Rollup merge of #88963 - fee1-dead:const-iterator, r=oli-obk

Coerce const FnDefs to implement const Fn traits

You can now pass a FnDef to a function expecting `F` where `F: ~const FnTrait`.

r? ``@oli-obk``

``@rustbot`` label T-compiler F-const_trait_impl

2 files changed, 3 insertions, 23 deletions

diff --git a/compiler/rustc_const_eval/src/const_eval/fn_queries.rs b/compiler/rustc_const_eval/src/const_eval/fn_queries.rs
index 10afd9560fa..df4cc295fac 100644
--- a/compiler/rustc_const_eval/src/const_eval/fn_queries.rs
+++ b/compiler/rustc_const_eval/src/const_eval/fn_queries.rs
@@ -6,23 +6,6 @@ use rustc_middle::ty::TyCtxt;
 use rustc_span::symbol::Symbol;
 use rustc_target::spec::abi::Abi;
 
-/// Whether the `def_id` counts as const fn in your current crate, considering all active
-/// feature gates
-pub fn is_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
-    tcx.is_const_fn_raw(def_id)
-        && match is_unstable_const_fn(tcx, def_id) {
-            Some(feature_name) => {
-                // has a `rustc_const_unstable` attribute, check whether the user enabled the
-                // corresponding feature gate.
-                tcx.features().declared_lib_features.iter().any(|&(sym, _)| sym == feature_name)
-            }
-            // functions without const stability are either stable user written
-            // const fn or the user is using feature gates and we thus don't
-            // care what they do
-            None => true,
-        }
-}
-
 /// Whether the `def_id` is an unstable const fn and what feature gate is necessary to enable it
 pub fn is_unstable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Symbol> {
     if tcx.is_const_fn_raw(def_id) {
@@ -77,7 +60,7 @@ fn is_const_fn_raw(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 }
 
 fn is_promotable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
-    is_const_fn(tcx, def_id)
+    tcx.is_const_fn(def_id)
         && match tcx.lookup_const_stability(def_id) {
             Some(stab) => {
                 if cfg!(debug_assertions) && stab.promotable {
diff --git a/compiler/rustc_const_eval/src/transform/promote_consts.rs b/compiler/rustc_const_eval/src/transform/promote_consts.rs
index 9408dfa956b..be1b827f235 100644
--- a/compiler/rustc_const_eval/src/transform/promote_consts.rs
+++ b/compiler/rustc_const_eval/src/transform/promote_consts.rs
@@ -26,7 +26,6 @@ use rustc_index::vec::{Idx, IndexVec};
 use std::cell::Cell;
 use std::{cmp, iter, mem};
 
-use crate::const_eval::{is_const_fn, is_unstable_const_fn};
 use crate::transform::check_consts::{is_lang_panic_fn, qualifs, ConstCx};
 use crate::transform::MirPass;
 
@@ -658,9 +657,7 @@ impl<'tcx> Validator<'_, 'tcx> {
 
         let is_const_fn = match *fn_ty.kind() {
             ty::FnDef(def_id, _) => {
-                is_const_fn(self.tcx, def_id)
-                    || is_unstable_const_fn(self.tcx, def_id).is_some()
-                    || is_lang_panic_fn(self.tcx, def_id)
+                self.tcx.is_const_fn_raw(def_id) || is_lang_panic_fn(self.tcx, def_id)
             }
             _ => false,
         };
@@ -1081,7 +1078,7 @@ pub fn is_const_fn_in_array_repeat_expression<'tcx>(
                 if let ty::FnDef(def_id, _) = *literal.ty().kind() {
                     if let Some((destination_place, _)) = destination {
                         if destination_place == place {
-                            if is_const_fn(ccx.tcx, def_id) {
+                            if ccx.tcx.is_const_fn(def_id) {
                                 return true;
                             }
                         }