46 lines
1.9 KiB
Rust
46 lines
1.9 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::source::snippet_with_applicability;
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use clippy_utils::ty::walk_ptrs_ty_depth;
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use clippy_utils::{get_parent_expr, match_trait_method, paths};
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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 super::USELESS_ASREF;
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/// Checks for the `USELESS_ASREF` lint.
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pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, call_name: &str, recvr: &hir::Expr<'_>) {
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// when we get here, we've already checked that the call name is "as_ref" or "as_mut"
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// check if the call is to the actual `AsRef` or `AsMut` trait
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if match_trait_method(cx, expr, &paths::ASREF_TRAIT) || match_trait_method(cx, expr, &paths::ASMUT_TRAIT) {
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// check if the type after `as_ref` or `as_mut` is the same as before
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let rcv_ty = cx.typeck_results().expr_ty(recvr);
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let res_ty = cx.typeck_results().expr_ty(expr);
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let (base_res_ty, res_depth) = walk_ptrs_ty_depth(res_ty);
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let (base_rcv_ty, rcv_depth) = walk_ptrs_ty_depth(rcv_ty);
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if base_rcv_ty == base_res_ty && rcv_depth >= res_depth {
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// allow the `as_ref` or `as_mut` if it is followed by another method call
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if_chain! {
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if let Some(parent) = get_parent_expr(cx, expr);
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if let hir::ExprKind::MethodCall(_, ref span, _, _) = parent.kind;
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if span != &expr.span;
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then {
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return;
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}
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}
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let mut applicability = Applicability::MachineApplicable;
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span_lint_and_sugg(
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cx,
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USELESS_ASREF,
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expr.span,
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&format!("this call to `{}` does nothing", call_name),
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"try this",
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snippet_with_applicability(cx, recvr.span, "..", &mut applicability).to_string(),
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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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