Add a helper function for checking whether a default function in a trait can be treated as `const`

3 files changed, 8 insertions, 11 deletions

diff --git a/compiler/rustc_const_eval/src/const_eval/machine.rs b/compiler/rustc_const_eval/src/const_eval/machine.rs
index 8bd8280497c..ac529bf152f 100644
--- a/compiler/rustc_const_eval/src/const_eval/machine.rs
+++ b/compiler/rustc_const_eval/src/const_eval/machine.rs
@@ -278,8 +278,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
             // at all.
             if !ecx.tcx.is_const_fn_raw(def.did) {
                 // allow calling functions inside a trait marked with #[const_trait].
-                if !matches!(ecx.tcx.trait_of_item(def.did), Some(trait_id) if ecx.tcx.has_attr(trait_id, sym::const_trait))
-                {
+                if !ecx.tcx.is_const_default_method(def.did) {
                     // We certainly do *not* want to actually call the fn
                     // though, so be sure we return here.
                     throw_unsup_format!("calling non-const function `{}`", instance)
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/check.rs b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
index 57c073cca4d..458f733df10 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
@@ -872,13 +872,11 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 let is_intrinsic = tcx.is_intrinsic(callee);
 
                 if !tcx.is_const_fn_raw(callee) {
-                    if tcx.trait_of_item(callee).is_some() {
-                        if let Some(callee_trait) = tcx.trait_of_item(callee) && tcx.has_attr(callee_trait, sym::const_trait) {
-                            // To get to here we must have already found a const impl for the
-                            // trait, but for it to still be non-const can be that the impl is
-                            // using default method bodies.
-                            nonconst_call_permission = true;
-                        }
+                    if tcx.is_const_default_method(callee) {
+                        // To get to here we must have already found a const impl for the
+                        // trait, but for it to still be non-const can be that the impl is
+                        // using default method bodies.
+                        nonconst_call_permission = true;
                     }
 
                     if !nonconst_call_permission {
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/mod.rs b/compiler/rustc_const_eval/src/transform/check_consts/mod.rs
index 32cabb1f899..25b420bed17 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/mod.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/mod.rs
@@ -9,7 +9,7 @@ use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::mir;
 use rustc_middle::ty::{self, TyCtxt};
-use rustc_span::{sym, Symbol};
+use rustc_span::Symbol;
 
 pub use self::qualifs::Qualif;
 
@@ -87,7 +87,7 @@ pub fn is_const_stable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
     // A default body in a `#[const_trait]` is not const-stable because const
     // trait fns currently cannot be const-stable. We shouldn't
     // restrict default bodies to only call const-stable functions.
-    if let Some(trait_id) = tcx.trait_of_item(def_id) && tcx.has_attr(trait_id, sym::const_trait) {
+    if tcx.is_const_default_method(def_id) {
         return false;
     }