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Rollup merge of #90529 - b-naber:reborrows-consts, r=lcnr

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Skip reborrows in AbstractConstBuilder

Fixes https://github.com/rust-lang/rust/issues/90455

Temporary fix to prevent confusing diagnostics that refer to implicit borrows and derefs until we allow borrows and derefs on constant expressions.

r? `@oli-obk`
This commit is contained in:
Matthias Krüger 2021-12-05 15:04:20 +01:00 • committed by GitHub
commit 214b2a126b
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4 changed files with 39 additions and 5 deletions
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20
compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
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@ -399,13 +399,25 @@ impl<'a, 'tcx> AbstractConstBuilder<'a, 'tcx> {
let arg = self.recurse_build(source)?;
self.nodes.push(Node::Cast(abstract_const::CastKind::As, arg, node.ty))
}
ExprKind::Borrow{ arg, ..} => {
let arg_node = &self.body.exprs[*arg];
// Skip reborrows for now until we allow Deref/Borrow/AddressOf
// expressions.
// FIXME(generic_const_exprs): Verify/explain why this is sound
if let ExprKind::Deref {arg} = arg_node.kind {
self.recurse_build(arg)?
} else {
self.maybe_supported_error(
node.span,
"borrowing is not supported in generic constants",
)?
}
}
// FIXME(generic_const_exprs): We may want to support these.
ExprKind::AddressOf { .. }
| ExprKind::Borrow { .. }
| ExprKind::Deref { .. } => self.maybe_supported_error(
ExprKind::AddressOf { .. } | ExprKind::Deref {..}=> self.maybe_supported_error(
node.span,
"dereferencing is not supported in generic constants",
"dereferencing or taking the address is not supported in generic constants",
)?,
ExprKind::Repeat { .. } | ExprKind::Array { .. } => self.maybe_supported_error(
node.span,