Rename many interner functions.

(This is a large commit. The changes to
`compiler/rustc_middle/src/ty/context.rs` are the most important ones.)

The current naming scheme is a mess, with a mix of `_intern_`, `intern_`
and `mk_` prefixes, with little consistency. In particular, in many
cases it's easy to use an iterator interner when a (preferable) slice
interner is available.

The guiding principles of the new naming system:
- No `_intern_` prefixes.
- The `intern_` prefix is for internal operations.
- The `mk_` prefix is for external operations.
- For cases where there is a slice interner and an iterator interner,
  the former is `mk_foo` and the latter is `mk_foo_from_iter`.

Also, `slice_interners!` and `direct_interners!` can now be `pub` or
non-`pub`, which helps enforce the internal/external operations
division.

It's not perfect, but I think it's a clear improvement.

The following lists show everything that was renamed.

slice_interners
- const_list
  - mk_const_list -> mk_const_list_from_iter
  - intern_const_list -> mk_const_list
- substs
  - mk_substs -> mk_substs_from_iter
  - intern_substs -> mk_substs
  - check_substs -> check_and_mk_substs (this is a weird one)
- canonical_var_infos
  - intern_canonical_var_infos -> mk_canonical_var_infos
- poly_existential_predicates
  - mk_poly_existential_predicates -> mk_poly_existential_predicates_from_iter
  - intern_poly_existential_predicates -> mk_poly_existential_predicates
  - _intern_poly_existential_predicates -> intern_poly_existential_predicates
- predicates
  - mk_predicates -> mk_predicates_from_iter
  - intern_predicates -> mk_predicates
  - _intern_predicates -> intern_predicates
- projs
  - intern_projs -> mk_projs
- place_elems
  - mk_place_elems -> mk_place_elems_from_iter
  - intern_place_elems -> mk_place_elems
- bound_variable_kinds
  - mk_bound_variable_kinds -> mk_bound_variable_kinds_from_iter
  - intern_bound_variable_kinds -> mk_bound_variable_kinds

direct_interners
- region
  - intern_region (unchanged)
- const
  - mk_const_internal -> intern_const
- const_allocation
  - intern_const_alloc -> mk_const_alloc
- layout
  - intern_layout -> mk_layout
- adt_def
  - intern_adt_def -> mk_adt_def_from_data (unusual case, hard to avoid)
  - alloc_adt_def(!) -> mk_adt_def
- external_constraints
  - intern_external_constraints -> mk_external_constraints

Other
- type_list
  - mk_type_list -> mk_type_list_from_iter
  - intern_type_list -> mk_type_list
- tup
  - mk_tup -> mk_tup_from_iter
  - intern_tup -> mk_tup

clippy_lints/src/derive.rs

@@ -514,7 +514,7 @@ fn param_env_for_derived_eq(tcx: TyCtxt<'_>, did: DefId, eq_trait_id: DefId) ->
     }
 
     ParamEnv::new(
-        tcx.mk_predicates(ty_predicates.iter().map(|&(p, _)| p).chain(
+        tcx.mk_predicates_from_iter(ty_predicates.iter().map(|&(p, _)| p).chain(
             params.iter().filter(|&&(_, needs_eq)| needs_eq).map(|&(param, _)| {
                 tcx.mk_predicate(Binder::dummy(PredicateKind::Clause(Clause::Trait(TraitPredicate {
                     trait_ref: tcx.mk_trait_ref(eq_trait_id, [tcx.mk_param_from_def(param)]),

clippy_lints/src/methods/needless_collect.rs

@@ -173,7 +173,7 @@ fn is_contains_sig(cx: &LateContext<'_>, call_id: HirId, iter_expr: &Expr<'_>) -
         && let Some(iter_item) = cx.tcx
             .associated_items(iter_trait)
             .find_by_name_and_kind(cx.tcx, Ident::with_dummy_span(Symbol::intern("Item")), AssocKind::Type, iter_trait)
-        && let substs = cx.tcx.intern_substs(&[GenericArg::from(typeck.expr_ty_adjusted(iter_expr))])
+        && let substs = cx.tcx.mk_substs(&[GenericArg::from(typeck.expr_ty_adjusted(iter_expr))])
         && let proj_ty = cx.tcx.mk_projection(iter_item.def_id, substs)
         && let Ok(item_ty) = cx.tcx.try_normalize_erasing_regions(cx.param_env, proj_ty)
     {

clippy_lints/src/methods/unnecessary_to_owned.rs

@@ -414,7 +414,7 @@ fn can_change_type<'a>(cx: &LateContext<'a>, mut expr: &'a Expr<'a>, mut ty: Ty<
                             }
                         });
 
-                        let new_subst = cx.tcx.mk_substs(
+                        let new_subst = cx.tcx.mk_substs_from_iter(
                             call_substs.iter()
                                 .enumerate()
                                 .map(|(i, t)|

clippy_lints/src/redundant_slicing.rs

@@ -134,7 +134,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantSlicing {
                 } else if let Some(target_id) = cx.tcx.lang_items().deref_target() {
                     if let Ok(deref_ty) = cx.tcx.try_normalize_erasing_regions(
                         cx.param_env,
-                        cx.tcx.mk_projection(target_id, cx.tcx.intern_substs(&[GenericArg::from(indexed_ty)])),
+                        cx.tcx.mk_projection(target_id, cx.tcx.mk_substs(&[GenericArg::from(indexed_ty)])),
                     ) {
                         if deref_ty == expr_ty {
                             let snip = snippet_with_context(cx, indexed.span, ctxt, "..", &mut app).0;

clippy_utils/src/consts.rs

@@ -237,7 +237,7 @@ pub fn constant<'tcx>(
         typeck_results,
         param_env: lcx.param_env,
         needed_resolution: false,
-        substs: lcx.tcx.intern_substs(&[]),
+        substs: lcx.tcx.mk_substs(&[]),
     };
     cx.expr(e).map(|cst| (cst, cx.needed_resolution))
 }
@@ -306,7 +306,7 @@ pub fn constant_context<'a, 'tcx>(
         typeck_results,
         param_env: lcx.param_env,
         needed_resolution: false,
-        substs: lcx.tcx.intern_substs(&[]),
+        substs: lcx.tcx.mk_substs(&[]),
     }
 }
 

clippy_utils/src/ty.rs

@@ -237,7 +237,7 @@ pub fn implements_trait_with_env<'tcx>(
         kind: TypeVariableOriginKind::MiscVariable,
         span: DUMMY_SP,
     };
-    let ty_params = tcx.mk_substs(
+    let ty_params = tcx.mk_substs_from_iter(
         ty_params
             .into_iter()
             .map(|arg| arg.unwrap_or_else(|| infcx.next_ty_var(orig).into())),
@@ -1065,7 +1065,7 @@ pub fn make_projection<'tcx>(
         tcx,
         container_id,
         assoc_ty,
-        tcx.mk_substs(substs.into_iter().map(Into::into)),
+        tcx.mk_substs_from_iter(substs.into_iter().map(Into::into)),
     )
 }