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rust/compiler/rustc_lint/src/builtin.rs
Aaron Hill fb5fec017b
Combine HasAttrs and HasTokens into AstLike 
When token-based attribute handling is implemeneted in #80689,
we will need to access tokens from `HasAttrs` (to perform
cfg-stripping), and we will to access attributes from `HasTokens` (to
construct a `PreexpTokenStream`).

This PR merges the `HasAttrs` and `HasTokens` traits into a new
`AstLike` trait. The previous `HasAttrs` impls from `Vec<Attribute>` and `AttrVec`
are removed - they aren't attribute targets, so the impls never really
made sense.
2021-02-27 00:14:13 -05:00

2989 lines
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//! Lints in the Rust compiler.
//!
//! This contains lints which can feasibly be implemented as their own
//! AST visitor. Also see `rustc_session::lint::builtin`, which contains the
//! definitions of lints that are emitted directly inside the main compiler.
//!
//! To add a new lint to rustc, declare it here using `declare_lint!()`.
//! Then add code to emit the new lint in the appropriate circumstances.
//! You can do that in an existing `LintPass` if it makes sense, or in a
//! new `LintPass`, or using `Session::add_lint` elsewhere in the
//! compiler. Only do the latter if the check can't be written cleanly as a
//! `LintPass` (also, note that such lints will need to be defined in
//! `rustc_session::lint::builtin`, not here).
//!
//! If you define a new `EarlyLintPass`, you will also need to add it to the
//! `add_early_builtin!` or `add_early_builtin_with_new!` invocation in
//! `lib.rs`. Use the former for unit-like structs and the latter for structs
//! with a `pub fn new()`.
//!
//! If you define a new `LateLintPass`, you will also need to add it to the
//! `late_lint_methods!` invocation in `lib.rs`.
use crate::{
types::{transparent_newtype_field, CItemKind},
EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext,
};
use rustc_ast::attr;
use rustc_ast::tokenstream::{TokenStream, TokenTree};
use rustc_ast::visit::{FnCtxt, FnKind};
use rustc_ast::{self as ast, *};
use rustc_ast_pretty::pprust::{self, expr_to_string};
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
use rustc_feature::{deprecated_attributes, AttributeGate, AttributeTemplate, AttributeType};
use rustc_feature::{GateIssue, Stability};
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::{DefId, LocalDefId, LocalDefIdSet};
use rustc_hir::{ForeignItemKind, GenericParamKind, PatKind};
use rustc_hir::{HirId, Node};
use rustc_index::vec::Idx;
use rustc_middle::lint::LintDiagnosticBuilder;
use rustc_middle::ty::print::with_no_trimmed_paths;
use rustc_middle::ty::subst::{GenericArgKind, Subst};
use rustc_middle::ty::Instance;
use rustc_middle::ty::{self, layout::LayoutError, Ty, TyCtxt};
use rustc_session::Session;
use rustc_span::edition::Edition;
use rustc_span::source_map::Spanned;
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_span::{BytePos, Span};
use rustc_target::abi::{LayoutOf, VariantIdx};
use rustc_trait_selection::traits::misc::can_type_implement_copy;
use crate::nonstandard_style::{method_context, MethodLateContext};
use std::fmt::Write;
use tracing::{debug, trace};
// hardwired lints from librustc_middle
pub use rustc_session::lint::builtin::*;
declare_lint! {
/// The `while_true` lint detects `while true { }`.
///
/// ### Example
///
/// ```rust,no_run
/// while true {
///
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// `while true` should be replaced with `loop`. A `loop` expression is
/// the preferred way to write an infinite loop because it more directly
/// expresses the intent of the loop.
WHILE_TRUE,
Warn,
"suggest using `loop { }` instead of `while true { }`"
}
declare_lint_pass!(WhileTrue => [WHILE_TRUE]);
/// Traverse through any amount of parenthesis and return the first non-parens expression.
fn pierce_parens(mut expr: &ast::Expr) -> &ast::Expr {
while let ast::ExprKind::Paren(sub) = &expr.kind {
expr = sub;
}
expr
}
impl EarlyLintPass for WhileTrue {
fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
if let ast::ExprKind::While(cond, _, label) = &e.kind {
if let ast::ExprKind::Lit(ref lit) = pierce_parens(cond).kind {
if let ast::LitKind::Bool(true) = lit.kind {
if !lit.span.from_expansion() {
let msg = "denote infinite loops with `loop { ... }`";
let condition_span = e.span.with_hi(cond.span.hi());
cx.struct_span_lint(WHILE_TRUE, condition_span, |lint| {
lint.build(msg)
.span_suggestion_short(
condition_span,
"use `loop`",
format!(
"{}loop",
label.map_or_else(String::new, |label| format!(
"{}: ",
label.ident,
))
),
Applicability::MachineApplicable,
)
.emit();
})
}
}
}
}
}
}
declare_lint! {
/// The `box_pointers` lints use of the Box type.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(box_pointers)]
/// struct Foo {
/// x: Box<isize>,
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This lint is mostly historical, and not particularly useful. `Box<T>`
/// used to be built into the language, and the only way to do heap
/// allocation. Today's Rust can call into other allocators, etc.
BOX_POINTERS,
Allow,
"use of owned (Box type) heap memory"
}
declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
impl BoxPointers {
fn check_heap_type(&self, cx: &LateContext<'_>, span: Span, ty: Ty<'_>) {
for leaf in ty.walk() {
if let GenericArgKind::Type(leaf_ty) = leaf.unpack() {
if leaf_ty.is_box() {
cx.struct_span_lint(BOX_POINTERS, span, |lint| {
lint.build(&format!("type uses owned (Box type) pointers: {}", ty)).emit()
});
}
}
}
}
}
impl<'tcx> LateLintPass<'tcx> for BoxPointers {
fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
match it.kind {
hir::ItemKind::Fn(..)
| hir::ItemKind::TyAlias(..)
| hir::ItemKind::Enum(..)
| hir::ItemKind::Struct(..)
| hir::ItemKind::Union(..) => {
self.check_heap_type(cx, it.span, cx.tcx.type_of(it.def_id))
}
_ => (),
}
// If it's a struct, we also have to check the fields' types
match it.kind {
hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
for struct_field in struct_def.fields() {
let def_id = cx.tcx.hir().local_def_id(struct_field.hir_id);
self.check_heap_type(cx, struct_field.span, cx.tcx.type_of(def_id));
}
}
_ => (),
}
}
fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
let ty = cx.typeck_results().node_type(e.hir_id);
self.check_heap_type(cx, e.span, ty);
}
}
declare_lint! {
/// The `non_shorthand_field_patterns` lint detects using `Struct { x: x }`
/// instead of `Struct { x }` in a pattern.
///
/// ### Example
///
/// ```rust
/// struct Point {
/// x: i32,
/// y: i32,
/// }
///
///
/// fn main() {
/// let p = Point {
/// x: 5,
/// y: 5,
/// };
///
/// match p {
/// Point { x: x, y: y } => (),
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The preferred style is to avoid the repetition of specifying both the
/// field name and the binding name if both identifiers are the same.
NON_SHORTHAND_FIELD_PATTERNS,
Warn,
"using `Struct { x: x }` instead of `Struct { x }` in a pattern"
}
declare_lint_pass!(NonShorthandFieldPatterns => [NON_SHORTHAND_FIELD_PATTERNS]);
impl<'tcx> LateLintPass<'tcx> for NonShorthandFieldPatterns {
fn check_pat(&mut self, cx: &LateContext<'_>, pat: &hir::Pat<'_>) {
if let PatKind::Struct(ref qpath, field_pats, _) = pat.kind {
let variant = cx
.typeck_results()
.pat_ty(pat)
.ty_adt_def()
.expect("struct pattern type is not an ADT")
.variant_of_res(cx.qpath_res(qpath, pat.hir_id));
for fieldpat in field_pats {
if fieldpat.is_shorthand {
continue;
}
if fieldpat.span.from_expansion() {
// Don't lint if this is a macro expansion: macro authors
// shouldn't have to worry about this kind of style issue
// (Issue #49588)
continue;
}
if let PatKind::Binding(binding_annot, _, ident, None) = fieldpat.pat.kind {
if cx.tcx.find_field_index(ident, &variant)
== Some(cx.tcx.field_index(fieldpat.hir_id, cx.typeck_results()))
{
cx.struct_span_lint(NON_SHORTHAND_FIELD_PATTERNS, fieldpat.span, |lint| {
let mut err = lint
.build(&format!("the `{}:` in this pattern is redundant", ident));
let binding = match binding_annot {
hir::BindingAnnotation::Unannotated => None,
hir::BindingAnnotation::Mutable => Some("mut"),
hir::BindingAnnotation::Ref => Some("ref"),
hir::BindingAnnotation::RefMut => Some("ref mut"),
};
let ident = if let Some(binding) = binding {
format!("{} {}", binding, ident)
} else {
ident.to_string()
};
err.span_suggestion(
fieldpat.span,
"use shorthand field pattern",
ident,
Applicability::MachineApplicable,
);
err.emit();
});
}
}
}
}
}
}
declare_lint! {
/// The `unsafe_code` lint catches usage of `unsafe` code.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(unsafe_code)]
/// fn main() {
/// unsafe {
///
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This lint is intended to restrict the usage of `unsafe`, which can be
/// difficult to use correctly.
UNSAFE_CODE,
Allow,
"usage of `unsafe` code"
}
declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
impl UnsafeCode {
fn report_unsafe(
&self,
cx: &EarlyContext<'_>,
span: Span,
decorate: impl for<'a> FnOnce(LintDiagnosticBuilder<'a>),
) {
// This comes from a macro that has `#[allow_internal_unsafe]`.
if span.allows_unsafe() {
return;
}
cx.struct_span_lint(UNSAFE_CODE, span, decorate);
}
fn report_overriden_symbol_name(&self, cx: &EarlyContext<'_>, span: Span, msg: &str) {
self.report_unsafe(cx, span, |lint| {
lint.build(msg)
.note(
"the linker's behavior with multiple libraries exporting duplicate symbol \
names is undefined and Rust cannot provide guarantees when you manually \
override them",
)
.emit();
})
}
}
impl EarlyLintPass for UnsafeCode {
fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
if cx.sess().check_name(attr, sym::allow_internal_unsafe) {
self.report_unsafe(cx, attr.span, |lint| {
lint.build(
"`allow_internal_unsafe` allows defining \
macros using unsafe without triggering \
the `unsafe_code` lint at their call site",
)
.emit()
});
}
}
fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
if let ast::ExprKind::Block(ref blk, _) = e.kind {
// Don't warn about generated blocks; that'll just pollute the output.
if blk.rules == ast::BlockCheckMode::Unsafe(ast::UserProvided) {
self.report_unsafe(cx, blk.span, |lint| {
lint.build("usage of an `unsafe` block").emit()
});
}
}
}
fn check_item(&mut self, cx: &EarlyContext<'_>, it: &ast::Item) {
match it.kind {
ast::ItemKind::Trait(box ast::TraitKind(_, ast::Unsafe::Yes(_), ..)) => self
.report_unsafe(cx, it.span, |lint| {
lint.build("declaration of an `unsafe` trait").emit()
}),
ast::ItemKind::Impl(box ast::ImplKind { unsafety: ast::Unsafe::Yes(_), .. }) => self
.report_unsafe(cx, it.span, |lint| {
lint.build("implementation of an `unsafe` trait").emit()
}),
ast::ItemKind::Fn(..) => {
if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
self.report_overriden_symbol_name(
cx,
attr.span,
"declaration of a `no_mangle` function",
);
}
if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
self.report_overriden_symbol_name(
cx,
attr.span,
"declaration of a function with `export_name`",
);
}
}
ast::ItemKind::Static(..) => {
if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
self.report_overriden_symbol_name(
cx,
attr.span,
"declaration of a `no_mangle` static",
);
}
if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::export_name) {
self.report_overriden_symbol_name(
cx,
attr.span,
"declaration of a static with `export_name`",
);
}
}
_ => {}
}
}
fn check_fn(&mut self, cx: &EarlyContext<'_>, fk: FnKind<'_>, span: Span, _: ast::NodeId) {
if let FnKind::Fn(
ctxt,
_,
ast::FnSig { header: ast::FnHeader { unsafety: ast::Unsafe::Yes(_), .. }, .. },
_,
body,
) = fk
{
let msg = match ctxt {
FnCtxt::Foreign => return,
FnCtxt::Free => "declaration of an `unsafe` function",
FnCtxt::Assoc(_) if body.is_none() => "declaration of an `unsafe` method",
FnCtxt::Assoc(_) => "implementation of an `unsafe` method",
};
self.report_unsafe(cx, span, |lint| lint.build(msg).emit());
}
}
}
declare_lint! {
/// The `missing_docs` lint detects missing documentation for public items.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(missing_docs)]
/// pub fn foo() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This lint is intended to ensure that a library is well-documented.
/// Items without documentation can be difficult for users to understand
/// how to use properly.
///
/// This lint is "allow" by default because it can be noisy, and not all
/// projects may want to enforce everything to be documented.
pub MISSING_DOCS,
Allow,
"detects missing documentation for public members",
report_in_external_macro
}
pub struct MissingDoc {
/// Stack of whether `#[doc(hidden)]` is set at each level which has lint attributes.
doc_hidden_stack: Vec<bool>,
/// Private traits or trait items that leaked through. Don't check their methods.
private_traits: FxHashSet<hir::HirId>,
}
impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
fn has_doc(sess: &Session, attr: &ast::Attribute) -> bool {
if attr.is_doc_comment() {
return true;
}
if !sess.check_name(attr, sym::doc) {
return false;
}
if attr.is_value_str() {
return true;
}
if let Some(list) = attr.meta_item_list() {
for meta in list {
if meta.has_name(sym::include) || meta.has_name(sym::hidden) {
return true;
}
}
}
false
}
impl MissingDoc {
pub fn new() -> MissingDoc {
MissingDoc { doc_hidden_stack: vec![false], private_traits: FxHashSet::default() }
}
fn doc_hidden(&self) -> bool {
*self.doc_hidden_stack.last().expect("empty doc_hidden_stack")
}
fn check_missing_docs_attrs(
&self,
cx: &LateContext<'_>,
id: Option<hir::HirId>,
attrs: &[ast::Attribute],
sp: Span,
article: &'static str,
desc: &'static str,
) {
// If we're building a test harness, then warning about
// documentation is probably not really relevant right now.
if cx.sess().opts.test {
return;
}
// `#[doc(hidden)]` disables missing_docs check.
if self.doc_hidden() {
return;
}
// Only check publicly-visible items, using the result from the privacy pass.
// It's an option so the crate root can also use this function (it doesn't
// have a `NodeId`).
if let Some(id) = id {
if !cx.access_levels.is_exported(id) {
return;
}
}
let has_doc = attrs.iter().any(|a| has_doc(cx.sess(), a));
if !has_doc {
cx.struct_span_lint(
MISSING_DOCS,
cx.tcx.sess.source_map().guess_head_span(sp),
|lint| {
lint.build(&format!("missing documentation for {} {}", article, desc)).emit()
},
);
}
}
}
impl<'tcx> LateLintPass<'tcx> for MissingDoc {
fn enter_lint_attrs(&mut self, cx: &LateContext<'_>, attrs: &[ast::Attribute]) {
let doc_hidden = self.doc_hidden()
|| attrs.iter().any(|attr| {
cx.sess().check_name(attr, sym::doc)
&& match attr.meta_item_list() {
None => false,
Some(l) => attr::list_contains_name(&l, sym::hidden),
}
});
self.doc_hidden_stack.push(doc_hidden);
}
fn exit_lint_attrs(&mut self, _: &LateContext<'_>, _attrs: &[ast::Attribute]) {
self.doc_hidden_stack.pop().expect("empty doc_hidden_stack");
}
fn check_crate(&mut self, cx: &LateContext<'_>, krate: &hir::Crate<'_>) {
self.check_missing_docs_attrs(cx, None, &krate.item.attrs, krate.item.span, "the", "crate");
for macro_def in krate.exported_macros {
let has_doc = macro_def.attrs.iter().any(|a| has_doc(cx.sess(), a));
if !has_doc {
cx.struct_span_lint(
MISSING_DOCS,
cx.tcx.sess.source_map().guess_head_span(macro_def.span),
|lint| lint.build("missing documentation for macro").emit(),
);
}
}
}
fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
match it.kind {
hir::ItemKind::Trait(.., trait_item_refs) => {
// Issue #11592: traits are always considered exported, even when private.
if let hir::VisibilityKind::Inherited = it.vis.node {
self.private_traits.insert(it.hir_id());
for trait_item_ref in trait_item_refs {
self.private_traits.insert(trait_item_ref.id.hir_id());
}
return;
}
}
hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref trait_ref), items, .. }) => {
// If the trait is private, add the impl items to `private_traits` so they don't get
// reported for missing docs.
let real_trait = trait_ref.path.res.def_id();
if let Some(def_id) = real_trait.as_local() {
let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
if let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) {
if let hir::VisibilityKind::Inherited = item.vis.node {
for impl_item_ref in items {
self.private_traits.insert(impl_item_ref.id.hir_id());
}
}
}
}
return;
}
hir::ItemKind::TyAlias(..)
| hir::ItemKind::Fn(..)
| hir::ItemKind::Mod(..)
| hir::ItemKind::Enum(..)
| hir::ItemKind::Struct(..)
| hir::ItemKind::Union(..)
| hir::ItemKind::Const(..)
| hir::ItemKind::Static(..) => {}
_ => return,
};
let (article, desc) = cx.tcx.article_and_description(it.def_id.to_def_id());
self.check_missing_docs_attrs(cx, Some(it.hir_id()), &it.attrs, it.span, article, desc);
}
fn check_trait_item(&mut self, cx: &LateContext<'_>, trait_item: &hir::TraitItem<'_>) {
if self.private_traits.contains(&trait_item.hir_id()) {
return;
}
let (article, desc) = cx.tcx.article_and_description(trait_item.def_id.to_def_id());
self.check_missing_docs_attrs(
cx,
Some(trait_item.hir_id()),
&trait_item.attrs,
trait_item.span,
article,
desc,
);
}
fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
// If the method is an impl for a trait, don't doc.
if method_context(cx, impl_item.hir_id()) == MethodLateContext::TraitImpl {
return;
}
let (article, desc) = cx.tcx.article_and_description(impl_item.def_id.to_def_id());
self.check_missing_docs_attrs(
cx,
Some(impl_item.hir_id()),
&impl_item.attrs,
impl_item.span,
article,
desc,
);
}
fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'_>) {
let (article, desc) = cx.tcx.article_and_description(foreign_item.def_id.to_def_id());
self.check_missing_docs_attrs(
cx,
Some(foreign_item.hir_id()),
&foreign_item.attrs,
foreign_item.span,
article,
desc,
);
}
fn check_struct_field(&mut self, cx: &LateContext<'_>, sf: &hir::StructField<'_>) {
if !sf.is_positional() {
self.check_missing_docs_attrs(
cx,
Some(sf.hir_id),
&sf.attrs,
sf.span,
"a",
"struct field",
)
}
}
fn check_variant(&mut self, cx: &LateContext<'_>, v: &hir::Variant<'_>) {
self.check_missing_docs_attrs(cx, Some(v.id), &v.attrs, v.span, "a", "variant");
}
}
declare_lint! {
/// The `missing_copy_implementations` lint detects potentially-forgotten
/// implementations of [`Copy`].
///
/// [`Copy`]: https://doc.rust-lang.org/std/marker/trait.Copy.html
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(missing_copy_implementations)]
/// pub struct Foo {
/// pub field: i32
/// }
/// # fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Historically (before 1.0), types were automatically marked as `Copy`
/// if possible. This was changed so that it required an explicit opt-in
/// by implementing the `Copy` trait. As part of this change, a lint was
/// added to alert if a copyable type was not marked `Copy`.
///
/// This lint is "allow" by default because this code isn't bad; it is
/// common to write newtypes like this specifically so that a `Copy` type
/// is no longer `Copy`. `Copy` types can result in unintended copies of
/// large data which can impact performance.
pub MISSING_COPY_IMPLEMENTATIONS,
Allow,
"detects potentially-forgotten implementations of `Copy`"
}
declare_lint_pass!(MissingCopyImplementations => [MISSING_COPY_IMPLEMENTATIONS]);
impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
if !cx.access_levels.is_reachable(item.hir_id()) {
return;
}
let (def, ty) = match item.kind {
hir::ItemKind::Struct(_, ref ast_generics) => {
if !ast_generics.params.is_empty() {
return;
}
let def = cx.tcx.adt_def(item.def_id);
(def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
}
hir::ItemKind::Union(_, ref ast_generics) => {
if !ast_generics.params.is_empty() {
return;
}
let def = cx.tcx.adt_def(item.def_id);
(def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
}
hir::ItemKind::Enum(_, ref ast_generics) => {
if !ast_generics.params.is_empty() {
return;
}
let def = cx.tcx.adt_def(item.def_id);
(def, cx.tcx.mk_adt(def, cx.tcx.intern_substs(&[])))
}
_ => return,
};
if def.has_dtor(cx.tcx) {
return;
}
let param_env = ty::ParamEnv::empty();
if ty.is_copy_modulo_regions(cx.tcx.at(item.span), param_env) {
return;
}
if can_type_implement_copy(cx.tcx, param_env, ty).is_ok() {
cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
lint.build(
"type could implement `Copy`; consider adding `impl \
Copy`",
)
.emit()
})
}
}
}
declare_lint! {
/// The `missing_debug_implementations` lint detects missing
/// implementations of [`fmt::Debug`].
///
/// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(missing_debug_implementations)]
/// pub struct Foo;
/// # fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Having a `Debug` implementation on all types can assist with
/// debugging, as it provides a convenient way to format and display a
/// value. Using the `#[derive(Debug)]` attribute will automatically
/// generate a typical implementation, or a custom implementation can be
/// added by manually implementing the `Debug` trait.
///
/// This lint is "allow" by default because adding `Debug` to all types can
/// have a negative impact on compile time and code size. It also requires
/// boilerplate to be added to every type, which can be an impediment.
MISSING_DEBUG_IMPLEMENTATIONS,
Allow,
"detects missing implementations of Debug"
}
#[derive(Default)]
pub struct MissingDebugImplementations {
impling_types: Option<LocalDefIdSet>,
}
impl_lint_pass!(MissingDebugImplementations => [MISSING_DEBUG_IMPLEMENTATIONS]);
impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
if !cx.access_levels.is_reachable(item.hir_id()) {
return;
}
match item.kind {
hir::ItemKind::Struct(..) | hir::ItemKind::Union(..) | hir::ItemKind::Enum(..) => {}
_ => return,
}
let debug = match cx.tcx.get_diagnostic_item(sym::debug_trait) {
Some(debug) => debug,
None => return,
};
if self.impling_types.is_none() {
let mut impls = LocalDefIdSet::default();
cx.tcx.for_each_impl(debug, |d| {
if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() {
if let Some(def_id) = ty_def.did.as_local() {
impls.insert(def_id);
}
}
});
self.impling_types = Some(impls);
debug!("{:?}", self.impling_types);
}
if !self.impling_types.as_ref().unwrap().contains(&item.def_id) {
cx.struct_span_lint(MISSING_DEBUG_IMPLEMENTATIONS, item.span, |lint| {
lint.build(&format!(
"type does not implement `{}`; consider adding `#[derive(Debug)]` \
or a manual implementation",
cx.tcx.def_path_str(debug)
))
.emit()
});
}
}
}
declare_lint! {
/// The `anonymous_parameters` lint detects anonymous parameters in trait
/// definitions.
///
/// ### Example
///
/// ```rust,edition2015,compile_fail
/// #![deny(anonymous_parameters)]
/// // edition 2015
/// pub trait Foo {
/// fn foo(usize);
/// }
/// fn main() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This syntax is mostly a historical accident, and can be worked around
/// quite easily by adding an `_` pattern or a descriptive identifier:
///
/// ```rust
/// trait Foo {
/// fn foo(_: usize);
/// }
/// ```
///
/// This syntax is now a hard error in the 2018 edition. In the 2015
/// edition, this lint is "allow" by default, because the old code is
/// still valid, and warning for all old code can be noisy. This lint
/// enables the [`cargo fix`] tool with the `--edition` flag to
/// automatically transition old code from the 2015 edition to 2018. The
/// tool will switch this lint to "warn" and will automatically apply the
/// suggested fix from the compiler (which is to add `_` to each
/// parameter). This provides a completely automated way to update old
/// code for a new edition. See [issue #41686] for more details.
///
/// [issue #41686]: https://github.com/rust-lang/rust/issues/41686
/// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
pub ANONYMOUS_PARAMETERS,
Allow,
"detects anonymous parameters",
@future_incompatible = FutureIncompatibleInfo {
reference: "issue #41686 <https://github.com/rust-lang/rust/issues/41686>",
edition: Some(Edition::Edition2018),
};
}
declare_lint_pass!(
/// Checks for use of anonymous parameters (RFC 1685).
AnonymousParameters => [ANONYMOUS_PARAMETERS]
);
impl EarlyLintPass for AnonymousParameters {
fn check_trait_item(&mut self, cx: &EarlyContext<'_>, it: &ast::AssocItem) {
if let ast::AssocItemKind::Fn(box FnKind(_, ref sig, _, _)) = it.kind {
for arg in sig.decl.inputs.iter() {
if let ast::PatKind::Ident(_, ident, None) = arg.pat.kind {
if ident.name == kw::Empty {
cx.struct_span_lint(ANONYMOUS_PARAMETERS, arg.pat.span, |lint| {
let ty_snip = cx.sess.source_map().span_to_snippet(arg.ty.span);
let (ty_snip, appl) = if let Ok(ref snip) = ty_snip {
(snip.as_str(), Applicability::MachineApplicable)
} else {
("<type>", Applicability::HasPlaceholders)
};
lint.build(
"anonymous parameters are deprecated and will be \
removed in the next edition.",
)
.span_suggestion(
arg.pat.span,
"try naming the parameter or explicitly \
ignoring it",
format!("_: {}", ty_snip),
appl,
)
.emit();
})
}
}
}
}
}
}
/// Check for use of attributes which have been deprecated.
#[derive(Clone)]
pub struct DeprecatedAttr {
// This is not free to compute, so we want to keep it around, rather than
// compute it for every attribute.
depr_attrs: Vec<&'static (Symbol, AttributeType, AttributeTemplate, AttributeGate)>,
}
impl_lint_pass!(DeprecatedAttr => []);
impl DeprecatedAttr {
pub fn new() -> DeprecatedAttr {
DeprecatedAttr { depr_attrs: deprecated_attributes() }
}
}
fn lint_deprecated_attr(
cx: &EarlyContext<'_>,
attr: &ast::Attribute,
msg: &str,
suggestion: Option<&str>,
) {
cx.struct_span_lint(DEPRECATED, attr.span, |lint| {
lint.build(msg)
.span_suggestion_short(
attr.span,
suggestion.unwrap_or("remove this attribute"),
String::new(),
Applicability::MachineApplicable,
)
.emit();
})
}
impl EarlyLintPass for DeprecatedAttr {
fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &ast::Attribute) {
for &&(n, _, _, ref g) in &self.depr_attrs {
if attr.ident().map(|ident| ident.name) == Some(n) {
if let &AttributeGate::Gated(
Stability::Deprecated(link, suggestion),
name,
reason,
_,
) = g
{
let msg =
format!("use of deprecated attribute `{}`: {}. See {}", name, reason, link);
lint_deprecated_attr(cx, attr, &msg, suggestion);
}
return;
}
}
if cx.sess().check_name(attr, sym::no_start) || cx.sess().check_name(attr, sym::crate_id) {
let path_str = pprust::path_to_string(&attr.get_normal_item().path);
let msg = format!("use of deprecated attribute `{}`: no longer used.", path_str);
lint_deprecated_attr(cx, attr, &msg, None);
}
}
}
fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
let mut attrs = attrs.iter().peekable();
// Accumulate a single span for sugared doc comments.
let mut sugared_span: Option<Span> = None;
while let Some(attr) = attrs.next() {
if attr.is_doc_comment() {
sugared_span =
Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
}
if attrs.peek().map(|next_attr| next_attr.is_doc_comment()).unwrap_or_default() {
continue;
}
let span = sugared_span.take().unwrap_or(attr.span);
if attr.is_doc_comment() || cx.sess().check_name(attr, sym::doc) {
cx.struct_span_lint(UNUSED_DOC_COMMENTS, span, |lint| {
let mut err = lint.build("unused doc comment");
err.span_label(
node_span,
format!("rustdoc does not generate documentation for {}", node_kind),
);
err.emit();
});
}
}
}
impl EarlyLintPass for UnusedDocComment {
fn check_stmt(&mut self, cx: &EarlyContext<'_>, stmt: &ast::Stmt) {
let kind = match stmt.kind {
ast::StmtKind::Local(..) => "statements",
// Disabled pending discussion in #78306
ast::StmtKind::Item(..) => return,
// expressions will be reported by `check_expr`.
ast::StmtKind::Empty
| ast::StmtKind::Semi(_)
| ast::StmtKind::Expr(_)
| ast::StmtKind::MacCall(_) => return,
};
warn_if_doc(cx, stmt.span, kind, stmt.kind.attrs());
}
fn check_arm(&mut self, cx: &EarlyContext<'_>, arm: &ast::Arm) {
let arm_span = arm.pat.span.with_hi(arm.body.span.hi());
warn_if_doc(cx, arm_span, "match arms", &arm.attrs);
}
fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
warn_if_doc(cx, expr.span, "expressions", &expr.attrs);
}
}
declare_lint! {
/// The `no_mangle_const_items` lint detects any `const` items with the
/// [`no_mangle` attribute].
///
/// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
///
/// ### Example
///
/// ```rust,compile_fail
/// #[no_mangle]
/// const FOO: i32 = 5;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Constants do not have their symbols exported, and therefore, this
/// probably means you meant to use a [`static`], not a [`const`].
///
/// [`static`]: https://doc.rust-lang.org/reference/items/static-items.html
/// [`const`]: https://doc.rust-lang.org/reference/items/constant-items.html
NO_MANGLE_CONST_ITEMS,
Deny,
"const items will not have their symbols exported"
}
declare_lint! {
/// The `no_mangle_generic_items` lint detects generic items that must be
/// mangled.
///
/// ### Example
///
/// ```rust
/// #[no_mangle]
/// fn foo<T>(t: T) {
///
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// An function with generics must have its symbol mangled to accommodate
/// the generic parameter. The [`no_mangle` attribute] has no effect in
/// this situation, and should be removed.
///
/// [`no_mangle` attribute]: https://doc.rust-lang.org/reference/abi.html#the-no_mangle-attribute
NO_MANGLE_GENERIC_ITEMS,
Warn,
"generic items must be mangled"
}
declare_lint_pass!(InvalidNoMangleItems => [NO_MANGLE_CONST_ITEMS, NO_MANGLE_GENERIC_ITEMS]);
impl<'tcx> LateLintPass<'tcx> for InvalidNoMangleItems {
fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
match it.kind {
hir::ItemKind::Fn(.., ref generics, _) => {
if let Some(no_mangle_attr) = cx.sess().find_by_name(&it.attrs, sym::no_mangle) {
for param in generics.params {
match param.kind {
GenericParamKind::Lifetime { .. } => {}
GenericParamKind::Type { .. } | GenericParamKind::Const { .. } => {
cx.struct_span_lint(NO_MANGLE_GENERIC_ITEMS, it.span, |lint| {
lint.build(
"functions generic over types or consts must be mangled",
)
.span_suggestion_short(
no_mangle_attr.span,
"remove this attribute",
String::new(),
// Use of `#[no_mangle]` suggests FFI intent; correct
// fix may be to monomorphize source by hand
Applicability::MaybeIncorrect,
)
.emit();
});
break;
}
}
}
}
}
hir::ItemKind::Const(..) => {
if cx.sess().contains_name(&it.attrs, sym::no_mangle) {
// Const items do not refer to a particular location in memory, and therefore
// don't have anything to attach a symbol to
cx.struct_span_lint(NO_MANGLE_CONST_ITEMS, it.span, |lint| {
let msg = "const items should never be `#[no_mangle]`";
let mut err = lint.build(msg);
// account for "pub const" (#45562)
let start = cx
.tcx
.sess
.source_map()
.span_to_snippet(it.span)
.map(|snippet| snippet.find("const").unwrap_or(0))
.unwrap_or(0) as u32;
// `const` is 5 chars
let const_span = it.span.with_hi(BytePos(it.span.lo().0 + start + 5));
err.span_suggestion(
const_span,
"try a static value",
"pub static".to_owned(),
Applicability::MachineApplicable,
);
err.emit();
});
}
}
_ => {}
}
}
}
declare_lint! {
/// The `mutable_transmutes` lint catches transmuting from `&T` to `&mut
/// T` because it is [undefined behavior].
///
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
///
/// ### Example
///
/// ```rust,compile_fail
/// unsafe {
/// let y = std::mem::transmute::<&i32, &mut i32>(&5);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Certain assumptions are made about aliasing of data, and this transmute
/// violates those assumptions. Consider using [`UnsafeCell`] instead.
///
/// [`UnsafeCell`]: https://doc.rust-lang.org/std/cell/struct.UnsafeCell.html
MUTABLE_TRANSMUTES,
Deny,
"mutating transmuted &mut T from &T may cause undefined behavior"
}
declare_lint_pass!(MutableTransmutes => [MUTABLE_TRANSMUTES]);
impl<'tcx> LateLintPass<'tcx> for MutableTransmutes {
fn check_expr(&mut self, cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
use rustc_target::spec::abi::Abi::RustIntrinsic;
if let Some((&ty::Ref(_, _, from_mt), &ty::Ref(_, _, to_mt))) =
get_transmute_from_to(cx, expr).map(|(ty1, ty2)| (ty1.kind(), ty2.kind()))
{
if to_mt == hir::Mutability::Mut && from_mt == hir::Mutability::Not {
let msg = "mutating transmuted &mut T from &T may cause undefined behavior, \
consider instead using an UnsafeCell";
cx.struct_span_lint(MUTABLE_TRANSMUTES, expr.span, |lint| lint.build(msg).emit());
}
}
fn get_transmute_from_to<'tcx>(
cx: &LateContext<'tcx>,
expr: &hir::Expr<'_>,
) -> Option<(Ty<'tcx>, Ty<'tcx>)> {
let def = if let hir::ExprKind::Path(ref qpath) = expr.kind {
cx.qpath_res(qpath, expr.hir_id)
} else {
return None;
};
if let Res::Def(DefKind::Fn, did) = def {
if !def_id_is_transmute(cx, did) {
return None;
}
let sig = cx.typeck_results().node_type(expr.hir_id).fn_sig(cx.tcx);
let from = sig.inputs().skip_binder()[0];
let to = sig.output().skip_binder();
return Some((from, to));
}
None
}
fn def_id_is_transmute(cx: &LateContext<'_>, def_id: DefId) -> bool {
cx.tcx.fn_sig(def_id).abi() == RustIntrinsic
&& cx.tcx.item_name(def_id) == sym::transmute
}
}
}
declare_lint! {
/// The `unstable_features` is deprecated and should no longer be used.
UNSTABLE_FEATURES,
Allow,
"enabling unstable features (deprecated. do not use)"
}
declare_lint_pass!(
/// Forbids using the `#[feature(...)]` attribute
UnstableFeatures => [UNSTABLE_FEATURES]
);
impl<'tcx> LateLintPass<'tcx> for UnstableFeatures {
fn check_attribute(&mut self, cx: &LateContext<'_>, attr: &ast::Attribute) {
if cx.sess().check_name(attr, sym::feature) {
if let Some(items) = attr.meta_item_list() {
for item in items {
cx.struct_span_lint(UNSTABLE_FEATURES, item.span(), |lint| {
lint.build("unstable feature").emit()
});
}
}
}
}
}
declare_lint! {
/// The `unreachable_pub` lint triggers for `pub` items not reachable from
/// the crate root.
///
/// ### Example
///
/// ```rust,compile_fail
/// #![deny(unreachable_pub)]
/// mod foo {
/// pub mod bar {
///
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// A bare `pub` visibility may be misleading if the item is not actually
/// publicly exported from the crate. The `pub(crate)` visibility is
/// recommended to be used instead, which more clearly expresses the intent
/// that the item is only visible within its own crate.
///
/// This lint is "allow" by default because it will trigger for a large
/// amount existing Rust code, and has some false-positives. Eventually it
/// is desired for this to become warn-by-default.
pub UNREACHABLE_PUB,
Allow,
"`pub` items not reachable from crate root"
}
declare_lint_pass!(
/// Lint for items marked `pub` that aren't reachable from other crates.
UnreachablePub => [UNREACHABLE_PUB]
);
impl UnreachablePub {
fn perform_lint(
&self,
cx: &LateContext<'_>,
what: &str,
id: hir::HirId,
vis: &hir::Visibility<'_>,
span: Span,
exportable: bool,
) {
let mut applicability = Applicability::MachineApplicable;
match vis.node {
hir::VisibilityKind::Public if !cx.access_levels.is_reachable(id) => {
if span.from_expansion() {
applicability = Applicability::MaybeIncorrect;
}
let def_span = cx.tcx.sess.source_map().guess_head_span(span);
cx.struct_span_lint(UNREACHABLE_PUB, def_span, |lint| {
let mut err = lint.build(&format!("unreachable `pub` {}", what));
let replacement = if cx.tcx.features().crate_visibility_modifier {
"crate"
} else {
"pub(crate)"
}
.to_owned();
err.span_suggestion(
vis.span,
"consider restricting its visibility",
replacement,
applicability,
);
if exportable {
err.help("or consider exporting it for use by other crates");
}
err.emit();
});
}
_ => {}
}
}
}
impl<'tcx> LateLintPass<'tcx> for UnreachablePub {
fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
self.perform_lint(cx, "item", item.hir_id(), &item.vis, item.span, true);
}
fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'tcx>) {
self.perform_lint(
cx,
"item",
foreign_item.hir_id(),
&foreign_item.vis,
foreign_item.span,
true,
);
}
fn check_struct_field(&mut self, cx: &LateContext<'_>, field: &hir::StructField<'_>) {
self.perform_lint(cx, "field", field.hir_id, &field.vis, field.span, false);
}
fn check_impl_item(&mut self, cx: &LateContext<'_>, impl_item: &hir::ImplItem<'_>) {
self.perform_lint(cx, "item", impl_item.hir_id(), &impl_item.vis, impl_item.span, false);
}
}
declare_lint! {
/// The `type_alias_bounds` lint detects bounds in type aliases.
///
/// ### Example
///
/// ```rust
/// type SendVec<T: Send> = Vec<T>;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The trait bounds in a type alias are currently ignored, and should not
/// be included to avoid confusion. This was previously allowed
/// unintentionally; this may become a hard error in the future.
TYPE_ALIAS_BOUNDS,
Warn,
"bounds in type aliases are not enforced"
}
declare_lint_pass!(
/// Lint for trait and lifetime bounds in type aliases being mostly ignored.
/// They are relevant when using associated types, but otherwise neither checked
/// at definition site nor enforced at use site.
TypeAliasBounds => [TYPE_ALIAS_BOUNDS]
);
impl TypeAliasBounds {
fn is_type_variable_assoc(qpath: &hir::QPath<'_>) -> bool {
match *qpath {
hir::QPath::TypeRelative(ref ty, _) => {
// If this is a type variable, we found a `T::Assoc`.
match ty.kind {
hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
matches!(path.res, Res::Def(DefKind::TyParam, _))
}
_ => false,
}
}
hir::QPath::Resolved(..) | hir::QPath::LangItem(..) => false,
}
}
fn suggest_changing_assoc_types(ty: &hir::Ty<'_>, err: &mut DiagnosticBuilder<'_>) {
// Access to associates types should use `<T as Bound>::Assoc`, which does not need a
// bound. Let's see if this type does that.
// We use a HIR visitor to walk the type.
use rustc_hir::intravisit::{self, Visitor};
struct WalkAssocTypes<'a, 'db> {
err: &'a mut DiagnosticBuilder<'db>,
}
impl<'a, 'db, 'v> Visitor<'v> for WalkAssocTypes<'a, 'db> {
type Map = intravisit::ErasedMap<'v>;
fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
intravisit::NestedVisitorMap::None
}
fn visit_qpath(&mut self, qpath: &'v hir::QPath<'v>, id: hir::HirId, span: Span) {
if TypeAliasBounds::is_type_variable_assoc(qpath) {
self.err.span_help(
span,
"use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to \
associated types in type aliases",
);
}
intravisit::walk_qpath(self, qpath, id, span)
}
}
// Let's go for a walk!
let mut visitor = WalkAssocTypes { err };
visitor.visit_ty(ty);
}
}
impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
let (ty, type_alias_generics) = match item.kind {
hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
_ => return,
};
if let hir::TyKind::OpaqueDef(..) = ty.kind {
// Bounds are respected for `type X = impl Trait`
return;
}
let mut suggested_changing_assoc_types = false;
// There must not be a where clause
if !type_alias_generics.where_clause.predicates.is_empty() {
cx.lint(
TYPE_ALIAS_BOUNDS,
|lint| {
let mut err = lint.build("where clauses are not enforced in type aliases");
let spans: Vec<_> = type_alias_generics
.where_clause
.predicates
.iter()
.map(|pred| pred.span())
.collect();
err.set_span(spans);
err.span_suggestion(
type_alias_generics.where_clause.span_for_predicates_or_empty_place(),
"the clause will not be checked when the type alias is used, and should be removed",
String::new(),
Applicability::MachineApplicable,
);
if !suggested_changing_assoc_types {
TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
suggested_changing_assoc_types = true;
}
err.emit();
},
);
}
// The parameters must not have bounds
for param in type_alias_generics.params.iter() {
let spans: Vec<_> = param.bounds.iter().map(|b| b.span()).collect();
let suggestion = spans
.iter()
.map(|sp| {
let start = param.span.between(*sp); // Include the `:` in `T: Bound`.
(start.to(*sp), String::new())
})
.collect();
if !spans.is_empty() {
cx.struct_span_lint(TYPE_ALIAS_BOUNDS, spans, |lint| {
let mut err =
lint.build("bounds on generic parameters are not enforced in type aliases");
let msg = "the bound will not be checked when the type alias is used, \
and should be removed";
err.multipart_suggestion(&msg, suggestion, Applicability::MachineApplicable);
if !suggested_changing_assoc_types {
TypeAliasBounds::suggest_changing_assoc_types(ty, &mut err);
suggested_changing_assoc_types = true;
}
err.emit();
});
}
}
}
}
declare_lint_pass!(
/// Lint constants that are erroneous.
/// Without this lint, we might not get any diagnostic if the constant is
/// unused within this crate, even though downstream crates can't use it
/// without producing an error.
UnusedBrokenConst => []
);
impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
match it.kind {
hir::ItemKind::Const(_, body_id) => {
let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
// trigger the query once for all constants since that will already report the errors
// FIXME: Use ensure here
let _ = cx.tcx.const_eval_poly(def_id);
}
hir::ItemKind::Static(_, _, body_id) => {
let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
// FIXME: Use ensure here
let _ = cx.tcx.eval_static_initializer(def_id);
}
_ => {}
}
}
}
declare_lint! {
/// The `trivial_bounds` lint detects trait bounds that don't depend on
/// any type parameters.
///
/// ### Example
///
/// ```rust
/// #![feature(trivial_bounds)]
/// pub struct A where i32: Copy;
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Usually you would not write a trait bound that you know is always
/// true, or never true. However, when using macros, the macro may not
/// know whether or not the constraint would hold or not at the time when
/// generating the code. Currently, the compiler does not alert you if the
/// constraint is always true, and generates an error if it is never true.
/// The `trivial_bounds` feature changes this to be a warning in both
/// cases, giving macros more freedom and flexibility to generate code,
/// while still providing a signal when writing non-macro code that
/// something is amiss.
///
/// See [RFC 2056] for more details. This feature is currently only
/// available on the nightly channel, see [tracking issue #48214].
///
/// [RFC 2056]: https://github.com/rust-lang/rfcs/blob/master/text/2056-allow-trivial-where-clause-constraints.md
/// [tracking issue #48214]: https://github.com/rust-lang/rust/issues/48214
TRIVIAL_BOUNDS,
Warn,
"these bounds don't depend on an type parameters"
}
declare_lint_pass!(
/// Lint for trait and lifetime bounds that don't depend on type parameters
/// which either do nothing, or stop the item from being used.
TrivialConstraints => [TRIVIAL_BOUNDS]
);
impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
use rustc_middle::ty::fold::TypeFoldable;
use rustc_middle::ty::PredicateKind::*;
if cx.tcx.features().trivial_bounds {
let predicates = cx.tcx.predicates_of(item.def_id);
for &(predicate, span) in predicates.predicates {
let predicate_kind_name = match predicate.kind().skip_binder() {
Trait(..) => "Trait",
TypeOutlives(..) |
RegionOutlives(..) => "Lifetime",
// Ignore projections, as they can only be global
// if the trait bound is global
Projection(..) |
// Ignore bounds that a user can't type
WellFormed(..) |
ObjectSafe(..) |
ClosureKind(..) |
Subtype(..) |
ConstEvaluatable(..) |
ConstEquate(..) |
TypeWellFormedFromEnv(..) => continue,
};
if predicate.is_global() {
cx.struct_span_lint(TRIVIAL_BOUNDS, span, |lint| {
lint.build(&format!(
"{} bound {} does not depend on any type \
or lifetime parameters",
predicate_kind_name, predicate
))
.emit()
});
}
}
}
}
}
declare_lint_pass!(
/// Does nothing as a lint pass, but registers some `Lint`s
/// which are used by other parts of the compiler.
SoftLints => [
WHILE_TRUE,
BOX_POINTERS,
NON_SHORTHAND_FIELD_PATTERNS,
UNSAFE_CODE,
MISSING_DOCS,
MISSING_COPY_IMPLEMENTATIONS,
MISSING_DEBUG_IMPLEMENTATIONS,
ANONYMOUS_PARAMETERS,
UNUSED_DOC_COMMENTS,
NO_MANGLE_CONST_ITEMS,
NO_MANGLE_GENERIC_ITEMS,
MUTABLE_TRANSMUTES,
UNSTABLE_FEATURES,
UNREACHABLE_PUB,
TYPE_ALIAS_BOUNDS,
TRIVIAL_BOUNDS
]
);
declare_lint! {
/// The `ellipsis_inclusive_range_patterns` lint detects the [`...` range
/// pattern], which is deprecated.
///
/// [`...` range pattern]: https://doc.rust-lang.org/reference/patterns.html#range-patterns
///
/// ### Example
///
/// ```rust
/// let x = 123;
/// match x {
/// 0...100 => {}
/// _ => {}
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// The `...` range pattern syntax was changed to `..=` to avoid potential
/// confusion with the [`..` range expression]. Use the new form instead.
///
/// [`..` range expression]: https://doc.rust-lang.org/reference/expressions/range-expr.html
pub ELLIPSIS_INCLUSIVE_RANGE_PATTERNS,
Warn,
"`...` range patterns are deprecated"
}
#[derive(Default)]
pub struct EllipsisInclusiveRangePatterns {
/// If `Some(_)`, suppress all subsequent pattern
/// warnings for better diagnostics.
node_id: Option<ast::NodeId>,
}
impl_lint_pass!(EllipsisInclusiveRangePatterns => [ELLIPSIS_INCLUSIVE_RANGE_PATTERNS]);
impl EarlyLintPass for EllipsisInclusiveRangePatterns {
fn check_pat(&mut self, cx: &EarlyContext<'_>, pat: &ast::Pat) {
if self.node_id.is_some() {
// Don't recursively warn about patterns inside range endpoints.
return;
}
use self::ast::{PatKind, RangeSyntax::DotDotDot};
/// If `pat` is a `...` pattern, return the start and end of the range, as well as the span
/// corresponding to the ellipsis.
fn matches_ellipsis_pat(pat: &ast::Pat) -> Option<(Option<&Expr>, &Expr, Span)> {
match &pat.kind {
PatKind::Range(
a,
Some(b),
Spanned { span, node: RangeEnd::Included(DotDotDot) },
) => Some((a.as_deref(), b, *span)),
_ => None,
}
}
let (parenthesise, endpoints) = match &pat.kind {
PatKind::Ref(subpat, _) => (true, matches_ellipsis_pat(&subpat)),
_ => (false, matches_ellipsis_pat(pat)),
};
if let Some((start, end, join)) = endpoints {
let msg = "`...` range patterns are deprecated";
let suggestion = "use `..=` for an inclusive range";
if parenthesise {
self.node_id = Some(pat.id);
cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, pat.span, |lint| {
let end = expr_to_string(&end);
let replace = match start {
Some(start) => format!("&({}..={})", expr_to_string(&start), end),
None => format!("&(..={})", end),
};
lint.build(msg)
.span_suggestion(
pat.span,
suggestion,
replace,
Applicability::MachineApplicable,
)
.emit();
});
} else {
cx.struct_span_lint(ELLIPSIS_INCLUSIVE_RANGE_PATTERNS, join, |lint| {
lint.build(msg)
.span_suggestion_short(
join,
suggestion,
"..=".to_owned(),
Applicability::MachineApplicable,
)
.emit();
});
};
}
}
fn check_pat_post(&mut self, _cx: &EarlyContext<'_>, pat: &ast::Pat) {
if let Some(node_id) = self.node_id {
if pat.id == node_id {
self.node_id = None
}
}
}
}
declare_lint! {
/// The `unnameable_test_items` lint detects [`#[test]`][test] functions
/// that are not able to be run by the test harness because they are in a
/// position where they are not nameable.
///
/// [test]: https://doc.rust-lang.org/reference/attributes/testing.html#the-test-attribute
///
/// ### Example
///
/// ```rust,test
/// fn main() {
/// #[test]
/// fn foo() {
/// // This test will not fail because it does not run.
/// assert_eq!(1, 2);
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In order for the test harness to run a test, the test function must be
/// located in a position where it can be accessed from the crate root.
/// This generally means it must be defined in a module, and not anywhere
/// else such as inside another function. The compiler previously allowed
/// this without an error, so a lint was added as an alert that a test is
/// not being used. Whether or not this should be allowed has not yet been
/// decided, see [RFC 2471] and [issue #36629].
///
/// [RFC 2471]: https://github.com/rust-lang/rfcs/pull/2471#issuecomment-397414443
/// [issue #36629]: https://github.com/rust-lang/rust/issues/36629
UNNAMEABLE_TEST_ITEMS,
Warn,
"detects an item that cannot be named being marked as `#[test_case]`",
report_in_external_macro
}
pub struct UnnameableTestItems {
boundary: Option<LocalDefId>, // Id of the item under which things are not nameable
items_nameable: bool,
}
impl_lint_pass!(UnnameableTestItems => [UNNAMEABLE_TEST_ITEMS]);
impl UnnameableTestItems {
pub fn new() -> Self {
Self { boundary: None, items_nameable: true }
}
}
impl<'tcx> LateLintPass<'tcx> for UnnameableTestItems {
fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
if self.items_nameable {
if let hir::ItemKind::Mod(..) = it.kind {
} else {
self.items_nameable = false;
self.boundary = Some(it.def_id);
}
return;
}
if let Some(attr) = cx.sess().find_by_name(&it.attrs, sym::rustc_test_marker) {
cx.struct_span_lint(UNNAMEABLE_TEST_ITEMS, attr.span, |lint| {
lint.build("cannot test inner items").emit()
});
}
}
fn check_item_post(&mut self, _cx: &LateContext<'_>, it: &hir::Item<'_>) {
if !self.items_nameable && self.boundary == Some(it.def_id) {
self.items_nameable = true;
}
}
}
declare_lint! {
/// The `keyword_idents` lint detects edition keywords being used as an
/// identifier.
///
/// ### Example
///
/// ```rust,edition2015,compile_fail
/// #![deny(keyword_idents)]
/// // edition 2015
/// fn dyn() {}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Rust [editions] allow the language to evolve without breaking
/// backwards compatibility. This lint catches code that uses new keywords
/// that are added to the language that are used as identifiers (such as a
/// variable name, function name, etc.). If you switch the compiler to a
/// new edition without updating the code, then it will fail to compile if
/// you are using a new keyword as an identifier.
///
/// You can manually change the identifiers to a non-keyword, or use a
/// [raw identifier], for example `r#dyn`, to transition to a new edition.
///
/// This lint solves the problem automatically. It is "allow" by default
/// because the code is perfectly valid in older editions. The [`cargo
/// fix`] tool with the `--edition` flag will switch this lint to "warn"
/// and automatically apply the suggested fix from the compiler (which is
/// to use a raw identifier). This provides a completely automated way to
/// update old code for a new edition.
///
/// [editions]: https://doc.rust-lang.org/edition-guide/
/// [raw identifier]: https://doc.rust-lang.org/reference/identifiers.html
/// [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
pub KEYWORD_IDENTS,
Allow,
"detects edition keywords being used as an identifier",
@future_incompatible = FutureIncompatibleInfo {
reference: "issue #49716 <https://github.com/rust-lang/rust/issues/49716>",
edition: Some(Edition::Edition2018),
};
}
declare_lint_pass!(
/// Check for uses of edition keywords used as an identifier.
KeywordIdents => [KEYWORD_IDENTS]
);
struct UnderMacro(bool);
impl KeywordIdents {
fn check_tokens(&mut self, cx: &EarlyContext<'_>, tokens: TokenStream) {
for tt in tokens.into_trees() {
match tt {
// Only report non-raw idents.
TokenTree::Token(token) => {
if let Some((ident, false)) = token.ident() {
self.check_ident_token(cx, UnderMacro(true), ident);
}
}
TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
}
}
}
fn check_ident_token(
&mut self,
cx: &EarlyContext<'_>,
UnderMacro(under_macro): UnderMacro,
ident: Ident,
) {
let next_edition = match cx.sess.edition() {
Edition::Edition2015 => {
match ident.name {
kw::Async | kw::Await | kw::Try => Edition::Edition2018,
// rust-lang/rust#56327: Conservatively do not
// attempt to report occurrences of `dyn` within
// macro definitions or invocations, because `dyn`
// can legitimately occur as a contextual keyword
// in 2015 code denoting its 2018 meaning, and we
// do not want rustfix to inject bugs into working
// code by rewriting such occurrences.
//
// But if we see `dyn` outside of a macro, we know
// its precise role in the parsed AST and thus are
// assured this is truly an attempt to use it as
// an identifier.
kw::Dyn if !under_macro => Edition::Edition2018,
_ => return,
}
}
// There are no new keywords yet for the 2018 edition and beyond.
_ => return,
};
// Don't lint `r#foo`.
if cx.sess.parse_sess.raw_identifier_spans.borrow().contains(&ident.span) {
return;
}
cx.struct_span_lint(KEYWORD_IDENTS, ident.span, |lint| {
lint.build(&format!("`{}` is a keyword in the {} edition", ident, next_edition))
.span_suggestion(
ident.span,
"you can use a raw identifier to stay compatible",
format!("r#{}", ident),
Applicability::MachineApplicable,
)
.emit()
});
}
}
impl EarlyLintPass for KeywordIdents {
fn check_mac_def(&mut self, cx: &EarlyContext<'_>, mac_def: &ast::MacroDef, _id: ast::NodeId) {
self.check_tokens(cx, mac_def.body.inner_tokens());
}
fn check_mac(&mut self, cx: &EarlyContext<'_>, mac: &ast::MacCall) {
self.check_tokens(cx, mac.args.inner_tokens());
}
fn check_ident(&mut self, cx: &EarlyContext<'_>, ident: Ident) {
self.check_ident_token(cx, UnderMacro(false), ident);
}
}
declare_lint_pass!(ExplicitOutlivesRequirements => [EXPLICIT_OUTLIVES_REQUIREMENTS]);
impl ExplicitOutlivesRequirements {
fn lifetimes_outliving_lifetime<'tcx>(
inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
index: u32,
) -> Vec<ty::Region<'tcx>> {
inferred_outlives
.iter()
.filter_map(|(pred, _)| match pred.kind().skip_binder() {
ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => match a {
ty::ReEarlyBound(ebr) if ebr.index == index => Some(b),
_ => None,
},
_ => None,
})
.collect()
}
fn lifetimes_outliving_type<'tcx>(
inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
index: u32,
) -> Vec<ty::Region<'tcx>> {
inferred_outlives
.iter()
.filter_map(|(pred, _)| match pred.kind().skip_binder() {
ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
a.is_param(index).then_some(b)
}
_ => None,
})
.collect()
}
fn collect_outlived_lifetimes<'tcx>(
&self,
param: &'tcx hir::GenericParam<'tcx>,
tcx: TyCtxt<'tcx>,
inferred_outlives: &'tcx [(ty::Predicate<'tcx>, Span)],
ty_generics: &'tcx ty::Generics,
) -> Vec<ty::Region<'tcx>> {
let index =
ty_generics.param_def_id_to_index[&tcx.hir().local_def_id(param.hir_id).to_def_id()];
match param.kind {
hir::GenericParamKind::Lifetime { .. } => {
Self::lifetimes_outliving_lifetime(inferred_outlives, index)
}
hir::GenericParamKind::Type { .. } => {
Self::lifetimes_outliving_type(inferred_outlives, index)
}
hir::GenericParamKind::Const { .. } => Vec::new(),
}
}
fn collect_outlives_bound_spans<'tcx>(
&self,
tcx: TyCtxt<'tcx>,
bounds: &hir::GenericBounds<'_>,
inferred_outlives: &[ty::Region<'tcx>],
infer_static: bool,
) -> Vec<(usize, Span)> {
use rustc_middle::middle::resolve_lifetime::Region;
bounds
.iter()
.enumerate()
.filter_map(|(i, bound)| {
if let hir::GenericBound::Outlives(lifetime) = bound {
let is_inferred = match tcx.named_region(lifetime.hir_id) {
Some(Region::Static) if infer_static => {
inferred_outlives.iter().any(|r| matches!(r, ty::ReStatic))
}
Some(Region::EarlyBound(index, ..)) => inferred_outlives.iter().any(|r| {
if let ty::ReEarlyBound(ebr) = r { ebr.index == index } else { false }
}),
_ => false,
};
is_inferred.then_some((i, bound.span()))
} else {
None
}
})
.collect()
}
fn consolidate_outlives_bound_spans(
&self,
lo: Span,
bounds: &hir::GenericBounds<'_>,
bound_spans: Vec<(usize, Span)>,
) -> Vec<Span> {
if bounds.is_empty() {
return Vec::new();
}
if bound_spans.len() == bounds.len() {
let (_, last_bound_span) = bound_spans[bound_spans.len() - 1];
// If all bounds are inferable, we want to delete the colon, so
// start from just after the parameter (span passed as argument)
vec![lo.to(last_bound_span)]
} else {
let mut merged = Vec::new();
let mut last_merged_i = None;
let mut from_start = true;
for (i, bound_span) in bound_spans {
match last_merged_i {
// If the first bound is inferable, our span should also eat the leading `+`.
None if i == 0 => {
merged.push(bound_span.to(bounds[1].span().shrink_to_lo()));
last_merged_i = Some(0);
}
// If consecutive bounds are inferable, merge their spans
Some(h) if i == h + 1 => {
if let Some(tail) = merged.last_mut() {
// Also eat the trailing `+` if the first
// more-than-one bound is inferable
let to_span = if from_start && i < bounds.len() {
bounds[i + 1].span().shrink_to_lo()
} else {
bound_span
};
*tail = tail.to(to_span);
last_merged_i = Some(i);
} else {
bug!("another bound-span visited earlier");
}
}
_ => {
// When we find a non-inferable bound, subsequent inferable bounds
// won't be consecutive from the start (and we'll eat the leading
// `+` rather than the trailing one)
from_start = false;
merged.push(bounds[i - 1].span().shrink_to_hi().to(bound_span));
last_merged_i = Some(i);
}
}
}
merged
}
}
}
impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
use rustc_middle::middle::resolve_lifetime::Region;
let infer_static = cx.tcx.features().infer_static_outlives_requirements;
let def_id = item.def_id;
if let hir::ItemKind::Struct(_, ref hir_generics)
| hir::ItemKind::Enum(_, ref hir_generics)
| hir::ItemKind::Union(_, ref hir_generics) = item.kind
{
let inferred_outlives = cx.tcx.inferred_outlives_of(def_id);
if inferred_outlives.is_empty() {
return;
}
let ty_generics = cx.tcx.generics_of(def_id);
let mut bound_count = 0;
let mut lint_spans = Vec::new();
for param in hir_generics.params {
let has_lifetime_bounds = param
.bounds
.iter()
.any(|bound| matches!(bound, hir::GenericBound::Outlives(_)));
if !has_lifetime_bounds {
continue;
}
let relevant_lifetimes =
self.collect_outlived_lifetimes(param, cx.tcx, inferred_outlives, ty_generics);
if relevant_lifetimes.is_empty() {
continue;
}
let bound_spans = self.collect_outlives_bound_spans(
cx.tcx,
&param.bounds,
&relevant_lifetimes,
infer_static,
);
bound_count += bound_spans.len();
lint_spans.extend(self.consolidate_outlives_bound_spans(
param.span.shrink_to_hi(),
&param.bounds,
bound_spans,
));
}
let mut where_lint_spans = Vec::new();
let mut dropped_predicate_count = 0;
let num_predicates = hir_generics.where_clause.predicates.len();
for (i, where_predicate) in hir_generics.where_clause.predicates.iter().enumerate() {
let (relevant_lifetimes, bounds, span) = match where_predicate {
hir::WherePredicate::RegionPredicate(predicate) => {
if let Some(Region::EarlyBound(index, ..)) =
cx.tcx.named_region(predicate.lifetime.hir_id)
{
(
Self::lifetimes_outliving_lifetime(inferred_outlives, index),
&predicate.bounds,
predicate.span,
)
} else {
continue;
}
}
hir::WherePredicate::BoundPredicate(predicate) => {
// FIXME we can also infer bounds on associated types,
// and should check for them here.
match predicate.bounded_ty.kind {
hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
if let Res::Def(DefKind::TyParam, def_id) = path.res {
let index = ty_generics.param_def_id_to_index[&def_id];
(
Self::lifetimes_outliving_type(inferred_outlives, index),
&predicate.bounds,
predicate.span,
)
} else {
continue;
}
}
_ => {
continue;
}
}
}
_ => continue,
};
if relevant_lifetimes.is_empty() {
continue;
}
let bound_spans = self.collect_outlives_bound_spans(
cx.tcx,
bounds,
&relevant_lifetimes,
infer_static,
);
bound_count += bound_spans.len();
let drop_predicate = bound_spans.len() == bounds.len();
if drop_predicate {
dropped_predicate_count += 1;
}
// If all the bounds on a predicate were inferable and there are
// further predicates, we want to eat the trailing comma.
if drop_predicate && i + 1 < num_predicates {
let next_predicate_span = hir_generics.where_clause.predicates[i + 1].span();
where_lint_spans.push(span.to(next_predicate_span.shrink_to_lo()));
} else {
where_lint_spans.extend(self.consolidate_outlives_bound_spans(
span.shrink_to_lo(),
bounds,
bound_spans,
));
}
}
// If all predicates are inferable, drop the entire clause
// (including the `where`)
if num_predicates > 0 && dropped_predicate_count == num_predicates {
let where_span = hir_generics
.where_clause
.span()
.expect("span of (nonempty) where clause should exist");
// Extend the where clause back to the closing `>` of the
// generics, except for tuple struct, which have the `where`
// after the fields of the struct.
let full_where_span =
if let hir::ItemKind::Struct(hir::VariantData::Tuple(..), _) = item.kind {
where_span
} else {
hir_generics.span.shrink_to_hi().to(where_span)
};
lint_spans.push(full_where_span);
} else {
lint_spans.extend(where_lint_spans);
}
if !lint_spans.is_empty() {
cx.struct_span_lint(EXPLICIT_OUTLIVES_REQUIREMENTS, lint_spans.clone(), |lint| {
lint.build("outlives requirements can be inferred")
.multipart_suggestion(
if bound_count == 1 {
"remove this bound"
} else {
"remove these bounds"
},
lint_spans
.into_iter()
.map(|span| (span, "".to_owned()))
.collect::<Vec<_>>(),
Applicability::MachineApplicable,
)
.emit();
});
}
}
}
}
declare_lint! {
/// The `incomplete_features` lint detects unstable features enabled with
/// the [`feature` attribute] that may function improperly in some or all
/// cases.
///
/// [`feature` attribute]: https://doc.rust-lang.org/nightly/unstable-book/
///
/// ### Example
///
/// ```rust
/// #![feature(generic_associated_types)]
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Although it is encouraged for people to experiment with unstable
/// features, some of them are known to be incomplete or faulty. This lint
/// is a signal that the feature has not yet been finished, and you may
/// experience problems with it.
pub INCOMPLETE_FEATURES,
Warn,
"incomplete features that may function improperly in some or all cases"
}
declare_lint_pass!(
/// Check for used feature gates in `INCOMPLETE_FEATURES` in `librustc_feature/active.rs`.
IncompleteFeatures => [INCOMPLETE_FEATURES]
);
impl EarlyLintPass for IncompleteFeatures {
fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
let features = cx.sess.features_untracked();
features
.declared_lang_features
.iter()
.map(|(name, span, _)| (name, span))
.chain(features.declared_lib_features.iter().map(|(name, span)| (name, span)))
.filter(|(name, _)| rustc_feature::INCOMPLETE_FEATURES.iter().any(|f| name == &f))
.for_each(|(&name, &span)| {
cx.struct_span_lint(INCOMPLETE_FEATURES, span, |lint| {
let mut builder = lint.build(&format!(
"the feature `{}` is incomplete and may not be safe to use \
and/or cause compiler crashes",
name,
));
if let Some(n) = rustc_feature::find_feature_issue(name, GateIssue::Language) {
builder.note(&format!(
"see issue #{} <https://github.com/rust-lang/rust/issues/{}> \
for more information",
n, n,
));
}
if HAS_MIN_FEATURES.contains(&name) {
builder.help(&format!(
"consider using `min_{}` instead, which is more stable and complete",
name,
));
}
builder.emit();
})
});
}
}
const HAS_MIN_FEATURES: &[Symbol] = &[sym::specialization];
declare_lint! {
/// The `invalid_value` lint detects creating a value that is not valid,
/// such as a NULL reference.
///
/// ### Example
///
/// ```rust,no_run
/// # #![allow(unused)]
/// unsafe {
/// let x: &'static i32 = std::mem::zeroed();
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// In some situations the compiler can detect that the code is creating
/// an invalid value, which should be avoided.
///
/// In particular, this lint will check for improper use of
/// [`mem::zeroed`], [`mem::uninitialized`], [`mem::transmute`], and
/// [`MaybeUninit::assume_init`] that can cause [undefined behavior]. The
/// lint should provide extra information to indicate what the problem is
/// and a possible solution.
///
/// [`mem::zeroed`]: https://doc.rust-lang.org/std/mem/fn.zeroed.html
/// [`mem::uninitialized`]: https://doc.rust-lang.org/std/mem/fn.uninitialized.html
/// [`mem::transmute`]: https://doc.rust-lang.org/std/mem/fn.transmute.html
/// [`MaybeUninit::assume_init`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#method.assume_init
/// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
pub INVALID_VALUE,
Warn,
"an invalid value is being created (such as a NULL reference)"
}
declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
impl<'tcx> LateLintPass<'tcx> for InvalidValue {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &hir::Expr<'_>) {
#[derive(Debug, Copy, Clone, PartialEq)]
enum InitKind {
Zeroed,
Uninit,
}
/// Information about why a type cannot be initialized this way.
/// Contains an error message and optionally a span to point at.
type InitError = (String, Option<Span>);
/// Test if this constant is all-0.
fn is_zero(expr: &hir::Expr<'_>) -> bool {
use hir::ExprKind::*;
use rustc_ast::LitKind::*;
match &expr.kind {
Lit(lit) => {
if let Int(i, _) = lit.node {
i == 0
} else {
false
}
}
Tup(tup) => tup.iter().all(is_zero),
_ => false,
}
}
/// Determine if this expression is a "dangerous initialization".
fn is_dangerous_init(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> Option<InitKind> {
if let hir::ExprKind::Call(ref path_expr, ref args) = expr.kind {
// Find calls to `mem::{uninitialized,zeroed}` methods.
if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
if cx.tcx.is_diagnostic_item(sym::mem_zeroed, def_id) {
return Some(InitKind::Zeroed);
} else if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, def_id) {
return Some(InitKind::Uninit);
} else if cx.tcx.is_diagnostic_item(sym::transmute, def_id) && is_zero(&args[0])
{
return Some(InitKind::Zeroed);
}
}
} else if let hir::ExprKind::MethodCall(_, _, ref args, _) = expr.kind {
// Find problematic calls to `MaybeUninit::assume_init`.
let def_id = cx.typeck_results().type_dependent_def_id(expr.hir_id)?;
if cx.tcx.is_diagnostic_item(sym::assume_init, def_id) {
// This is a call to *some* method named `assume_init`.
// See if the `self` parameter is one of the dangerous constructors.
if let hir::ExprKind::Call(ref path_expr, _) = args[0].kind {
if let hir::ExprKind::Path(ref qpath) = path_expr.kind {
let def_id = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id()?;
if cx.tcx.is_diagnostic_item(sym::maybe_uninit_zeroed, def_id) {
return Some(InitKind::Zeroed);
} else if cx.tcx.is_diagnostic_item(sym::maybe_uninit_uninit, def_id) {
return Some(InitKind::Uninit);
}
}
}
}
}
None
}
/// Test if this enum has several actually "existing" variants.
/// Zero-sized uninhabited variants do not always have a tag assigned and thus do not "exist".
fn is_multi_variant(adt: &ty::AdtDef) -> bool {
// As an approximation, we only count dataless variants. Those are definitely inhabited.
let existing_variants = adt.variants.iter().filter(|v| v.fields.is_empty()).count();
existing_variants > 1
}
/// Return `Some` only if we are sure this type does *not*
/// allow zero initialization.
fn ty_find_init_error<'tcx>(
tcx: TyCtxt<'tcx>,
ty: Ty<'tcx>,
init: InitKind,
) -> Option<InitError> {
use rustc_middle::ty::TyKind::*;
match ty.kind() {
// Primitive types that don't like 0 as a value.
Ref(..) => Some(("references must be non-null".to_string(), None)),
Adt(..) if ty.is_box() => Some(("`Box` must be non-null".to_string(), None)),
FnPtr(..) => Some(("function pointers must be non-null".to_string(), None)),
Never => Some(("the `!` type has no valid value".to_string(), None)),
RawPtr(tm) if matches!(tm.ty.kind(), Dynamic(..)) =>
// raw ptr to dyn Trait
{
Some(("the vtable of a wide raw pointer must be non-null".to_string(), None))
}
// Primitive types with other constraints.
Bool if init == InitKind::Uninit => {
Some(("booleans must be either `true` or `false`".to_string(), None))
}
Char if init == InitKind::Uninit => {
Some(("characters must be a valid Unicode codepoint".to_string(), None))
}
// Recurse and checks for some compound types.
Adt(adt_def, substs) if !adt_def.is_union() => {
// First check if this ADT has a layout attribute (like `NonNull` and friends).
use std::ops::Bound;
match tcx.layout_scalar_valid_range(adt_def.did) {
// We exploit here that `layout_scalar_valid_range` will never
// return `Bound::Excluded`. (And we have tests checking that we
// handle the attribute correctly.)
(Bound::Included(lo), _) if lo > 0 => {
return Some((format!("`{}` must be non-null", ty), None));
}
(Bound::Included(_), _) | (_, Bound::Included(_))
if init == InitKind::Uninit =>
{
return Some((
format!(
"`{}` must be initialized inside its custom valid range",
ty,
),
None,
));
}
_ => {}
}
// Now, recurse.
match adt_def.variants.len() {
0 => Some(("enums with no variants have no valid value".to_string(), None)),
1 => {
// Struct, or enum with exactly one variant.
// Proceed recursively, check all fields.
let variant = &adt_def.variants[VariantIdx::from_u32(0)];
variant.fields.iter().find_map(|field| {
ty_find_init_error(tcx, field.ty(tcx, substs), init).map(
|(mut msg, span)| {
if span.is_none() {
// Point to this field, should be helpful for figuring
// out where the source of the error is.
let span = tcx.def_span(field.did);
write!(
&mut msg,
" (in this {} field)",
adt_def.descr()
)
.unwrap();
(msg, Some(span))
} else {
// Just forward.
(msg, span)
}
},
)
})
}
// Multi-variant enum.
_ => {
if init == InitKind::Uninit && is_multi_variant(adt_def) {
let span = tcx.def_span(adt_def.did);
Some((
"enums have to be initialized to a variant".to_string(),
Some(span),
))
} else {
// In principle, for zero-initialization we could figure out which variant corresponds
// to tag 0, and check that... but for now we just accept all zero-initializations.
None
}
}
}
}
Tuple(..) => {
// Proceed recursively, check all fields.
ty.tuple_fields().find_map(|field| ty_find_init_error(tcx, field, init))
}
// Conservative fallback.
_ => None,
}
}
if let Some(init) = is_dangerous_init(cx, expr) {
// This conjures an instance of a type out of nothing,
// using zeroed or uninitialized memory.
// We are extremely conservative with what we warn about.
let conjured_ty = cx.typeck_results().expr_ty(expr);
if let Some((msg, span)) =
with_no_trimmed_paths(|| ty_find_init_error(cx.tcx, conjured_ty, init))
{
cx.struct_span_lint(INVALID_VALUE, expr.span, |lint| {
let mut err = lint.build(&format!(
"the type `{}` does not permit {}",
conjured_ty,
match init {
InitKind::Zeroed => "zero-initialization",
InitKind::Uninit => "being left uninitialized",
},
));
err.span_label(expr.span, "this code causes undefined behavior when executed");
err.span_label(
expr.span,
"help: use `MaybeUninit<T>` instead, \
and only call `assume_init` after initialization is done",
);
if let Some(span) = span {
err.span_note(span, &msg);
} else {
err.note(&msg);
}
err.emit();
});
}
}
}
}
declare_lint! {
/// The `clashing_extern_declarations` lint detects when an `extern fn`
/// has been declared with the same name but different types.
///
/// ### Example
///
/// ```rust
/// mod m {
/// extern "C" {
/// fn foo();
/// }
/// }
///
/// extern "C" {
/// fn foo(_: u32);
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Because two symbols of the same name cannot be resolved to two
/// different functions at link time, and one function cannot possibly
/// have two types, a clashing extern declaration is almost certainly a
/// mistake. Check to make sure that the `extern` definitions are correct
/// and equivalent, and possibly consider unifying them in one location.
///
/// This lint does not run between crates because a project may have
/// dependencies which both rely on the same extern function, but declare
/// it in a different (but valid) way. For example, they may both declare
/// an opaque type for one or more of the arguments (which would end up
/// distinct types), or use types that are valid conversions in the
/// language the `extern fn` is defined in. In these cases, the compiler
/// can't say that the clashing declaration is incorrect.
pub CLASHING_EXTERN_DECLARATIONS,
Warn,
"detects when an extern fn has been declared with the same name but different types"
}
pub struct ClashingExternDeclarations {
/// Map of function symbol name to the first-seen hir id for that symbol name.. If seen_decls
/// contains an entry for key K, it means a symbol with name K has been seen by this lint and
/// the symbol should be reported as a clashing declaration.
// FIXME: Technically, we could just store a &'tcx str here without issue; however, the
// `impl_lint_pass` macro doesn't currently support lints parametric over a lifetime.
seen_decls: FxHashMap<Symbol, HirId>,
}
/// Differentiate between whether the name for an extern decl came from the link_name attribute or
/// just from declaration itself. This is important because we don't want to report clashes on
/// symbol name if they don't actually clash because one or the other links against a symbol with a
/// different name.
enum SymbolName {
/// The name of the symbol + the span of the annotation which introduced the link name.
Link(Symbol, Span),
/// No link name, so just the name of the symbol.
Normal(Symbol),
}
impl SymbolName {
fn get_name(&self) -> Symbol {
match self {
SymbolName::Link(s, _) | SymbolName::Normal(s) => *s,
}
}
}
impl ClashingExternDeclarations {
crate fn new() -> Self {
ClashingExternDeclarations { seen_decls: FxHashMap::default() }
}
/// Insert a new foreign item into the seen set. If a symbol with the same name already exists
/// for the item, return its HirId without updating the set.
fn insert(&mut self, tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> Option<HirId> {
let did = fi.def_id.to_def_id();
let instance = Instance::new(did, ty::List::identity_for_item(tcx, did));
let name = Symbol::intern(tcx.symbol_name(instance).name);
if let Some(&hir_id) = self.seen_decls.get(&name) {
// Avoid updating the map with the new entry when we do find a collision. We want to
// make sure we're always pointing to the first definition as the previous declaration.
// This lets us avoid emitting "knock-on" diagnostics.
Some(hir_id)
} else {
self.seen_decls.insert(name, fi.hir_id())
}
}
/// Get the name of the symbol that's linked against for a given extern declaration. That is,
/// the name specified in a #[link_name = ...] attribute if one was specified, else, just the
/// symbol's name.
fn name_of_extern_decl(tcx: TyCtxt<'_>, fi: &hir::ForeignItem<'_>) -> SymbolName {
if let Some((overridden_link_name, overridden_link_name_span)) =
tcx.codegen_fn_attrs(fi.def_id).link_name.map(|overridden_link_name| {
// FIXME: Instead of searching through the attributes again to get span
// information, we could have codegen_fn_attrs also give span information back for
// where the attribute was defined. However, until this is found to be a
// bottleneck, this does just fine.
(
overridden_link_name,
tcx.get_attrs(fi.def_id.to_def_id())
.iter()
.find(|at| tcx.sess.check_name(at, sym::link_name))
.unwrap()
.span,
)
})
{
SymbolName::Link(overridden_link_name, overridden_link_name_span)
} else {
SymbolName::Normal(fi.ident.name)
}
}
/// Checks whether two types are structurally the same enough that the declarations shouldn't
/// clash. We need this so we don't emit a lint when two modules both declare an extern struct,
/// with the same members (as the declarations shouldn't clash).
fn structurally_same_type<'tcx>(
cx: &LateContext<'tcx>,
a: Ty<'tcx>,
b: Ty<'tcx>,
ckind: CItemKind,
) -> bool {
fn structurally_same_type_impl<'tcx>(
seen_types: &mut FxHashSet<(Ty<'tcx>, Ty<'tcx>)>,
cx: &LateContext<'tcx>,
a: Ty<'tcx>,
b: Ty<'tcx>,
ckind: CItemKind,
) -> bool {
debug!("structurally_same_type_impl(cx, a = {:?}, b = {:?})", a, b);
let tcx = cx.tcx;
// Given a transparent newtype, reach through and grab the inner
// type unless the newtype makes the type non-null.
let non_transparent_ty = |ty: Ty<'tcx>| -> Ty<'tcx> {
let mut ty = ty;
loop {
if let ty::Adt(def, substs) = *ty.kind() {
let is_transparent = def.subst(tcx, substs).repr.transparent();
let is_non_null = crate::types::nonnull_optimization_guaranteed(tcx, &def);
debug!(
"non_transparent_ty({:?}) -- type is transparent? {}, type is non-null? {}",
ty, is_transparent, is_non_null
);
if is_transparent && !is_non_null {
debug_assert!(def.variants.len() == 1);
let v = &def.variants[VariantIdx::new(0)];
ty = transparent_newtype_field(tcx, v)
.expect(
"single-variant transparent structure with zero-sized field",
)
.ty(tcx, substs);
continue;
}
}
debug!("non_transparent_ty -> {:?}", ty);
return ty;
}
};
let a = non_transparent_ty(a);
let b = non_transparent_ty(b);
if !seen_types.insert((a, b)) {
// We've encountered a cycle. There's no point going any further -- the types are
// structurally the same.
return true;
}
let tcx = cx.tcx;
if a == b || rustc_middle::ty::TyS::same_type(a, b) {
// All nominally-same types are structurally same, too.
true
} else {
// Do a full, depth-first comparison between the two.
use rustc_middle::ty::TyKind::*;
let a_kind = a.kind();
let b_kind = b.kind();
let compare_layouts = |a, b| -> Result<bool, LayoutError<'tcx>> {
debug!("compare_layouts({:?}, {:?})", a, b);
let a_layout = &cx.layout_of(a)?.layout.abi;
let b_layout = &cx.layout_of(b)?.layout.abi;
debug!(
"comparing layouts: {:?} == {:?} = {}",
a_layout,
b_layout,
a_layout == b_layout
);
Ok(a_layout == b_layout)
};
#[allow(rustc::usage_of_ty_tykind)]
let is_primitive_or_pointer = |kind: &ty::TyKind<'_>| {
kind.is_primitive() || matches!(kind, RawPtr(..) | Ref(..))
};
ensure_sufficient_stack(|| {
match (a_kind, b_kind) {
(Adt(a_def, a_substs), Adt(b_def, b_substs)) => {
let a = a.subst(cx.tcx, a_substs);
let b = b.subst(cx.tcx, b_substs);
debug!("Comparing {:?} and {:?}", a, b);
// We can immediately rule out these types as structurally same if
// their layouts differ.
match compare_layouts(a, b) {
Ok(false) => return false,
_ => (), // otherwise, continue onto the full, fields comparison
}
// Grab a flattened representation of all fields.
let a_fields = a_def.variants.iter().flat_map(|v| v.fields.iter());
let b_fields = b_def.variants.iter().flat_map(|v| v.fields.iter());
// Perform a structural comparison for each field.
a_fields.eq_by(
b_fields,
|&ty::FieldDef { did: a_did, .. },
&ty::FieldDef { did: b_did, .. }| {
structurally_same_type_impl(
seen_types,
cx,
tcx.type_of(a_did),
tcx.type_of(b_did),
ckind,
)
},
)
}
(Array(a_ty, a_const), Array(b_ty, b_const)) => {
// For arrays, we also check the constness of the type.
a_const.val == b_const.val
&& structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
}
(Slice(a_ty), Slice(b_ty)) => {
structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
}
(RawPtr(a_tymut), RawPtr(b_tymut)) => {
a_tymut.mutbl == b_tymut.mutbl
&& structurally_same_type_impl(
seen_types,
cx,
&a_tymut.ty,
&b_tymut.ty,
ckind,
)
}
(Ref(_a_region, a_ty, a_mut), Ref(_b_region, b_ty, b_mut)) => {
// For structural sameness, we don't need the region to be same.
a_mut == b_mut
&& structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
}
(FnDef(..), FnDef(..)) => {
let a_poly_sig = a.fn_sig(tcx);
let b_poly_sig = b.fn_sig(tcx);
// As we don't compare regions, skip_binder is fine.
let a_sig = a_poly_sig.skip_binder();
let b_sig = b_poly_sig.skip_binder();
(a_sig.abi, a_sig.unsafety, a_sig.c_variadic)
== (b_sig.abi, b_sig.unsafety, b_sig.c_variadic)
&& a_sig.inputs().iter().eq_by(b_sig.inputs().iter(), |a, b| {
structurally_same_type_impl(seen_types, cx, a, b, ckind)
})
&& structurally_same_type_impl(
seen_types,
cx,
a_sig.output(),
b_sig.output(),
ckind,
)
}
(Tuple(a_substs), Tuple(b_substs)) => {
a_substs.types().eq_by(b_substs.types(), |a_ty, b_ty| {
structurally_same_type_impl(seen_types, cx, a_ty, b_ty, ckind)
})
}
// For these, it's not quite as easy to define structural-sameness quite so easily.
// For the purposes of this lint, take the conservative approach and mark them as
// not structurally same.
(Dynamic(..), Dynamic(..))
| (Error(..), Error(..))
| (Closure(..), Closure(..))
| (Generator(..), Generator(..))
| (GeneratorWitness(..), GeneratorWitness(..))
| (Projection(..), Projection(..))
| (Opaque(..), Opaque(..)) => false,
// These definitely should have been caught above.
(Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),
// An Adt and a primitive or pointer type. This can be FFI-safe if non-null
// enum layout optimisation is being applied.
(Adt(..), other_kind) | (other_kind, Adt(..))
if is_primitive_or_pointer(other_kind) =>
{
let (primitive, adt) =
if is_primitive_or_pointer(a.kind()) { (a, b) } else { (b, a) };
if let Some(ty) = crate::types::repr_nullable_ptr(cx, adt, ckind) {
ty == primitive
} else {
compare_layouts(a, b).unwrap_or(false)
}
}
// Otherwise, just compare the layouts. This may fail to lint for some
// incompatible types, but at the very least, will stop reads into
// uninitialised memory.
_ => compare_layouts(a, b).unwrap_or(false),
}
})
}
}
let mut seen_types = FxHashSet::default();
structurally_same_type_impl(&mut seen_types, cx, a, b, ckind)
}
}
impl_lint_pass!(ClashingExternDeclarations => [CLASHING_EXTERN_DECLARATIONS]);
impl<'tcx> LateLintPass<'tcx> for ClashingExternDeclarations {
fn check_foreign_item(&mut self, cx: &LateContext<'tcx>, this_fi: &hir::ForeignItem<'_>) {
trace!("ClashingExternDeclarations: check_foreign_item: {:?}", this_fi);
if let ForeignItemKind::Fn(..) = this_fi.kind {
let tcx = cx.tcx;
if let Some(existing_hid) = self.insert(tcx, this_fi) {
let existing_decl_ty = tcx.type_of(tcx.hir().local_def_id(existing_hid));
let this_decl_ty = tcx.type_of(this_fi.def_id);
debug!(
"ClashingExternDeclarations: Comparing existing {:?}: {:?} to this {:?}: {:?}",
existing_hid, existing_decl_ty, this_fi.def_id, this_decl_ty
);
// Check that the declarations match.
if !Self::structurally_same_type(
cx,
existing_decl_ty,
this_decl_ty,
CItemKind::Declaration,
) {
let orig_fi = tcx.hir().expect_foreign_item(existing_hid);
let orig = Self::name_of_extern_decl(tcx, orig_fi);
// We want to ensure that we use spans for both decls that include where the
// name was defined, whether that was from the link_name attribute or not.
let get_relevant_span =
|fi: &hir::ForeignItem<'_>| match Self::name_of_extern_decl(tcx, fi) {
SymbolName::Normal(_) => fi.span,
SymbolName::Link(_, annot_span) => fi.span.to(annot_span),
};
// Finally, emit the diagnostic.
tcx.struct_span_lint_hir(
CLASHING_EXTERN_DECLARATIONS,
this_fi.hir_id(),
get_relevant_span(this_fi),
|lint| {
let mut expected_str = DiagnosticStyledString::new();
expected_str.push(existing_decl_ty.fn_sig(tcx).to_string(), false);
let mut found_str = DiagnosticStyledString::new();
found_str.push(this_decl_ty.fn_sig(tcx).to_string(), true);
lint.build(&format!(
"`{}` redeclare{} with a different signature",
this_fi.ident.name,
if orig.get_name() == this_fi.ident.name {
"d".to_string()
} else {
format!("s `{}`", orig.get_name())
}
))
.span_label(
get_relevant_span(orig_fi),
&format!("`{}` previously declared here", orig.get_name()),
)
.span_label(
get_relevant_span(this_fi),
"this signature doesn't match the previous declaration",
)
.note_expected_found(&"", expected_str, &"", found_str)
.emit()
},
);
}
}
}
}
}
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