83 lines
3.2 KiB
Rust
83 lines
3.2 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_help;
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use clippy_utils::ty::{is_type_diagnostic_item, ty_from_hir_ty};
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use rustc_hir::{self as hir, AmbigArg, HirId, ItemKind, Node};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty::layout::LayoutOf as _;
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use rustc_middle::ty::{self, TypeVisitableExt};
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use rustc_session::declare_lint_pass;
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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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/// Checks for maps with zero-sized value types anywhere in the code.
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///
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/// ### Why is this bad?
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/// Since there is only a single value for a zero-sized type, a map
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/// containing zero sized values is effectively a set. Using a set in that case improves
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/// readability and communicates intent more clearly.
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///
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/// ### Known problems
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/// * A zero-sized type cannot be recovered later if it contains private fields.
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/// * This lints the signature of public items
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///
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/// ### Example
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/// ```no_run
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/// # use std::collections::HashMap;
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/// fn unique_words(text: &str) -> HashMap<&str, ()> {
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/// todo!();
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/// }
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/// ```
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/// Use instead:
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/// ```no_run
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/// # use std::collections::HashSet;
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/// fn unique_words(text: &str) -> HashSet<&str> {
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/// todo!();
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/// }
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/// ```
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#[clippy::version = "1.50.0"]
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pub ZERO_SIZED_MAP_VALUES,
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pedantic,
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"usage of map with zero-sized value type"
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}
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declare_lint_pass!(ZeroSizedMapValues => [ZERO_SIZED_MAP_VALUES]);
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impl LateLintPass<'_> for ZeroSizedMapValues {
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fn check_ty<'tcx>(&mut self, cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'tcx, AmbigArg>) {
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if !hir_ty.span.from_expansion()
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&& !in_trait_impl(cx, hir_ty.hir_id)
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// We don't care about infer vars
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&& let ty = ty_from_hir_ty(cx, hir_ty.as_unambig_ty())
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&& (is_type_diagnostic_item(cx, ty, sym::HashMap) || is_type_diagnostic_item(cx, ty, sym::BTreeMap))
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&& let ty::Adt(_, args) = ty.kind()
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&& let ty = args.type_at(1)
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// Ensure that no type information is missing, to avoid a delayed bug in the compiler if this is not the case.
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// This might happen when computing a reference/pointer metadata on a type for which we
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// cannot check if it is `Sized` or not, such as an incomplete associated type in a
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// type alias. See an example in `issue14822()` of `tests/ui/zero_sized_hashmap_values.rs`.
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&& !ty.has_non_region_param()
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&& let Ok(layout) = cx.layout_of(ty)
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&& layout.is_zst()
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{
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span_lint_and_help(
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cx,
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ZERO_SIZED_MAP_VALUES,
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hir_ty.span,
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"map with zero-sized value type",
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None,
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"consider using a set instead",
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);
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}
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}
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}
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fn in_trait_impl(cx: &LateContext<'_>, hir_id: HirId) -> bool {
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let parent_id = cx.tcx.hir_get_parent_item(hir_id);
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let second_parent_id = cx.tcx.hir_get_parent_item(parent_id.into()).def_id;
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if let Node::Item(item) = cx.tcx.hir_node_by_def_id(second_parent_id)
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&& let ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = item.kind
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{
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return true;
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}
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false
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}
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