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#![allow(rustc::default_hash_types)]
use std::borrow::Cow;
use std::cmp::Ordering;
use std::collections::BTreeMap;
use if_chain::if_chain;
use rustc::hir;
use rustc::hir::intravisit::{walk_body, walk_expr, walk_ty, FnKind, NestedVisitorMap, Visitor};
use rustc::hir::*;
use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintContext, LintPass};
use rustc::ty::layout::LayoutOf;
use rustc::ty::{self, InferTy, Ty, TyCtxt, TypeckTables};
use rustc::{declare_lint_pass, impl_lint_pass};
use rustc_errors::Applicability;
use rustc_session::declare_tool_lint;
use rustc_target::spec::abi::Abi;
use rustc_typeck::hir_ty_to_ty;
use syntax::ast::{FloatTy, IntTy, LitFloatType, LitIntType, LitKind, UintTy};
use syntax::errors::DiagnosticBuilder;
use syntax::source_map::Span;
use syntax::symbol::{sym, Symbol};
use syntax_pos::hygiene::{ExpnKind, MacroKind};
use crate::consts::{constant, Constant};
use crate::utils::paths;
use crate::utils::{
clip, comparisons, differing_macro_contexts, higher, in_constant, int_bits, last_path_segment, match_def_path,
match_path, multispan_sugg, qpath_res, same_tys, sext, snippet, snippet_opt, snippet_with_applicability,
snippet_with_macro_callsite, span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then, unsext,
};
declare_clippy_lint! {
/// **What it does:** Checks for use of `Box<Vec<_>>` anywhere in the code.
///
/// **Why is this bad?** `Vec` already keeps its contents in a separate area on
/// the heap. So if you `Box` it, you just add another level of indirection
/// without any benefit whatsoever.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// struct X {
/// values: Box<Vec<Foo>>,
/// }
/// ```
///
/// Better:
///
/// ```rust,ignore
/// struct X {
/// values: Vec<Foo>,
/// }
/// ```
pub BOX_VEC,
perf,
"usage of `Box<Vec<T>>`, vector elements are already on the heap"
}
declare_clippy_lint! {
/// **What it does:** Checks for use of `Vec<Box<T>>` where T: Sized anywhere in the code.
///
/// **Why is this bad?** `Vec` already keeps its contents in a separate area on
/// the heap. So if you `Box` its contents, you just add another level of indirection.
///
/// **Known problems:** Vec<Box<T: Sized>> makes sense if T is a large type (see #3530,
/// 1st comment).
///
/// **Example:**
/// ```rust
/// struct X {
/// values: Vec<Box<i32>>,
/// }
/// ```
///
/// Better:
///
/// ```rust
/// struct X {
/// values: Vec<i32>,
/// }
/// ```
pub VEC_BOX,
complexity,
"usage of `Vec<Box<T>>` where T: Sized, vector elements are already on the heap"
}
declare_clippy_lint! {
/// **What it does:** Checks for use of `Option<Option<_>>` in function signatures and type
/// definitions
///
/// **Why is this bad?** `Option<_>` represents an optional value. `Option<Option<_>>`
/// represents an optional optional value which is logically the same thing as an optional
/// value but has an unneeded extra level of wrapping.
///
/// **Known problems:** None.
///
/// **Example**
/// ```rust
/// fn x() -> Option<Option<u32>> {
/// None
/// }
/// ```
pub OPTION_OPTION,
complexity,
"usage of `Option<Option<T>>`"
}
declare_clippy_lint! {
/// **What it does:** Checks for usage of any `LinkedList`, suggesting to use a
/// `Vec` or a `VecDeque` (formerly called `RingBuf`).
///
/// **Why is this bad?** Gankro says:
///
/// > The TL;DR of `LinkedList` is that it's built on a massive amount of
/// pointers and indirection.
/// > It wastes memory, it has terrible cache locality, and is all-around slow.
/// `RingBuf`, while
/// > "only" amortized for push/pop, should be faster in the general case for
/// almost every possible
/// > workload, and isn't even amortized at all if you can predict the capacity
/// you need.
/// >
/// > `LinkedList`s are only really good if you're doing a lot of merging or
/// splitting of lists.
/// > This is because they can just mangle some pointers instead of actually
/// copying the data. Even
/// > if you're doing a lot of insertion in the middle of the list, `RingBuf`
/// can still be better
/// > because of how expensive it is to seek to the middle of a `LinkedList`.
///
/// **Known problems:** False positives – the instances where using a
/// `LinkedList` makes sense are few and far between, but they can still happen.
///
/// **Example:**
/// ```rust
/// # use std::collections::LinkedList;
/// let x: LinkedList<usize> = LinkedList::new();
/// ```
pub LINKEDLIST,
pedantic,
"usage of LinkedList, usually a vector is faster, or a more specialized data structure like a VecDeque"
}
declare_clippy_lint! {
/// **What it does:** Checks for use of `&Box<T>` anywhere in the code.
///
/// **Why is this bad?** Any `&Box<T>` can also be a `&T`, which is more
/// general.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// fn foo(bar: &Box<T>) { ... }
/// ```
///
/// Better:
///
/// ```rust,ignore
/// fn foo(bar: &T) { ... }
/// ```
pub BORROWED_BOX,
complexity,
"a borrow of a boxed type"
}
declare_lint_pass!(Types => [BOX_VEC, VEC_BOX, OPTION_OPTION, LINKEDLIST, BORROWED_BOX]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Types {
fn check_fn(&mut self, cx: &LateContext<'_, '_>, _: FnKind<'_>, decl: &FnDecl, _: &Body, _: Span, id: HirId) {
// Skip trait implementations; see issue #605.
if let Some(hir::Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_item(id)) {
if let ItemKind::Impl(_, _, _, _, Some(..), _, _) = item.kind {
return;
}
}
check_fn_decl(cx, decl);
}
fn check_struct_field(&mut self, cx: &LateContext<'_, '_>, field: &hir::StructField) {
check_ty(cx, &field.ty, false);
}
fn check_trait_item(&mut self, cx: &LateContext<'_, '_>, item: &TraitItem) {
match item.kind {
TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => check_ty(cx, ty, false),
TraitItemKind::Method(ref sig, _) => check_fn_decl(cx, &sig.decl),
_ => (),
}
}
fn check_local(&mut self, cx: &LateContext<'_, '_>, local: &Local) {
if let Some(ref ty) = local.ty {
check_ty(cx, ty, true);
}
}
}
fn check_fn_decl(cx: &LateContext<'_, '_>, decl: &FnDecl) {
for input in &decl.inputs {
check_ty(cx, input, false);
}
if let FunctionRetTy::Return(ref ty) = decl.output {
check_ty(cx, ty, false);
}
}
/// Checks if `qpath` has last segment with type parameter matching `path`
fn match_type_parameter(cx: &LateContext<'_, '_>, qpath: &QPath, path: &[&str]) -> bool {
let last = last_path_segment(qpath);
if_chain! {
if let Some(ref params) = last.args;
if !params.parenthesized;
if let Some(ty) = params.args.iter().find_map(|arg| match arg {
GenericArg::Type(ty) => Some(ty),
_ => None,
});
if let TyKind::Path(ref qpath) = ty.kind;
if let Some(did) = qpath_res(cx, qpath, ty.hir_id).opt_def_id();
if match_def_path(cx, did, path);
then {
return true;
}
}
false
}
/// Recursively check for `TypePass` lints in the given type. Stop at the first
/// lint found.
///
/// The parameter `is_local` distinguishes the context of the type; types from
/// local bindings should only be checked for the `BORROWED_BOX` lint.
#[allow(clippy::too_many_lines)]
fn check_ty(cx: &LateContext<'_, '_>, hir_ty: &hir::Ty, is_local: bool) {
if hir_ty.span.from_expansion() {
return;
}
match hir_ty.kind {
TyKind::Path(ref qpath) if !is_local => {
let hir_id = hir_ty.hir_id;
let res = qpath_res(cx, qpath, hir_id);
if let Some(def_id) = res.opt_def_id() {
if Some(def_id) == cx.tcx.lang_items().owned_box() {
if match_type_parameter(cx, qpath, &paths::VEC) {
span_help_and_lint(
cx,
BOX_VEC,
hir_ty.span,
"you seem to be trying to use `Box<Vec<T>>`. Consider using just `Vec<T>`",
"`Vec<T>` is already on the heap, `Box<Vec<T>>` makes an extra allocation.",
);
return; // don't recurse into the type
}
} else if cx.tcx.is_diagnostic_item(Symbol::intern("vec_type"), def_id) {
if_chain! {
// Get the _ part of Vec<_>
if let Some(ref last) = last_path_segment(qpath).args;
if let Some(ty) = last.args.iter().find_map(|arg| match arg {
GenericArg::Type(ty) => Some(ty),
_ => None,
});
// ty is now _ at this point
if let TyKind::Path(ref ty_qpath) = ty.kind;
let res = qpath_res(cx, ty_qpath, ty.hir_id);
if let Some(def_id) = res.opt_def_id();
if Some(def_id) == cx.tcx.lang_items().owned_box();
// At this point, we know ty is Box<T>, now get T
if let Some(ref last) = last_path_segment(ty_qpath).args;
if let Some(boxed_ty) = last.args.iter().find_map(|arg| match arg {
GenericArg::Type(ty) => Some(ty),
_ => None,
});
then {
let ty_ty = hir_ty_to_ty(cx.tcx, boxed_ty);
if ty_ty.is_sized(cx.tcx.at(ty.span), cx.param_env) {
span_lint_and_sugg(
cx,
VEC_BOX,
hir_ty.span,
"`Vec<T>` is already on the heap, the boxing is unnecessary.",
"try",
format!("Vec<{}>", ty_ty),
Applicability::MachineApplicable,
);
return; // don't recurse into the type
}
}
}
} else if match_def_path(cx, def_id, &paths::OPTION) {
if match_type_parameter(cx, qpath, &paths::OPTION) {
span_lint(
cx,
OPTION_OPTION,
hir_ty.span,
"consider using `Option<T>` instead of `Option<Option<T>>` or a custom \
enum if you need to distinguish all 3 cases",
);
return; // don't recurse into the type
}
} else if match_def_path(cx, def_id, &paths::LINKED_LIST) {
span_help_and_lint(
cx,
LINKEDLIST,
hir_ty.span,
"I see you're using a LinkedList! Perhaps you meant some other data structure?",
"a VecDeque might work",
);
return; // don't recurse into the type
}
}
match *qpath {
QPath::Resolved(Some(ref ty), ref p) => {
check_ty(cx, ty, is_local);
for ty in p.segments.iter().flat_map(|seg| {
seg.args
.as_ref()
.map_or_else(|| [].iter(), |params| params.args.iter())
.filter_map(|arg| match arg {
GenericArg::Type(ty) => Some(ty),
_ => None,
})
}) {
check_ty(cx, ty, is_local);
}
},
QPath::Resolved(None, ref p) => {
for ty in p.segments.iter().flat_map(|seg| {
seg.args
.as_ref()
.map_or_else(|| [].iter(), |params| params.args.iter())
.filter_map(|arg| match arg {
GenericArg::Type(ty) => Some(ty),
_ => None,
})
}) {
check_ty(cx, ty, is_local);
}
},
QPath::TypeRelative(ref ty, ref seg) => {
check_ty(cx, ty, is_local);
if let Some(ref params) = seg.args {
for ty in params.args.iter().filter_map(|arg| match arg {
GenericArg::Type(ty) => Some(ty),
_ => None,
}) {
check_ty(cx, ty, is_local);
}
}
},
}
},
TyKind::Rptr(ref lt, ref mut_ty) => check_ty_rptr(cx, hir_ty, is_local, lt, mut_ty),
// recurse
TyKind::Slice(ref ty) | TyKind::Array(ref ty, _) | TyKind::Ptr(MutTy { ref ty, .. }) => {
check_ty(cx, ty, is_local)
},
TyKind::Tup(ref tys) => {
for ty in tys {
check_ty(cx, ty, is_local);
}
},
_ => {},
}
}
fn check_ty_rptr(cx: &LateContext<'_, '_>, hir_ty: &hir::Ty, is_local: bool, lt: &Lifetime, mut_ty: &MutTy) {
match mut_ty.ty.kind {
TyKind::Path(ref qpath) => {
let hir_id = mut_ty.ty.hir_id;
let def = qpath_res(cx, qpath, hir_id);
if_chain! {
if let Some(def_id) = def.opt_def_id();
if Some(def_id) == cx.tcx.lang_items().owned_box();
if let QPath::Resolved(None, ref path) = *qpath;
if let [ref bx] = *path.segments;
if let Some(ref params) = bx.args;
if !params.parenthesized;
if let Some(inner) = params.args.iter().find_map(|arg| match arg {
GenericArg::Type(ty) => Some(ty),
_ => None,
});
then {
if is_any_trait(inner) {
// Ignore `Box<Any>` types; see issue #1884 for details.
return;
}
let ltopt = if lt.is_elided() {
String::new()
} else {
format!("{} ", lt.name.ident().as_str())
};
let mutopt = if mut_ty.mutbl == Mutability::Mutable {
"mut "
} else {
""
};
let mut applicability = Applicability::MachineApplicable;
span_lint_and_sugg(
cx,
BORROWED_BOX,
hir_ty.span,
"you seem to be trying to use `&Box<T>`. Consider using just `&T`",
"try",
format!(
"&{}{}{}",
ltopt,
mutopt,
&snippet_with_applicability(cx, inner.span, "..", &mut applicability)
),
Applicability::Unspecified,
);
return; // don't recurse into the type
}
};
check_ty(cx, &mut_ty.ty, is_local);
},
_ => check_ty(cx, &mut_ty.ty, is_local),
}
}
// Returns true if given type is `Any` trait.
fn is_any_trait(t: &hir::Ty) -> bool {
if_chain! {
if let TyKind::TraitObject(ref traits, _) = t.kind;
if traits.len() >= 1;
// Only Send/Sync can be used as additional traits, so it is enough to
// check only the first trait.
if match_path(&traits[0].trait_ref.path, &paths::ANY_TRAIT);
then {
return true;
}
}
false
}
declare_clippy_lint! {
/// **What it does:** Checks for binding a unit value.
///
/// **Why is this bad?** A unit value cannot usefully be used anywhere. So
/// binding one is kind of pointless.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// let x = {
/// 1;
/// };
/// ```
pub LET_UNIT_VALUE,
style,
"creating a let binding to a value of unit type, which usually can't be used afterwards"
}
declare_lint_pass!(LetUnitValue => [LET_UNIT_VALUE]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for LetUnitValue {
fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
if let StmtKind::Local(ref local) = stmt.kind {
if is_unit(cx.tables.pat_ty(&local.pat)) {
if in_external_macro(cx.sess(), stmt.span) || local.pat.span.from_expansion() {
return;
}
if higher::is_from_for_desugar(local) {
return;
}
span_lint_and_then(cx, LET_UNIT_VALUE, stmt.span, "this let-binding has unit value", |db| {
if let Some(expr) = &local.init {
let snip = snippet_with_macro_callsite(cx, expr.span, "()");
db.span_suggestion(
stmt.span,
"omit the `let` binding",
format!("{};", snip),
Applicability::MachineApplicable, // snippet
);
}
});
}
}
}
}
declare_clippy_lint! {
/// **What it does:** Checks for comparisons to unit. This includes all binary
/// comparisons (like `==` and `<`) and asserts.
///
/// **Why is this bad?** Unit is always equal to itself, and thus is just a
/// clumsily written constant. Mostly this happens when someone accidentally
/// adds semicolons at the end of the operands.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// # fn foo() {};
/// # fn bar() {};
/// # fn baz() {};
/// if {
/// foo();
/// } == {
/// bar();
/// } {
/// baz();
/// }
/// ```
/// is equal to
/// ```rust
/// # fn foo() {};
/// # fn bar() {};
/// # fn baz() {};
/// {
/// foo();
/// bar();
/// baz();
/// }
/// ```
///
/// For asserts:
/// ```rust
/// # fn foo() {};
/// # fn bar() {};
/// assert_eq!({ foo(); }, { bar(); });
/// ```
/// will always succeed
pub UNIT_CMP,
correctness,
"comparing unit values"
}
declare_lint_pass!(UnitCmp => [UNIT_CMP]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnitCmp {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if expr.span.from_expansion() {
if let Some(callee) = expr.span.source_callee() {
if let ExpnKind::Macro(MacroKind::Bang, symbol) = callee.kind {
if let ExprKind::Binary(ref cmp, ref left, _) = expr.kind {
let op = cmp.node;
if op.is_comparison() && is_unit(cx.tables.expr_ty(left)) {
let result = match &*symbol.as_str() {
"assert_eq" | "debug_assert_eq" => "succeed",
"assert_ne" | "debug_assert_ne" => "fail",
_ => return,
};
span_lint(
cx,
UNIT_CMP,
expr.span,
&format!(
"`{}` of unit values detected. This will always {}",
symbol.as_str(),
result
),
);
}
}
}
}
return;
}
if let ExprKind::Binary(ref cmp, ref left, _) = expr.kind {
let op = cmp.node;
if op.is_comparison() && is_unit(cx.tables.expr_ty(left)) {
let result = match op {
BinOpKind::Eq | BinOpKind::Le | BinOpKind::Ge => "true",
_ => "false",
};
span_lint(
cx,
UNIT_CMP,
expr.span,
&format!(
"{}-comparison of unit values detected. This will always be {}",
op.as_str(),
result
),
);
}
}
}
}
declare_clippy_lint! {
/// **What it does:** Checks for passing a unit value as an argument to a function without using a
/// unit literal (`()`).
///
/// **Why is this bad?** This is likely the result of an accidental semicolon.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// foo({
/// let a = bar();
/// baz(a);
/// })
/// ```
pub UNIT_ARG,
complexity,
"passing unit to a function"
}
declare_lint_pass!(UnitArg => [UNIT_ARG]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnitArg {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if expr.span.from_expansion() {
return;
}
// apparently stuff in the desugaring of `?` can trigger this
// so check for that here
// only the calls to `Try::from_error` is marked as desugared,
// so we need to check both the current Expr and its parent.
if is_questionmark_desugar_marked_call(expr) {
return;
}
if_chain! {
let map = &cx.tcx.hir();
let opt_parent_node = map.find(map.get_parent_node(expr.hir_id));
if let Some(hir::Node::Expr(parent_expr)) = opt_parent_node;
if is_questionmark_desugar_marked_call(parent_expr);
then {
return;
}
}
match expr.kind {
ExprKind::Call(_, ref args) | ExprKind::MethodCall(_, _, ref args) => {
for arg in args {
if is_unit(cx.tables.expr_ty(arg)) && !is_unit_literal(arg) {
if let ExprKind::Match(.., match_source) = &arg.kind {
if *match_source == MatchSource::TryDesugar {
continue;
}
}
span_lint_and_sugg(
cx,
UNIT_ARG,
arg.span,
"passing a unit value to a function",
"if you intended to pass a unit value, use a unit literal instead",
"()".to_string(),
Applicability::MachineApplicable,
);
}
}
},
_ => (),
}
}
}
fn is_questionmark_desugar_marked_call(expr: &Expr) -> bool {
use syntax_pos::hygiene::DesugaringKind;
if let ExprKind::Call(ref callee, _) = expr.kind {
callee.span.is_desugaring(DesugaringKind::QuestionMark)
} else {
false
}
}
fn is_unit(ty: Ty<'_>) -> bool {
match ty.kind {
ty::Tuple(slice) if slice.is_empty() => true,
_ => false,
}
}
fn is_unit_literal(expr: &Expr) -> bool {
match expr.kind {
ExprKind::Tup(ref slice) if slice.is_empty() => true,
_ => false,
}
}
declare_clippy_lint! {
/// **What it does:** Checks for casts from any numerical to a float type where
/// the receiving type cannot store all values from the original type without
/// rounding errors. This possible rounding is to be expected, so this lint is
/// `Allow` by default.
///
/// Basically, this warns on casting any integer with 32 or more bits to `f32`
/// or any 64-bit integer to `f64`.
///
/// **Why is this bad?** It's not bad at all. But in some applications it can be
/// helpful to know where precision loss can take place. This lint can help find
/// those places in the code.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// let x = std::u64::MAX;
/// x as f64;
/// ```
pub CAST_PRECISION_LOSS,
pedantic,
"casts that cause loss of precision, e.g., `x as f32` where `x: u64`"
}
declare_clippy_lint! {
/// **What it does:** Checks for casts from a signed to an unsigned numerical
/// type. In this case, negative values wrap around to large positive values,
/// which can be quite surprising in practice. However, as the cast works as
/// defined, this lint is `Allow` by default.
///
/// **Why is this bad?** Possibly surprising results. You can activate this lint
/// as a one-time check to see where numerical wrapping can arise.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// let y: i8 = -1;
/// y as u128; // will return 18446744073709551615
/// ```
pub CAST_SIGN_LOSS,
pedantic,
"casts from signed types to unsigned types, e.g., `x as u32` where `x: i32`"
}
declare_clippy_lint! {
/// **What it does:** Checks for casts between numerical types that may
/// truncate large values. This is expected behavior, so the cast is `Allow` by
/// default.
///
/// **Why is this bad?** In some problem domains, it is good practice to avoid
/// truncation. This lint can be activated to help assess where additional
/// checks could be beneficial.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// fn as_u8(x: u64) -> u8 {
/// x as u8
/// }
/// ```
pub CAST_POSSIBLE_TRUNCATION,
pedantic,
"casts that may cause truncation of the value, e.g., `x as u8` where `x: u32`, or `x as i32` where `x: f32`"
}
declare_clippy_lint! {
/// **What it does:** Checks for casts from an unsigned type to a signed type of
/// the same size. Performing such a cast is a 'no-op' for the compiler,
/// i.e., nothing is changed at the bit level, and the binary representation of
/// the value is reinterpreted. This can cause wrapping if the value is too big
/// for the target signed type. However, the cast works as defined, so this lint
/// is `Allow` by default.
///
/// **Why is this bad?** While such a cast is not bad in itself, the results can
/// be surprising when this is not the intended behavior, as demonstrated by the
/// example below.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// std::u32::MAX as i32; // will yield a value of `-1`
/// ```
pub CAST_POSSIBLE_WRAP,
pedantic,
"casts that may cause wrapping around the value, e.g., `x as i32` where `x: u32` and `x > i32::MAX`"
}
declare_clippy_lint! {
/// **What it does:** Checks for casts between numerical types that may
/// be replaced by safe conversion functions.
///
/// **Why is this bad?** Rust's `as` keyword will perform many kinds of
/// conversions, including silently lossy conversions. Conversion functions such
/// as `i32::from` will only perform lossless conversions. Using the conversion
/// functions prevents conversions from turning into silent lossy conversions if
/// the types of the input expressions ever change, and make it easier for
/// people reading the code to know that the conversion is lossless.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// fn as_u64(x: u8) -> u64 {
/// x as u64
/// }
/// ```
///
/// Using `::from` would look like this:
///
/// ```rust
/// fn as_u64(x: u8) -> u64 {
/// u64::from(x)
/// }
/// ```
pub CAST_LOSSLESS,
pedantic,
"casts using `as` that are known to be lossless, e.g., `x as u64` where `x: u8`"
}
declare_clippy_lint! {
/// **What it does:** Checks for casts to the same type.
///
/// **Why is this bad?** It's just unnecessary.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// let _ = 2i32 as i32;
/// ```
pub UNNECESSARY_CAST,
complexity,
"cast to the same type, e.g., `x as i32` where `x: i32`"
}
declare_clippy_lint! {
/// **What it does:** Checks for casts from a less-strictly-aligned pointer to a
/// more-strictly-aligned pointer
///
/// **Why is this bad?** Dereferencing the resulting pointer may be undefined
/// behavior.
///
/// **Known problems:** Using `std::ptr::read_unaligned` and `std::ptr::write_unaligned` or similar
/// on the resulting pointer is fine.
///
/// **Example:**
/// ```rust
/// let _ = (&1u8 as *const u8) as *const u16;
/// let _ = (&mut 1u8 as *mut u8) as *mut u16;
/// ```
pub CAST_PTR_ALIGNMENT,
correctness,
"cast from a pointer to a more-strictly-aligned pointer"
}
declare_clippy_lint! {
/// **What it does:** Checks for casts of function pointers to something other than usize
///
/// **Why is this bad?**
/// Casting a function pointer to anything other than usize/isize is not portable across
/// architectures, because you end up losing bits if the target type is too small or end up with a
/// bunch of extra bits that waste space and add more instructions to the final binary than
/// strictly necessary for the problem
///
/// Casting to isize also doesn't make sense since there are no signed addresses.
///
/// **Example**
///
/// ```rust
/// // Bad
/// fn fun() -> i32 { 1 }
/// let a = fun as i64;
///
/// // Good
/// fn fun2() -> i32 { 1 }
/// let a = fun2 as usize;
/// ```
pub FN_TO_NUMERIC_CAST,
style,
"casting a function pointer to a numeric type other than usize"
}
declare_clippy_lint! {
/// **What it does:** Checks for casts of a function pointer to a numeric type not wide enough to
/// store address.
///
/// **Why is this bad?**
/// Such a cast discards some bits of the function's address. If this is intended, it would be more
/// clearly expressed by casting to usize first, then casting the usize to the intended type (with
/// a comment) to perform the truncation.
///
/// **Example**
///
/// ```rust
/// // Bad
/// fn fn1() -> i16 {
/// 1
/// };
/// let _ = fn1 as i32;
///
/// // Better: Cast to usize first, then comment with the reason for the truncation
/// fn fn2() -> i16 {
/// 1
/// };
/// let fn_ptr = fn2 as usize;
/// let fn_ptr_truncated = fn_ptr as i32;
/// ```
pub FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
style,
"casting a function pointer to a numeric type not wide enough to store the address"
}
/// Returns the size in bits of an integral type.
/// Will return 0 if the type is not an int or uint variant
fn int_ty_to_nbits(typ: Ty<'_>, tcx: TyCtxt<'_>) -> u64 {
match typ.kind {
ty::Int(i) => match i {
IntTy::Isize => tcx.data_layout.pointer_size.bits(),
IntTy::I8 => 8,
IntTy::I16 => 16,
IntTy::I32 => 32,
IntTy::I64 => 64,
IntTy::I128 => 128,
},
ty::Uint(i) => match i {
UintTy::Usize => tcx.data_layout.pointer_size.bits(),
UintTy::U8 => 8,
UintTy::U16 => 16,
UintTy::U32 => 32,
UintTy::U64 => 64,
UintTy::U128 => 128,
},
_ => 0,
}
}
fn is_isize_or_usize(typ: Ty<'_>) -> bool {
match typ.kind {
ty::Int(IntTy::Isize) | ty::Uint(UintTy::Usize) => true,
_ => false,
}
}
fn span_precision_loss_lint(cx: &LateContext<'_, '_>, expr: &Expr, cast_from: Ty<'_>, cast_to_f64: bool) {
let mantissa_nbits = if cast_to_f64 { 52 } else { 23 };
let arch_dependent = is_isize_or_usize(cast_from) && cast_to_f64;
let arch_dependent_str = "on targets with 64-bit wide pointers ";
let from_nbits_str = if arch_dependent {
"64".to_owned()
} else if is_isize_or_usize(cast_from) {
"32 or 64".to_owned()
} else {
int_ty_to_nbits(cast_from, cx.tcx).to_string()
};
span_lint(
cx,
CAST_PRECISION_LOSS,
expr.span,
&format!(
"casting {0} to {1} causes a loss of precision {2}({0} is {3} bits wide, but {1}'s mantissa \
is only {4} bits wide)",
cast_from,
if cast_to_f64 { "f64" } else { "f32" },
if arch_dependent { arch_dependent_str } else { "" },
from_nbits_str,
mantissa_nbits
),
);
}
fn should_strip_parens(op: &Expr, snip: &str) -> bool {
if let ExprKind::Binary(_, _, _) = op.kind {
if snip.starts_with('(') && snip.ends_with(')') {
return true;
}
}
false
}
fn span_lossless_lint(cx: &LateContext<'_, '_>, expr: &Expr, op: &Expr, cast_from: Ty<'_>, cast_to: Ty<'_>) {
// Do not suggest using From in consts/statics until it is valid to do so (see #2267).
if in_constant(cx, expr.hir_id) {
return;
}
// The suggestion is to use a function call, so if the original expression
// has parens on the outside, they are no longer needed.
let mut applicability = Applicability::MachineApplicable;
let opt = snippet_opt(cx, op.span);
let sugg = if let Some(ref snip) = opt {
if should_strip_parens(op, snip) {
&snip[1..snip.len() - 1]
} else {
snip.as_str()
}
} else {
applicability = Applicability::HasPlaceholders;
".."
};
span_lint_and_sugg(
cx,
CAST_LOSSLESS,
expr.span,
&format!(
"casting {} to {} may become silently lossy if you later change the type",
cast_from, cast_to
),
"try",
format!("{}::from({})", cast_to, sugg),
applicability,
);
}
enum ArchSuffix {
_32,
_64,
None,
}
fn check_loss_of_sign(cx: &LateContext<'_, '_>, expr: &Expr, op: &Expr, cast_from: Ty<'_>, cast_to: Ty<'_>) {
if !cast_from.is_signed() || cast_to.is_signed() {
return;
}
// don't lint for positive constants
let const_val = constant(cx, &cx.tables, op);
if_chain! {
if let Some((const_val, _)) = const_val;
if let Constant::Int(n) = const_val;
if let ty::Int(ity) = cast_from.kind;
if sext(cx.tcx, n, ity) >= 0;
then {
return
}
}
// don't lint for the result of `abs`
// `abs` is an inherent impl of `i{N}`, so a method call with ident `abs` will always
// resolve to that spesific method
if_chain! {
if let ExprKind::MethodCall(ref path, _, _) = op.kind;
if path.ident.name.as_str() == "abs";
then {
return
}
}
span_lint(
cx,
CAST_SIGN_LOSS,
expr.span,
&format!("casting {} to {} may lose the sign of the value", cast_from, cast_to),
);
}
fn check_truncation_and_wrapping(cx: &LateContext<'_, '_>, expr: &Expr, cast_from: Ty<'_>, cast_to: Ty<'_>) {
let arch_64_suffix = " on targets with 64-bit wide pointers";
let arch_32_suffix = " on targets with 32-bit wide pointers";
let cast_unsigned_to_signed = !cast_from.is_signed() && cast_to.is_signed();
let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
let (span_truncation, suffix_truncation, span_wrap, suffix_wrap) =
match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {
(true, true) | (false, false) => (
to_nbits < from_nbits,
ArchSuffix::None,
to_nbits == from_nbits && cast_unsigned_to_signed,
ArchSuffix::None,
),
(true, false) => (
to_nbits <= 32,
if to_nbits == 32 {
ArchSuffix::_64
} else {
ArchSuffix::None
},
to_nbits <= 32 && cast_unsigned_to_signed,
ArchSuffix::_32,
),
(false, true) => (
from_nbits == 64,
ArchSuffix::_32,
cast_unsigned_to_signed,
if from_nbits == 64 {
ArchSuffix::_64
} else {
ArchSuffix::_32
},
),
};
if span_truncation {
span_lint(
cx,
CAST_POSSIBLE_TRUNCATION,
expr.span,
&format!(
"casting {} to {} may truncate the value{}",
cast_from,
cast_to,
match suffix_truncation {
ArchSuffix::_32 => arch_32_suffix,
ArchSuffix::_64 => arch_64_suffix,
ArchSuffix::None => "",
}
),
);
}
if span_wrap {
span_lint(
cx,
CAST_POSSIBLE_WRAP,
expr.span,
&format!(
"casting {} to {} may wrap around the value{}",
cast_from,
cast_to,
match suffix_wrap {
ArchSuffix::_32 => arch_32_suffix,
ArchSuffix::_64 => arch_64_suffix,
ArchSuffix::None => "",
}
),
);
}
}
fn check_lossless(cx: &LateContext<'_, '_>, expr: &Expr, op: &Expr, cast_from: Ty<'_>, cast_to: Ty<'_>) {
let cast_signed_to_unsigned = cast_from.is_signed() && !cast_to.is_signed();
let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
if !is_isize_or_usize(cast_from) && !is_isize_or_usize(cast_to) && from_nbits < to_nbits && !cast_signed_to_unsigned
{
span_lossless_lint(cx, expr, op, cast_from, cast_to);
}
}
declare_lint_pass!(Casts => [
CAST_PRECISION_LOSS,
CAST_SIGN_LOSS,
CAST_POSSIBLE_TRUNCATION,
CAST_POSSIBLE_WRAP,
CAST_LOSSLESS,
UNNECESSARY_CAST,
CAST_PTR_ALIGNMENT,
FN_TO_NUMERIC_CAST,
FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
]);
// Check if the given type is either `core::ffi::c_void` or
// one of the platform specific `libc::<platform>::c_void` of libc.
fn is_c_void(cx: &LateContext<'_, '_>, ty: Ty<'_>) -> bool {
if let ty::Adt(adt, _) = ty.kind {
let names = cx.get_def_path(adt.did);
if names.is_empty() {
return false;
}
if names[0] == sym!(libc) || names[0] == sym::core && *names.last().unwrap() == sym!(c_void) {
return true;
}
}
false
}
/// Returns the mantissa bits wide of a fp type.
/// Will return 0 if the type is not a fp
fn fp_ty_mantissa_nbits(typ: Ty<'_>) -> u32 {
match typ.kind {
ty::Float(FloatTy::F32) => 23,
ty::Float(FloatTy::F64) | ty::Infer(InferTy::FloatVar(_)) => 52,
_ => 0,
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Casts {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if expr.span.from_expansion() {
return;
}
if let ExprKind::Cast(ref ex, _) = expr.kind {
let (cast_from, cast_to) = (cx.tables.expr_ty(ex), cx.tables.expr_ty(expr));
lint_fn_to_numeric_cast(cx, expr, ex, cast_from, cast_to);
if let ExprKind::Lit(ref lit) = ex.kind {
if let LitKind::Int(n, _) = lit.node {
if cast_to.is_floating_point() {
let from_nbits = 128 - n.leading_zeros();
let to_nbits = fp_ty_mantissa_nbits(cast_to);
if from_nbits != 0 && to_nbits != 0 && from_nbits <= to_nbits {
span_lint_and_sugg(
cx,
UNNECESSARY_CAST,
expr.span,
&format!("casting integer literal to {} is unnecessary", cast_to),
"try",
format!("{}_{}", n, cast_to),
Applicability::MachineApplicable,
);
return;
}
}
}
match lit.node {
LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed) => {},
_ => {
if cast_from.kind == cast_to.kind && !in_external_macro(cx.sess(), expr.span) {
span_lint(
cx,
UNNECESSARY_CAST,
expr.span,
&format!(
"casting to the same type is unnecessary (`{}` -> `{}`)",
cast_from, cast_to
),
);
}
},
}
}
if cast_from.is_numeric() && cast_to.is_numeric() && !in_external_macro(cx.sess(), expr.span) {
lint_numeric_casts(cx, expr, ex, cast_from, cast_to);
}
lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
}
}
}
fn lint_numeric_casts<'tcx>(
cx: &LateContext<'_, 'tcx>,
expr: &Expr,
cast_expr: &Expr,
cast_from: Ty<'tcx>,
cast_to: Ty<'tcx>,
) {
match (cast_from.is_integral(), cast_to.is_integral()) {
(true, false) => {
let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
let to_nbits = if let ty::Float(FloatTy::F32) = cast_to.kind {
32
} else {
64
};
if is_isize_or_usize(cast_from) || from_nbits >= to_nbits {
span_precision_loss_lint(cx, expr, cast_from, to_nbits == 64);
}
if from_nbits < to_nbits {
span_lossless_lint(cx, expr, cast_expr, cast_from, cast_to);
}
},
(false, true) => {
span_lint(
cx,
CAST_POSSIBLE_TRUNCATION,
expr.span,
&format!("casting {} to {} may truncate the value", cast_from, cast_to),
);
if !cast_to.is_signed() {
span_lint(
cx,
CAST_SIGN_LOSS,
expr.span,
&format!("casting {} to {} may lose the sign of the value", cast_from, cast_to),
);
}
},
(true, true) => {
check_loss_of_sign(cx, expr, cast_expr, cast_from, cast_to);
check_truncation_and_wrapping(cx, expr, cast_from, cast_to);
check_lossless(cx, expr, cast_expr, cast_from, cast_to);
},
(false, false) => {
if let (&ty::Float(FloatTy::F64), &ty::Float(FloatTy::F32)) = (&cast_from.kind, &cast_to.kind) {
span_lint(
cx,
CAST_POSSIBLE_TRUNCATION,
expr.span,
"casting f64 to f32 may truncate the value",
);
}
if let (&ty::Float(FloatTy::F32), &ty::Float(FloatTy::F64)) = (&cast_from.kind, &cast_to.kind) {
span_lossless_lint(cx, expr, cast_expr, cast_from, cast_to);
}
},
}
}
fn lint_cast_ptr_alignment<'tcx>(cx: &LateContext<'_, 'tcx>, expr: &Expr, cast_from: Ty<'tcx>, cast_to: Ty<'tcx>) {
if_chain! {
if let ty::RawPtr(from_ptr_ty) = &cast_from.kind;
if let ty::RawPtr(to_ptr_ty) = &cast_to.kind;
if let Ok(from_layout) = cx.layout_of(from_ptr_ty.ty);
if let Ok(to_layout) = cx.layout_of(to_ptr_ty.ty);
if from_layout.align.abi < to_layout.align.abi;
// with c_void, we inherently need to trust the user
if !is_c_void(cx, from_ptr_ty.ty);
// when casting from a ZST, we don't know enough to properly lint
if !from_layout.is_zst();
then {
span_lint(
cx,
CAST_PTR_ALIGNMENT,
expr.span,
&format!(
"casting from `{}` to a more-strictly-aligned pointer (`{}`) ({} < {} bytes)",
cast_from,
cast_to,
from_layout.align.abi.bytes(),
to_layout.align.abi.bytes(),
),
);
}
}
}
fn lint_fn_to_numeric_cast(
cx: &LateContext<'_, '_>,
expr: &Expr,
cast_expr: &Expr,
cast_from: Ty<'_>,
cast_to: Ty<'_>,
) {
// We only want to check casts to `ty::Uint` or `ty::Int`
match cast_to.kind {
ty::Uint(_) | ty::Int(..) => { /* continue on */ },
_ => return,
}
match cast_from.kind {
ty::FnDef(..) | ty::FnPtr(_) => {
let mut applicability = Applicability::MaybeIncorrect;
let from_snippet = snippet_with_applicability(cx, cast_expr.span, "x", &mut applicability);
let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
if to_nbits < cx.tcx.data_layout.pointer_size.bits() {
span_lint_and_sugg(
cx,
FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
expr.span,
&format!(
"casting function pointer `{}` to `{}`, which truncates the value",
from_snippet, cast_to
),
"try",
format!("{} as usize", from_snippet),
applicability,
);
} else if cast_to.kind != ty::Uint(UintTy::Usize) {
span_lint_and_sugg(
cx,
FN_TO_NUMERIC_CAST,
expr.span,
&format!("casting function pointer `{}` to `{}`", from_snippet, cast_to),
"try",
format!("{} as usize", from_snippet),
applicability,
);
}
},
_ => {},
}
}
declare_clippy_lint! {
/// **What it does:** Checks for types used in structs, parameters and `let`
/// declarations above a certain complexity threshold.
///
/// **Why is this bad?** Too complex types make the code less readable. Consider
/// using a `type` definition to simplify them.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// # use std::rc::Rc;
/// struct Foo {
/// inner: Rc<Vec<Vec<Box<(u32, u32, u32, u32)>>>>,
/// }
/// ```
pub TYPE_COMPLEXITY,
complexity,
"usage of very complex types that might be better factored into `type` definitions"
}
pub struct TypeComplexity {
threshold: u64,
}
impl TypeComplexity {
#[must_use]
pub fn new(threshold: u64) -> Self {
Self { threshold }
}
}
impl_lint_pass!(TypeComplexity => [TYPE_COMPLEXITY]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for TypeComplexity {
fn check_fn(
&mut self,
cx: &LateContext<'a, 'tcx>,
_: FnKind<'tcx>,
decl: &'tcx FnDecl,
_: &'tcx Body,
_: Span,
_: HirId,
) {
self.check_fndecl(cx, decl);
}
fn check_struct_field(&mut self, cx: &LateContext<'a, 'tcx>, field: &'tcx hir::StructField) {
// enum variants are also struct fields now
self.check_type(cx, &field.ty);
}
fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
match item.kind {
ItemKind::Static(ref ty, _, _) | ItemKind::Const(ref ty, _) => self.check_type(cx, ty),
// functions, enums, structs, impls and traits are covered
_ => (),
}
}
fn check_trait_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx TraitItem) {
match item.kind {
TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_type(cx, ty),
TraitItemKind::Method(FnSig { ref decl, .. }, TraitMethod::Required(_)) => self.check_fndecl(cx, decl),
// methods with default impl are covered by check_fn
_ => (),
}
}
fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx ImplItem) {
match item.kind {
ImplItemKind::Const(ref ty, _) | ImplItemKind::TyAlias(ref ty) => self.check_type(cx, ty),
// methods are covered by check_fn
_ => (),
}
}
fn check_local(&mut self, cx: &LateContext<'a, 'tcx>, local: &'tcx Local) {
if let Some(ref ty) = local.ty {
self.check_type(cx, ty);
}
}
}
impl<'a, 'tcx> TypeComplexity {
fn check_fndecl(&self, cx: &LateContext<'a, 'tcx>, decl: &'tcx FnDecl) {
for arg in &decl.inputs {
self.check_type(cx, arg);
}
if let Return(ref ty) = decl.output {
self.check_type(cx, ty);
}
}
fn check_type(&self, cx: &LateContext<'_, '_>, ty: &hir::Ty) {
if ty.span.from_expansion() {
return;
}
let score = {
let mut visitor = TypeComplexityVisitor { score: 0, nest: 1 };
visitor.visit_ty(ty);
visitor.score
};
if score > self.threshold {
span_lint(
cx,
TYPE_COMPLEXITY,
ty.span,
"very complex type used. Consider factoring parts into `type` definitions",
);
}
}
}
/// Walks a type and assigns a complexity score to it.
struct TypeComplexityVisitor {
/// total complexity score of the type
score: u64,
/// current nesting level
nest: u64,
}
impl<'tcx> Visitor<'tcx> for TypeComplexityVisitor {
fn visit_ty(&mut self, ty: &'tcx hir::Ty) {
let (add_score, sub_nest) = match ty.kind {
// _, &x and *x have only small overhead; don't mess with nesting level
TyKind::Infer | TyKind::Ptr(..) | TyKind::Rptr(..) => (1, 0),
// the "normal" components of a type: named types, arrays/tuples
TyKind::Path(..) | TyKind::Slice(..) | TyKind::Tup(..) | TyKind::Array(..) => (10 * self.nest, 1),
// function types bring a lot of overhead
TyKind::BareFn(ref bare) if bare.abi == Abi::Rust => (50 * self.nest, 1),
TyKind::TraitObject(ref param_bounds, _) => {
let has_lifetime_parameters = param_bounds.iter().any(|bound| {
bound.bound_generic_params.iter().any(|gen| match gen.kind {
GenericParamKind::Lifetime { .. } => true,
_ => false,
})
});
if has_lifetime_parameters {
// complex trait bounds like A<'a, 'b>
(50 * self.nest, 1)
} else {
// simple trait bounds like A + B
(20 * self.nest, 0)
}
},
_ => (0, 0),
};
self.score += add_score;
self.nest += sub_nest;
walk_ty(self, ty);
self.nest -= sub_nest;
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
declare_clippy_lint! {
/// **What it does:** Checks for expressions where a character literal is cast
/// to `u8` and suggests using a byte literal instead.
///
/// **Why is this bad?** In general, casting values to smaller types is
/// error-prone and should be avoided where possible. In the particular case of
/// converting a character literal to u8, it is easy to avoid by just using a
/// byte literal instead. As an added bonus, `b'a'` is even slightly shorter
/// than `'a' as u8`.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// 'x' as u8
/// ```
///
/// A better version, using the byte literal:
///
/// ```rust,ignore
/// b'x'
/// ```
pub CHAR_LIT_AS_U8,
complexity,
"casting a character literal to u8 truncates"
}
declare_lint_pass!(CharLitAsU8 => [CHAR_LIT_AS_U8]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for CharLitAsU8 {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if_chain! {
if !expr.span.from_expansion();
if let ExprKind::Cast(e, _) = &expr.kind;
if let ExprKind::Lit(l) = &e.kind;
if let LitKind::Char(c) = l.node;
if ty::Uint(UintTy::U8) == cx.tables.expr_ty(expr).kind;
then {
let mut applicability = Applicability::MachineApplicable;
let snippet = snippet_with_applicability(cx, e.span, "'x'", &mut applicability);
span_lint_and_then(
cx,
CHAR_LIT_AS_U8,
expr.span,
"casting a character literal to `u8` truncates",
|db| {
db.note("`char` is four bytes wide, but `u8` is a single byte");
if c.is_ascii() {
db.span_suggestion(
expr.span,
"use a byte literal instead",
format!("b{}", snippet),
applicability,
);
}
});
}
}
}
}
declare_clippy_lint! {
/// **What it does:** Checks for comparisons where one side of the relation is
/// either the minimum or maximum value for its type and warns if it involves a
/// case that is always true or always false. Only integer and boolean types are
/// checked.
///
/// **Why is this bad?** An expression like `min <= x` may misleadingly imply
/// that it is possible for `x` to be less than the minimum. Expressions like
/// `max < x` are probably mistakes.
///
/// **Known problems:** For `usize` the size of the current compile target will
/// be assumed (e.g., 64 bits on 64 bit systems). This means code that uses such
/// a comparison to detect target pointer width will trigger this lint. One can
/// use `mem::sizeof` and compare its value or conditional compilation
/// attributes
/// like `#[cfg(target_pointer_width = "64")] ..` instead.
///
/// **Example:**
///
/// ```rust
/// let vec: Vec<isize> = vec![];
/// if vec.len() <= 0 {}
/// if 100 > std::i32::MAX {}
/// ```
pub ABSURD_EXTREME_COMPARISONS,
correctness,
"a comparison with a maximum or minimum value that is always true or false"
}
declare_lint_pass!(AbsurdExtremeComparisons => [ABSURD_EXTREME_COMPARISONS]);
enum ExtremeType {
Minimum,
Maximum,
}
struct ExtremeExpr<'a> {
which: ExtremeType,
expr: &'a Expr,
}
enum AbsurdComparisonResult {
AlwaysFalse,
AlwaysTrue,
InequalityImpossible,
}
fn is_cast_between_fixed_and_target<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> bool {
if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
let precast_ty = cx.tables.expr_ty(cast_exp);
let cast_ty = cx.tables.expr_ty(expr);
return is_isize_or_usize(precast_ty) != is_isize_or_usize(cast_ty);
}
false
}
fn detect_absurd_comparison<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
op: BinOpKind,
lhs: &'tcx Expr,
rhs: &'tcx Expr,
) -> Option<(ExtremeExpr<'tcx>, AbsurdComparisonResult)> {
use crate::types::AbsurdComparisonResult::*;
use crate::types::ExtremeType::*;
use crate::utils::comparisons::*;
// absurd comparison only makes sense on primitive types
// primitive types don't implement comparison operators with each other
if cx.tables.expr_ty(lhs) != cx.tables.expr_ty(rhs) {
return None;
}
// comparisons between fix sized types and target sized types are considered unanalyzable
if is_cast_between_fixed_and_target(cx, lhs) || is_cast_between_fixed_and_target(cx, rhs) {
return None;
}
let normalized = normalize_comparison(op, lhs, rhs);
let (rel, normalized_lhs, normalized_rhs) = if let Some(val) = normalized {
val
} else {
return None;
};
let lx = detect_extreme_expr(cx, normalized_lhs);
let rx = detect_extreme_expr(cx, normalized_rhs);
Some(match rel {
Rel::Lt => {
match (lx, rx) {
(Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, AlwaysFalse), // max < x
(_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, AlwaysFalse), // x < min
_ => return None,
}
},
Rel::Le => {
match (lx, rx) {
(Some(l @ ExtremeExpr { which: Minimum, .. }), _) => (l, AlwaysTrue), // min <= x
(Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, InequalityImpossible), // max <= x
(_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, InequalityImpossible), // x <= min
(_, Some(r @ ExtremeExpr { which: Maximum, .. })) => (r, AlwaysTrue), // x <= max
_ => return None,
}
},
Rel::Ne | Rel::Eq => return None,
})
}
fn detect_extreme_expr<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> Option<ExtremeExpr<'tcx>> {
use crate::types::ExtremeType::*;
let ty = cx.tables.expr_ty(expr);
let cv = constant(cx, cx.tables, expr)?.0;
let which = match (&ty.kind, cv) {
(&ty::Bool, Constant::Bool(false)) | (&ty::Uint(_), Constant::Int(0)) => Minimum,
(&ty::Int(ity), Constant::Int(i))
if i == unsext(cx.tcx, i128::min_value() >> (128 - int_bits(cx.tcx, ity)), ity) =>
{
Minimum
},
(&ty::Bool, Constant::Bool(true)) => Maximum,
(&ty::Int(ity), Constant::Int(i))
if i == unsext(cx.tcx, i128::max_value() >> (128 - int_bits(cx.tcx, ity)), ity) =>
{
Maximum
},
(&ty::Uint(uty), Constant::Int(i)) if clip(cx.tcx, u128::max_value(), uty) == i => Maximum,
_ => return None,
};
Some(ExtremeExpr { which, expr })
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for AbsurdExtremeComparisons {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
use crate::types::AbsurdComparisonResult::*;
use crate::types::ExtremeType::*;
if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
if let Some((culprit, result)) = detect_absurd_comparison(cx, cmp.node, lhs, rhs) {
if !expr.span.from_expansion() {
let msg = "this comparison involving the minimum or maximum element for this \
type contains a case that is always true or always false";
let conclusion = match result {
AlwaysFalse => "this comparison is always false".to_owned(),
AlwaysTrue => "this comparison is always true".to_owned(),
InequalityImpossible => format!(
"the case where the two sides are not equal never occurs, consider using {} == {} \
instead",
snippet(cx, lhs.span, "lhs"),
snippet(cx, rhs.span, "rhs")
),
};
let help = format!(
"because {} is the {} value for this type, {}",
snippet(cx, culprit.expr.span, "x"),
match culprit.which {
Minimum => "minimum",
Maximum => "maximum",
},
conclusion
);
span_help_and_lint(cx, ABSURD_EXTREME_COMPARISONS, expr.span, msg, &help);
}
}
}
}
}
declare_clippy_lint! {
/// **What it does:** Checks for comparisons where the relation is always either
/// true or false, but where one side has been upcast so that the comparison is
/// necessary. Only integer types are checked.
///
/// **Why is this bad?** An expression like `let x : u8 = ...; (x as u32) > 300`
/// will mistakenly imply that it is possible for `x` to be outside the range of
/// `u8`.
///
/// **Known problems:**
/// https://github.com/rust-lang/rust-clippy/issues/886
///
/// **Example:**
/// ```rust
/// let x: u8 = 1;
/// (x as u32) > 300;
/// ```
pub INVALID_UPCAST_COMPARISONS,
pedantic,
"a comparison involving an upcast which is always true or false"
}
declare_lint_pass!(InvalidUpcastComparisons => [INVALID_UPCAST_COMPARISONS]);
#[derive(Copy, Clone, Debug, Eq)]
enum FullInt {
S(i128),
U(u128),
}
impl FullInt {
#[allow(clippy::cast_sign_loss)]
#[must_use]
fn cmp_s_u(s: i128, u: u128) -> Ordering {
if s < 0 {
Ordering::Less
} else if u > (i128::max_value() as u128) {
Ordering::Greater
} else {
(s as u128).cmp(&u)
}
}
}
impl PartialEq for FullInt {
#[must_use]
fn eq(&self, other: &Self) -> bool {
self.partial_cmp(other).expect("partial_cmp only returns Some(_)") == Ordering::Equal
}
}
impl PartialOrd for FullInt {
#[must_use]
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
Some(match (self, other) {
(&Self::S(s), &Self::S(o)) => s.cmp(&o),
(&Self::U(s), &Self::U(o)) => s.cmp(&o),
(&Self::S(s), &Self::U(o)) => Self::cmp_s_u(s, o),
(&Self::U(s), &Self::S(o)) => Self::cmp_s_u(o, s).reverse(),
})
}
}
impl Ord for FullInt {
#[must_use]
fn cmp(&self, other: &Self) -> Ordering {
self.partial_cmp(other)
.expect("partial_cmp for FullInt can never return None")
}
}
fn numeric_cast_precast_bounds<'a>(cx: &LateContext<'_, '_>, expr: &'a Expr) -> Option<(FullInt, FullInt)> {
use std::*;
if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
let pre_cast_ty = cx.tables.expr_ty(cast_exp);
let cast_ty = cx.tables.expr_ty(expr);
// if it's a cast from i32 to u32 wrapping will invalidate all these checks
if cx.layout_of(pre_cast_ty).ok().map(|l| l.size) == cx.layout_of(cast_ty).ok().map(|l| l.size) {
return None;
}
match pre_cast_ty.kind {
ty::Int(int_ty) => Some(match int_ty {
IntTy::I8 => (
FullInt::S(i128::from(i8::min_value())),
FullInt::S(i128::from(i8::max_value())),
),
IntTy::I16 => (
FullInt::S(i128::from(i16::min_value())),
FullInt::S(i128::from(i16::max_value())),
),
IntTy::I32 => (
FullInt::S(i128::from(i32::min_value())),
FullInt::S(i128::from(i32::max_value())),
),
IntTy::I64 => (
FullInt::S(i128::from(i64::min_value())),
FullInt::S(i128::from(i64::max_value())),
),
IntTy::I128 => (FullInt::S(i128::min_value()), FullInt::S(i128::max_value())),
IntTy::Isize => (
FullInt::S(isize::min_value() as i128),
FullInt::S(isize::max_value() as i128),
),
}),
ty::Uint(uint_ty) => Some(match uint_ty {
UintTy::U8 => (
FullInt::U(u128::from(u8::min_value())),
FullInt::U(u128::from(u8::max_value())),
),
UintTy::U16 => (
FullInt::U(u128::from(u16::min_value())),
FullInt::U(u128::from(u16::max_value())),
),
UintTy::U32 => (
FullInt::U(u128::from(u32::min_value())),
FullInt::U(u128::from(u32::max_value())),
),
UintTy::U64 => (
FullInt::U(u128::from(u64::min_value())),
FullInt::U(u128::from(u64::max_value())),
),
UintTy::U128 => (FullInt::U(u128::min_value()), FullInt::U(u128::max_value())),
UintTy::Usize => (
FullInt::U(usize::min_value() as u128),
FullInt::U(usize::max_value() as u128),
),
}),
_ => None,
}
} else {
None
}
}
fn node_as_const_fullint<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> Option<FullInt> {
let val = constant(cx, cx.tables, expr)?.0;
if let Constant::Int(const_int) = val {
match cx.tables.expr_ty(expr).kind {
ty::Int(ity) => Some(FullInt::S(sext(cx.tcx, const_int, ity))),
ty::Uint(_) => Some(FullInt::U(const_int)),
_ => None,
}
} else {
None
}
}
fn err_upcast_comparison(cx: &LateContext<'_, '_>, span: Span, expr: &Expr, always: bool) {
if let ExprKind::Cast(ref cast_val, _) = expr.kind {
span_lint(
cx,
INVALID_UPCAST_COMPARISONS,
span,
&format!(
"because of the numeric bounds on `{}` prior to casting, this expression is always {}",
snippet(cx, cast_val.span, "the expression"),
if always { "true" } else { "false" },
),
);
}
}
fn upcast_comparison_bounds_err<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
span: Span,
rel: comparisons::Rel,
lhs_bounds: Option<(FullInt, FullInt)>,
lhs: &'tcx Expr,
rhs: &'tcx Expr,
invert: bool,
) {
use crate::utils::comparisons::*;
if let Some((lb, ub)) = lhs_bounds {
if let Some(norm_rhs_val) = node_as_const_fullint(cx, rhs) {
if rel == Rel::Eq || rel == Rel::Ne {
if norm_rhs_val < lb || norm_rhs_val > ub {
err_upcast_comparison(cx, span, lhs, rel == Rel::Ne);
}
} else if match rel {
Rel::Lt => {
if invert {
norm_rhs_val < lb
} else {
ub < norm_rhs_val
}
},
Rel::Le => {
if invert {
norm_rhs_val <= lb
} else {
ub <= norm_rhs_val
}
},
Rel::Eq | Rel::Ne => unreachable!(),
} {
err_upcast_comparison(cx, span, lhs, true)
} else if match rel {
Rel::Lt => {
if invert {
norm_rhs_val >= ub
} else {
lb >= norm_rhs_val
}
},
Rel::Le => {
if invert {
norm_rhs_val > ub
} else {
lb > norm_rhs_val
}
},
Rel::Eq | Rel::Ne => unreachable!(),
} {
err_upcast_comparison(cx, span, lhs, false)
}
}
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidUpcastComparisons {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
let normalized = comparisons::normalize_comparison(cmp.node, lhs, rhs);
let (rel, normalized_lhs, normalized_rhs) = if let Some(val) = normalized {
val
} else {
return;
};
let lhs_bounds = numeric_cast_precast_bounds(cx, normalized_lhs);
let rhs_bounds = numeric_cast_precast_bounds(cx, normalized_rhs);
upcast_comparison_bounds_err(cx, expr.span, rel, lhs_bounds, normalized_lhs, normalized_rhs, false);
upcast_comparison_bounds_err(cx, expr.span, rel, rhs_bounds, normalized_rhs, normalized_lhs, true);
}
}
}
declare_clippy_lint! {
/// **What it does:** Checks for public `impl` or `fn` missing generalization
/// over different hashers and implicitly defaulting to the default hashing
/// algorithm (`SipHash`).
///
/// **Why is this bad?** `HashMap` or `HashSet` with custom hashers cannot be
/// used with them.
///
/// **Known problems:** Suggestions for replacing constructors can contain
/// false-positives. Also applying suggestions can require modification of other
/// pieces of code, possibly including external crates.
///
/// **Example:**
/// ```rust
/// # use std::collections::HashMap;
/// # use std::hash::{Hash, BuildHasher};
/// # trait Serialize {};
/// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
///
/// pub fn foo(map: &mut HashMap<i32, i32>) { }
/// ```
/// could be rewritten as
/// ```rust
/// # use std::collections::HashMap;
/// # use std::hash::{Hash, BuildHasher};
/// # trait Serialize {};
/// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
///
/// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
/// ```
pub IMPLICIT_HASHER,
style,
"missing generalization over different hashers"
}
declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ImplicitHasher {
#[allow(clippy::cast_possible_truncation, clippy::too_many_lines)]
fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx Item) {
use syntax_pos::BytePos;
fn suggestion<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
db: &mut DiagnosticBuilder<'_>,
generics_span: Span,
generics_suggestion_span: Span,
target: &ImplicitHasherType<'_>,
vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
) {
let generics_snip = snippet(cx, generics_span, "");
// trim `<` `>`
let generics_snip = if generics_snip.is_empty() {
""
} else {
&generics_snip[1..generics_snip.len() - 1]
};
multispan_sugg(
db,
"consider adding a type parameter".to_string(),
vec![
(
generics_suggestion_span,
format!(
"<{}{}S: ::std::hash::BuildHasher{}>",
generics_snip,
if generics_snip.is_empty() { "" } else { ", " },
if vis.suggestions.is_empty() {
""
} else {
// request users to add `Default` bound so that generic constructors can be used
" + Default"
},
),
),
(
target.span(),
format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
),
],
);
if !vis.suggestions.is_empty() {
multispan_sugg(db, "...and use generic constructor".into(), vis.suggestions);
}
}
if !cx.access_levels.is_exported(item.hir_id) {
return;
}
match item.kind {
ItemKind::Impl(_, _, _, ref generics, _, ref ty, ref items) => {
let mut vis = ImplicitHasherTypeVisitor::new(cx);
vis.visit_ty(ty);
for target in &vis.found {
if differing_macro_contexts(item.span, target.span()) {
return;
}
let generics_suggestion_span = generics.span.substitute_dummy({
let pos = snippet_opt(cx, item.span.until(target.span()))
.and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
if let Some(pos) = pos {
Span::new(pos, pos, item.span.data().ctxt)
} else {
return;
}
});
let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
for item in items.iter().map(|item| cx.tcx.hir().impl_item(item.id)) {
ctr_vis.visit_impl_item(item);
}
span_lint_and_then(
cx,
IMPLICIT_HASHER,
target.span(),
&format!(
"impl for `{}` should be generalized over different hashers",
target.type_name()
),
move |db| {
suggestion(cx, db, generics.span, generics_suggestion_span, target, ctr_vis);
},
);
}
},
ItemKind::Fn(ref sig, ref generics, body_id) => {
let body = cx.tcx.hir().body(body_id);
for ty in &sig.decl.inputs {
let mut vis = ImplicitHasherTypeVisitor::new(cx);
vis.visit_ty(ty);
for target in &vis.found {
if in_external_macro(cx.sess(), generics.span) {
continue;
}
let generics_suggestion_span = generics.span.substitute_dummy({
let pos = snippet_opt(cx, item.span.until(body.params[0].pat.span))
.and_then(|snip| {
let i = snip.find("fn")?;
Some(item.span.lo() + BytePos((i + (&snip[i..]).find('(')?) as u32))
})
.expect("failed to create span for type parameters");
Span::new(pos, pos, item.span.data().ctxt)
});
let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
ctr_vis.visit_body(body);
span_lint_and_then(
cx,
IMPLICIT_HASHER,
target.span(),
&format!(
"parameter of type `{}` should be generalized over different hashers",
target.type_name()
),
move |db| {
suggestion(cx, db, generics.span, generics_suggestion_span, target, ctr_vis);
},
);
}
}
},
_ => {},
}
}
}
enum ImplicitHasherType<'tcx> {
HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
HashSet(Span, Ty<'tcx>, Cow<'static, str>),
}
impl<'tcx> ImplicitHasherType<'tcx> {
/// Checks that `ty` is a target type without a `BuildHasher`.
fn new<'a>(cx: &LateContext<'a, 'tcx>, hir_ty: &hir::Ty) -> Option<Self> {
if let TyKind::Path(QPath::Resolved(None, ref path)) = hir_ty.kind {
let params: Vec<_> = path
.segments
.last()
.as_ref()?
.args
.as_ref()?
.args
.iter()
.filter_map(|arg| match arg {
GenericArg::Type(ty) => Some(ty),
_ => None,
})
.collect();
let params_len = params.len();
let ty = hir_ty_to_ty(cx.tcx, hir_ty);
if match_path(path, &paths::HASHMAP) && params_len == 2 {
Some(ImplicitHasherType::HashMap(
hir_ty.span,
ty,
snippet(cx, params[0].span, "K"),
snippet(cx, params[1].span, "V"),
))
} else if match_path(path, &paths::HASHSET) && params_len == 1 {
Some(ImplicitHasherType::HashSet(
hir_ty.span,
ty,
snippet(cx, params[0].span, "T"),
))
} else {
None
}
} else {
None
}
}
fn type_name(&self) -> &'static str {
match *self {
ImplicitHasherType::HashMap(..) => "HashMap",
ImplicitHasherType::HashSet(..) => "HashSet",
}
}
fn type_arguments(&self) -> String {
match *self {
ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{}, {}", k, v),
ImplicitHasherType::HashSet(.., ref t) => format!("{}", t),
}
}
fn ty(&self) -> Ty<'tcx> {
match *self {
ImplicitHasherType::HashMap(_, ty, ..) | ImplicitHasherType::HashSet(_, ty, ..) => ty,
}
}
fn span(&self) -> Span {
match *self {
ImplicitHasherType::HashMap(span, ..) | ImplicitHasherType::HashSet(span, ..) => span,
}
}
}
struct ImplicitHasherTypeVisitor<'a, 'tcx> {
cx: &'a LateContext<'a, 'tcx>,
found: Vec<ImplicitHasherType<'tcx>>,
}
impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
fn new(cx: &'a LateContext<'a, 'tcx>) -> Self {
Self { cx, found: vec![] }
}
}
impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
fn visit_ty(&mut self, t: &'tcx hir::Ty) {
if let Some(target) = ImplicitHasherType::new(self.cx, t) {
self.found.push(target);
}
walk_ty(self, t);
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
/// Looks for default-hasher-dependent constructors like `HashMap::new`.
struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
cx: &'a LateContext<'a, 'tcx>,
body: &'a TypeckTables<'tcx>,
target: &'b ImplicitHasherType<'tcx>,
suggestions: BTreeMap<Span, String>,
}
impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
fn new(cx: &'a LateContext<'a, 'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
Self {
cx,
body: cx.tables,
target,
suggestions: BTreeMap::new(),
}
}
}
impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
fn visit_body(&mut self, body: &'tcx Body) {
let prev_body = self.body;
self.body = self.cx.tcx.body_tables(body.id());
walk_body(self, body);
self.body = prev_body;
}
fn visit_expr(&mut self, e: &'tcx Expr) {
if_chain! {
if let ExprKind::Call(ref fun, ref args) = e.kind;
if let ExprKind::Path(QPath::TypeRelative(ref ty, ref method)) = fun.kind;
if let TyKind::Path(QPath::Resolved(None, ref ty_path)) = ty.kind;
then {
if !same_tys(self.cx, self.target.ty(), self.body.expr_ty(e)) {
return;
}
if match_path(ty_path, &paths::HASHMAP) {
if method.ident.name == sym!(new) {
self.suggestions
.insert(e.span, "HashMap::default()".to_string());
} else if method.ident.name == sym!(with_capacity) {
self.suggestions.insert(
e.span,
format!(
"HashMap::with_capacity_and_hasher({}, Default::default())",
snippet(self.cx, args[0].span, "capacity"),
),
);
}
} else if match_path(ty_path, &paths::HASHSET) {
if method.ident.name == sym!(new) {
self.suggestions
.insert(e.span, "HashSet::default()".to_string());
} else if method.ident.name == sym!(with_capacity) {
self.suggestions.insert(
e.span,
format!(
"HashSet::with_capacity_and_hasher({}, Default::default())",
snippet(self.cx, args[0].span, "capacity"),
),
);
}
}
}
}
walk_expr(self, e);
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::OnlyBodies(&self.cx.tcx.hir())
}
}
declare_clippy_lint! {
/// **What it does:** Checks for casts of `&T` to `&mut T` anywhere in the code.
///
/// **Why is this bad?** It’s basically guaranteed to be undefined behaviour.
/// `UnsafeCell` is the only way to obtain aliasable data that is considered
/// mutable.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// fn x(r: &i32) {
/// unsafe {
/// *(r as *const _ as *mut _) += 1;
/// }
/// }
/// ```
///
/// Instead consider using interior mutability types.
///
/// ```rust
/// use std::cell::UnsafeCell;
///
/// fn x(r: &UnsafeCell<i32>) {
/// unsafe {
/// *r.get() += 1;
/// }
/// }
/// ```
pub CAST_REF_TO_MUT,
correctness,
"a cast of reference to a mutable pointer"
}
declare_lint_pass!(RefToMut => [CAST_REF_TO_MUT]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for RefToMut {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if_chain! {
if let ExprKind::Unary(UnOp::UnDeref, e) = &expr.kind;
if let ExprKind::Cast(e, t) = &e.kind;
if let TyKind::Ptr(MutTy { mutbl: Mutability::Mutable, .. }) = t.kind;
if let ExprKind::Cast(e, t) = &e.kind;
if let TyKind::Ptr(MutTy { mutbl: Mutability::Immutable, .. }) = t.kind;
if let ty::Ref(..) = cx.tables.node_type(e.hir_id).kind;
then {
span_lint(
cx,
CAST_REF_TO_MUT,
expr.span,
"casting &T to &mut T may cause undefined behaviour, consider instead using an UnsafeCell",
);
}
}
}
}
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