syscall work, rename syscall to sysvar, rename current to clock (#5074)

* syscall work, rename syscall to sysvar, rename current to clock

* missed one

* nit

sdk/src/sysvar/clock.rs

@@ -0,0 +1,79 @@
+//! This account contains the clock slot, epoch, and stakers_epoch
+//!
+use crate::account::Account;
+use crate::sysvar;
+use bincode::serialized_size;
+
+pub use crate::timing::{Epoch, Slot};
+
+const ID: [u8; 32] = [
+    6, 167, 213, 23, 24, 199, 116, 201, 40, 86, 99, 152, 105, 29, 94, 182, 139, 94, 184, 163, 155,
+    75, 109, 92, 115, 85, 91, 33, 0, 0, 0, 0,
+];
+
+crate::solana_name_id!(ID, "SysvarC1ock11111111111111111111111111111111");
+
+#[repr(C)]
+#[derive(Serialize, Deserialize, Debug, Default, PartialEq)]
+pub struct Clock {
+    pub slot: Slot,
+    pub segment: Segment,
+    pub epoch: Epoch,
+    pub stakers_epoch: Epoch,
+}
+
+impl Clock {
+    pub fn from(account: &Account) -> Option<Self> {
+        account.deserialize_data().ok()
+    }
+    pub fn to(&self, account: &mut Account) -> Option<()> {
+        account.serialize_data(self).ok()
+    }
+
+    pub fn size_of() -> usize {
+        serialized_size(&Self::default()).unwrap() as usize
+    }
+}
+
+pub fn create_account(
+    lamports: u64,
+    slot: Slot,
+    segment: Segment,
+    epoch: Epoch,
+    stakers_epoch: Epoch,
+) -> Account {
+    Account::new_data(
+        lamports,
+        &Clock {
+            slot,
+            segment,
+            epoch,
+            stakers_epoch,
+        },
+        &sysvar::id(),
+    )
+    .unwrap()
+}
+
+use crate::account::KeyedAccount;
+use crate::instruction::InstructionError;
+use crate::timing::Segment;
+
+pub fn from_keyed_account(account: &KeyedAccount) -> Result<Clock, InstructionError> {
+    if !check_id(account.unsigned_key()) {
+        return Err(InstructionError::InvalidArgument);
+    }
+    Clock::from(account.account).ok_or(InstructionError::InvalidArgument)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_create_account() {
+        let account = create_account(1, 0, 0, 0, 0);
+        let clock = Clock::from(&account).unwrap();
+        assert_eq!(clock, Clock::default());
+    }
+}