frontend 0.4.0

rustc's frontend with no LLVM and no std: parsing through MIR, as a library
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// `#![no_std]`: these arrive with the standard prelude and name no path, so a `std::`
// search cannot see them - and a `#[derive]` can use them without the name appearing
// in this file at all, which is why they are not trimmed by inspection.
use alloc::borrow::ToOwned;
use alloc::boxed::Box;
use alloc::format;
use alloc::string::{String, ToString};
use alloc::vec;
use alloc::vec::Vec;

use crate::rustc_middle::mir::visit::{PlaceContext, Visitor};
use crate::rustc_middle::mir::*;
use crate::span_bug;
use crate::rustc_middle::ty::{self, TyCtxt};

use crate::rustc_mir_transform::{diagnostics, util};

pub(super) struct CheckPackedRef;

impl<'tcx> crate::rustc_mir_transform::MirLint<'tcx> for CheckPackedRef {
    fn run_lint(&self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
        let typing_env = body.typing_env(tcx);
        let source_info = SourceInfo::outermost(body.span);
        let mut checker = PackedRefChecker { body, tcx, typing_env, source_info };
        checker.visit_body(body);
    }
}

struct PackedRefChecker<'a, 'tcx> {
    body: &'a Body<'tcx>,
    tcx: TyCtxt<'tcx>,
    typing_env: ty::TypingEnv<'tcx>,
    source_info: SourceInfo,
}

impl<'tcx> Visitor<'tcx> for PackedRefChecker<'_, 'tcx> {
    fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
        // Make sure we know where in the MIR we are.
        self.source_info = terminator.source_info;
        self.super_terminator(terminator, location);
    }

    fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
        // Make sure we know where in the MIR we are.
        self.source_info = statement.source_info;
        self.super_statement(statement, location);
    }

    fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
        if context.is_borrow()
            && let Some((adt, pack)) =
                util::place_unalignment(self.tcx, self.body, self.typing_env, *place)
        {
            let def_id = self.body.source.instance.def_id();
            if let Some(impl_def_id) = self.tcx.trait_impl_of_assoc(def_id)
                && self.tcx.is_builtin_derived(impl_def_id)
            {
                // If we ever reach here it means that the generated derive
                // code is somehow doing an unaligned reference, which it
                // shouldn't do.
                span_bug!(self.source_info.span, "builtin derive created an unaligned reference");
            } else {
                self.tcx.dcx().emit_err(diagnostics::UnalignedPackedRef {
                    span: self.source_info.span,
                    ty_descr: adt.descr(),
                    align: pack.bytes(),
                });
            }
        }
    }
}