Cleanup nits (#16211)

programs/bpf/rust/sysvar/src/lib.rs

@@ -0,0 +1,61 @@
+//! @brief Example Rust-based BPF program that tests sysvar use
+
+extern crate solana_program;
+use solana_program::{
+    account_info::AccountInfo,
+    clock::DEFAULT_SLOTS_PER_EPOCH,
+    entrypoint,
+    entrypoint::ProgramResult,
+    msg,
+    pubkey::Pubkey,
+    rent,
+    sysvar::{
+        self, clock::Clock, fees::Fees, rent::Rent, slot_hashes::SlotHashes,
+        stake_history::StakeHistory, Sysvar,
+    },
+};
+
+entrypoint!(process_instruction);
+#[allow(clippy::unnecessary_wraps)]
+fn process_instruction(
+    _program_id: &Pubkey,
+    accounts: &[AccountInfo],
+    _instruction_data: &[u8],
+) -> ProgramResult {
+    // Clock
+    msg!("Clock identifier:");
+    sysvar::clock::id().log();
+    let clock = Clock::from_account_info(&accounts[2]).expect("clock");
+    assert_eq!(clock.slot, DEFAULT_SLOTS_PER_EPOCH + 1);
+
+    // Fees
+    msg!("Fees identifier:");
+    sysvar::fees::id().log();
+    let fees = Fees::from_account_info(&accounts[3]).expect("fees");
+    let fee_calculator = fees.fee_calculator;
+    assert_eq!(fee_calculator.lamports_per_signature, 0);
+
+    // Slot Hashes
+    msg!("SlotHashes identifier:");
+    sysvar::slot_hashes::id().log();
+    let slot_hashes = SlotHashes::from_account_info(&accounts[4]).expect("slot_hashes");
+    assert!(slot_hashes.len() >= 1);
+
+    // Stake History
+    msg!("StakeHistory identifier:");
+    sysvar::stake_history::id().log();
+    let stake_history = StakeHistory::from_account_info(&accounts[5]).expect("stake_history");
+    assert!(stake_history.len() >= 1);
+
+    let rent = Rent::from_account_info(&accounts[6]).unwrap();
+    assert_eq!(
+        rent.due(
+            rent::DEFAULT_LAMPORTS_PER_BYTE_YEAR * rent::DEFAULT_EXEMPTION_THRESHOLD as u64,
+            1,
+            1.0
+        ),
+        (0, true)
+    );
+
+    Ok(())
+}