64 lines
2.4 KiB
Rust
64 lines
2.4 KiB
Rust
use super::INEFFICIENT_TO_STRING;
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use crate::utils::{
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is_type_diagnostic_item, match_def_path, paths, snippet_with_applicability, span_lint_and_then, walk_ptrs_ty_depth,
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};
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use if_chain::if_chain;
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use rustc_errors::Applicability;
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use rustc_hir as hir;
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use rustc_lint::LateContext;
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use rustc_middle::ty::{self, Ty};
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use rustc_span::sym;
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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.typeck_results().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.typeck_results().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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|diag| {
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diag.help(&format!(
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"`{}` implements `ToString` through a slower blanket impl, but `{}` has a fast specialization of `ToString`",
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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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diag.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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if let ty::Str = ty.kind() {
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return true;
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}
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if is_type_diagnostic_item(cx, ty, sym::string_type) {
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return true;
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}
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if let ty::Adt(adt, substs) = ty.kind() {
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match_def_path(cx, adt.did, &paths::COW) && substs.type_at(1).is_str()
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} else {
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false
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}
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}
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