// This file was originally taken from
// https://raw.githubusercontent.com/rust-lang/rust/ae1b871cca56613b1af1a5121dd24ac810ff4b89/src/librustc_mir/transform/check_unsafety.rs
//
// This source code is licensed under the MIT or Apache 2 license found in
// https://raw.githubusercontent.com/rust-lang/rust/ae1b871cca56613b1af1a5121dd24ac810ff4b89/LICENSE-MIT and
// https://raw.githubusercontent.com/rust-lang/rust/ae1b871cca56613b1af1a5121dd24ac810ff4b89/LICENSE-APACHE.

#![allow(dead_code)]

use rustc_data_structures::fx::FxHashSet;

use rustc::hir;
use rustc::hir::def_id::DefId;
use rustc::hir::Node;
use rustc::lint::builtin::{SAFE_PACKED_BORROWS, UNUSED_UNSAFE};
use rustc::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
use rustc::mir::*;
use rustc::ty::cast::CastTy;
use rustc::ty::{self, TyCtxt};

use syntax::symbol::{sym, Symbol};

use std::ops::Bound;

use log::debug;
use rustc::{bug, span_bug};
use rustc_mir::util;
use syntax::struct_span_err;

use rustc_error_codes::*;

pub struct UnsafetyChecker<'a, 'tcx> {
    body: &'a Body<'tcx>,
    const_context: bool,
    min_const_fn: bool,
    violations: Vec<UnsafetyViolation>,
    source_info: SourceInfo,
    tcx: TyCtxt<'tcx>,
    param_env: ty::ParamEnv<'tcx>,
    /// Mark an `unsafe` block as used, so we don't lint it.
    used_unsafe: FxHashSet<hir::HirId>,
    inherited_blocks: Vec<(hir::HirId, bool)>,
    /// Does the analysed function use unsafe directly?
    fn_uses_unsafe: bool,
}

impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
    fn new(
        const_context: bool,
        min_const_fn: bool,
        body: &'a Body<'tcx>,
        tcx: TyCtxt<'tcx>,
        param_env: ty::ParamEnv<'tcx>,
    ) -> Self {
        // sanity check
        if min_const_fn {
            assert!(const_context);
        }
        Self {
            body,
            const_context,
            min_const_fn,
            violations: vec![],
            source_info: SourceInfo {
                span: body.span,
                scope: OUTERMOST_SOURCE_SCOPE,
            },
            tcx,
            param_env,
            used_unsafe: Default::default(),
            inherited_blocks: vec![],
            fn_uses_unsafe: false,
        }
    }
}

impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
    fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
        self.source_info = terminator.source_info;
        match terminator.kind {
            TerminatorKind::Goto { .. }
            | TerminatorKind::SwitchInt { .. }
            | TerminatorKind::Drop { .. }
            | TerminatorKind::Yield { .. }
            | TerminatorKind::Assert { .. }
            | TerminatorKind::DropAndReplace { .. }
            | TerminatorKind::GeneratorDrop
            | TerminatorKind::Resume
            | TerminatorKind::Abort
            | TerminatorKind::Return
            | TerminatorKind::Unreachable
            | TerminatorKind::FalseEdges { .. }
            | TerminatorKind::FalseUnwind { .. } => {
                // safe (at least as emitted during MIR construction)
            }

            TerminatorKind::Call { ref func, .. } => {
                let func_ty = func.ty(self.body, self.tcx);
                let sig = func_ty.fn_sig(self.tcx);
                if let hir::Unsafety::Unsafe = sig.unsafety() {
                    self.require_unsafe(
                        "call to unsafe function",
                        "consult the function's documentation for information on how to avoid \
                         undefined behavior",
                        UnsafetyViolationKind::GeneralAndConstFn,
                    )
                }
            }
        }
        self.super_terminator(terminator, location);
    }

    fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
        self.source_info = statement.source_info;
        match statement.kind {
            StatementKind::Assign(..)
            | StatementKind::FakeRead(..)
            | StatementKind::SetDiscriminant { .. }
            | StatementKind::StorageLive(..)
            | StatementKind::StorageDead(..)
            | StatementKind::Retag { .. }
            | StatementKind::AscribeUserType(..)
            | StatementKind::Nop => {
                // safe (at least as emitted during MIR construction)
            }

            StatementKind::InlineAsm { .. } => self.require_unsafe(
                "use of inline assembly",
                "inline assembly is entirely unchecked and can cause undefined behavior",
                UnsafetyViolationKind::General,
            ),
        }
        self.super_statement(statement, location);
    }

    fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
        match rvalue {
            Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
                &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
                &AggregateKind::Adt(ref def, ..) => {
                    match self.tcx.layout_scalar_valid_range(def.did) {
                        (Bound::Unbounded, Bound::Unbounded) => {}
                        _ => self.require_unsafe(
                            "initializing type with `rustc_layout_scalar_valid_range` attr",
                            "initializing a layout restricted type's field with a value \
                             outside the valid range is undefined behavior",
                            UnsafetyViolationKind::GeneralAndConstFn,
                        ),
                    }
                }
                &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
                    let UnsafetyCheckResult {
                        violations,
                        unsafe_blocks,
                    } = self.tcx.unsafety_check_result(def_id);
                    self.register_violations(&violations, &unsafe_blocks);
                }
            },
            // casting pointers to ints is unsafe in const fn because the const evaluator cannot
            // possibly know what the result of various operations like `address / 2` would be
            // pointers during const evaluation have no integral address, only an abstract one
            Rvalue::Cast(CastKind::Misc, ref operand, cast_ty)
                if self.const_context && self.tcx.features().const_raw_ptr_to_usize_cast =>
            {
                let operand_ty = operand.ty(self.body, self.tcx);
                let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
                let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
                match (cast_in, cast_out) {
                    (CastTy::Ptr(_), CastTy::Int(_)) | (CastTy::FnPtr, CastTy::Int(_)) => {
                        self.register_violations(
                            &[UnsafetyViolation {
                                source_info: self.source_info,
                                description: Symbol::intern("cast of pointer to int"),
                                details: Symbol::intern(
                                    "casting pointers to integers in constants",
                                ),
                                kind: UnsafetyViolationKind::General,
                            }],
                            &[],
                        );
                    }
                    _ => {}
                }
            }
            // raw pointer and fn pointer operations are unsafe as it is not clear whether one
            // pointer would be "less" or "equal" to another, because we cannot know where llvm
            // or the linker will place various statics in memory. Without this information the
            // result of a comparison of addresses would differ between runtime and compile-time.
            Rvalue::BinaryOp(_, ref lhs, _)
                if self.const_context && self.tcx.features().const_compare_raw_pointers =>
            {
                if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(self.body, self.tcx).kind {
                    self.register_violations(
                        &[UnsafetyViolation {
                            source_info: self.source_info,
                            description: Symbol::intern("pointer operation"),
                            details: Symbol::intern("operations on pointers in constants"),
                            kind: UnsafetyViolationKind::General,
                        }],
                        &[],
                    );
                }
            }
            _ => {}
        }
        self.super_rvalue(rvalue, location);
    }

    fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
        match place.base {
            PlaceBase::Local(..) => {
                // Locals are safe.
            }
            PlaceBase::Static(box Static {
                kind: StaticKind::Promoted(_, _),
                ..
            }) => {
                bug!("unsafety checking should happen before promotion");
            }
            PlaceBase::Static(box Static {
                kind: StaticKind::Static,
                ..
            }) => {
                bug!("StaticKind::Static should not exist");
            }
        }

        for (i, elem) in place.projection.iter().enumerate() {
            let proj_base = &place.projection[..i];

            if context.is_borrow() {
                if util::is_disaligned(self.tcx, self.body, self.param_env, place) {
                    let source_info = self.source_info;
                    let lint_root = self.body.source_scopes[source_info.scope]
                        .local_data
                        .as_ref()
                        .assert_crate_local()
                        .lint_root;
                    self.register_violations(
                        &[UnsafetyViolation {
                            source_info,
                            description: Symbol::intern("borrow of packed field"),
                            details: Symbol::intern(
                                "fields of packed structs might be misaligned: dereferencing a \
                                 misaligned pointer or even just creating a misaligned reference \
                                 is undefined behavior",
                            ),
                            kind: UnsafetyViolationKind::BorrowPacked(lint_root),
                        }],
                        &[],
                    );
                }
            }
            let is_borrow_of_interior_mut = context.is_borrow()
                && !Place::ty_from(&place.base, proj_base, self.body, self.tcx)
                    .ty
                    .is_freeze(self.tcx, self.param_env, self.source_info.span);
            // prevent
            // * `&mut x.field`
            // * `x.field = y;`
            // * `&x.field` if `field`'s type has interior mutability
            // because either of these would allow modifying the layout constrained field and
            // insert values that violate the layout constraints.
            if context.is_mutating_use() || is_borrow_of_interior_mut {
                self.check_mut_borrowing_layout_constrained_field(place, context.is_mutating_use());
            }
            let old_source_info = self.source_info;
            if let (PlaceBase::Local(local), []) = (&place.base, proj_base) {
                let decl = &self.body.local_decls[*local];
                if decl.internal {
                    // Internal locals are used in the `move_val_init` desugaring.
                    // We want to check unsafety against the source info of the
                    // desugaring, rather than the source info of the RHS.
                    self.source_info = self.body.local_decls[*local].source_info;
                } else if let LocalInfo::StaticRef { def_id, .. } = decl.local_info {
                    if self.tcx.is_mutable_static(def_id) {
                        self.require_unsafe(
                            "use of mutable static",
                            "mutable statics can be mutated by multiple threads: aliasing \
                             violations or data races will cause undefined behavior",
                            UnsafetyViolationKind::General,
                        );
                        return;
                    } else if self.tcx.is_foreign_item(def_id) {
                        self.require_unsafe(
                            "use of extern static",
                            "extern statics are not controlled by the Rust type system: \
                             invalid data, aliasing violations or data races will cause \
                             undefined behavior",
                            UnsafetyViolationKind::General,
                        );
                        return;
                    }
                }
            }
            let base_ty = Place::ty_from(&place.base, proj_base, self.body, self.tcx).ty;
            match base_ty.kind {
                ty::RawPtr(..) => self.require_unsafe(
                    "dereference of raw pointer",
                    "raw pointers may be NULL, dangling or unaligned; they can violate \
                     aliasing rules and cause data races: all of these are undefined \
                     behavior",
                    UnsafetyViolationKind::General,
                ),
                ty::Adt(adt, _) => {
                    if adt.is_union() {
                        if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
                            || context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
                            || context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
                        {
                            let elem_ty = match elem {
                                ProjectionElem::Field(_, ty) => ty,
                                _ => span_bug!(
                                    self.source_info.span,
                                    "non-field projection {:?} from union?",
                                    place
                                ),
                            };
                            if !elem_ty.is_copy_modulo_regions(
                                self.tcx,
                                self.param_env,
                                self.source_info.span,
                            ) {
                                self.require_unsafe(
                                    "assignment to non-`Copy` union field",
                                    "the previous content of the field will be dropped, which \
                                     causes undefined behavior if the field was not properly \
                                     initialized",
                                    UnsafetyViolationKind::GeneralAndConstFn,
                                )
                            } else {
                                // write to non-move union, safe
                            }
                        } else {
                            self.require_unsafe(
                                "access to union field",
                                "the field may not be properly initialized: using \
                                 uninitialized data will cause undefined behavior",
                                UnsafetyViolationKind::GeneralAndConstFn,
                            )
                        }
                    }
                }
                _ => {}
            }
            self.source_info = old_source_info;
        }
    }
}

impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
    fn require_unsafe(
        &mut self,
        description: &'static str,
        details: &'static str,
        kind: UnsafetyViolationKind,
    ) {
        let source_info = self.source_info;
        self.register_violations(
            &[UnsafetyViolation {
                source_info,
                description: Symbol::intern(description),
                details: Symbol::intern(details),
                kind,
            }],
            &[],
        );
    }

    fn register_violations(
        &mut self,
        violations: &[UnsafetyViolation],
        unsafe_blocks: &[(hir::HirId, bool)],
    ) {
        let safety = self.body.source_scopes[self.source_info.scope]
            .local_data
            .as_ref()
            .assert_crate_local()
            .safety;
        let within_unsafe = match safety {
            // `unsafe` blocks are required in safe code
            Safety::Safe => {
                for violation in violations {
                    let mut violation = violation.clone();
                    match violation.kind {
                        UnsafetyViolationKind::GeneralAndConstFn
                        | UnsafetyViolationKind::General => {}
                        UnsafetyViolationKind::BorrowPacked(_) => {
                            if self.min_const_fn {
                                // const fns don't need to be backwards compatible and can
                                // emit these violations as a hard error instead of a backwards
                                // compat lint
                                violation.kind = UnsafetyViolationKind::General;
                            }
                        }
                    }
                    if !self.violations.contains(&violation) {
                        self.violations.push(violation)
                    }
                }
                false
            }
            // `unsafe` function bodies allow unsafe without additional unsafe blocks
            Safety::BuiltinUnsafe | Safety::FnUnsafe => {
                self.fn_uses_unsafe = true;
                true
            }
            Safety::ExplicitUnsafe(hir_id) => {
                // mark unsafe block as used if there are any unsafe operations inside
                if !violations.is_empty() {
                    self.used_unsafe.insert(hir_id);
                }
                // only some unsafety is allowed in const fn
                if self.min_const_fn {
                    for violation in violations {
                        match violation.kind {
                            // these unsafe things are stable in const fn
                            UnsafetyViolationKind::GeneralAndConstFn => {}
                            // these things are forbidden in const fns
                            UnsafetyViolationKind::General
                            | UnsafetyViolationKind::BorrowPacked(_) => {
                                let mut violation = violation.clone();
                                // const fns don't need to be backwards compatible and can
                                // emit these violations as a hard error instead of a backwards
                                // compat lint
                                violation.kind = UnsafetyViolationKind::General;
                                if !self.violations.contains(&violation) {
                                    self.violations.push(violation)
                                }
                            }
                        }
                    }
                }
                true
            }
        };
        self.inherited_blocks.extend(
            unsafe_blocks
                .iter()
                .map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
        );
    }
    fn check_mut_borrowing_layout_constrained_field(
        &mut self,
        place: &Place<'tcx>,
        is_mut_use: bool,
    ) {
        let mut cursor = place.projection.as_ref();
        while let &[ref proj_base @ .., elem] = cursor {
            cursor = proj_base;

            match elem {
                ProjectionElem::Field(..) => {
                    let ty =
                        Place::ty_from(&place.base, proj_base, &self.body.local_decls, self.tcx).ty;
                    match ty.kind {
                        ty::Adt(def, _) => match self.tcx.layout_scalar_valid_range(def.did) {
                            (Bound::Unbounded, Bound::Unbounded) => {}
                            _ => {
                                let (description, details) = if is_mut_use {
                                    (
                                        "mutation of layout constrained field",
                                        "mutating layout constrained fields cannot statically be \
                                         checked for valid values",
                                    )
                                } else {
                                    (
                                        "borrow of layout constrained field with interior \
                                         mutability",
                                        "references to fields of layout constrained fields \
                                         lose the constraints. Coupled with interior mutability, \
                                         the field can be changed to invalid values",
                                    )
                                };
                                let source_info = self.source_info;
                                self.register_violations(
                                    &[UnsafetyViolation {
                                        source_info,
                                        description: Symbol::intern(description),
                                        details: Symbol::intern(details),
                                        kind: UnsafetyViolationKind::GeneralAndConstFn,
                                    }],
                                    &[],
                                );
                            }
                        },
                        _ => {}
                    }
                }
                _ => {}
            }
        }
    }
}

struct UnusedUnsafeVisitor<'a> {
    used_unsafe: &'a FxHashSet<hir::HirId>,
    unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
}

impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
    fn nested_visit_map<'this>(&'this mut self) -> hir::intravisit::NestedVisitorMap<'this, 'tcx> {
        hir::intravisit::NestedVisitorMap::None
    }

    fn visit_block(&mut self, block: &'tcx hir::Block) {
        hir::intravisit::walk_block(self, block);

        if let hir::UnsafeBlock(hir::UserProvided) = block.rules {
            self.unsafe_blocks
                .push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
        }
    }
}

fn check_unused_unsafe(
    tcx: TyCtxt<'_>,
    def_id: DefId,
    used_unsafe: &FxHashSet<hir::HirId>,
    unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
) {
    let body_id = tcx
        .hir()
        .as_local_hir_id(def_id)
        .and_then(|hir_id| tcx.hir().maybe_body_owned_by(hir_id));

    let body_id = match body_id {
        Some(body) => body,
        None => {
            debug!("check_unused_unsafe({:?}) - no body found", def_id);
            return;
        }
    };
    let body = tcx.hir().body(body_id);
    debug!(
        "check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})",
        def_id, body, used_unsafe
    );

    let mut visitor = UnusedUnsafeVisitor {
        used_unsafe,
        unsafe_blocks,
    };
    hir::intravisit::Visitor::visit_body(&mut visitor, body);
}

pub(crate) fn unsafety_check_result(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
    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 => (tcx.is_const_fn(def_id), tcx.is_min_const_fn(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,
    );
    checker.fn_uses_unsafe
}

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));

    // 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()
    };
    tcx.lint_hir(
        SAFE_PACKED_BORROWS,
        lint_hir_id,
        tcx.def_span(def_id),
        &message,
    );
}

/// 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().def_span(tcx.hir().span(id));
    let msg = "unnecessary `unsafe` block";
    let mut db = tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, msg);
    db.span_label(span, msg);
    if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
        db.span_label(
            tcx.sess.source_map().def_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.lint_node_note(
                        SAFE_PACKED_BORROWS,
                        lint_hir_id,
                        source_info.span,
                        &format!(
                            "{} is unsafe and requires unsafe function or block \
                             (error E0133)",
                            description
                        ),
                        &details.as_str(),
                    );
                }
            }
        }
    }

    let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
    unsafe_blocks.sort_by_cached_key(|(hir_id, _)| tcx.hir().hir_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);
        }
    }
}
