commitlog: Fix index truncation test.

Since #2771, and error is returned instead of the zero key if an offset
index lookup yields the zero key.

`truncate` removes the entry at its argument's key, i.e. `truncate(1)`
empties the index.

Adjust the `offset_index_writer_truncates_to_offset` test to handle this
edge case. Also de-randomize it so all keys are tested.

Author: kim

crates/commitlog/src/index/indexfile.rs

@@ -5,7 +5,7 @@ use std::{
     mem,
 };
 
-use log::debug;
+use log::{debug, trace};
 use memmap2::MmapMut;
 use spacetimedb_paths::server::OffsetIndexFile;
 
@@ -190,19 +190,32 @@ impl<Key: Into<u64> + From<u64>> IndexFileMut<Key> {
         self.inner.flush_async()
     }
 
-    /// Truncates the index file starting from the entry with a key greater than or equal to the given key.
+    /// Truncates the index file starting from the entry with a key greater than
+    /// or equal to the given key.
+    ///
+    /// If successful, `key` will no longer be in the index.
     pub(crate) fn truncate(&mut self, key: Key) -> Result<(), IndexError> {
         let key = key.into();
-        let (found_key, index) = self.find_index(Key::from(key))?;
+        let (found_key, index) = self
+            .find_index(Key::from(key))
+            .map(|(found, index)| (found.into(), index))?;
 
-        // If returned key is smalled than asked key, truncate from next entry
-        self.num_entries = if found_key.into() == key {
+        // If returned key is smaller than asked key, truncate from next entry
+        self.num_entries = if found_key == key {
             index as usize
         } else {
             index as usize + 1
         };
 
         let start = self.num_entries * ENTRY_SIZE;
+        trace!(
+            "truncate key={} found={} index={} num-entries={} start={}",
+            key,
+            found_key,
+            index,
+            self.num_entries,
+            start
+        );
 
         if start < self.inner.len() {
             self.inner[start..].fill(0);

crates/commitlog/src/segment.rs

@@ -695,6 +695,7 @@ mod tests {
     use super::*;
     use crate::{payload::ArrayDecoder, repo, Options};
     use itertools::Itertools;
+    use pretty_assertions::assert_matches;
     use proptest::prelude::*;
     use spacetimedb_paths::server::CommitLogDir;
     use tempfile::tempdir;
@@ -924,16 +925,28 @@ mod tests {
 
         // Truncating to any offset in the written range or larger
         // retains that offset - 1, or the max offset written.
-        let truncate_to: TxOffset = rand::random_range(1..=32);
-        let retained_key = truncate_to.saturating_sub(1).min(10);
-        let retained_val = retained_key * 128;
-        let retained = (retained_key, retained_val);
-
-        writer.ftruncate(truncate_to, rand::random()).unwrap();
-        assert_eq!(writer.head.key_lookup(truncate_to).unwrap(), retained);
-        // Make sure this also holds after reopen.
-        drop(writer);
-        let index = TxOffsetIndex::open_index_file(&index_path).unwrap();
-        assert_eq!(index.key_lookup(truncate_to).unwrap(), retained);
+        for truncate_to in (2..=10u64).rev() {
+            let retained_key = truncate_to.saturating_sub(1).min(10);
+            let retained_val = retained_key * 128;
+            let retained = (retained_key, retained_val);
+
+            writer.ftruncate(truncate_to, rand::random()).unwrap();
+            assert_matches!(
+                writer.head.key_lookup(truncate_to),
+                Ok(x) if x == retained,
+                "truncate to {truncate_to} should retain {retained:?}"
+            );
+            // Make sure this also holds after reopen.
+            let index = TxOffsetIndex::open_index_file(&index_path).unwrap();
+            assert_matches!(
+                index.key_lookup(truncate_to),
+                Ok(x) if x == retained,
+                "truncate to {truncate_to} should retain {retained:?} after reopen"
+            );
+        }
+
+        // Truncating to 1 leaves no entries in the index
+        writer.ftruncate(1, rand::random()).unwrap();
+        assert_matches!(writer.head.key_lookup(1), Err(IndexError::KeyNotFound));
     }
 }