Return sysvars via syscalls (#16422)

program-test/tests/sysvar.rs

@@ -0,0 +1,72 @@
+use {
+    solana_program_test::{processor, ProgramTest},
+    solana_sdk::{
+        account_info::AccountInfo,
+        clock::Clock,
+        entrypoint::ProgramResult,
+        epoch_schedule::EpochSchedule,
+        fee_calculator::FeeCalculator,
+        instruction::Instruction,
+        msg,
+        pubkey::Pubkey,
+        rent::Rent,
+        signature::Signer,
+        sysvar::{fees::Fees, Sysvar},
+        transaction::Transaction,
+    },
+};
+
+// Process instruction to invoke into another program
+fn sysvar_getter_process_instruction(
+    _program_id: &Pubkey,
+    _accounts: &[AccountInfo],
+    _input: &[u8],
+) -> ProgramResult {
+    msg!("sysvar_getter");
+
+    let clock = Clock::get()?;
+    assert_eq!(42, clock.slot);
+
+    let epoch_schedule = EpochSchedule::get()?;
+    assert_eq!(epoch_schedule, EpochSchedule::default());
+
+    let fees = Fees::get()?;
+    assert_eq!(
+        fees.fee_calculator,
+        FeeCalculator {
+            lamports_per_signature: 5000
+        }
+    );
+
+    let rent = Rent::get()?;
+    assert_eq!(rent, Rent::default());
+
+    Ok(())
+}
+
+#[tokio::test]
+async fn get_sysvar() {
+    let program_id = Pubkey::new_unique();
+    let program_test = ProgramTest::new(
+        "sysvar_getter",
+        program_id,
+        processor!(sysvar_getter_process_instruction),
+    );
+
+    let mut context = program_test.start_with_context().await;
+    context.warp_to_slot(42).unwrap();
+    let instructions = vec![Instruction::new_with_bincode(program_id, &(), vec![])];
+
+    let transaction = Transaction::new_signed_with_payer(
+        &instructions,
+        Some(&context.payer.pubkey()),
+        &[&context.payer],
+        context.last_blockhash,
+    );
+
+    context
+        .banks_client
+        .process_transaction(transaction)
+        .await
+        .unwrap();
+}