Allow SliceIndex to be indexed by ranges.

compiler/rustc_mir_transform/src/coverage/counters.rs

@@ -47,7 +47,7 @@ fn make_node_flow_priority_list(
     // A "reloop" node has exactly one out-edge, which jumps back to the top
     // of an enclosing loop. Reloop nodes are typically visited more times
     // than loop-exit nodes, so try to avoid giving them physical counters.
-    let is_reloop_node = IndexVec::from_fn_n(
+    let is_reloop_node = IndexVec::<BasicCoverageBlock, _>::from_fn_n(
         |node| match graph.successors[node].as_slice() {
             &[succ] => graph.dominates(succ, node),
             _ => false,

compiler/rustc_mir_transform/src/coverage/graph.rs

@@ -42,7 +42,7 @@ impl CoverageGraph {
         // `SwitchInt` to have multiple targets to the same destination `BasicBlock`, so
         // de-duplication is required. This is done without reordering the successors.
 
-        let successors = IndexVec::from_fn_n(
+        let successors = IndexVec::<BasicCoverageBlock, _>::from_fn_n(
             |bcb| {
                 let mut seen_bcbs = FxHashSet::default();
                 let terminator = mir_body[bcbs[bcb].last_bb()].terminator();