Auto merge of #108112 - nnethercote:clarify-iterator-interners, r=oli-obk,compiler-errors

Clarify iterator interners

I found the iterator interners very confusing. This PR clarifies things.

r? `@compiler-errors`

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -1608,7 +1608,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             .collect::<SmallVec<[_; 8]>>();
         v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
         v.dedup();
-        let existential_predicates = tcx.mk_poly_existential_predicates(v.into_iter());
+        let existential_predicates = tcx.intern_poly_existential_predicates(&v);
 
         // Use explicitly-specified region bound.
         let region_bound = if !lifetime.is_elided() {
@@ -3109,7 +3109,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         debug!(?output_ty);
 
-        let fn_ty = tcx.mk_fn_sig(input_tys.into_iter(), output_ty, decl.c_variadic, unsafety, abi);
+        let fn_ty = tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi);
         let bare_fn_ty = ty::Binder::bind_with_vars(fn_ty, bound_vars);
 
         if !self.allow_ty_infer() && !(visitor.0.is_empty() && infer_replacements.is_empty()) {

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -1936,7 +1936,7 @@ pub(super) fn check_type_bounds<'tcx>(
             .into()
         }
     });
-    let bound_vars = tcx.mk_bound_variable_kinds(bound_vars.into_iter());
+    let bound_vars = tcx.intern_bound_variable_kinds(&bound_vars);
     let impl_ty_substs = tcx.intern_substs(&substs);
     let container_id = impl_ty.container_id(tcx);
 

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -15,8 +15,6 @@ use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::symbol::{kw, sym, Symbol};
 use rustc_target::spec::abi::Abi;
 
-use std::iter;
-
 fn equate_intrinsic_type<'tcx>(
     tcx: TyCtxt<'tcx>,
     it: &hir::ForeignItem<'_>,
@@ -139,14 +137,10 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
     let intrinsic_name = tcx.item_name(intrinsic_id);
     let name_str = intrinsic_name.as_str();
 
-    let bound_vars = tcx.mk_bound_variable_kinds(
-        [
-            ty::BoundVariableKind::Region(ty::BrAnon(0, None)),
-            ty::BoundVariableKind::Region(ty::BrEnv),
-        ]
-        .iter()
-        .copied(),
-    );
+    let bound_vars = tcx.intern_bound_variable_kinds(&[
+        ty::BoundVariableKind::Region(ty::BrAnon(0, None)),
+        ty::BoundVariableKind::Region(ty::BrEnv),
+    ]);
     let mk_va_list_ty = |mutbl| {
         tcx.lang_items().va_list().map(|did| {
             let region = tcx.mk_re_late_bound(
@@ -378,21 +372,21 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
                 (
                     1,
                     vec![tcx.mk_imm_ref(tcx.mk_re_late_bound(ty::INNERMOST, br), param(0))],
-                    tcx.mk_projection(discriminant_def_id, tcx.mk_substs([param(0).into()].iter())),
+                    tcx.mk_projection(discriminant_def_id, tcx.intern_substs(&[param(0).into()])),
                 )
             }
 
             kw::Try => {
                 let mut_u8 = tcx.mk_mut_ptr(tcx.types.u8);
                 let try_fn_ty = ty::Binder::dummy(tcx.mk_fn_sig(
-                    iter::once(mut_u8),
+                    [mut_u8],
                     tcx.mk_unit(),
                     false,
                     hir::Unsafety::Normal,
                     Abi::Rust,
                 ));
                 let catch_fn_ty = ty::Binder::dummy(tcx.mk_fn_sig(
-                    [mut_u8, mut_u8].iter().cloned(),
+                    [mut_u8, mut_u8],
                     tcx.mk_unit(),
                     false,
                     hir::Unsafety::Normal,
@@ -447,7 +441,7 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
         };
         (n_tps, 0, inputs, output, unsafety)
     };
-    let sig = tcx.mk_fn_sig(inputs.into_iter(), output, false, unsafety, Abi::RustIntrinsic);
+    let sig = tcx.mk_fn_sig(inputs, output, false, unsafety, Abi::RustIntrinsic);
     let sig = ty::Binder::bind_with_vars(sig, bound_vars);
     equate_intrinsic_type(tcx, it, n_tps, n_lts, sig)
 }
@@ -545,13 +539,7 @@ pub fn check_platform_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>)
         }
     };
 
-    let sig = tcx.mk_fn_sig(
-        inputs.into_iter(),
-        output,
-        false,
-        hir::Unsafety::Unsafe,
-        Abi::PlatformIntrinsic,
-    );
+    let sig = tcx.mk_fn_sig(inputs, output, false, hir::Unsafety::Unsafe, Abi::PlatformIntrinsic);
     let sig = ty::Binder::dummy(sig);
     equate_intrinsic_type(tcx, it, n_tps, 0, sig)
 }

compiler/rustc_hir_analysis/src/lib.rs

@@ -113,7 +113,6 @@ use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt as _;
 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
 
-use std::iter;
 use std::ops::Not;
 
 use astconv::AstConv;
@@ -348,7 +347,7 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
     }
 
     let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
-        tcx.mk_fn_sig(iter::empty(), expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
+        tcx.mk_fn_sig([], expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
     }));
 
     require_same_types(
@@ -434,7 +433,7 @@ fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
             }
 
             let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
-                [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))].iter().cloned(),
+                [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))],
                 tcx.types.isize,
                 false,
                 hir::Unsafety::Normal,