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use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::ty::{is_normalizable, is_type_diagnostic_item};
use if_chain::if_chain;
use rustc_hir::{self as hir, HirId, ItemKind, Node};
use rustc_hir_analysis::hir_ty_to_ty;
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::layout::LayoutOf as _;
use rustc_middle::ty::{Adt, Ty, TypeVisitableExt};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for maps with zero-sized value types anywhere in the code.
///
/// ### Why is this bad?
/// Since there is only a single value for a zero-sized type, a map
/// containing zero sized values is effectively a set. Using a set in that case improves
/// readability and communicates intent more clearly.
///
/// ### Known problems
/// * A zero-sized type cannot be recovered later if it contains private fields.
/// * This lints the signature of public items
///
/// ### Example
/// ```rust
/// # use std::collections::HashMap;
/// fn unique_words(text: &str) -> HashMap<&str, ()> {
/// todo!();
/// }
/// ```
/// Use instead:
/// ```rust
/// # use std::collections::HashSet;
/// fn unique_words(text: &str) -> HashSet<&str> {
/// todo!();
/// }
/// ```
#[clippy::version = "1.50.0"]
pub ZERO_SIZED_MAP_VALUES,
pedantic,
"usage of map with zero-sized value type"
}
declare_lint_pass!(ZeroSizedMapValues => [ZERO_SIZED_MAP_VALUES]);
impl LateLintPass<'_> for ZeroSizedMapValues {
fn check_ty(&mut self, cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>) {
if_chain! {
if !hir_ty.span.from_expansion();
if !in_trait_impl(cx, hir_ty.hir_id);
let ty = ty_from_hir_ty(cx, hir_ty);
if is_type_diagnostic_item(cx, ty, sym::HashMap) || is_type_diagnostic_item(cx, ty, sym::BTreeMap);
if let Adt(_, substs) = ty.kind();
let ty = substs.type_at(1);
// Fixes https://github.com/rust-lang/rust-clippy/issues/7447 because of
// https://github.com/rust-lang/rust/blob/master/compiler/rustc_middle/src/ty/sty.rs#L968
if !ty.has_escaping_bound_vars();
// Do this to prevent `layout_of` crashing, being unable to fully normalize `ty`.
if is_normalizable(cx, cx.param_env, ty);
if let Ok(layout) = cx.layout_of(ty);
if layout.is_zst();
then {
span_lint_and_help(cx, ZERO_SIZED_MAP_VALUES, hir_ty.span, "map with zero-sized value type", None, "consider using a set instead");
}
}
}
}
fn in_trait_impl(cx: &LateContext<'_>, hir_id: HirId) -> bool {
let parent_id = cx.tcx.hir().get_parent_item(hir_id);
let second_parent_id = cx.tcx.hir().get_parent_item(parent_id.into()).def_id;
if let Some(Node::Item(item)) = cx.tcx.hir().find_by_def_id(second_parent_id) {
if let ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = item.kind {
return true;
}
}
false
}
fn ty_from_hir_ty<'tcx>(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Ty<'tcx> {
cx.maybe_typeck_results()
.and_then(|results| {
if results.hir_owner == hir_ty.hir_id.owner {
results.node_type_opt(hir_ty.hir_id)
} else {
None
}
})
.unwrap_or_else(|| hir_ty_to_ty(cx.tcx, hir_ty))
}
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