rust-clippy/clippy_lints/src/manual_non_exhaustive.rs

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use crate::utils::{get_inner_attr, meets_msrv, snippet_opt, span_lint_and_then};
use if_chain::if_chain;
use rustc_ast::ast::{Attribute, Item, ItemKind, StructField, Variant, VariantData, VisibilityKind};
use rustc_attr as attr;
use rustc_errors::Applicability;
use rustc_lint::{EarlyContext, EarlyLintPass};
use rustc_session::{declare_tool_lint, impl_lint_pass};
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use rustc_span::{sym, Span};
use semver::{Version, VersionReq};
const MANUAL_NON_EXHAUSTIVE_MSRV: Version = Version {
major: 1,
minor: 40,
patch: 0,
pre: Vec::new(),
build: Vec::new(),
};
declare_clippy_lint! {
/// **What it does:** Checks for manual implementations of the non-exhaustive pattern.
///
/// **Why is this bad?** Using the #[non_exhaustive] attribute expresses better the intent
/// and allows possible optimizations when applied to enums.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// struct S {
/// pub a: i32,
/// pub b: i32,
/// _c: (),
/// }
///
/// enum E {
/// A,
/// B,
/// #[doc(hidden)]
/// _C,
/// }
///
/// struct T(pub i32, pub i32, ());
/// ```
/// Use instead:
/// ```rust
/// #[non_exhaustive]
/// struct S {
/// pub a: i32,
/// pub b: i32,
/// }
///
/// #[non_exhaustive]
/// enum E {
/// A,
/// B,
/// }
///
/// #[non_exhaustive]
/// struct T(pub i32, pub i32);
/// ```
pub MANUAL_NON_EXHAUSTIVE,
style,
"manual implementations of the non-exhaustive pattern can be simplified using #[non_exhaustive]"
}
#[derive(Clone)]
pub struct ManualNonExhaustive {
msrv: Option<VersionReq>,
}
impl ManualNonExhaustive {
#[must_use]
pub fn new(msrv: Option<VersionReq>) -> Self {
Self { msrv }
}
}
impl_lint_pass!(ManualNonExhaustive => [MANUAL_NON_EXHAUSTIVE]);
impl EarlyLintPass for ManualNonExhaustive {
fn check_item(&mut self, cx: &EarlyContext<'_>, item: &Item) {
if !meets_msrv(self.msrv.as_ref(), &MANUAL_NON_EXHAUSTIVE_MSRV) {
return;
}
match &item.kind {
ItemKind::Enum(def, _) => {
check_manual_non_exhaustive_enum(cx, item, &def.variants);
},
ItemKind::Struct(variant_data, _) => {
if let VariantData::Unit(..) = variant_data {
return;
}
check_manual_non_exhaustive_struct(cx, item, variant_data);
},
_ => {},
}
}
extract_msrv_attr!(EarlyContext);
}
fn check_manual_non_exhaustive_enum(cx: &EarlyContext<'_>, item: &Item, variants: &[Variant]) {
fn is_non_exhaustive_marker(variant: &Variant) -> bool {
matches!(variant.data, VariantData::Unit(_))
&& variant.ident.as_str().starts_with('_')
&& variant.attrs.iter().any(|a| is_doc_hidden(a))
}
fn is_doc_hidden(attr: &Attribute) -> bool {
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attr.has_name(sym::doc)
&& match attr.meta_item_list() {
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Some(l) => attr::list_contains_name(&l, sym::hidden),
None => false,
}
}
if_chain! {
let mut markers = variants.iter().filter(|v| is_non_exhaustive_marker(v));
if let Some(marker) = markers.next();
if markers.count() == 0 && variants.len() > 1;
then {
span_lint_and_then(
cx,
MANUAL_NON_EXHAUSTIVE,
item.span,
"this seems like a manual implementation of the non-exhaustive pattern",
|diag| {
if_chain! {
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if !item.attrs.iter().any(|attr| attr.has_name(sym::non_exhaustive));
let header_span = cx.sess.source_map().span_until_char(item.span, '{');
if let Some(snippet) = snippet_opt(cx, header_span);
then {
diag.span_suggestion(
header_span,
"add the attribute",
format!("#[non_exhaustive] {}", snippet),
Applicability::Unspecified,
);
}
}
diag.span_help(marker.span, "remove this variant");
});
}
}
}
fn check_manual_non_exhaustive_struct(cx: &EarlyContext<'_>, item: &Item, data: &VariantData) {
fn is_private(field: &StructField) -> bool {
matches!(field.vis.kind, VisibilityKind::Inherited)
}
fn is_non_exhaustive_marker(field: &StructField) -> bool {
is_private(field) && field.ty.kind.is_unit() && field.ident.map_or(true, |n| n.as_str().starts_with('_'))
}
fn find_header_span(cx: &EarlyContext<'_>, item: &Item, data: &VariantData) -> Span {
let delimiter = match data {
VariantData::Struct(..) => '{',
VariantData::Tuple(..) => '(',
VariantData::Unit(_) => unreachable!("`VariantData::Unit` is already handled above"),
};
cx.sess.source_map().span_until_char(item.span, delimiter)
}
let fields = data.fields();
let private_fields = fields.iter().filter(|f| is_private(f)).count();
let public_fields = fields.iter().filter(|f| f.vis.kind.is_pub()).count();
if_chain! {
if private_fields == 1 && public_fields >= 1 && public_fields == fields.len() - 1;
if let Some(marker) = fields.iter().find(|f| is_non_exhaustive_marker(f));
then {
span_lint_and_then(
cx,
MANUAL_NON_EXHAUSTIVE,
item.span,
"this seems like a manual implementation of the non-exhaustive pattern",
|diag| {
if_chain! {
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if !item.attrs.iter().any(|attr| attr.has_name(sym::non_exhaustive));
let header_span = find_header_span(cx, item, data);
if let Some(snippet) = snippet_opt(cx, header_span);
then {
diag.span_suggestion(
header_span,
"add the attribute",
format!("#[non_exhaustive] {}", snippet),
Applicability::Unspecified,
);
}
}
diag.span_help(marker.span, "remove this field");
});
}
}
}