rust-clippy/clippy_lints/src/attrs.rs

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//! checks for attributes
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use crate::utils::{
first_line_of_span, is_present_in_source, match_panic_def_id, snippet_opt, span_lint, span_lint_and_help,
span_lint_and_sugg, span_lint_and_then, without_block_comments,
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};
use if_chain::if_chain;
use rustc_ast::{AttrKind, AttrStyle, Attribute, Lit, LitKind, MetaItemKind, NestedMetaItem};
use rustc_errors::Applicability;
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use rustc_hir::{
Block, Expr, ExprKind, ImplItem, ImplItemKind, Item, ItemKind, StmtKind, TraitFn, TraitItem, TraitItemKind,
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};
use rustc_lint::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
use rustc_span::sym;
use rustc_span::symbol::{Symbol, SymbolStr};
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use semver::Version;
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static UNIX_SYSTEMS: &[&str] = &[
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"android",
"dragonfly",
"emscripten",
"freebsd",
"fuchsia",
"haiku",
"illumos",
"ios",
"l4re",
"linux",
"macos",
"netbsd",
"openbsd",
"redox",
"solaris",
"vxworks",
];
// NOTE: windows is excluded from the list because it's also a valid target family.
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static NON_UNIX_SYSTEMS: &[&str] = &["hermit", "none", "wasi"];
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declare_clippy_lint! {
/// **What it does:** Checks for items annotated with `#[inline(always)]`,
/// unless the annotated function is empty or simply panics.
///
/// **Why is this bad?** While there are valid uses of this annotation (and once
/// you know when to use it, by all means `allow` this lint), it's a common
/// newbie-mistake to pepper one's code with it.
///
/// As a rule of thumb, before slapping `#[inline(always)]` on a function,
/// measure if that additional function call really affects your runtime profile
/// sufficiently to make up for the increase in compile time.
///
/// **Known problems:** False positives, big time. This lint is meant to be
/// deactivated by everyone doing serious performance work. This means having
/// done the measurement.
///
/// **Example:**
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/// ```ignore
/// #[inline(always)]
/// fn not_quite_hot_code(..) { ... }
/// ```
pub INLINE_ALWAYS,
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pedantic,
"use of `#[inline(always)]`"
}
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declare_clippy_lint! {
/// **What it does:** Checks for `extern crate` and `use` items annotated with
/// lint attributes.
///
/// This lint permits `#[allow(unused_imports)]`, `#[allow(deprecated)]`,
/// `#[allow(unreachable_pub)]`, `#[allow(clippy::wildcard_imports)]` and
/// `#[allow(clippy::enum_glob_use)]` on `use` items and `#[allow(unused_imports)]` on
/// `extern crate` items with a `#[macro_use]` attribute.
///
/// **Why is this bad?** Lint attributes have no effect on crate imports. Most
/// likely a `!` was forgotten.
///
/// **Known problems:** None.
///
/// **Example:**
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/// ```ignore
/// // Bad
/// #[deny(dead_code)]
/// extern crate foo;
/// #[forbid(dead_code)]
/// use foo::bar;
///
/// // Ok
/// #[allow(unused_imports)]
/// use foo::baz;
/// #[allow(unused_imports)]
/// #[macro_use]
/// extern crate baz;
/// ```
pub USELESS_ATTRIBUTE,
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correctness,
"use of lint attributes on `extern crate` items"
}
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declare_clippy_lint! {
/// **What it does:** Checks for `#[deprecated]` annotations with a `since`
/// field that is not a valid semantic version.
///
/// **Why is this bad?** For checking the version of the deprecation, it must be
/// a valid semver. Failing that, the contained information is useless.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// #[deprecated(since = "forever")]
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/// fn something_else() { /* ... */ }
/// ```
pub DEPRECATED_SEMVER,
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correctness,
"use of `#[deprecated(since = \"x\")]` where x is not semver"
}
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declare_clippy_lint! {
/// **What it does:** Checks for empty lines after outer attributes
///
/// **Why is this bad?**
/// Most likely the attribute was meant to be an inner attribute using a '!'.
/// If it was meant to be an outer attribute, then the following item
/// should not be separated by empty lines.
///
/// **Known problems:** Can cause false positives.
///
/// From the clippy side it's difficult to detect empty lines between an attributes and the
/// following item because empty lines and comments are not part of the AST. The parsing
/// currently works for basic cases but is not perfect.
///
/// **Example:**
/// ```rust
/// // Good (as inner attribute)
/// #![allow(dead_code)]
///
/// fn this_is_fine() { }
///
/// // Bad
/// #[allow(dead_code)]
///
/// fn not_quite_good_code() { }
///
/// // Good (as outer attribute)
/// #[allow(dead_code)]
/// fn this_is_fine_too() { }
/// ```
pub EMPTY_LINE_AFTER_OUTER_ATTR,
nursery,
"empty line after outer attribute"
}
declare_clippy_lint! {
/// **What it does:** Checks for `warn`/`deny`/`forbid` attributes targeting the whole clippy::restriction category.
///
/// **Why is this bad?** Restriction lints sometimes are in contrast with other lints or even go against idiomatic rust.
/// These lints should only be enabled on a lint-by-lint basis and with careful consideration.
///
/// **Known problems:** None.
///
/// **Example:**
/// Bad:
/// ```rust
/// #![deny(clippy::restriction)]
/// ```
///
/// Good:
/// ```rust
/// #![deny(clippy::as_conversions)]
/// ```
pub BLANKET_CLIPPY_RESTRICTION_LINTS,
style,
"enabling the complete restriction group"
}
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declare_clippy_lint! {
/// **What it does:** Checks for `#[cfg_attr(rustfmt, rustfmt_skip)]` and suggests to replace it
/// with `#[rustfmt::skip]`.
///
/// **Why is this bad?** Since tool_attributes ([rust-lang/rust#44690](https://github.com/rust-lang/rust/issues/44690))
/// are stable now, they should be used instead of the old `cfg_attr(rustfmt)` attributes.
///
/// **Known problems:** This lint doesn't detect crate level inner attributes, because they get
/// processed before the PreExpansionPass lints get executed. See
/// [#3123](https://github.com/rust-lang/rust-clippy/pull/3123#issuecomment-422321765)
///
/// **Example:**
///
/// Bad:
/// ```rust
/// #[cfg_attr(rustfmt, rustfmt_skip)]
/// fn main() { }
/// ```
///
/// Good:
/// ```rust
/// #[rustfmt::skip]
/// fn main() { }
/// ```
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pub DEPRECATED_CFG_ATTR,
complexity,
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"usage of `cfg_attr(rustfmt)` instead of tool attributes"
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}
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declare_clippy_lint! {
/// **What it does:** Checks for cfg attributes having operating systems used in target family position.
///
/// **Why is this bad?** The configuration option will not be recognised and the related item will not be included
/// by the conditional compilation engine.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// Bad:
/// ```rust
/// #[cfg(linux)]
/// fn conditional() { }
/// ```
///
/// Good:
/// ```rust
/// #[cfg(target_os = "linux")]
/// fn conditional() { }
/// ```
///
/// Or:
/// ```rust
/// #[cfg(unix)]
/// fn conditional() { }
/// ```
/// Check the [Rust Reference](https://doc.rust-lang.org/reference/conditional-compilation.html#target_os) for more details.
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pub MISMATCHED_TARGET_OS,
correctness,
"usage of `cfg(operating_system)` instead of `cfg(target_os = \"operating_system\")`"
}
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declare_lint_pass!(Attributes => [
INLINE_ALWAYS,
DEPRECATED_SEMVER,
USELESS_ATTRIBUTE,
BLANKET_CLIPPY_RESTRICTION_LINTS,
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]);
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impl<'tcx> LateLintPass<'tcx> for Attributes {
fn check_attribute(&mut self, cx: &LateContext<'tcx>, attr: &'tcx Attribute) {
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if let Some(items) = &attr.meta_item_list() {
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if let Some(ident) = attr.ident() {
let ident = &*ident.as_str();
match ident {
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"allow" | "warn" | "deny" | "forbid" => {
check_clippy_lint_names(cx, ident, items);
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},
_ => {},
}
if items.is_empty() || !attr.has_name(sym::deprecated) {
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return;
}
for item in items {
if_chain! {
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if let NestedMetaItem::MetaItem(mi) = &item;
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if let MetaItemKind::NameValue(lit) = &mi.kind;
if mi.has_name(sym::since);
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then {
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check_semver(cx, item.span(), lit);
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}
}
}
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}
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}
}
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fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
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let attrs = cx.tcx.hir().attrs(item.hir_id());
if is_relevant_item(cx, item) {
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check_attrs(cx, item.span, item.ident.name, attrs)
}
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match item.kind {
ItemKind::ExternCrate(..) | ItemKind::Use(..) => {
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let skip_unused_imports = attrs.iter().any(|attr| attr.has_name(sym::macro_use));
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for attr in attrs {
if in_external_macro(cx.sess(), attr.span) {
return;
}
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if let Some(lint_list) = &attr.meta_item_list() {
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if let Some(ident) = attr.ident() {
match &*ident.as_str() {
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"allow" | "warn" | "deny" | "forbid" => {
// permit `unused_imports`, `deprecated`, `unreachable_pub`,
// `clippy::wildcard_imports`, and `clippy::enum_glob_use` for `use` items
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// and `unused_imports` for `extern crate` items with `macro_use`
for lint in lint_list {
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match item.kind {
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ItemKind::Use(..) => {
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if is_word(lint, sym!(unused_imports))
|| is_word(lint, sym::deprecated)
|| is_word(lint, sym!(unreachable_pub))
|| is_word(lint, sym!(unused))
|| extract_clippy_lint(lint)
.map_or(false, |s| s == "wildcard_imports")
|| extract_clippy_lint(lint).map_or(false, |s| s == "enum_glob_use")
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{
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return;
}
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},
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ItemKind::ExternCrate(..) => {
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if is_word(lint, sym!(unused_imports)) && skip_unused_imports {
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return;
}
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if is_word(lint, sym!(unused_extern_crates)) {
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return;
}
},
_ => {},
}
}
let line_span = first_line_of_span(cx, attr.span);
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if let Some(mut sugg) = snippet_opt(cx, line_span) {
if sugg.contains("#[") {
span_lint_and_then(
cx,
USELESS_ATTRIBUTE,
line_span,
"useless lint attribute",
|diag| {
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sugg = sugg.replacen("#[", "#![", 1);
diag.span_suggestion(
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line_span,
"if you just forgot a `!`, use",
sugg,
Applicability::MaybeIncorrect,
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);
},
);
}
}
},
_ => {},
}
}
}
}
},
_ => {},
}
}
fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
if is_relevant_impl(cx, item) {
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check_attrs(cx, item.span, item.ident.name, cx.tcx.hir().attrs(item.hir_id()))
}
}
fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
if is_relevant_trait(cx, item) {
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check_attrs(cx, item.span, item.ident.name, cx.tcx.hir().attrs(item.hir_id()))
}
}
}
/// Returns the lint name if it is clippy lint.
fn extract_clippy_lint(lint: &NestedMetaItem) -> Option<SymbolStr> {
if_chain! {
if let Some(meta_item) = lint.meta_item();
if meta_item.path.segments.len() > 1;
if let tool_name = meta_item.path.segments[0].ident;
if tool_name.name == sym::clippy;
let lint_name = meta_item.path.segments.last().unwrap().ident.name;
then {
return Some(lint_name.as_str());
}
}
None
}
fn check_clippy_lint_names(cx: &LateContext<'_>, ident: &str, items: &[NestedMetaItem]) {
for lint in items {
if let Some(lint_name) = extract_clippy_lint(lint) {
if lint_name == "restriction" && ident != "allow" {
span_lint_and_help(
cx,
BLANKET_CLIPPY_RESTRICTION_LINTS,
lint.span(),
"restriction lints are not meant to be all enabled",
None,
"try enabling only the lints you really need",
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);
}
}
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}
}
fn is_relevant_item(cx: &LateContext<'_>, item: &Item<'_>) -> bool {
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if let ItemKind::Fn(_, _, eid) = item.kind {
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is_relevant_expr(cx, cx.tcx.typeck_body(eid), &cx.tcx.hir().body(eid).value)
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} else {
true
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}
}
fn is_relevant_impl(cx: &LateContext<'_>, item: &ImplItem<'_>) -> bool {
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match item.kind {
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ImplItemKind::Fn(_, eid) => is_relevant_expr(cx, cx.tcx.typeck_body(eid), &cx.tcx.hir().body(eid).value),
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_ => false,
}
}
fn is_relevant_trait(cx: &LateContext<'_>, item: &TraitItem<'_>) -> bool {
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match item.kind {
TraitItemKind::Fn(_, TraitFn::Required(_)) => true,
TraitItemKind::Fn(_, TraitFn::Provided(eid)) => {
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is_relevant_expr(cx, cx.tcx.typeck_body(eid), &cx.tcx.hir().body(eid).value)
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},
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_ => false,
}
}
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fn is_relevant_block(cx: &LateContext<'_>, typeck_results: &ty::TypeckResults<'_>, block: &Block<'_>) -> bool {
block.stmts.first().map_or(
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block
.expr
.as_ref()
.map_or(false, |e| is_relevant_expr(cx, typeck_results, e)),
|stmt| match &stmt.kind {
StmtKind::Local(_) => true,
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StmtKind::Expr(expr) | StmtKind::Semi(expr) => is_relevant_expr(cx, typeck_results, expr),
_ => false,
},
)
}
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fn is_relevant_expr(cx: &LateContext<'_>, typeck_results: &ty::TypeckResults<'_>, expr: &Expr<'_>) -> bool {
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match &expr.kind {
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ExprKind::Block(block, _) => is_relevant_block(cx, typeck_results, block),
ExprKind::Ret(Some(e)) => is_relevant_expr(cx, typeck_results, e),
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ExprKind::Ret(None) | ExprKind::Break(_, None) => false,
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ExprKind::Call(path_expr, _) => {
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if let ExprKind::Path(qpath) = &path_expr.kind {
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typeck_results
.qpath_res(qpath, path_expr.hir_id)
.opt_def_id()
.map_or(true, |fun_id| !match_panic_def_id(cx, fun_id))
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} else {
true
}
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},
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_ => true,
}
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}
fn check_attrs(cx: &LateContext<'_>, span: Span, name: Symbol, attrs: &[Attribute]) {
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if span.from_expansion() {
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return;
}
for attr in attrs {
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if let Some(values) = attr.meta_item_list() {
if values.len() != 1 || !attr.has_name(sym::inline) {
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continue;
}
if is_word(&values[0], sym::always) {
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span_lint(
cx,
INLINE_ALWAYS,
attr.span,
&format!(
"you have declared `#[inline(always)]` on `{}`. This is usually a bad idea",
name
),
);
}
}
}
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}
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fn check_semver(cx: &LateContext<'_>, span: Span, lit: &Lit) {
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if let LitKind::Str(is, _) = lit.kind {
if Version::parse(&is.as_str()).is_ok() {
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return;
}
}
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span_lint(
cx,
DEPRECATED_SEMVER,
span,
"the since field must contain a semver-compliant version",
);
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}
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fn is_word(nmi: &NestedMetaItem, expected: Symbol) -> bool {
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if let NestedMetaItem::MetaItem(mi) = &nmi {
mi.is_word() && mi.has_name(expected)
} else {
false
}
}
declare_lint_pass!(EarlyAttributes => [
DEPRECATED_CFG_ATTR,
MISMATCHED_TARGET_OS,
EMPTY_LINE_AFTER_OUTER_ATTR,
]);
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impl EarlyLintPass for EarlyAttributes {
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fn check_item(&mut self, cx: &EarlyContext<'_>, item: &rustc_ast::Item) {
check_empty_line_after_outer_attr(cx, item);
}
fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &Attribute) {
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check_deprecated_cfg_attr(cx, attr);
check_mismatched_target_os(cx, attr);
}
}
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fn check_empty_line_after_outer_attr(cx: &EarlyContext<'_>, item: &rustc_ast::Item) {
for attr in &item.attrs {
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let attr_item = if let AttrKind::Normal(ref attr, _) = attr.kind {
attr
} else {
return;
};
if attr.style == AttrStyle::Outer {
if attr_item.args.inner_tokens().is_empty() || !is_present_in_source(cx, attr.span) {
return;
}
let begin_of_attr_to_item = Span::new(attr.span.lo(), item.span.lo(), item.span.ctxt());
let end_of_attr_to_item = Span::new(attr.span.hi(), item.span.lo(), item.span.ctxt());
if let Some(snippet) = snippet_opt(cx, end_of_attr_to_item) {
let lines = snippet.split('\n').collect::<Vec<_>>();
let lines = without_block_comments(lines);
if lines.iter().filter(|l| l.trim().is_empty()).count() > 2 {
span_lint(
cx,
EMPTY_LINE_AFTER_OUTER_ATTR,
begin_of_attr_to_item,
"found an empty line after an outer attribute. \
Perhaps you forgot to add a `!` to make it an inner attribute?",
);
}
}
}
}
}
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fn check_deprecated_cfg_attr(cx: &EarlyContext<'_>, attr: &Attribute) {
if_chain! {
// check cfg_attr
if attr.has_name(sym::cfg_attr);
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if let Some(items) = attr.meta_item_list();
if items.len() == 2;
// check for `rustfmt`
if let Some(feature_item) = items[0].meta_item();
if feature_item.has_name(sym::rustfmt);
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// check for `rustfmt_skip` and `rustfmt::skip`
if let Some(skip_item) = &items[1].meta_item();
if skip_item.has_name(sym!(rustfmt_skip)) ||
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skip_item.path.segments.last().expect("empty path in attribute").ident.name == sym!(skip);
// Only lint outer attributes, because custom inner attributes are unstable
// Tracking issue: https://github.com/rust-lang/rust/issues/54726
if let AttrStyle::Outer = attr.style;
then {
span_lint_and_sugg(
cx,
DEPRECATED_CFG_ATTR,
attr.span,
"`cfg_attr` is deprecated for rustfmt and got replaced by tool attributes",
"use",
"#[rustfmt::skip]".to_string(),
Applicability::MachineApplicable,
);
}
}
}
fn check_mismatched_target_os(cx: &EarlyContext<'_>, attr: &Attribute) {
fn find_os(name: &str) -> Option<&'static str> {
UNIX_SYSTEMS
.iter()
.chain(NON_UNIX_SYSTEMS.iter())
.find(|&&os| os == name)
.copied()
}
fn is_unix(name: &str) -> bool {
UNIX_SYSTEMS.iter().any(|&os| os == name)
}
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fn find_mismatched_target_os(items: &[NestedMetaItem]) -> Vec<(&str, Span)> {
let mut mismatched = Vec::new();
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for item in items {
if let NestedMetaItem::MetaItem(meta) = item {
match &meta.kind {
MetaItemKind::List(list) => {
mismatched.extend(find_mismatched_target_os(&list));
},
MetaItemKind::Word => {
if_chain! {
if let Some(ident) = meta.ident();
if let Some(os) = find_os(&*ident.name.as_str());
then {
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mismatched.push((os, ident.span));
}
}
},
_ => {},
}
}
}
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mismatched
}
if_chain! {
if attr.has_name(sym::cfg);
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if let Some(list) = attr.meta_item_list();
let mismatched = find_mismatched_target_os(&list);
if !mismatched.is_empty();
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then {
let mess = "operating system used in target family position";
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span_lint_and_then(cx, MISMATCHED_TARGET_OS, attr.span, &mess, |diag| {
// Avoid showing the unix suggestion multiple times in case
// we have more than one mismatch for unix-like systems
let mut unix_suggested = false;
for (os, span) in mismatched {
let sugg = format!("target_os = \"{}\"", os);
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diag.span_suggestion(span, "try", sugg, Applicability::MaybeIncorrect);
if !unix_suggested && is_unix(os) {
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diag.help("did you mean `unix`?");
unix_suggested = true;
}
}
});
}
}
}