Always evaluate free lifetime-generic constants

Co-authored-by: Michael Goulet <[email protected]>

Author: fmease

compiler/rustc_hir_analysis/src/lib.rs

@@ -215,7 +215,9 @@ pub fn check_crate(tcx: TyCtxt<'_>) {
                 tcx.ensure_ok().eval_static_initializer(item_def_id);
                 check::maybe_check_static_with_link_section(tcx, item_def_id);
             }
-            DefKind::Const if tcx.generics_of(item_def_id).is_empty() => {
+            DefKind::Const if !tcx.generics_of(item_def_id).own_requires_monomorphization() => {
+                // FIXME(generic_const_items): Passing empty instead of identity args is fishy but
+                //                             seems to be fine for now. Revisit this!
                 let instance = ty::Instance::new(item_def_id.into(), ty::GenericArgs::empty());
                 let cid = GlobalId { instance, promoted: None };
                 let typing_env = ty::TypingEnv::fully_monomorphized();

compiler/rustc_middle/src/mir/interpret/queries.rs

@@ -9,7 +9,6 @@ use super::{
     ReportedErrorInfo,
 };
 use crate::mir;
-use crate::query::TyCtxtEnsureOk;
 use crate::ty::{self, GenericArgs, TyCtxt, TypeVisitableExt};
 
 impl<'tcx> TyCtxt<'tcx> {
@@ -197,24 +196,3 @@ impl<'tcx> TyCtxt<'tcx> {
         }
     }
 }
-
-impl<'tcx> TyCtxtEnsureOk<'tcx> {
-    /// Evaluates a constant without providing any generic parameters. This is useful to evaluate consts
-    /// that can't take any generic arguments like const items or enum discriminants. If a
-    /// generic parameter is used within the constant `ErrorHandled::TooGeneric` will be returned.
-    #[instrument(skip(self), level = "debug")]
-    pub fn const_eval_poly(self, def_id: DefId) {
-        // In some situations def_id will have generic parameters within scope, but they aren't allowed
-        // to be used. So we can't use `Instance::mono`, instead we feed unresolved generic parameters
-        // into `const_eval` which will return `ErrorHandled::TooGeneric` if any of them are
-        // encountered.
-        let args = GenericArgs::identity_for_item(self.tcx, def_id);
-        let instance = ty::Instance::new(def_id, self.tcx.erase_regions(args));
-        let cid = GlobalId { instance, promoted: None };
-        let typing_env = ty::TypingEnv::post_analysis(self.tcx, def_id);
-        // Const-eval shouldn't depend on lifetimes at all, so we can erase them, which should
-        // improve caching of queries.
-        let inputs = self.tcx.erase_regions(typing_env.as_query_input(cid));
-        self.eval_to_const_value_raw(inputs)
-    }
-}

compiler/rustc_monomorphize/src/collector.rs

@@ -1465,7 +1465,7 @@ impl<'v> RootCollector<'_, 'v> {
 
                 // But even just declaring them must collect the items they refer to
                 // unless their generics require monomorphization.
-                if !self.tcx.generics_of(id.owner_id).requires_monomorphization(self.tcx)
+                if !self.tcx.generics_of(id.owner_id).own_requires_monomorphization()
                     && let Ok(val) = self.tcx.const_eval_poly(id.owner_id.to_def_id())
                 {
                     collect_const_value(self.tcx, val, self.output);

tests/ui/generic-const-items/def-site-eval.fail.stderr

@@ -1,5 +1,5 @@
 error[E0080]: evaluation of `_::<'_>` failed
-  --> $DIR/def-site-eval.rs:14:20
+  --> $DIR/def-site-eval.rs:13:20
    |
 LL | const _<'_a>: () = panic!();
    |                    ^^^^^^^^ evaluation panicked: explicit panic

tests/ui/generic-const-items/def-site-eval.rs

@@ -4,7 +4,6 @@
 #![allow(incomplete_features)]
 
 //@ revisions: fail pass
-//@[fail] build-fail (we require monomorphization)
 //@[pass] build-pass (we require monomorphization)
 
 const _<_T>: () = panic!();