From 4268918a502f899c4bc9041e7610c3bbc4d76517 Mon Sep 17 00:00:00 2001
From: Ben Kimock <kimockb@gmail.com>
Date: Tue, 19 Jul 2022 20:53:48 -0400
Subject: [PATCH] Clarify implementation a bit

---
 src/stacked_borrows/stack.rs                               | 7 ++++---
 tests/pass/{issues => stacked-borrows}/issue-miri-2389.rs  | 0
 .../{issues => stacked-borrows}/issue-miri-2389.stderr     | 0
 3 files changed, 4 insertions(+), 3 deletions(-)
 rename tests/pass/{issues => stacked-borrows}/issue-miri-2389.rs (100%)
 rename tests/pass/{issues => stacked-borrows}/issue-miri-2389.stderr (100%)

diff --git a/src/stacked_borrows/stack.rs b/src/stacked_borrows/stack.rs
index 9fab5433d84..32c1be5fb1e 100644
--- a/src/stacked_borrows/stack.rs
+++ b/src/stacked_borrows/stack.rs
@@ -105,6 +105,7 @@ fn verify_cache_consistency(&self) {
         }
 
         // Check that the unique_range is a valid index into the borrow stack.
+        // This asserts that the unique_range's start <= end.
         let uniques = &self.borrows[self.unique_range.clone()];
 
         // Check that the start of the unique_range is precise.
@@ -113,7 +114,7 @@ fn verify_cache_consistency(&self) {
         }
         // We cannot assert that the unique range is exact on the upper end.
         // When we pop items within the unique range, setting the end of the range precisely
-        // require doing a linear search of the borrow stack, which is exactly the kind of
+        // requires doing a linear search of the borrow stack, which is exactly the kind of
         // operation that all this caching exists to avoid.
     }
 
@@ -240,8 +241,8 @@ fn insert_cache(&mut self, new_idx: usize, new: Item) {
             self.unique_range.end += 1;
         }
         if new.perm() == Permission::Unique {
-            // If this is the first Unique, set the range to contain just the new item.
-            if self.unique_range == (0..0) {
+            // If this is the only Unique, set the range to contain just the new item.
+            if self.unique_range.is_empty() {
                 self.unique_range = new_idx..new_idx + 1;
             } else {
                 // We already have other Unique items, expand the range to include the new item
diff --git a/tests/pass/issues/issue-miri-2389.rs b/tests/pass/stacked-borrows/issue-miri-2389.rs
similarity index 100%
rename from tests/pass/issues/issue-miri-2389.rs
rename to tests/pass/stacked-borrows/issue-miri-2389.rs
diff --git a/tests/pass/issues/issue-miri-2389.stderr b/tests/pass/stacked-borrows/issue-miri-2389.stderr
similarity index 100%
rename from tests/pass/issues/issue-miri-2389.stderr
rename to tests/pass/stacked-borrows/issue-miri-2389.stderr