chore: add eslint rule to prevent unused expressions (#6445)

* chore: add eslint rule to prevent unused expressions

* Fix unit tests

.eslintrc.js

@@ -80,6 +80,7 @@ module.exports = {
     "@typescript-eslint/no-unsafe-call": "error",
     "@typescript-eslint/no-unsafe-member-access": "error",
     "@typescript-eslint/no-unsafe-return": "error",
+    "@typescript-eslint/no-unused-expressions": "error",
     "@typescript-eslint/no-unused-vars": ["error", {varsIgnorePattern: "^_", argsIgnorePattern: "^_"}],
     "@typescript-eslint/no-use-before-define": "off",
     "@typescript-eslint/restrict-template-expressions": [
@@ -209,6 +210,13 @@ module.exports = {
         "import/no-named-as-default-member": "off",
       },
     },
+    {
+      files: ["**/perf/**/*.ts"],
+      rules: {
+        // A lot of benchmarks just need to execute expressions without using the result
+        "@typescript-eslint/no-unused-expressions": "off",
+      },
+    },
     {
       files: ["**/test/**/*.test.ts"],
       plugins: ["vitest"],

packages/beacon-node/src/eth1/utils/eth1Vote.ts

@@ -80,7 +80,6 @@ export function pickEth1Vote(state: BeaconStateAllForks, votesToConsider: phase0
   else {
     const latestMostVotedRoot =
       eth1DataVotesOrder[Math.max(...eth1DataRootsMaxVotes.map((root) => eth1DataVotesOrder.indexOf(root)))];
-    eth1DataHashToEth1Data;
     return eth1DataHashToEth1Data.get(latestMostVotedRoot) ?? state.eth1Data;
   }
 }

packages/beacon-node/src/network/peers/discover.ts

@@ -506,6 +506,6 @@ function formatLibp2pDialError(e: Error): void {
     e.message.includes("stream ended before 1 bytes became available") ||
     e.message.includes("The operation was aborted")
   ) {
-    e.stack === undefined;
+    e.stack = undefined;
   }
 }

packages/beacon-node/test/unit/monitoring/service.test.ts

@@ -257,7 +257,7 @@ describe("monitoring / service", () => {
     await waitForInterval();
 
     afterAll(() => {
-      service.close;
+      service.close();
     });
 
     return service;

packages/cli/test/utils/simulation/TableReporter.ts

@@ -89,19 +89,19 @@ export class TableReporter extends SimulationReporter<typeof defaultAssertions>
 
     for (const node of nodes) {
       const finalized = stores["finalized"][node.beacon.id][slot];
-      !isNullish(finalized) && finalizedSlots.push(finalized);
+      if (!isNullish(finalized)) finalizedSlots.push(finalized);
 
       const inclusionDelay = stores["inclusionDelay"][node.beacon.id][slot];
-      !isNullish(inclusionDelay) && inclusionDelays.push(inclusionDelay);
+      if (!isNullish(inclusionDelay)) inclusionDelays.push(inclusionDelay);
 
       const attestationsCount = stores["attestationsCount"][node.beacon.id][slot];
-      !isNullish(attestationsCount) && attestationCounts.push(attestationsCount);
+      if (!isNullish(attestationsCount)) attestationCounts.push(attestationsCount);
 
       const head = stores["head"][node.beacon.id][slot];
-      !isNullish(head) && heads.push(head);
+      if (!isNullish(head)) heads.push(head);
 
       const connectedPeerCount = stores["connectedPeerCount"][node.beacon.id][slot];
-      !isNullish(connectedPeerCount) && peersCount.push(connectedPeerCount);
+      if (!isNullish(connectedPeerCount)) peersCount.push(connectedPeerCount);
     }
 
     const head0 = heads.length > 0 ? heads[0] : null;

packages/params/test/e2e/overridePresetError.ts

@@ -1,11 +1,9 @@
 // This script is should be run in an e2e !!
-// It demostrates how NOT to change the Lodestar preset
+// It demonstrates how NOT to change the Lodestar preset
 
 // 1. Import from not only @lodestar/params/setPreset will trigger an error
-import {SLOTS_PER_EPOCH} from "../../lib/index.js";
+import "../../lib/index.js";
 import {setActivePreset, PresetName} from "../../lib/setPreset.js";
 // This line should throw
 // eslint-disable-next-line @typescript-eslint/naming-convention
 setActivePreset(PresetName.minimal, {SLOTS_PER_EPOCH: 2});
-
-SLOTS_PER_EPOCH;

packages/params/test/e2e/setPresetError.ts

@@ -1,10 +1,8 @@
 // This script is should be run in an e2e !!
-// It demostrates how NOT to change the Lodestar preset
+// It demonstrates how NOT to change the Lodestar preset
 
 // 1. Import from not only @lodestar/params/setPreset will trigger an error
-import {SLOTS_PER_EPOCH} from "../../lib/index.js";
+import "../../lib/index.js";
 import {setActivePreset, PresetName} from "../../lib/setPreset.js";
 // This line should throw
 setActivePreset(PresetName.minimal);
-
-SLOTS_PER_EPOCH;