69 lines
2.4 KiB
Rust
69 lines
2.4 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::source::snippet_with_applicability;
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use clippy_utils::ty::{is_type_lang_item, walk_ptrs_ty_depth};
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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::symbol::{sym, Symbol};
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use super::INEFFICIENT_TO_STRING;
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/// Checks for the `INEFFICIENT_TO_STRING` lint
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pub fn check(
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cx: &LateContext<'_>,
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expr: &hir::Expr<'_>,
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method_name: Symbol,
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receiver: &hir::Expr<'_>,
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args: &[hir::Expr<'_>],
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) {
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if args.is_empty()
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&& method_name == sym::to_string
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&& let Some(to_string_meth_did) = cx.typeck_results().type_dependent_def_id(expr.hir_id)
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&& cx.tcx.is_diagnostic_item(sym::to_string_method, to_string_meth_did)
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&& let Some(args) = cx.typeck_results().node_args_opt(expr.hir_id)
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&& let arg_ty = cx.typeck_results().expr_ty_adjusted(receiver)
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&& let self_ty = args.type_at(0)
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&& let (deref_self_ty, deref_count) = walk_ptrs_ty_depth(self_ty)
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&& deref_count >= 1
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&& specializes_tostring(cx, deref_self_ty)
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{
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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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"`{self_ty}` implements `ToString` through a slower blanket impl, but `{deref_self_ty}` has a fast specialization of `ToString`"
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));
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let mut applicability = Applicability::MachineApplicable;
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let arg_snippet = snippet_with_applicability(cx, receiver.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!("({}{arg_snippet}).to_string()", "*".repeat(deref_count)),
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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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/// 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_lang_item(cx, ty, hir::LangItem::String) {
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return true;
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}
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if let ty::Adt(adt, args) = ty.kind() {
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cx.tcx.is_diagnostic_item(sym::Cow, adt.did()) && args.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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