Rollup merge of #92780 - b-naber:postpone-const-eval-coherence, r=lcnr

Directly use ConstValue for single literals in blocks

Addresses the minimal repro in https://github.com/rust-lang/rust/issues/92186, but doesn't fix the underlying problem (which would be solved by solving the anon subst problem afaict).

I do, however, think that it makes sense in general to treat single literals in anon blocks as const values directly, especially in light of the problem that the issue refers to (anon const evaluation being postponed until infer variables in substs can be resolved, which was introduced by https://github.com/rust-lang/rust/pull/90023), i.e. while we do get warnings for those unnecessary braces, we should try to avoid errors caused by those braces if possible.

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -53,6 +53,7 @@ pub fn add_placeholder_note(err: &mut rustc_errors::DiagnosticBuilder<'_>) {
 /// If there are types that satisfy both impls, invokes `on_overlap`
 /// with a suitably-freshened `ImplHeader` with those types
 /// substituted. Otherwise, invokes `no_overlap`.
+#[instrument(skip(tcx, skip_leak_check, on_overlap, no_overlap), level = "debug")]
 pub fn overlapping_impls<F1, F2, R>(
     tcx: TyCtxt<'_>,
     impl1_def_id: DefId,
@@ -65,12 +66,6 @@ where
     F1: FnOnce(OverlapResult<'_>) -> R,
     F2: FnOnce() -> R,
 {
-    debug!(
-        "overlapping_impls(\
-           impl1_def_id={:?}, \
-           impl2_def_id={:?})",
-        impl1_def_id, impl2_def_id,
-    );
     // Before doing expensive operations like entering an inference context, do
     // a quick check via fast_reject to tell if the impl headers could possibly
     // unify.
@@ -85,6 +80,7 @@ where
     .any(|(ty1, ty2)| {
         let t1 = fast_reject::simplify_type(tcx, ty1, SimplifyParams::No, StripReferences::No);
         let t2 = fast_reject::simplify_type(tcx, ty2, SimplifyParams::No, StripReferences::No);
+
         if let (Some(t1), Some(t2)) = (t1, t2) {
             // Simplified successfully
             t1 != t2

compiler/rustc_trait_selection/src/traits/specialize/mod.rs

@@ -117,9 +117,8 @@ pub fn translate_substs<'a, 'tcx>(
 /// Specialization is determined by the sets of types to which the impls apply;
 /// `impl1` specializes `impl2` if it applies to a subset of the types `impl2` applies
 /// to.
+#[instrument(skip(tcx), level = "debug")]
 pub(super) fn specializes(tcx: TyCtxt<'_>, (impl1_def_id, impl2_def_id): (DefId, DefId)) -> bool {
-    debug!("specializes({:?}, {:?})", impl1_def_id, impl2_def_id);
-
     // The feature gate should prevent introducing new specializations, but not
     // taking advantage of upstream ones.
     let features = tcx.features();