95 lines
3.5 KiB
Rust
95 lines
3.5 KiB
Rust
use clippy_utils::diagnostics::span_lint_and_help;
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use clippy_utils::ty::{is_normalizable, is_type_diagnostic_item};
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use if_chain::if_chain;
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use rustc_hir::{self as hir, 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::{Adt, Ty, TypeVisitable};
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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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use rustc_typeck::hir_ty_to_ty;
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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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/// ```rust
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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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/// ```rust
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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(&mut self, cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>) {
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if_chain! {
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if !hir_ty.span.from_expansion();
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if !in_trait_impl(cx, hir_ty.hir_id);
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let ty = ty_from_hir_ty(cx, hir_ty);
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if is_type_diagnostic_item(cx, ty, sym::HashMap) || is_type_diagnostic_item(cx, ty, sym::BTreeMap);
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if let Adt(_, substs) = ty.kind();
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let ty = substs.type_at(1);
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// Fixes https://github.com/rust-lang/rust-clippy/issues/7447 because of
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// https://github.com/rust-lang/rust/blob/master/compiler/rustc_middle/src/ty/sty.rs#L968
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if !ty.has_escaping_bound_vars();
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// Do this to prevent `layout_of` crashing, being unable to fully normalize `ty`.
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if is_normalizable(cx, cx.param_env, ty);
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if let Ok(layout) = cx.layout_of(ty);
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if layout.is_zst();
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then {
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span_lint_and_help(cx, ZERO_SIZED_MAP_VALUES, hir_ty.span, "map with zero-sized value type", None, "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
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.tcx
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.hir()
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.get_parent_item(cx.tcx.hir().local_def_id_to_hir_id(parent_id));
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if let Some(Node::Item(item)) = cx.tcx.hir().find_by_def_id(second_parent_id) {
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if let ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = item.kind {
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return true;
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}
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}
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false
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}
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fn ty_from_hir_ty<'tcx>(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
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cx.maybe_typeck_results()
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.and_then(|results| {
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if results.hir_owner == hir_ty.hir_id.owner {
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results.node_type_opt(hir_ty.hir_id)
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} else {
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None
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}
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})
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.unwrap_or_else(|| hir_ty_to_ty(cx.tcx, hir_ty))
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}
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