Audit: Remove unused fn, add comments (#935)

(cherry picked from commit 9df73a0dfd)

programs/mango-v4/src/health/account_retriever.rs

@@ -26,6 +26,7 @@ use crate::state::{Bank, MangoAccountRef, PerpMarket, PerpMarketIndex, TokenInde
 ///   are passed because health needs to be computed for different baskets in
 ///   one instruction (such as for liquidation instructions).
 pub trait AccountRetriever {
+    /// Returns the token indexes of the available banks. Unordered and may have duplicates.
     fn available_banks(&self) -> Result<Vec<TokenIndex>>;
 
     fn bank_and_oracle(
@@ -67,6 +68,9 @@ pub struct FixedOrderAccountRetriever<T: KeyedAccountReader> {
 }
 
 /// Creates a FixedOrderAccountRetriever where all banks are present
+///
+/// Note that this does not eagerly validate that the right accounts were passed. That
+/// validation happens only when banks, perps etc are requested.
 pub fn new_fixed_order_account_retriever<'a, 'info>(
     ais: &'a [AccountInfo<'info>],
     account: &MangoAccountRef,
@@ -84,6 +88,9 @@ pub fn new_fixed_order_account_retriever<'a, 'info>(
 
 /// A FixedOrderAccountRetriever with n_banks <= active_token_positions().count(),
 /// depending on which banks were passed.
+///
+/// Note that this does not eagerly validate that the right accounts were passed. That
+/// validation happens only when banks, perps etc are requested.
 pub fn new_fixed_order_account_retriever_with_optional_banks<'a, 'info>(
     ais: &'a [AccountInfo<'info>],
     account: &MangoAccountRef,

programs/mango-v4/src/health/cache.rs

@@ -1230,45 +1230,37 @@ pub fn new_health_cache(
     retriever: &impl AccountRetriever,
     now_ts: u64,
 ) -> Result<HealthCache> {
-    new_health_cache_impl(account, retriever, now_ts, false, false)
+    new_health_cache_impl(account, retriever, now_ts, false)
 }
 
 /// Generate a special HealthCache for an account and its health accounts
-/// where nonnegative token positions for bad oracles are skipped.
+/// where nonnegative token positions for bad oracles are skipped as well as missing banks.
 ///
 /// This health cache must be used carefully, since it doesn't provide the actual
 /// account health, just a value that is guaranteed to be less than it.
-pub fn new_health_cache_skipping_bad_oracles(
-    account: &MangoAccountRef,
-    retriever: &impl AccountRetriever,
-    now_ts: u64,
-) -> Result<HealthCache> {
-    new_health_cache_impl(account, retriever, now_ts, true, false)
-}
-
 pub fn new_health_cache_skipping_missing_banks_and_bad_oracles(
     account: &MangoAccountRef,
     retriever: &impl AccountRetriever,
     now_ts: u64,
 ) -> Result<HealthCache> {
-    new_health_cache_impl(account, retriever, now_ts, true, true)
+    new_health_cache_impl(account, retriever, now_ts, true)
 }
 
+// On `allow_skipping_banks`:
+//   If (a Bank is not provided or its oracle is stale or inconfident) and the health contribution would
+//   not be negative, skip it. This decreases health, but many operations are still allowed as long
+//   as the decreased amount stays positive.
 fn new_health_cache_impl(
     account: &MangoAccountRef,
     retriever: &impl AccountRetriever,
     now_ts: u64,
-    // If an oracle is stale or inconfident and the health contribution would
+    allow_skipping_banks: bool,
-    // not be negative, skip it. This decreases health, but maybe overall it's
-    // still positive?
-    skip_bad_oracles: bool,
-    skip_missing_banks: bool,
 ) -> Result<HealthCache> {
     // token contribution from token accounts
     let mut token_infos = Vec::with_capacity(account.active_token_positions().count());
 
     // As a CU optimization, don't call available_banks() unless necessary
-    let available_banks_opt = if skip_missing_banks {
+    let available_banks_opt = if allow_skipping_banks {
         Some(retriever.available_banks()?)
     } else {
         None
@@ -1276,7 +1268,7 @@ fn new_health_cache_impl(
 
     for (i, position) in account.active_token_positions().enumerate() {
         // Allow skipping of missing banks only if the account has a nonnegative balance
-        if skip_missing_banks {
+        if allow_skipping_banks {
             let bank_is_available = available_banks_opt
                 .as_ref()
                 .unwrap()
@@ -1296,7 +1288,7 @@ fn new_health_cache_impl(
             retriever.bank_and_oracle(&account.fixed.group, i, position.token_index);
 
         // Allow skipping of bad-oracle banks if the account has a nonnegative balance
-        if skip_bad_oracles
+        if allow_skipping_banks
             && bank_oracle_result.is_oracle_error()
             && position.indexed_position >= 0
         {
@@ -1345,7 +1337,7 @@ fn new_health_cache_impl(
             (Ok(base), Ok(quote)) => (base, quote),
             _ => {
                 require_msg_typed!(
-                    skip_bad_oracles || skip_missing_banks,
+                    allow_skipping_banks,
                     MangoError::InvalidBank,
                     "serum market {} misses health accounts for bank {} or {}",
                     serum_account.market_index,
@@ -1382,7 +1374,7 @@ fn new_health_cache_impl(
         )?;
 
         // Ensure the settle token is available in the health cache
-        if skip_bad_oracles || skip_missing_banks {
+        if allow_skipping_banks {
             find_token_info_index(&token_infos, perp_market.settle_token_index)?;
         }