Merge pull request #2832 from kennytm/non-copy-const
Lint against const items which are interior mutable.
This commit is contained in:
Oliver Schneider
GitHub
commit
656b26ea4f
4 changed files with 696 additions and 0 deletions
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@ -148,6 +148,7 @@ pub mod neg_cmp_op_on_partial_ord;
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pub mod neg_multiply;
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pub mod new_without_default;
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pub mod no_effect;
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pub mod non_copy_const;
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pub mod non_expressive_names;
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pub mod ok_if_let;
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pub mod open_options;
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@ -405,6 +406,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
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reg.register_late_lint_pass(box duration_subsec::DurationSubsec);
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reg.register_late_lint_pass(box default_trait_access::DefaultTraitAccess);
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reg.register_late_lint_pass(box indexing_slicing::IndexingSlicing);
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reg.register_late_lint_pass(box non_copy_const::NonCopyConst);
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reg.register_lint_group("clippy_restriction", vec![
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arithmetic::FLOAT_ARITHMETIC,
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@ -613,6 +615,8 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
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new_without_default::NEW_WITHOUT_DEFAULT_DERIVE,
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no_effect::NO_EFFECT,
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no_effect::UNNECESSARY_OPERATION,
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non_copy_const::BORROW_INTERIOR_MUTABLE_CONST,
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non_copy_const::DECLARE_INTERIOR_MUTABLE_CONST,
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non_expressive_names::JUST_UNDERSCORES_AND_DIGITS,
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non_expressive_names::MANY_SINGLE_CHAR_NAMES,
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ok_if_let::IF_LET_SOME_RESULT,
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@ -868,6 +872,8 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry) {
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misc::CMP_NAN,
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misc::FLOAT_CMP,
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misc::MODULO_ONE,
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non_copy_const::BORROW_INTERIOR_MUTABLE_CONST,
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non_copy_const::DECLARE_INTERIOR_MUTABLE_CONST,
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open_options::NONSENSICAL_OPEN_OPTIONS,
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ptr::MUT_FROM_REF,
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ranges::ITERATOR_STEP_BY_ZERO,
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268
clippy_lints/src/non_copy_const.rs
Normal file
268
clippy_lints/src/non_copy_const.rs
Normal file
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@ -0,0 +1,268 @@
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//! Checks for uses of const which the type is not Freeze (Cell-free).
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//!
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//! This lint is **deny** by default.
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use rustc::lint::{LateContext, LateLintPass, Lint, LintArray, LintPass};
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use rustc::hir::*;
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use rustc::hir::def::Def;
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use rustc::ty::{self, TyRef, TypeFlags};
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use rustc::ty::adjustment::Adjust;
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use rustc_errors::Applicability;
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use rustc_typeck::hir_ty_to_ty;
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use syntax_pos::{DUMMY_SP, Span};
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use std::ptr;
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use crate::utils::{in_constant, in_macro, is_copy, span_lint_and_then};
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/// **What it does:** Checks for declaration of `const` items which is interior
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/// mutable (e.g. contains a `Cell`, `Mutex`, `AtomicXxxx` etc).
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///
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/// **Why is this bad?** Consts are copied everywhere they are referenced, i.e.
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/// every time you refer to the const a fresh instance of the `Cell` or `Mutex`
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/// or `AtomicXxxx` will be created, which defeats the whole purpose of using
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/// these types in the first place.
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///
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/// The `const` should better be replaced by a `static` item if a global
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/// variable is wanted, or replaced by a `const fn` if a constructor is wanted.
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///
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/// **Known problems:** A "non-constant" const item is a legacy way to supply an
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/// initialized value to downstream `static` items (e.g. the
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/// `std::sync::ONCE_INIT` constant). In this case the use of `const` is legit,
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/// and this lint should be suppressed.
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///
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/// **Example:**
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/// ```rust
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/// use std::sync::atomic::{Ordering::SeqCst, AtomicUsize};
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///
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/// // Bad.
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/// const CONST_ATOM: AtomicUsize = AtomicUsize::new(12);
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/// CONST_ATOM.store(6, SeqCst); // the content of the atomic is unchanged
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/// assert_eq!(CONST_ATOM.load(SeqCst), 12); // because the CONST_ATOM in these lines are distinct
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///
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/// // Good.
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/// static STATIC_ATOM: AtomicUsize = AtomicUsize::new(15);
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/// STATIC_ATOM.store(9, SeqCst);
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/// assert_eq!(STATIC_ATOM.load(SeqCst), 9); // use a `static` item to refer to the same instance
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/// ```
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declare_clippy_lint! {
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pub DECLARE_INTERIOR_MUTABLE_CONST,
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correctness,
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"declaring const with interior mutability"
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}
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/// **What it does:** Checks if `const` items which is interior mutable (e.g.
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/// contains a `Cell`, `Mutex`, `AtomicXxxx` etc) has been borrowed directly.
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///
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/// **Why is this bad?** Consts are copied everywhere they are referenced, i.e.
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/// every time you refer to the const a fresh instance of the `Cell` or `Mutex`
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/// or `AtomicXxxx` will be created, which defeats the whole purpose of using
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/// these types in the first place.
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///
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/// The `const` value should be stored inside a `static` item.
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///
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/// **Known problems:** None
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///
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/// **Example:**
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/// ```rust
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/// use std::sync::atomic::{Ordering::SeqCst, AtomicUsize};
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/// const CONST_ATOM: AtomicUsize = AtomicUsize::new(12);
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///
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/// // Bad.
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/// CONST_ATOM.store(6, SeqCst); // the content of the atomic is unchanged
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/// assert_eq!(CONST_ATOM.load(SeqCst), 12); // because the CONST_ATOM in these lines are distinct
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///
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/// // Good.
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/// static STATIC_ATOM: AtomicUsize = CONST_ATOM;
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/// STATIC_ATOM.store(9, SeqCst);
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/// assert_eq!(STATIC_ATOM.load(SeqCst), 9); // use a `static` item to refer to the same instance
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/// ```
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declare_clippy_lint! {
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pub BORROW_INTERIOR_MUTABLE_CONST,
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correctness,
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"referencing const with interior mutability"
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}
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#[derive(Copy, Clone)]
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enum Source {
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Item {
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item: Span,
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},
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Assoc {
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item: Span,
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ty: Span,
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},
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Expr {
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expr: Span,
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},
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}
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impl Source {
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fn lint(&self) -> (&'static Lint, &'static str, Span) {
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match self {
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Source::Item { item } | Source::Assoc { item, .. } => (
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DECLARE_INTERIOR_MUTABLE_CONST,
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"a const item should never be interior mutable",
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*item,
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),
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Source::Expr { expr } => (
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BORROW_INTERIOR_MUTABLE_CONST,
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"a const item with interior mutability should not be borrowed",
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*expr,
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),
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}
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}
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}
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fn verify_ty_bound<'a, 'tcx>(
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cx: &LateContext<'a, 'tcx>,
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ty: ty::Ty<'tcx>,
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source: Source,
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) {
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if ty.is_freeze(cx.tcx, cx.param_env, DUMMY_SP) || is_copy(cx, ty) {
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// an UnsafeCell is !Copy, and an UnsafeCell is also the only type which
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// is !Freeze, thus if our type is Copy we can be sure it must be Freeze
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// as well.
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return;
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}
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let (lint, msg, span) = source.lint();
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span_lint_and_then(cx, lint, span, msg, |db| {
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if in_macro(span) {
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return; // Don't give suggestions into macros.
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}
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match source {
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Source::Item { .. } => {
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let const_kw_span = span.from_inner_byte_pos(0, 5);
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db.span_suggestion_with_applicability(
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const_kw_span,
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"make this a static item",
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"static".to_string(),
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Applicability::MachineApplicable,
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);
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}
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Source::Assoc { ty: ty_span, .. } => {
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if ty.flags.contains(TypeFlags::HAS_FREE_LOCAL_NAMES) {
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db.span_help(ty_span, &format!("consider requiring `{}` to be `Copy`", ty));
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}
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}
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Source::Expr { .. } => {
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db.help(
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"assign this const to a local or static variable, and use the variable here",
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);
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}
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}
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});
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}
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pub struct NonCopyConst;
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impl LintPass for NonCopyConst {
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fn get_lints(&self) -> LintArray {
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lint_array!(DECLARE_INTERIOR_MUTABLE_CONST, BORROW_INTERIOR_MUTABLE_CONST)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NonCopyConst {
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fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, it: &'tcx Item) {
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if let ItemConst(hir_ty, ..) = &it.node {
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let ty = hir_ty_to_ty(cx.tcx, hir_ty);
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verify_ty_bound(cx, ty, Source::Item { item: it.span });
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}
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}
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fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, trait_item: &'tcx TraitItem) {
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if let TraitItemKind::Const(hir_ty, ..) = &trait_item.node {
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let ty = hir_ty_to_ty(cx.tcx, hir_ty);
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verify_ty_bound(cx, ty, Source::Assoc { ty: hir_ty.span, item: trait_item.span });
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}
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}
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fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, impl_item: &'tcx ImplItem) {
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if let ImplItemKind::Const(hir_ty, ..) = &impl_item.node {
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let item_node_id = cx.tcx.hir.get_parent_node(impl_item.id);
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let item = cx.tcx.hir.expect_item(item_node_id);
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// ensure the impl is an inherent impl.
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if let ItemImpl(_, _, _, _, None, _, _) = item.node {
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let ty = hir_ty_to_ty(cx.tcx, hir_ty);
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verify_ty_bound(cx, ty, Source::Assoc { ty: hir_ty.span, item: impl_item.span });
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}
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}
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}
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if let ExprPath(qpath) = &expr.node {
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// Only lint if we use the const item inside a function.
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if in_constant(cx, expr.id) {
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return;
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}
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// make sure it is a const item.
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match cx.tables.qpath_def(qpath, expr.hir_id) {
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Def::Const(_) | Def::AssociatedConst(_) => {},
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_ => return,
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};
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// climb up to resolve any field access and explicit referencing.
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let mut cur_expr = expr;
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let mut dereferenced_expr = expr;
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let mut needs_check_adjustment = true;
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loop {
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let parent_id = cx.tcx.hir.get_parent_node(cur_expr.id);
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if parent_id == cur_expr.id {
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break;
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}
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if let Some(map::NodeExpr(parent_expr)) = cx.tcx.hir.find(parent_id) {
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match &parent_expr.node {
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ExprAddrOf(..) => {
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// `&e` => `e` must be referenced
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needs_check_adjustment = false;
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}
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ExprField(..) => {
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dereferenced_expr = parent_expr;
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needs_check_adjustment = true;
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}
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ExprIndex(e, _) if ptr::eq(&**e, cur_expr) => {
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// `e[i]` => desugared to `*Index::index(&e, i)`,
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// meaning `e` must be referenced.
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// no need to go further up since a method call is involved now.
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needs_check_adjustment = false;
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break;
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}
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ExprUnary(UnDeref, _) => {
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// `*e` => desugared to `*Deref::deref(&e)`,
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// meaning `e` must be referenced.
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// no need to go further up since a method call is involved now.
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needs_check_adjustment = false;
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break;
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}
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_ => break,
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}
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cur_expr = parent_expr;
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} else {
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break;
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}
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}
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let ty = if !needs_check_adjustment {
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cx.tables.expr_ty(dereferenced_expr)
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} else {
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let adjustments = cx.tables.expr_adjustments(dereferenced_expr);
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if let Some(i) = adjustments.iter().position(|adj| match adj.kind {
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Adjust::Borrow(_) | Adjust::Deref(_) => true,
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_ => false,
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}) {
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if i == 0 {
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cx.tables.expr_ty(dereferenced_expr)
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} else {
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adjustments[i - 1].target
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}
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} else {
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// No borrow adjustments = the entire const is moved.
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return;
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}
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};
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verify_ty_bound(cx, ty, Source::Expr { expr: expr.span });
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}
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}
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}
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