Cleanup nits (#16211)

programs/bpf/rust/sysvar/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "solana-bpf-rust-sysvar"
+version = "1.7.0"
+description = "Solana BPF test program written in Rust"
+authors = ["Solana Maintainers <maintainers@solana.foundation>"]
+repository = "https://github.com/solana-labs/solana"
+license = "Apache-2.0"
+homepage = "https://solana.com/"
+documentation = "https://docs.rs/solana-bpf-rust-sysvar"
+edition = "2018"
+
+[dependencies]
+solana-program = { path = "../../../../sdk/program", version = "=1.7.0" }
+
+[lib]
+crate-type = ["cdylib"]
+
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]

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(())
+}