mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-30 06:53:27 +00:00
56 lines
2.2 KiB
Rust
56 lines
2.2 KiB
Rust
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use super::INEFFICIENT_TO_STRING;
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use crate::utils::{match_def_path, paths, snippet_with_applicability, span_lint_and_then, walk_ptrs_ty_depth};
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use if_chain::if_chain;
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use rustc::hir;
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use rustc::lint::LateContext;
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use rustc::ty::{self, Ty};
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use rustc_errors::Applicability;
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/// Checks for the `INEFFICIENT_TO_STRING` lint
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pub fn lint<'tcx>(cx: &LateContext<'_, 'tcx>, expr: &hir::Expr, arg: &hir::Expr, arg_ty: Ty<'tcx>) {
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if_chain! {
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if let Some(to_string_meth_did) = cx.tables.type_dependent_def_id(expr.hir_id);
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if match_def_path(cx, to_string_meth_did, &paths::TO_STRING_METHOD);
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if let Some(substs) = cx.tables.node_substs_opt(expr.hir_id);
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let self_ty = substs.type_at(0);
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let (deref_self_ty, deref_count) = walk_ptrs_ty_depth(self_ty);
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if deref_count >= 1;
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if specializes_tostring(cx, deref_self_ty);
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then {
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span_lint_and_then(
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cx,
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INEFFICIENT_TO_STRING,
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expr.span,
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&format!("calling `to_string` on `{}`", arg_ty),
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|db| {
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db.help(&format!(
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"`{}` implements `ToString` through the blanket impl, but `{}` specializes `ToString` directly",
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self_ty, deref_self_ty
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));
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let mut applicability = Applicability::MachineApplicable;
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let arg_snippet = snippet_with_applicability(cx, arg.span, "..", &mut applicability);
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db.span_suggestion(
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expr.span,
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"try dereferencing the receiver",
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format!("({}{}).to_string()", "*".repeat(deref_count), arg_snippet),
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applicability,
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);
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},
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);
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}
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}
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}
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/// Returns whether `ty` specializes `ToString`.
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/// Currently, these are `str`, `String`, and `Cow<'_, str>`.
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fn specializes_tostring(cx: &LateContext<'_, '_>, ty: Ty<'_>) -> bool {
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match ty.kind {
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ty::Str => true,
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ty::Adt(adt, substs) => {
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match_def_path(cx, adt.did, &paths::STRING)
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|| (match_def_path(cx, adt.did, &paths::COW) && substs.type_at(1).is_str())
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},
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_ => false,
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}
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}
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