117 lines
3.5 KiB
Rust
117 lines
3.5 KiB
Rust
use rustc::lint::*;
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use rustc::ty::TypeVariants;
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use rustc::hir::*;
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use syntax::codemap::Span;
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use syntax::ptr::P;
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use utils::{is_expn_of, match_path, paths, recover_for_loop, snippet, span_lint_and_then};
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/// **What it does:** This lint warns about using `&vec![..]` when using `&[..]` would 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 UselessVec;
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impl LintPass for UselessVec {
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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 LateLintPass for UselessVec {
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fn check_expr(&mut self, cx: &LateContext, expr: &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 TypeVariants::TyRef(_, ref ty) = cx.tcx.expr_ty_adjusted(expr).sty,
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let TypeVariants::TySlice(..) = ty.ty.sty,
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let ExprAddrOf(_, ref addressee) = expr.node,
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], {
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check_vec_macro(cx, addressee, expr.span);
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}}
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// search for `for _ in vec![…]`
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if let Some((_, arg, _)) = recover_for_loop(expr) {
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// report the error around the `vec!` not inside `<std macros>:`
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let span = cx.sess().codemap().source_callsite(arg.span);
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check_vec_macro(cx, arg, span);
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}
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}
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}
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fn check_vec_macro(cx: &LateContext, vec: &Expr, span: Span) {
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if let Some(vec_args) = unexpand_vec(cx, vec) {
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let snippet = match vec_args {
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VecArgs::Repeat(elem, len) => {
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format!("&[{}; {}]", snippet(cx, elem.span, "elem"), snippet(cx, len.span, "len")).into()
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}
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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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expn_id: args[0].span.expn_id,
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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_then(cx, USELESS_VEC, span, "useless use of `vec!`", |db| {
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db.span_suggestion(span, "you can use a slice directly", snippet);
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});
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}
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}
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/// Represent the pre-expansion arguments of a `vec!` invocation.
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pub enum VecArgs<'a> {
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/// `vec![elem; len]`
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Repeat(&'a P<Expr>, &'a P<Expr>),
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/// `vec![a, b, c]`
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Vec(&'a [P<Expr>]),
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}
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/// Returns the arguments of the `vec!` macro if this expression was expanded from `vec!`.
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pub fn unexpand_vec<'e>(cx: &LateContext, expr: &'e Expr) -> Option<VecArgs<'e>> {
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if_let_chain!{[
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let ExprCall(ref fun, ref args) = expr.node,
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let ExprPath(_, ref path) = fun.node,
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is_expn_of(cx, fun.span, "vec").is_some()
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], {
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return if match_path(path, &paths::VEC_FROM_ELEM) && args.len() == 2 {
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// `vec![elem; size]` case
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Some(VecArgs::Repeat(&args[0], &args[1]))
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}
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else if match_path(path, &["into_vec"]) && args.len() == 1 {
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// `vec![a, b, c]` case
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if_let_chain!{[
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let ExprBox(ref boxed) = args[0].node,
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let ExprVec(ref args) = boxed.node
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], {
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return Some(VecArgs::Vec(&*args));
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}}
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None
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}
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else {
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None
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};
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}}
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None
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}
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