Auto merge of #112006 - kylematsuda:earlybinder-private, r=jackh726

Make `EarlyBinder`'s inner value private

Currently, `EarlyBinder(T)`'s inner value is public, which allows implicitly skipping the binder by indexing into the tuple struct (i.e., `x.0`). `@lcnr` suggested making `EarlyBinder`'s inner value private so users are required to explicitly call `skip_binder` (#105779 (comment)) .

This PR makes the inner value private, adds `EarlyBinder::new` for constructing a new instance, and replaces uses of `x.0` with `x.skip_binder()` (or similar). It also adds some documentation to `EarlyBinder::skip_binder` explaining how to skip the binder of `&EarlyBinder<T>` to get `&T` now that the inner value is private (since previously we could just do `&x.0`).

r? `@lcnr`

Author: bors

compiler/rustc_codegen_cranelift/src/common.rs

@@ -361,7 +361,7 @@ impl<'tcx> FunctionCx<'_, '_, 'tcx> {
         self.instance.subst_mir_and_normalize_erasing_regions(
             self.tcx,
             ty::ParamEnv::reveal_all(),
-            ty::EarlyBinder(value),
+            ty::EarlyBinder::new(value),
         )
     }
 

compiler/rustc_codegen_llvm/src/debuginfo/create_scope_map.rs

@@ -93,7 +93,7 @@ fn make_mir_scope<'ll, 'tcx>(
             let callee = cx.tcx.subst_and_normalize_erasing_regions(
                 instance.substs,
                 ty::ParamEnv::reveal_all(),
-                ty::EarlyBinder(callee),
+                ty::EarlyBinder::new(callee),
             );
             let callee_fn_abi = cx.fn_abi_of_instance(callee, ty::List::empty());
             cx.dbg_scope_fn(callee, callee_fn_abi, None)

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -111,7 +111,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         self.instance.subst_mir_and_normalize_erasing_regions(
             self.cx.tcx(),
             ty::ParamEnv::reveal_all(),
-            ty::EarlyBinder(value),
+            ty::EarlyBinder::new(value),
         )
     }
 }

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -497,7 +497,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             .try_subst_mir_and_normalize_erasing_regions(
                 *self.tcx,
                 self.param_env,
-                ty::EarlyBinder(value),
+                ty::EarlyBinder::new(value),
             )
             .map_err(|_| err_inval!(TooGeneric))
     }

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -1278,7 +1278,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             // params (and trait ref's late bound params). This logic is very similar to
             // `Predicate::subst_supertrait`, and it's no coincidence why.
             let shifted_output = tcx.shift_bound_var_indices(num_bound_vars, output);
-            let subst_output = ty::EarlyBinder(shifted_output).subst(tcx, substs);
+            let subst_output = ty::EarlyBinder::new(shifted_output).subst(tcx, substs);
 
             let bound_vars = tcx.late_bound_vars(binding.hir_id);
             ty::Binder::bind_with_vars(subst_output, bound_vars)

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -794,14 +794,14 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
                     })
                 });
                 debug!(%ty);
-                collected_tys.insert(def_id, ty::EarlyBinder(ty));
+                collected_tys.insert(def_id, ty::EarlyBinder::new(ty));
             }
             Err(err) => {
                 let reported = tcx.sess.delay_span_bug(
                     return_span,
                     format!("could not fully resolve: {ty} => {err:?}"),
                 );
-                collected_tys.insert(def_id, ty::EarlyBinder(tcx.ty_error(reported)));
+                collected_tys.insert(def_id, ty::EarlyBinder::new(tcx.ty_error(reported)));
             }
         }
     }

compiler/rustc_hir_analysis/src/check/dropck.rs

@@ -128,7 +128,7 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
     // We don't need to normalize this param-env or anything, since we're only
     // substituting it with free params, so no additional param-env normalization
     // can occur on top of what has been done in the param_env query itself.
-    let param_env = ty::EarlyBinder(tcx.param_env(adt_def_id))
+    let param_env = ty::EarlyBinder::new(tcx.param_env(adt_def_id))
         .subst(tcx, adt_to_impl_substs)
         .with_constness(tcx.constness(drop_impl_def_id));
 

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1398,7 +1398,7 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
             }
             let mut param_count = CountParams::default();
             let has_region = pred.visit_with(&mut param_count).is_break();
-            let substituted_pred = ty::EarlyBinder(pred).subst(tcx, substs);
+            let substituted_pred = ty::EarlyBinder::new(pred).subst(tcx, substs);
             // Don't check non-defaulted params, dependent defaults (including lifetimes)
             // or preds with multiple params.
             if substituted_pred.has_non_region_param() || param_count.params.len() > 1 || has_region

compiler/rustc_hir_analysis/src/collect.rs

@@ -1124,7 +1124,7 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<ty::PolyFnSig<
             bug!("unexpected sort of node in fn_sig(): {:?}", x);
         }
     };
-    ty::EarlyBinder(output)
+    ty::EarlyBinder::new(output)
 }
 
 fn infer_return_ty_for_fn_sig<'tcx>(
@@ -1312,7 +1312,7 @@ fn impl_trait_ref(
                 check_impl_constness(tcx, impl_.constness, ast_trait_ref),
             )
         })
-        .map(ty::EarlyBinder)
+        .map(ty::EarlyBinder::new)
 }
 
 fn check_impl_constness(

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -86,7 +86,7 @@ pub(super) fn explicit_item_bounds(
         Some(ty::ImplTraitInTraitData::Trait { opaque_def_id, .. }) => {
             let item = tcx.hir().get_by_def_id(opaque_def_id.expect_local()).expect_item();
             let opaque_ty = item.expect_opaque_ty();
-            return ty::EarlyBinder(opaque_type_bounds(
+            return ty::EarlyBinder::new(opaque_type_bounds(
                 tcx,
                 opaque_def_id.expect_local(),
                 opaque_ty.bounds,
@@ -124,7 +124,7 @@ pub(super) fn explicit_item_bounds(
         }
         _ => bug!("item_bounds called on {:?}", def_id),
     };
-    ty::EarlyBinder(bounds)
+    ty::EarlyBinder::new(bounds)
 }
 
 pub(super) fn item_bounds(