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|
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::msrvs::{self, Msrv};
use clippy_utils::source::indent_of;
use clippy_utils::{is_default_equivalent, peel_blocks};
use rustc_errors::Applicability;
use rustc_hir::{
def::{CtorKind, CtorOf, DefKind, Res},
Body, Expr, ExprKind, GenericArg, Impl, ImplItemKind, Item, ItemKind, Node, PathSegment, QPath, Ty, TyKind,
};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::{AdtDef, DefIdTree};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Detects manual `std::default::Default` implementations that are identical to a derived implementation.
///
/// ### Why is this bad?
/// It is less concise.
///
/// ### Example
/// ```rust
/// struct Foo {
/// bar: bool
/// }
///
/// impl Default for Foo {
/// fn default() -> Self {
/// Self {
/// bar: false
/// }
/// }
/// }
/// ```
///
/// Use instead:
/// ```rust
/// #[derive(Default)]
/// struct Foo {
/// bar: bool
/// }
/// ```
///
/// ### Known problems
/// Derive macros [sometimes use incorrect bounds](https://github.com/rust-lang/rust/issues/26925)
/// in generic types and the user defined `impl` may be more generalized or
/// specialized than what derive will produce. This lint can't detect the manual `impl`
/// has exactly equal bounds, and therefore this lint is disabled for types with
/// generic parameters.
#[clippy::version = "1.57.0"]
pub DERIVABLE_IMPLS,
complexity,
"manual implementation of the `Default` trait which is equal to a derive"
}
pub struct DerivableImpls {
msrv: Msrv,
}
impl DerivableImpls {
#[must_use]
pub fn new(msrv: Msrv) -> Self {
DerivableImpls { msrv }
}
}
impl_lint_pass!(DerivableImpls => [DERIVABLE_IMPLS]);
fn is_path_self(e: &Expr<'_>) -> bool {
if let ExprKind::Path(QPath::Resolved(_, p)) = e.kind {
matches!(p.res, Res::SelfCtor(..) | Res::Def(DefKind::Ctor(..), _))
} else {
false
}
}
fn check_struct<'tcx>(
cx: &LateContext<'tcx>,
item: &'tcx Item<'_>,
self_ty: &Ty<'_>,
func_expr: &Expr<'_>,
adt_def: AdtDef<'_>,
) {
if let TyKind::Path(QPath::Resolved(_, p)) = self_ty.kind {
if let Some(PathSegment { args: Some(a), .. }) = p.segments.last() {
for arg in a.args {
if !matches!(arg, GenericArg::Lifetime(_)) {
return;
}
}
}
}
let should_emit = match peel_blocks(func_expr).kind {
ExprKind::Tup(fields) => fields.iter().all(|e| is_default_equivalent(cx, e)),
ExprKind::Call(callee, args) if is_path_self(callee) => args.iter().all(|e| is_default_equivalent(cx, e)),
ExprKind::Struct(_, fields, _) => fields.iter().all(|ef| is_default_equivalent(cx, ef.expr)),
_ => false,
};
if should_emit {
let struct_span = cx.tcx.def_span(adt_def.did());
span_lint_and_then(cx, DERIVABLE_IMPLS, item.span, "this `impl` can be derived", |diag| {
diag.span_suggestion_hidden(
item.span,
"remove the manual implementation...",
String::new(),
Applicability::MachineApplicable,
);
diag.span_suggestion(
struct_span.shrink_to_lo(),
"...and instead derive it",
"#[derive(Default)]\n".to_string(),
Applicability::MachineApplicable,
);
});
}
}
fn check_enum<'tcx>(cx: &LateContext<'tcx>, item: &'tcx Item<'_>, func_expr: &Expr<'_>, adt_def: AdtDef<'_>) {
if_chain! {
if let ExprKind::Path(QPath::Resolved(None, p)) = &peel_blocks(func_expr).kind;
if let Res::Def(DefKind::Ctor(CtorOf::Variant, CtorKind::Const), id) = p.res;
if let variant_id = cx.tcx.parent(id);
if let Some(variant_def) = adt_def.variants().iter().find(|v| v.def_id == variant_id);
if variant_def.fields.is_empty();
if !variant_def.is_field_list_non_exhaustive();
then {
let enum_span = cx.tcx.def_span(adt_def.did());
let indent_enum = indent_of(cx, enum_span).unwrap_or(0);
let variant_span = cx.tcx.def_span(variant_def.def_id);
let indent_variant = indent_of(cx, variant_span).unwrap_or(0);
span_lint_and_then(
cx,
DERIVABLE_IMPLS,
item.span,
"this `impl` can be derived",
|diag| {
diag.span_suggestion_hidden(
item.span,
"remove the manual implementation...",
String::new(),
Applicability::MachineApplicable
);
diag.span_suggestion(
enum_span.shrink_to_lo(),
"...and instead derive it...",
format!(
"#[derive(Default)]\n{indent}",
indent = " ".repeat(indent_enum),
),
Applicability::MachineApplicable
);
diag.span_suggestion(
variant_span.shrink_to_lo(),
"...and mark the default variant",
format!(
"#[default]\n{indent}",
indent = " ".repeat(indent_variant),
),
Applicability::MachineApplicable
);
}
);
}
}
}
impl<'tcx> LateLintPass<'tcx> for DerivableImpls {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
if_chain! {
if let ItemKind::Impl(Impl {
of_trait: Some(ref trait_ref),
items: [child],
self_ty,
..
}) = item.kind;
if !cx.tcx.has_attr(item.owner_id.to_def_id(), sym::automatically_derived);
if !item.span.from_expansion();
if let Some(def_id) = trait_ref.trait_def_id();
if cx.tcx.is_diagnostic_item(sym::Default, def_id);
if let impl_item_hir = child.id.hir_id();
if let Some(Node::ImplItem(impl_item)) = cx.tcx.hir().find(impl_item_hir);
if let ImplItemKind::Fn(_, b) = &impl_item.kind;
if let Body { value: func_expr, .. } = cx.tcx.hir().body(*b);
if let Some(adt_def) = cx.tcx.type_of(item.owner_id).ty_adt_def();
if let attrs = cx.tcx.hir().attrs(item.hir_id());
if !attrs.iter().any(|attr| attr.doc_str().is_some());
if let child_attrs = cx.tcx.hir().attrs(impl_item_hir);
if !child_attrs.iter().any(|attr| attr.doc_str().is_some());
then {
if adt_def.is_struct() {
check_struct(cx, item, self_ty, func_expr, adt_def);
} else if adt_def.is_enum() && self.msrv.meets(msrvs::DEFAULT_ENUM_ATTRIBUTE) {
check_enum(cx, item, func_expr, adt_def);
}
}
}
}
extract_msrv_attr!(LateContext);
}
|
