79 lines
2.6 KiB
Rust
79 lines
2.6 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_then;
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use clippy_utils::source::snippet;
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use rustc_errors::Applicability;
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use rustc_hir::{Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::sym;
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declare_clippy_lint! {
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/// ### What it does
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/// Detects `().hash(_)`.
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///
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/// ### Why is this bad?
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/// Hashing a unit value doesn't do anything as the implementation of `Hash` for `()` is a no-op.
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///
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/// ### Example
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/// ```rust
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/// # use std::hash::Hash;
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/// # use std::collections::hash_map::DefaultHasher;
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/// # enum Foo { Empty, WithValue(u8) }
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/// # use Foo::*;
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/// # let mut state = DefaultHasher::new();
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/// # let my_enum = Foo::Empty;
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/// match my_enum {
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/// Empty => ().hash(&mut state),
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/// WithValue(x) => x.hash(&mut state),
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/// }
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/// ```
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/// Use instead:
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/// ```rust
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/// # use std::hash::Hash;
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/// # use std::collections::hash_map::DefaultHasher;
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/// # enum Foo { Empty, WithValue(u8) }
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/// # use Foo::*;
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/// # let mut state = DefaultHasher::new();
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/// # let my_enum = Foo::Empty;
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/// match my_enum {
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/// Empty => 0_u8.hash(&mut state),
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/// WithValue(x) => x.hash(&mut state),
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/// }
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/// ```
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#[clippy::version = "1.58.0"]
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pub UNIT_HASH,
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correctness,
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"hashing a unit value, which does nothing"
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}
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declare_lint_pass!(UnitHash => [UNIT_HASH]);
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impl<'tcx> LateLintPass<'tcx> for UnitHash {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
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if_chain! {
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if let ExprKind::MethodCall(name_ident, args, _) = &expr.kind;
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if name_ident.ident.name == sym::hash;
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if let [recv, state_param] = args;
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if cx.typeck_results().expr_ty(recv).is_unit();
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then {
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span_lint_and_then(
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cx,
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UNIT_HASH,
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expr.span,
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"this call to `hash` on the unit type will do nothing",
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|diag| {
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diag.span_suggestion(
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expr.span,
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"remove the call to `hash` or consider using",
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format!(
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"0_u8.hash({})",
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snippet(cx, state_param.span, ".."),
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),
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Applicability::MaybeIncorrect,
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);
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diag.note("the implementation of `Hash` for `()` is a no-op");
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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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