Auto merge of #118937 - lcnr:rename-solver-flag, r=compiler-errors

`-Ztrait-solver=next` to `-Znext-solver`

renames the feature flag to enable the new trait solver.

still want some feedback before merging: https://rust-lang.zulipchat.com/#narrow/stream/364551-t-types.2Ftrait-system-refactor/topic/renaming.20the.20feature.20flag.20to.20.60-Znew-solver.60.

The idea is to make it easier to add another option, e.g. to enable the solver in wfcheck or to optionally change its behavior to our new coinduction approach.

r? `@compiler-errors`

Author: bors

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -315,7 +315,7 @@ fn check_opaque_type_well_formed<'tcx>(
         parent_def_id = tcx.local_parent(parent_def_id);
     }
 
-    // FIXME(-Ztrait-solver=next): We probably should use `DefiningAnchor::Error`
+    // FIXME(-Znext-solver): We probably should use `DefiningAnchor::Error`
     // and prepopulate this `InferCtxt` with known opaque values, rather than
     // using the `Bind` anchor here. For now it's fine.
     let infcx = tcx

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -1003,16 +1003,16 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             reported_errors: Default::default(),
         };
 
-        // FIXME(-Ztrait-solver=next): A bit dubious that we're only registering
+        // FIXME(-Znext-solver): A bit dubious that we're only registering
         // predefined opaques in the typeck root.
         if infcx.next_trait_solver() && !infcx.tcx.is_typeck_child(body.source.def_id()) {
-            checker.register_predefined_opaques_in_new_solver();
+            checker.register_predefined_opaques_for_next_solver();
         }
 
         checker
     }
 
-    pub(super) fn register_predefined_opaques_in_new_solver(&mut self) {
+    pub(super) fn register_predefined_opaques_for_next_solver(&mut self) {
         // OK to use the identity arguments for each opaque type key, since
         // we remap opaques from HIR typeck back to their definition params.
         let opaques: Vec<_> = self