refactor(experimental): sysvars package: last restart slot

This commit introduces the `LastRestartSlot` sysvar to the `@solana/sysvars` package.

packages/sysvars/src/__tests__/last-restart-slot-test.ts

@@ -0,0 +1,25 @@
+import type { GetAccountInfoApi } from '@solana/rpc-api';
+import type { Rpc } from '@solana/rpc-spec';
+
+import { fetchSysvarLastRestartSlot, getSysvarLastRestartSlotCodec } from '../last-restart-slot';
+import { createLocalhostSolanaRpc } from './__setup__';
+
+describe('last restart slot', () => {
+    let rpc: Rpc<GetAccountInfoApi>;
+    beforeEach(() => {
+        rpc = createLocalhostSolanaRpc();
+    });
+    it('decode', () => {
+        const lastRestartSlotState = new Uint8Array([119, 233, 246, 16, 0, 0, 0, 0]);
+        expect(getSysvarLastRestartSlotCodec().decode(lastRestartSlotState)).toMatchObject({
+            lastRestartSlot: 284_617_079n,
+        });
+    });
+    it('fetch', async () => {
+        expect.assertions(1);
+        const lastRestartSlot = await fetchSysvarLastRestartSlot(rpc);
+        expect(lastRestartSlot).toMatchObject({
+            lastRestartSlot: expect.any(BigInt),
+        });
+    });
+});

packages/sysvars/src/__tests__/sysvar-test.ts

@@ -7,6 +7,7 @@ import {
     SYSVAR_CLOCK_ADDRESS,
     SYSVAR_EPOCH_SCHEDULE_ADDRESS,
     SYSVAR_FEES_ADDRESS,
+    SYSVAR_LAST_RESTART_SLOT_ADDRESS,
 } from '../sysvar';
 import { createLocalhostSolanaRpc } from './__setup__';
 
@@ -88,4 +89,18 @@ describe('sysvar account', () => {
         });
     });
     // `Instructions` does not exist on-chain.
+    describe('last restart slot', () => {
+        it('fetch encoded', async () => {
+            expect.assertions(3);
+            await assertValidEncodedSysvarAccount(SYSVAR_LAST_RESTART_SLOT_ADDRESS);
+        });
+        it('fetch JSON-parsed', async () => {
+            expect.assertions(3);
+            await assertValidJsonParsedSysvarAccount(SYSVAR_LAST_RESTART_SLOT_ADDRESS, {
+                data: {
+                    lastRestartSlot: expect.any(BigInt),
+                },
+            });
+        });
+    });
 });

packages/sysvars/src/__typetests__/sysvar-typetest.ts

@@ -6,6 +6,7 @@ import { fetchSysvarClock, type SysvarClock } from '../clock';
 import { fetchSysvarEpochRewards, type SysvarEpochRewards } from '../epoch-rewards';
 import { fetchSysvarEpochSchedule, type SysvarEpochSchedule } from '../epoch-schedule';
 import { fetchSysvarFees, type SysvarFees } from '../fees';
+import { fetchSysvarLastRestartSlot, type SysvarLastRestartSlot } from '../last-restart-slot';
 import { fetchEncodedSysvarAccount, fetchJsonParsedSysvarAccount, SYSVAR_CLOCK_ADDRESS } from '../sysvar';
 
 const rpc = null as unknown as Parameters<typeof fetchEncodedSysvarAccount>[0];
@@ -79,3 +80,11 @@ const rpc = null as unknown as Parameters<typeof fetchEncodedSysvarAccount>[0];
     // @ts-expect-error Returns a `SysvarFees`.
     fetchSysvarFees(rpc) satisfies Promise<{ foo: string }>;
 }
+
+// `fetchSysvarLastRestartSlot`
+{
+    // Returns a `SysvarLastRestartSlot`.
+    fetchSysvarLastRestartSlot(rpc) satisfies Promise<SysvarLastRestartSlot>;
+    // @ts-expect-error Returns a `SysvarLastRestartSlot`.
+    fetchSysvarLastRestartSlot(rpc) satisfies Promise<{ foo: string }>;
+}

packages/sysvars/src/index.ts

@@ -2,4 +2,5 @@ export * from './clock';
 export * from './epoch-rewards';
 export * from './epoch-schedule';
 export * from './fees';
+export * from './last-restart-slot';
 export * from './sysvar';

packages/sysvars/src/last-restart-slot.ts

@@ -0,0 +1,72 @@
+import { assertAccountExists, decodeAccount, type FetchAccountConfig } from '@solana/accounts';
+import {
+    combineCodec,
+    type FixedSizeCodec,
+    type FixedSizeDecoder,
+    type FixedSizeEncoder,
+    getStructDecoder,
+    getStructEncoder,
+    getU64Decoder,
+    getU64Encoder,
+} from '@solana/codecs';
+import type { GetAccountInfoApi } from '@solana/rpc-api';
+import type { Rpc } from '@solana/rpc-spec';
+import type { Slot } from '@solana/rpc-types';
+
+import { fetchEncodedSysvarAccount, SYSVAR_LAST_RESTART_SLOT_ADDRESS } from './sysvar';
+
+type SysvarLastRestartSlotSize = 8;
+
+/**
+ * The `LastRestartSlot` sysvar.
+ *
+ * Information about the last restart slot (hard fork).
+ *
+ * The `LastRestartSlot` sysvar provides access to the last restart slot kept in the
+ * bank fork for the slot on the fork that executes the current transaction.
+ * In case there was no fork it returns `0`.
+ */
+export type SysvarLastRestartSlot = Readonly<{
+    lastRestartSlot: Slot;
+}>;
+
+export function getSysvarLastRestartSlotEncoder(): FixedSizeEncoder<SysvarLastRestartSlot, SysvarLastRestartSlotSize> {
+    return getStructEncoder([['lastRestartSlot', getU64Encoder()]]) as FixedSizeEncoder<
+        SysvarLastRestartSlot,
+        SysvarLastRestartSlotSize
+    >;
+}
+
+export function getSysvarLastRestartSlotDecoder(): FixedSizeDecoder<SysvarLastRestartSlot, SysvarLastRestartSlotSize> {
+    return getStructDecoder([['lastRestartSlot', getU64Decoder()]]) as FixedSizeDecoder<
+        SysvarLastRestartSlot,
+        SysvarLastRestartSlotSize
+    >;
+}
+
+export function getSysvarLastRestartSlotCodec(): FixedSizeCodec<
+    SysvarLastRestartSlot,
+    SysvarLastRestartSlot,
+    SysvarLastRestartSlotSize
+> {
+    return combineCodec(getSysvarLastRestartSlotEncoder(), getSysvarLastRestartSlotDecoder());
+}
+
+/**
+ * Fetch the `LastRestartSlot` sysvar.
+ *
+ * Information about the last restart slot (hard fork).
+ *
+ * The `LastRestartSlot` sysvar provides access to the last restart slot kept in the
+ * bank fork for the slot on the fork that executes the current transaction.
+ * In case there was no fork it returns `0`.
+ */
+export async function fetchSysvarLastRestartSlot(
+    rpc: Rpc<GetAccountInfoApi>,
+    config?: FetchAccountConfig,
+): Promise<SysvarLastRestartSlot> {
+    const account = await fetchEncodedSysvarAccount(rpc, SYSVAR_LAST_RESTART_SLOT_ADDRESS, config);
+    assertAccountExists(account);
+    const decoded = decodeAccount(account, getSysvarLastRestartSlotDecoder());
+    return decoded.data;
+}

packages/sysvars/src/sysvar.ts

@@ -20,13 +20,16 @@ export const SYSVAR_FEES_ADDRESS =
     'SysvarFees111111111111111111111111111111111' as Address<'SysvarFees111111111111111111111111111111111'>;
 export const SYSVAR_INSTRUCTIONS_ADDRESS =
     'Sysvar1nstructions1111111111111111111111111' as Address<'Sysvar1nstructions1111111111111111111111111'>;
+export const SYSVAR_LAST_RESTART_SLOT_ADDRESS =
+    'SysvarLastRestartS1ot1111111111111111111111' as Address<'SysvarLastRestartS1ot1111111111111111111111'>;
 
 type SysvarAddress =
     | typeof SYSVAR_CLOCK_ADDRESS
     | typeof SYSVAR_EPOCH_REWARDS_ADDRESS
     | typeof SYSVAR_EPOCH_SCHEDULE_ADDRESS
     | typeof SYSVAR_FEES_ADDRESS
-    | typeof SYSVAR_INSTRUCTIONS_ADDRESS;
+    | typeof SYSVAR_INSTRUCTIONS_ADDRESS
+    | typeof SYSVAR_LAST_RESTART_SLOT_ADDRESS;
 
 /**
  * Fetch an encoded sysvar account.