654 lines
27 KiB
Rust
654 lines
27 KiB
Rust
use rustc_data_structures::fx::FxHashSet;
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use rustc_errors::struct_span_err;
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use rustc_hir as hir;
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use rustc_hir::def_id::DefId;
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use rustc_hir::intravisit;
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use rustc_hir::Node;
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use rustc_middle::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
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use rustc_middle::mir::*;
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use rustc_middle::ty::cast::CastTy;
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use rustc_middle::ty::query::Providers;
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use rustc_middle::ty::{self, TyCtxt};
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use rustc_session::lint::builtin::{SAFE_PACKED_BORROWS, UNUSED_UNSAFE};
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use rustc_span::symbol::{sym, Symbol};
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use std::ops::Bound;
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use crate::const_eval::{is_const_fn, is_min_const_fn};
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use crate::util;
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pub struct UnsafetyChecker<'a, 'tcx> {
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body: &'a Body<'tcx>,
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const_context: bool,
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min_const_fn: bool,
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violations: Vec<UnsafetyViolation>,
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source_info: SourceInfo,
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tcx: TyCtxt<'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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/// Mark an `unsafe` block as used, so we don't lint it.
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used_unsafe: FxHashSet<hir::HirId>,
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inherited_blocks: Vec<(hir::HirId, bool)>,
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}
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impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
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fn new(
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const_context: bool,
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min_const_fn: bool,
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body: &'a Body<'tcx>,
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tcx: TyCtxt<'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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) -> Self {
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// sanity check
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if min_const_fn {
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assert!(const_context);
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}
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Self {
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body,
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const_context,
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min_const_fn,
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violations: vec![],
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source_info: SourceInfo { span: body.span, scope: OUTERMOST_SOURCE_SCOPE },
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tcx,
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param_env,
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used_unsafe: Default::default(),
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inherited_blocks: vec![],
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}
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}
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}
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impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
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fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
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self.source_info = terminator.source_info;
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match terminator.kind {
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TerminatorKind::Goto { .. }
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| TerminatorKind::SwitchInt { .. }
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| TerminatorKind::Drop { .. }
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| TerminatorKind::Yield { .. }
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| TerminatorKind::Assert { .. }
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| TerminatorKind::DropAndReplace { .. }
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| TerminatorKind::GeneratorDrop
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| TerminatorKind::Resume
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| TerminatorKind::Abort
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| TerminatorKind::Return
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| TerminatorKind::Unreachable
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| TerminatorKind::FalseEdges { .. }
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| TerminatorKind::FalseUnwind { .. } => {
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// safe (at least as emitted during MIR construction)
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}
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TerminatorKind::Call { ref func, .. } => {
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let func_ty = func.ty(self.body, self.tcx);
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let sig = func_ty.fn_sig(self.tcx);
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if let hir::Unsafety::Unsafe = sig.unsafety() {
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self.require_unsafe(
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"call to unsafe function",
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"consult the function's documentation for information on how to avoid \
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undefined behavior",
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UnsafetyViolationKind::GeneralAndConstFn,
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)
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}
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}
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}
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self.super_terminator(terminator, location);
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}
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fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
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self.source_info = statement.source_info;
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match statement.kind {
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StatementKind::Assign(..)
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| StatementKind::FakeRead(..)
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| StatementKind::SetDiscriminant { .. }
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| StatementKind::StorageLive(..)
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| StatementKind::StorageDead(..)
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| StatementKind::Retag { .. }
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| StatementKind::AscribeUserType(..)
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| StatementKind::Nop => {
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// safe (at least as emitted during MIR construction)
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}
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StatementKind::LlvmInlineAsm { .. } => self.require_unsafe(
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"use of inline assembly",
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"inline assembly is entirely unchecked and can cause undefined behavior",
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UnsafetyViolationKind::General,
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),
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}
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self.super_statement(statement, location);
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}
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fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
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match rvalue {
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Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
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&AggregateKind::Array(..) | &AggregateKind::Tuple => {}
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&AggregateKind::Adt(ref def, ..) => {
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match self.tcx.layout_scalar_valid_range(def.did) {
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(Bound::Unbounded, Bound::Unbounded) => {}
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_ => self.require_unsafe(
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"initializing type with `rustc_layout_scalar_valid_range` attr",
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"initializing a layout restricted type's field with a value \
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outside the valid range is undefined behavior",
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UnsafetyViolationKind::GeneralAndConstFn,
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),
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}
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}
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&AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
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let UnsafetyCheckResult { violations, unsafe_blocks } =
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self.tcx.unsafety_check_result(def_id);
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self.register_violations(&violations, &unsafe_blocks);
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}
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},
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// casting pointers to ints is unsafe in const fn because the const evaluator cannot
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// possibly know what the result of various operations like `address / 2` would be
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// pointers during const evaluation have no integral address, only an abstract one
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Rvalue::Cast(CastKind::Misc, ref operand, cast_ty)
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if self.const_context && self.tcx.features().const_raw_ptr_to_usize_cast =>
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{
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let operand_ty = operand.ty(self.body, self.tcx);
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let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
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let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
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match (cast_in, cast_out) {
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(CastTy::Ptr(_), CastTy::Int(_)) | (CastTy::FnPtr, CastTy::Int(_)) => {
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self.require_unsafe(
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"cast of pointer to int",
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"casting pointers to integers in constants",
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UnsafetyViolationKind::General,
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);
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}
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_ => {}
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}
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}
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// raw pointer and fn pointer operations are unsafe as it is not clear whether one
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// pointer would be "less" or "equal" to another, because we cannot know where llvm
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// or the linker will place various statics in memory. Without this information the
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// result of a comparison of addresses would differ between runtime and compile-time.
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Rvalue::BinaryOp(_, ref lhs, _)
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if self.const_context && self.tcx.features().const_compare_raw_pointers =>
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{
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if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(self.body, self.tcx).kind {
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self.require_unsafe(
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"pointer operation",
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"operations on pointers in constants",
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UnsafetyViolationKind::General,
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);
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}
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}
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_ => {}
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}
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self.super_rvalue(rvalue, location);
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}
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fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
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// prevent
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// * `&mut x.field`
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// * `x.field = y;`
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// * `&x.field` if `field`'s type has interior mutability
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// because either of these would allow modifying the layout constrained field and
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// insert values that violate the layout constraints.
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if context.is_mutating_use() || context.is_borrow() {
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self.check_mut_borrowing_layout_constrained_field(*place, context.is_mutating_use());
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}
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for (i, elem) in place.projection.iter().enumerate() {
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let proj_base = &place.projection[..i];
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if context.is_borrow() {
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if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
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let source_info = self.source_info;
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let lint_root = self.body.source_scopes[source_info.scope]
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.local_data
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.as_ref()
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.assert_crate_local()
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.lint_root;
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self.require_unsafe(
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"borrow of packed field",
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"fields of packed structs might be misaligned: dereferencing a \
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misaligned pointer or even just creating a misaligned reference \
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is undefined behavior",
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UnsafetyViolationKind::BorrowPacked(lint_root),
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);
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}
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}
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let old_source_info = self.source_info;
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if let [] = proj_base {
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let decl = &self.body.local_decls[place.local];
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if decl.internal {
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if let LocalInfo::StaticRef { def_id, .. } = decl.local_info {
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if self.tcx.is_mutable_static(def_id) {
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self.require_unsafe(
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"use of mutable static",
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"mutable statics can be mutated by multiple threads: aliasing \
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violations or data races will cause undefined behavior",
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UnsafetyViolationKind::General,
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);
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return;
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} else if self.tcx.is_foreign_item(def_id) {
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self.require_unsafe(
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"use of extern static",
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"extern statics are not controlled by the Rust type system: \
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invalid data, aliasing violations or data races will cause \
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undefined behavior",
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UnsafetyViolationKind::General,
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);
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return;
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}
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} else {
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// Internal locals are used in the `move_val_init` desugaring.
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// We want to check unsafety against the source info of the
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// desugaring, rather than the source info of the RHS.
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self.source_info = self.body.local_decls[place.local].source_info;
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}
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}
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}
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let base_ty = Place::ty_from(place.local, proj_base, self.body, self.tcx).ty;
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match base_ty.kind {
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ty::RawPtr(..) => self.require_unsafe(
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"dereference of raw pointer",
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"raw pointers may be NULL, dangling or unaligned; they can violate \
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aliasing rules and cause data races: all of these are undefined \
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behavior",
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UnsafetyViolationKind::General,
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),
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ty::Adt(adt, _) => {
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if adt.is_union() {
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if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
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|| context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
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|| context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
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{
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let elem_ty = match elem {
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ProjectionElem::Field(_, ty) => ty,
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_ => span_bug!(
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self.source_info.span,
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"non-field projection {:?} from union?",
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place
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),
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};
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if !elem_ty.is_copy_modulo_regions(
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self.tcx,
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self.param_env,
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self.source_info.span,
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) {
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self.require_unsafe(
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"assignment to non-`Copy` union field",
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"the previous content of the field will be dropped, which \
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causes undefined behavior if the field was not properly \
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initialized",
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UnsafetyViolationKind::GeneralAndConstFn,
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)
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} else {
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// write to non-move union, safe
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}
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} else {
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self.require_unsafe(
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"access to union field",
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"the field may not be properly initialized: using \
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uninitialized data will cause undefined behavior",
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UnsafetyViolationKind::GeneralAndConstFn,
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)
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}
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}
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}
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_ => {}
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}
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self.source_info = old_source_info;
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}
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}
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}
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impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
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fn require_unsafe(
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&mut self,
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description: &'static str,
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details: &'static str,
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kind: UnsafetyViolationKind,
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) {
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let source_info = self.source_info;
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self.register_violations(
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&[UnsafetyViolation {
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source_info,
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description: Symbol::intern(description),
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details: Symbol::intern(details),
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kind,
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}],
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&[],
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);
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}
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fn register_violations(
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&mut self,
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violations: &[UnsafetyViolation],
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unsafe_blocks: &[(hir::HirId, bool)],
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) {
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let safety = self.body.source_scopes[self.source_info.scope]
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.local_data
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.as_ref()
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.assert_crate_local()
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.safety;
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let within_unsafe = match safety {
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// `unsafe` blocks are required in safe code
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Safety::Safe => {
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for violation in violations {
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let mut violation = *violation;
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match violation.kind {
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UnsafetyViolationKind::GeneralAndConstFn
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| UnsafetyViolationKind::General => {}
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UnsafetyViolationKind::BorrowPacked(_) => {
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if self.min_const_fn {
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// const fns don't need to be backwards compatible and can
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// emit these violations as a hard error instead of a backwards
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// compat lint
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violation.kind = UnsafetyViolationKind::General;
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}
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}
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}
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if !self.violations.contains(&violation) {
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self.violations.push(violation)
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}
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}
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false
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}
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// `unsafe` function bodies allow unsafe without additional unsafe blocks
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Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
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Safety::ExplicitUnsafe(hir_id) => {
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// mark unsafe block as used if there are any unsafe operations inside
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if !violations.is_empty() {
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self.used_unsafe.insert(hir_id);
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}
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// only some unsafety is allowed in const fn
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if self.min_const_fn {
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for violation in violations {
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match violation.kind {
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// these unsafe things are stable in const fn
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UnsafetyViolationKind::GeneralAndConstFn => {}
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// these things are forbidden in const fns
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UnsafetyViolationKind::General
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| UnsafetyViolationKind::BorrowPacked(_) => {
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let mut violation = *violation;
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// const fns don't need to be backwards compatible and can
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// emit these violations as a hard error instead of a backwards
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// compat lint
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violation.kind = UnsafetyViolationKind::General;
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if !self.violations.contains(&violation) {
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self.violations.push(violation)
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}
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}
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}
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}
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}
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true
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}
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};
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self.inherited_blocks.extend(
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unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
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);
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}
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fn check_mut_borrowing_layout_constrained_field(
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&mut self,
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place: Place<'tcx>,
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is_mut_use: bool,
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) {
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let mut cursor = place.projection.as_ref();
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while let &[ref proj_base @ .., elem] = cursor {
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cursor = proj_base;
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match elem {
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// Modifications behind a dereference don't affect the value of
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// the pointer.
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ProjectionElem::Deref => return,
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ProjectionElem::Field(..) => {
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let ty =
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Place::ty_from(place.local, proj_base, &self.body.local_decls, self.tcx).ty;
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if let ty::Adt(def, _) = ty.kind {
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if self.tcx.layout_scalar_valid_range(def.did)
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!= (Bound::Unbounded, Bound::Unbounded)
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{
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let (description, details) = if is_mut_use {
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(
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"mutation of layout constrained field",
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"mutating layout constrained fields cannot statically be \
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checked for valid values",
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)
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// Check `is_freeze` as late as possible to avoid cycle errors
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// with opaque types.
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} else if !place.ty(self.body, self.tcx).ty.is_freeze(
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self.tcx,
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self.param_env,
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self.source_info.span,
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) {
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(
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"borrow of layout constrained field with interior \
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mutability",
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"references to fields of layout constrained fields \
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lose the constraints. Coupled with interior mutability, \
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the field can be changed to invalid values",
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)
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} else {
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continue;
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};
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self.require_unsafe(
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description,
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details,
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UnsafetyViolationKind::GeneralAndConstFn,
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);
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}
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}
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}
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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(crate) fn provide(providers: &mut Providers<'_>) {
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*providers = Providers { unsafety_check_result, unsafe_derive_on_repr_packed, ..*providers };
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}
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struct UnusedUnsafeVisitor<'a> {
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used_unsafe: &'a FxHashSet<hir::HirId>,
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unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
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}
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impl<'a, 'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
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type Map = intravisit::ErasedMap<'tcx>;
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fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
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intravisit::NestedVisitorMap::None
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}
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fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
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intravisit::walk_block(self, block);
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if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
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self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
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}
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}
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}
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fn check_unused_unsafe(
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tcx: TyCtxt<'_>,
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def_id: DefId,
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used_unsafe: &FxHashSet<hir::HirId>,
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unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
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) {
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let body_id =
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tcx.hir().as_local_hir_id(def_id).and_then(|hir_id| tcx.hir().maybe_body_owned_by(hir_id));
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let body_id = match body_id {
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Some(body) => body,
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None => {
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debug!("check_unused_unsafe({:?}) - no body found", def_id);
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return;
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}
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};
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let body = tcx.hir().body(body_id);
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debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
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let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
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intravisit::Visitor::visit_body(&mut visitor, body);
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}
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fn unsafety_check_result(tcx: TyCtxt<'_>, def_id: DefId) -> UnsafetyCheckResult {
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|
debug!("unsafety_violations({:?})", def_id);
|
|
|
|
// N.B., this borrow is valid because all the consumers of
|
|
// `mir_built` force this.
|
|
let body = &tcx.mir_built(def_id).borrow();
|
|
|
|
let param_env = tcx.param_env(def_id);
|
|
|
|
let id = tcx.hir().as_local_hir_id(def_id).unwrap();
|
|
let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
|
|
hir::BodyOwnerKind::Closure => (false, false),
|
|
hir::BodyOwnerKind::Fn => (is_const_fn(tcx, def_id), is_min_const_fn(tcx, def_id)),
|
|
hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
|
|
};
|
|
let mut checker = UnsafetyChecker::new(const_context, min_const_fn, body, tcx, param_env);
|
|
// mir_built ensures that body has a computed cache, so we don't (and can't) attempt to
|
|
// recompute it here.
|
|
let body = body.unwrap_read_only();
|
|
checker.visit_body(&body);
|
|
|
|
check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
|
|
UnsafetyCheckResult {
|
|
violations: checker.violations.into(),
|
|
unsafe_blocks: checker.inherited_blocks.into(),
|
|
}
|
|
}
|
|
|
|
fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: DefId) {
|
|
let lint_hir_id = tcx
|
|
.hir()
|
|
.as_local_hir_id(def_id)
|
|
.unwrap_or_else(|| bug!("checking unsafety for non-local def id {:?}", def_id));
|
|
|
|
tcx.struct_span_lint_hir(SAFE_PACKED_BORROWS, lint_hir_id, tcx.def_span(def_id), |lint| {
|
|
// FIXME: when we make this a hard error, this should have its
|
|
// own error code.
|
|
let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
|
|
"`#[derive]` can't be used on a `#[repr(packed)]` struct with \
|
|
type or const parameters (error E0133)"
|
|
.to_string()
|
|
} else {
|
|
"`#[derive]` can't be used on a `#[repr(packed)]` struct that \
|
|
does not derive Copy (error E0133)"
|
|
.to_string()
|
|
};
|
|
lint.build(&message).emit()
|
|
});
|
|
}
|
|
|
|
/// Returns the `HirId` for an enclosing scope that is also `unsafe`.
|
|
fn is_enclosed(
|
|
tcx: TyCtxt<'_>,
|
|
used_unsafe: &FxHashSet<hir::HirId>,
|
|
id: hir::HirId,
|
|
) -> Option<(String, hir::HirId)> {
|
|
let parent_id = tcx.hir().get_parent_node(id);
|
|
if parent_id != id {
|
|
if used_unsafe.contains(&parent_id) {
|
|
Some(("block".to_string(), parent_id))
|
|
} else if let Some(Node::Item(&hir::Item {
|
|
kind: hir::ItemKind::Fn(ref sig, _, _), ..
|
|
})) = tcx.hir().find(parent_id)
|
|
{
|
|
match sig.header.unsafety {
|
|
hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
|
|
hir::Unsafety::Normal => None,
|
|
}
|
|
} else {
|
|
is_enclosed(tcx, used_unsafe, parent_id)
|
|
}
|
|
} else {
|
|
None
|
|
}
|
|
}
|
|
|
|
fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
|
|
let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id));
|
|
tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
|
|
let msg = "unnecessary `unsafe` block";
|
|
let mut db = lint.build(msg);
|
|
db.span_label(span, msg);
|
|
if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
|
|
db.span_label(
|
|
tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
|
|
format!("because it's nested under this `unsafe` {}", kind),
|
|
);
|
|
}
|
|
db.emit();
|
|
});
|
|
}
|
|
|
|
fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
|
|
debug!("builtin_derive_def_id({:?})", def_id);
|
|
if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
|
|
if tcx.has_attr(impl_def_id, sym::automatically_derived) {
|
|
debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
|
|
Some(impl_def_id)
|
|
} else {
|
|
debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
|
|
None
|
|
}
|
|
} else {
|
|
debug!("builtin_derive_def_id({:?}) - not a method", def_id);
|
|
None
|
|
}
|
|
}
|
|
|
|
pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
|
|
debug!("check_unsafety({:?})", def_id);
|
|
|
|
// closures are handled by their parent fn.
|
|
if tcx.is_closure(def_id) {
|
|
return;
|
|
}
|
|
|
|
let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
|
|
|
|
for &UnsafetyViolation { source_info, description, details, kind } in violations.iter() {
|
|
// Report an error.
|
|
match kind {
|
|
UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
|
|
struct_span_err!(
|
|
tcx.sess,
|
|
source_info.span,
|
|
E0133,
|
|
"{} is unsafe and requires unsafe function or block",
|
|
description
|
|
)
|
|
.span_label(source_info.span, &*description.as_str())
|
|
.note(&details.as_str())
|
|
.emit();
|
|
}
|
|
UnsafetyViolationKind::BorrowPacked(lint_hir_id) => {
|
|
if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
|
|
tcx.unsafe_derive_on_repr_packed(impl_def_id);
|
|
} else {
|
|
tcx.struct_span_lint_hir(
|
|
SAFE_PACKED_BORROWS,
|
|
lint_hir_id,
|
|
source_info.span,
|
|
|lint| {
|
|
lint.build(&format!(
|
|
"{} is unsafe and requires unsafe function or block (error E0133)",
|
|
description
|
|
))
|
|
.note(&details.as_str())
|
|
.emit()
|
|
},
|
|
)
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
let mut unsafe_blocks: Vec<_> = unsafe_blocks.iter().collect();
|
|
unsafe_blocks.sort_by_cached_key(|(hir_id, _)| tcx.hir().hir_id_to_node_id(*hir_id));
|
|
let used_unsafe: FxHashSet<_> =
|
|
unsafe_blocks.iter().flat_map(|&&(id, used)| used.then_some(id)).collect();
|
|
for &(block_id, is_used) in unsafe_blocks {
|
|
if !is_used {
|
|
report_unused_unsafe(tcx, &used_unsafe, block_id);
|
|
}
|
|
}
|
|
}
|