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Use let chains instead of let else

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This makes it more obvious that we're looking at a special case.
This commit is contained in:
Nilstrieb 2023-07-02 17:50:42 +02:00
parent b6657a8ad4
commit e8a4814d6d
1 changed files with 13 additions and 19 deletions
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32
compiler/rustc_mir_build/src/thir/cx/expr.rs
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@ -191,11 +191,16 @@ fn mirror_expr_cast(
source: self.mirror_expr(source),
cast: PointerCoercion::ArrayToPointer,
}
} else {
// check whether this is casting an enum variant discriminant
// to prevent cycles, we refer to the discriminant initializer
} else if let hir::ExprKind::Path(ref qpath) = source.kind
&& let res = self.typeck_results().qpath_res(qpath, source.hir_id)
&& let ty = self.typeck_results().node_type(source.hir_id)
&& let ty::Adt(adt_def, args) = ty.kind()
&& let Res::Def(DefKind::Ctor(CtorOf::Variant, CtorKind::Const), variant_ctor_id) = res
{
// Check whether this is casting an enum variant discriminant.
// To prevent cycles, we refer to the discriminant initializer,
// which is always an integer and thus doesn't need to know the
// enum's layout (or its tag type) to compute it during const eval
// enum's layout (or its tag type) to compute it during const eval.
// Example:
// enum Foo {
// A,
@ -204,21 +209,6 @@ fn mirror_expr_cast(
// The correct solution would be to add symbolic computations to miri,
// so we wouldn't have to compute and store the actual value
let hir::ExprKind::Path(ref qpath) = source.kind else {
return ExprKind::Cast { source: self.mirror_expr(source) };
};
let res = self.typeck_results().qpath_res(qpath, source.hir_id);
let ty = self.typeck_results().node_type(source.hir_id);
let ty::Adt(adt_def, args) = ty.kind() else {
return ExprKind::Cast { source: self.mirror_expr(source) };
};
let Res::Def(DefKind::Ctor(CtorOf::Variant, CtorKind::Const), variant_ctor_id) = res
else {
return ExprKind::Cast { source: self.mirror_expr(source) };
};
let idx = adt_def.variant_index_with_ctor_id(variant_ctor_id);
let (discr_did, discr_offset) = adt_def.discriminant_def_for_variant(idx);
@ -255,6 +245,10 @@ fn mirror_expr_cast(
};
ExprKind::Cast { source }
} else {
// Default to `ExprKind::Cast` for all explicit casts.
// MIR building then picks the right MIR casts based on the types.
ExprKind::Cast { source: self.mirror_expr(source) }
}
}