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Rollup merge of #138374 - celinval:issue-136925-const-contract, r=compiler-errors,oli-obk,RalfJung

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Enable contracts for const functions

Use `const_eval_select!()` macro to enable contract checking only at runtime. The existing contract logic relies on closures, which are not supported in constant functions.

This commit also removes one level of indirection for ensures clauses since we no longer build a closure around the ensures predicate.

Resolves #136925

**Call-out:** This is still a draft PR since CI is broken due to a new warning message for unreachable code when the bottom of the function is indeed unreachable. It's not clear to me why the warning wasn't triggered before.

r? ```@compiler-errors```
This commit is contained in:
Stuart Cook 2025-04-15 15:47:24 +10:00 • committed by GitHub
commit 380ad1b5d4
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16 changed files with 183 additions and 39 deletions
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14
compiler/rustc_ast_lowering/src/expr.rs
View file

@ -399,12 +399,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
&mut self,
expr: &'hir hir::Expr<'hir>,
span: Span,
check_ident: Ident,
check_hir_id: HirId,
cond_ident: Ident,
cond_hir_id: HirId,
) -> &'hir hir::Expr<'hir> {
let checker_fn = self.expr_ident(span, check_ident, check_hir_id);
let span = self.mark_span_with_reason(DesugaringKind::Contract, span, None);
self.expr_call(span, checker_fn, std::slice::from_ref(expr))
let cond_fn = self.expr_ident(span, cond_ident, cond_hir_id);
let call_expr = self.expr_call_lang_item_fn_mut(
span,
hir::LangItem::ContractCheckEnsures,
arena_vec![self; *cond_fn, *expr],
);
self.arena.alloc(call_expr)
}
pub(crate) fn lower_const_block(&mut self, c: &AnonConst) -> hir::ConstBlock {

9
compiler/rustc_ast_lowering/src/item.rs
View file

@ -1206,8 +1206,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
let precond = if let Some(req) = &contract.requires {
// Lower the precondition check intrinsic.
let lowered_req = this.lower_expr_mut(&req);
let req_span = this.mark_span_with_reason(
DesugaringKind::Contract,
lowered_req.span,
None,
);
let precond = this.expr_call_lang_item_fn_mut(
req.span,
req_span,
hir::LangItem::ContractCheckRequires,
&*arena_vec![this; lowered_req],
);
@ -1217,6 +1222,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
};
let (postcond, body) = if let Some(ens) = &contract.ensures {
let ens_span = this.lower_span(ens.span);
let ens_span =
this.mark_span_with_reason(DesugaringKind::Contract, ens_span, None);
// Set up the postcondition `let` statement.
let check_ident: Ident =
Ident::from_str_and_span("__ensures_checker", ens_span);