Auto merge of #126813 - compiler-errors:SliceLike, r=lcnr

Add `SliceLike` to `rustc_type_ir`, use it in the generic solver code (+ some other changes)

First, we split out `TraitRef::new_from_args` which takes *just* `ty::GenericArgsRef` from `TraitRef::new` which takes `impl IntoIterator<Item: Into<GenericArg>>`. I will explain in a minute why.

Second, we introduce `SliceLike`, which allows us to be generic over `List<T>` and `[T]`. This trait has an `as_slice()` and `into_iter()` method, and some other convenience functions. However, importantly, since types like `I::GenericArgs` now implement `SliceLike` rather than `IntoIter<Item = I::GenericArg>`, we can't use `TraitRef::new` on this directly. That's where `new_from_args` comes in.

Finally, we adjust all the code to use these slice operators. Some things get simpler, some things get a bit more annoying since we need to use `as_slice()` in a few places. 🤷

r? lcnr

clippy_lints/src/bool_assert_comparison.rs

@@ -61,7 +61,7 @@ fn is_impl_not_trait_with_bool_out<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -
             )
         })
         .map_or(false, |assoc_item| {
-            let proj = Ty::new_projection(cx.tcx, assoc_item.def_id, cx.tcx.mk_args_trait(ty, []));
+            let proj = Ty::new_projection_from_args(cx.tcx, assoc_item.def_id, cx.tcx.mk_args_trait(ty, []));
             let nty = cx.tcx.normalize_erasing_regions(cx.param_env, proj);
 
             nty.is_bool()

clippy_lints/src/methods/needless_collect.rs

@@ -206,7 +206,7 @@ fn iterates_same_ty<'tcx>(cx: &LateContext<'tcx>, iter_ty: Ty<'tcx>, collect_ty:
         && let Some(into_iter_item_proj) = make_projection(cx.tcx, into_iter_trait, sym::Item, [collect_ty])
         && let Ok(into_iter_item_ty) = cx.tcx.try_normalize_erasing_regions(
             cx.param_env,
-            Ty::new_projection(cx.tcx, into_iter_item_proj.def_id, into_iter_item_proj.args),
+            Ty::new_projection_from_args(cx.tcx, into_iter_item_proj.def_id, into_iter_item_proj.args),
         )
     {
         iter_item_ty == into_iter_item_ty
@@ -235,7 +235,7 @@ fn is_contains_sig(cx: &LateContext<'_>, call_id: HirId, iter_expr: &Expr<'_>) -
             iter_trait,
         )
         && let args = cx.tcx.mk_args(&[GenericArg::from(typeck.expr_ty_adjusted(iter_expr))])
-        && let proj_ty = Ty::new_projection(cx.tcx, iter_item.def_id, args)
+        && let proj_ty = Ty::new_projection_from_args(cx.tcx, iter_item.def_id, args)
         && let Ok(item_ty) = cx.tcx.try_normalize_erasing_regions(cx.param_env, proj_ty)
     {
         item_ty == EarlyBinder::bind(search_ty).instantiate(cx.tcx, cx.typeck_results().node_args(call_id))

clippy_lints/src/needless_borrows_for_generic_args.rs

@@ -267,7 +267,7 @@ fn needless_borrow_count<'tcx>(
                 return false;
             }
 
-            let predicate = EarlyBinder::bind(predicate).instantiate(cx.tcx, &args_with_referent_ty);
+            let predicate = EarlyBinder::bind(predicate).instantiate(cx.tcx, &args_with_referent_ty[..]);
             let obligation = Obligation::new(cx.tcx, ObligationCause::dummy(), cx.param_env, predicate);
             let infcx = cx.tcx.infer_ctxt().build();
             infcx.predicate_must_hold_modulo_regions(&obligation)

clippy_lints/src/redundant_slicing.rs

@@ -133,7 +133,7 @@ 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,
-                    Ty::new_projection(cx.tcx, target_id, cx.tcx.mk_args(&[GenericArg::from(indexed_ty)])),
+                    Ty::new_projection_from_args(cx.tcx, target_id, cx.tcx.mk_args(&[GenericArg::from(indexed_ty)])),
                 ) {
                     if deref_ty == expr_ty {
                         let snip = snippet_with_context(cx, indexed.span, ctxt, "..", &mut app).0;

clippy_utils/src/ty.rs

@@ -292,7 +292,7 @@ pub fn implements_trait_with_env_from_iter<'tcx>(
     let trait_ref = TraitRef::new(
         tcx,
         trait_id,
-        Some(GenericArg::from(ty)).into_iter().chain(args).chain(effect_arg),
+        [GenericArg::from(ty)].into_iter().chain(args).chain(effect_arg),
     );
 
     debug_assert_matches!(
@@ -1126,7 +1126,7 @@ pub fn make_projection<'tcx>(
         #[cfg(debug_assertions)]
         assert_generic_args_match(tcx, assoc_item.def_id, args);
 
-        Some(AliasTy::new(tcx, assoc_item.def_id, args))
+        Some(AliasTy::new_from_args(tcx, assoc_item.def_id, args))
     }
     helper(
         tcx,
@@ -1165,7 +1165,7 @@ pub fn make_normalized_projection<'tcx>(
             );
             return None;
         }
-        match tcx.try_normalize_erasing_regions(param_env, Ty::new_projection(tcx, ty.def_id, ty.args)) {
+        match tcx.try_normalize_erasing_regions(param_env, Ty::new_projection_from_args(tcx, ty.def_id, ty.args)) {
             Ok(ty) => Some(ty),
             Err(e) => {
                 debug_assert!(false, "failed to normalize type `{ty}`: {e:#?}");
@@ -1289,7 +1289,7 @@ pub fn make_normalized_projection_with_regions<'tcx>(
             .infer_ctxt()
             .build()
             .at(&cause, param_env)
-            .query_normalize(Ty::new_projection(tcx, ty.def_id, ty.args))
+            .query_normalize(Ty::new_projection_from_args(tcx, ty.def_id, ty.args))
         {
             Ok(ty) => Some(ty.value),
             Err(e) => {