rust-clippy/clippy_lints/src/vec.rs

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// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use crate::consts::constant;
use crate::utils::{higher, is_copy, snippet_with_applicability, span_lint_and_sugg};
use if_chain::if_chain;
use rustc::hir::*;
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::ty::{self, Ty};
use rustc::{declare_tool_lint, lint_array};
use rustc_errors::Applicability;
use syntax::source_map::Span;
/// **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])
/// ```
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declare_clippy_lint! {
pub USELESS_VEC,
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perf,
"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_chain! {
if let ty::Ref(_, ty, _) = cx.tables.expr_ty_adjusted(expr).sty;
if let ty::Slice(..) = ty.sty;
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if let ExprKind::AddrOf(_, ref addressee) = expr.node;
if let Some(vec_args) = higher::vec_macro(cx, addressee);
then {
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.tables.expr_ty_adjusted(arg)));
then {
// 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 mut applicability = Applicability::MachineApplicable;
let snippet = match *vec_args {
higher::VecArgs::Repeat(elem, len) => {
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if constant(cx, cx.tables, len).is_some() {
format!(
"&[{}; {}]",
snippet_with_applicability(cx, elem.span, "elem", &mut applicability),
snippet_with_applicability(cx, len.span, "len", &mut applicability)
)
} 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_with_applicability(cx, span, "..", &mut applicability))
} 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,
applicability,
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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<'_> {
if let ty::Adt(_, substs) = ty.sty {
substs.type_at(0)
} else {
panic!("The type of `vec!` is a not a struct?");
}
}