Some cleanup of index types in `rustc_hir_typeck`

2 files changed, 23 insertions, 19 deletions

diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/arg_matrix.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/arg_matrix.rs
index 358bc389bd1..f6298adf2eb 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/arg_matrix.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/arg_matrix.rs
@@ -22,6 +22,12 @@ impl ExpectedIdx {
     }
 }
 
+impl ProvidedIdx {
+    pub(crate) fn to_expected_idx(self) -> ExpectedIdx {
+        ExpectedIdx::from_u32(self.as_u32())
+    }
+}
+
 // An issue that might be found in the compatibility matrix
 #[derive(Debug)]
 enum Issue {
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
index e90474cabb4..29ee120a675 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs
@@ -773,7 +773,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // First, check if we just need to wrap some arguments in a tuple.
         if let Some((mismatch_idx, terr)) =
-            compatibility_diagonal.iter().enumerate().find_map(|(i, c)| {
+            compatibility_diagonal.iter_enumerated().find_map(|(i, c)| {
                 if let Compatibility::Incompatible(Some(terr)) = c {
                     Some((i, *terr))
                 } else {
@@ -785,24 +785,25 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // Do we have as many extra provided arguments as the tuple's length?
             // If so, we might have just forgotten to wrap some args in a tuple.
             if let Some(ty::Tuple(tys)) =
-                formal_and_expected_inputs.get(mismatch_idx.into()).map(|tys| tys.1.kind())
+                formal_and_expected_inputs.get(mismatch_idx.to_expected_idx()).map(|tys| tys.1.kind())
                 // If the tuple is unit, we're not actually wrapping any arguments.
                 && !tys.is_empty()
                 && provided_arg_tys.len() == formal_and_expected_inputs.len() - 1 + tys.len()
             {
                 // Wrap up the N provided arguments starting at this position in a tuple.
-                let provided_as_tuple = Ty::new_tup_from_iter(
-                    tcx,
-                    provided_arg_tys.iter().map(|(ty, _)| *ty).skip(mismatch_idx).take(tys.len()),
-                );
+                let provided_args_to_tuple = &provided_arg_tys.raw[mismatch_idx.idx()..];
+                let (provided_args_to_tuple, provided_args_after_tuple) =
+                    provided_args_to_tuple.split_at(tys.len());
+                let provided_as_tuple =
+                    Ty::new_tup_from_iter(tcx, provided_args_to_tuple.iter().map(|&(ty, _)| ty));
 
                 let mut satisfied = true;
                 // Check if the newly wrapped tuple + rest of the arguments are compatible.
                 for ((_, expected_ty), provided_ty) in std::iter::zip(
-                    formal_and_expected_inputs.iter().skip(mismatch_idx),
-                    [provided_as_tuple].into_iter().chain(
-                        provided_arg_tys.iter().map(|(ty, _)| *ty).skip(mismatch_idx + tys.len()),
-                    ),
+                    formal_and_expected_inputs[mismatch_idx.to_expected_idx()..].iter(),
+                    [provided_as_tuple]
+                        .into_iter()
+                        .chain(provided_args_after_tuple.iter().map(|&(ty, _)| ty)),
                 ) {
                     if !self.may_coerce(provided_ty, *expected_ty) {
                         satisfied = false;
@@ -814,10 +815,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // Take some care with spans, so we don't suggest wrapping a macro's
                 // innards in parenthesis, for example.
                 if satisfied
-                    && let Some((_, lo)) =
-                        provided_arg_tys.get(ProvidedIdx::from_usize(mismatch_idx))
-                    && let Some((_, hi)) =
-                        provided_arg_tys.get(ProvidedIdx::from_usize(mismatch_idx + tys.len() - 1))
+                    && let &[(_, hi @ lo)] | &[(_, lo), .., (_, hi)] = provided_args_to_tuple
                 {
                     let mut err;
                     if tys.len() == 1 {
@@ -825,9 +823,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         // so don't do anything special here.
                         err = self.err_ctxt().report_and_explain_type_error(
                             mk_trace(
-                                *lo,
-                                formal_and_expected_inputs[mismatch_idx.into()],
-                                provided_arg_tys[mismatch_idx.into()].0,
+                                lo,
+                                formal_and_expected_inputs[mismatch_idx.to_expected_idx()],
+                                provided_arg_tys[mismatch_idx].0,
                             ),
                             self.param_env,
                             terr,
@@ -866,7 +864,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         callee_ty,
                         call_expr,
                         None,
-                        Some(mismatch_idx),
+                        Some(mismatch_idx.as_usize()),
                         &matched_inputs,
                         &formal_and_expected_inputs,
                         is_method,
@@ -2648,7 +2646,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
 
                 let expected_display_type = self
-                    .resolve_vars_if_possible(formal_and_expected_inputs[idx.into()].1)
+                    .resolve_vars_if_possible(formal_and_expected_inputs[idx].1)
                     .sort_string(self.tcx);
                 let label = if idxs_matched == params_with_generics.len() - 1 {
                     format!(