vec.rs

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use rustc::hir::*;
use rustc::lint::*;
use rustc::ty;
use rustc_const_eval::EvalHint::ExprTypeChecked;
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use rustc_const_eval::ConstContext;
use syntax::codemap::Span;
use utils::{higher, is_copy, snippet, span_lint_and_then};
/// **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!{[
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let ty::TypeVariants::TyRef(_, ref ty) = cx.tables.expr_ty_adjusted(expr).sty,
let ty::TypeVariants::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),
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is_copy(cx, vec_type(cx.tables.expr_ty_adjusted(arg)), cx.tcx.map.get_parent(expr.id)),
], {
// report the error around the `vec!` not inside `<std macros>:`
let span = cx.sess().codemap().source_callsite(arg.span);
check_vec_macro(cx, &vec_args, span);
}}
}
}
fn check_vec_macro(cx: &LateContext, vec_args: &higher::VecArgs, span: Span) {
let snippet = match *vec_args {
higher::VecArgs::Repeat(elem, len) => {
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if ConstContext::with_tables(cx.tcx, cx.tables).eval(len, ExprTypeChecked).is_ok() {
format!("&[{}; {}]", snippet(cx, elem.span, "elem"), snippet(cx, len.span, "len")).into()
} else {
return;
}
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},
higher::VecArgs::Vec(args) => {
if let Some(last) = args.iter().last() {
let span = Span {
lo: args[0].span.lo,
hi: last.span.hi,
expn_id: args[0].span.expn_id,
};
format!("&[{}]", snippet(cx, span, "..")).into()
} else {
"&[]".into()
}
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},
};
span_lint_and_then(cx, USELESS_VEC, span, "useless use of `vec!`", |db| {
db.span_suggestion(span, "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) -> ty::Ty {
if let ty::TyAdt(_, substs) = ty.sty {
substs.type_at(0)
} else {
panic!("The type of `vec!` is a not a struct?");
}
}