GraemeF · Sep 30, 2026 · Sep 30, 2026
diff --git a/.changeset/eslint-effect-eslint-10.md b/.changeset/eslint-effect-eslint-10.md
@@ -0,0 +1,7 @@
+---
+'@codeforbreakfast/eslint-effect': patch
+---
+
+The rules now run under ESLint 10. Before this, ESLint 10 stopped with "context.getSourceCode is not a function" as soon as it loaded one of them.
+
+The `eslint` peer dependency is now `>=8.40.0` instead of `>=8.0.0`. ESLint 8.40 is the first release with `context.sourceCode`, which the rules now use. One rule already needed it, so the plugin did not fully work on older ESLint 8 releases anyway. If you are on ESLint 8.40 or later, there is nothing to change on your side.
diff --git a/.changeset/websocket-readonly-auth-metadata.md b/.changeset/websocket-readonly-auth-metadata.md
@@ -0,0 +1,5 @@
+---
+'@codeforbreakfast/eventsourcing-transport-websocket': patch
+---
+
+Internal typing fix so the WebSocket server passes the stricter immutability checks in `eslint-plugin-functional` 10. There is nothing to change on your side: runtime behaviour and the public API are the same.
diff --git a/bun.lock b/bun.lock
diff --git a/package.json b/package.json
@@ -54,18 +54,15 @@
     "@effect/rpc": "0.76.2",
     "@effect/workflow": "0.19.1",
     "@types/bun": "1.4.2",
-    "@typescript-eslint/eslint-plugin": "8.70.1",
-    "@typescript-eslint/parser": "8.70.1",
+    "@typescript-eslint/eslint-plugin": "8.71.0",
+    "@typescript-eslint/parser": "8.71.0",
     "dependency-cruiser": "17.4.3",
     "effect": "3.22.2",
-    "eslint": "9.39.5",
+    "eslint": "10.11.0",
     "eslint-config-prettier": "10.1.8",
-    "eslint-plugin-compat": "6.2.1",
     "@eslint-community/eslint-plugin-eslint-comments": "4.8.1",
-    "eslint-plugin-expect-type": "0.7.0",
-    "eslint-plugin-functional": "9.0.5",
+    "eslint-plugin-functional": "10.0.1",
     "eslint-plugin-import": "2.32.0",
-    "eslint-plugin-package-json": "0.91.2",
     "eslint-plugin-unused-imports": "4.4.1",
     "fast-check": "4.10.2",
     "husky": "9.1.7",

diff --git a/packages/eslint-effect/package.json b/packages/eslint-effect/package.json
@@ -42,11 +42,11 @@
     "check:publishable": "npm view $npm_package_name@$npm_package_version version >/dev/null 2>&1 && exit 1 || exit 0"
   },
   "peerDependencies": {
-    "eslint": ">=8.0.0"
+    "eslint": ">=8.40.0"
   },
   "devDependencies": {
-    "eslint": "9.39.5",
-    "@typescript-eslint/eslint-plugin": "8.70.1",
+    "eslint": "10.11.0",
+    "@typescript-eslint/eslint-plugin": "8.71.0",
     "typescript": "5.9.3",
     "effect": "3.22.2"
   }

diff --git a/packages/eslint-effect/src/rules/no-effect-if-option-check.js b/packages/eslint-effect/src/rules/no-effect-if-option-check.js
@@ -14,7 +14,7 @@ export default {
   },
 
   create(context) {
-    const sourceCode = context.getSourceCode();
+    const sourceCode = context.sourceCode;
 
     const isEffectIfCall = (node) => {
       return (

diff --git a/packages/eslint-effect/src/rules/no-unnecessary-function-alias.js b/packages/eslint-effect/src/rules/no-unnecessary-function-alias.js
@@ -26,7 +26,7 @@ export default {
 
   create(context) {
     const maxReferences = context.options[0]?.maxReferences ?? 2;
-    const sourceCode = context.getSourceCode();
+    const sourceCode = context.sourceCode;
 
     const getOriginalName = (node) => {
       if (node.type === 'Identifier') {

diff --git a/packages/eslint-effect/src/rules/prefer-andThen.js b/packages/eslint-effect/src/rules/prefer-andThen.js
@@ -16,7 +16,7 @@ export default {
   },
 
   create(context) {
-    const sourceCode = context.getSourceCode();
+    const sourceCode = context.sourceCode;
 
     const isFlatMapCall = (node) => {
       return (

diff --git a/packages/eslint-effect/src/rules/prefer-as.js b/packages/eslint-effect/src/rules/prefer-as.js
@@ -27,7 +27,7 @@ export default {
   },
 
   create(context) {
-    const sourceCode = context.getSourceCode();
+    const sourceCode = context.sourceCode;
 
     const isMapCall = (node) => {
       return (

diff --git a/packages/eslint-effect/src/rules/prefer-flatten.js b/packages/eslint-effect/src/rules/prefer-flatten.js
@@ -16,7 +16,7 @@ export default {
   },
 
   create(context) {
-    const sourceCode = context.getSourceCode();
+    const sourceCode = context.sourceCode;
 
     const isFlatMapCall = (node) => {
       return (

diff --git a/packages/eslint-effect/src/rules/prefer-from-nullable.js b/packages/eslint-effect/src/rules/prefer-from-nullable.js
@@ -14,7 +14,7 @@ export default {
   },
 
   create(context) {
-    const sourceCode = context.getSourceCode();
+    const sourceCode = context.sourceCode;
 
     const isOptionSomeCall = (node) => {
       return (

diff --git a/packages/eslint-effect/src/rules/prefer-get-or-else.js b/packages/eslint-effect/src/rules/prefer-get-or-else.js
@@ -14,7 +14,7 @@ export default {
   },
 
   create(context) {
-    const sourceCode = context.getSourceCode();
+    const sourceCode = context.sourceCode;
 
     const isOptionIsSomeCall = (node, expectedArg) => {
       if (

diff --git a/packages/eslint-effect/src/rules/prefer-ignore-logged.js b/packages/eslint-effect/src/rules/prefer-ignore-logged.js
@@ -17,7 +17,7 @@ export default {
   },
 
   create(context) {
-    const sourceCode = context.getSourceCode();
+    const sourceCode = context.sourceCode;
 
     const isMatchCauseEffectCall = (node) => {
       return (

diff --git a/packages/eslint-effect/src/rules/prefer-ignore.js b/packages/eslint-effect/src/rules/prefer-ignore.js
@@ -19,7 +19,7 @@ export default {
   },
 
   create(context) {
-    const sourceCode = context.getSourceCode();
+    const sourceCode = context.sourceCode;
 
     return {
       CallExpression(node) {

diff --git a/packages/eslint-effect/src/rules/prefer-match-tag.js b/packages/eslint-effect/src/rules/prefer-match-tag.js
@@ -52,7 +52,7 @@ export default {
                   tagValue,
                 },
                 fix(fixer) {
-                  const sourceCode = context.getSourceCode();
+                  const sourceCode = context.sourceCode;
                   const tagString = sourceCode.getText(prop.value);
                   const restArgs = node.arguments.slice(1);
                   const restArgsText = restArgs.map((arg) => sourceCode.getText(arg)).join(', ');

diff --git a/packages/eslint-effect/src/rules/prefer-zip-left.js b/packages/eslint-effect/src/rules/prefer-zip-left.js
@@ -20,7 +20,7 @@ export default {
   },
 
   create(context) {
-    const sourceCode = context.getSourceCode();
+    const sourceCode = context.sourceCode;
 
     const isZipLeftPattern = (arrowFunc, effectType) => {
       if (!arrowFunc || arrowFunc.type !== 'ArrowFunctionExpression') {

diff --git a/packages/eslint-effect/src/rules/prefer-zip-right.js b/packages/eslint-effect/src/rules/prefer-zip-right.js
@@ -20,7 +20,7 @@ export default {
   },
 
   create(context) {
-    const sourceCode = context.getSourceCode();
+    const sourceCode = context.sourceCode;
 
     const isZipRightPattern = (arrowFunc) => {
       if (!arrowFunc || arrowFunc.type !== 'ArrowFunctionExpression') {

diff --git a/packages/eslint-effect/src/rules/suggest-currying-opportunity.js b/packages/eslint-effect/src/rules/suggest-currying-opportunity.js
@@ -156,7 +156,7 @@ export default {
       const functionName = getFunctionName(callExpr.callee);
       if (!functionName) return null;
 
-      const sourceCode = context.sourceCode || context.getSourceCode();
+      const sourceCode = context.sourceCode;
 
       const lastParamArgIndex = Math.max(...argsFromParams.map((item) => item.index));
       const lastNonParamIndex = Math.max(...argsNotFromParams.map((item) => item.index));

diff --git a/packages/eventsourcing-aggregates/package.json b/packages/eventsourcing-aggregates/package.json
@@ -74,7 +74,7 @@
     "@codeforbreakfast/eventsourcing-store-inmemory": "workspace:*",
     "effect": "3.22.2",
     "typescript": "5.9.3",
-    "eslint": "9.39.5"
+    "eslint": "10.11.0"
   },
   "publishConfig": {
     "access": "public"

diff --git a/packages/eventsourcing-commands/package.json b/packages/eventsourcing-commands/package.json
@@ -69,7 +69,7 @@
     "@types/node": "24.19.0",
     "effect": "3.22.2",
     "typescript": "5.9.3",
-    "eslint": "9.39.5"
+    "eslint": "10.11.0"
   },
   "publishConfig": {
     "access": "public"

diff --git a/packages/eventsourcing-projections/package.json b/packages/eventsourcing-projections/package.json
@@ -69,7 +69,7 @@
     "@types/node": "24.19.0",
     "effect": "3.22.2",
     "typescript": "5.9.3",
-    "eslint": "9.39.5"
+    "eslint": "10.11.0"
   },
   "publishConfig": {
     "access": "public"

diff --git a/packages/eventsourcing-protocol/package.json b/packages/eventsourcing-protocol/package.json
@@ -79,7 +79,7 @@
     "@types/node": "24.19.0",
     "effect": "3.22.2",
     "typescript": "5.9.3",
-    "eslint": "9.39.5"
+    "eslint": "10.11.0"
   },
   "publishConfig": {
     "access": "public"

diff --git a/packages/eventsourcing-server/package.json b/packages/eventsourcing-server/package.json
@@ -70,7 +70,7 @@
     "@codeforbreakfast/bun-test-effect": "workspace:*",
     "effect": "3.22.2",
     "typescript": "5.9.3",
-    "eslint": "9.39.5"
+    "eslint": "10.11.0"
   },
   "publishConfig": {
     "access": "public"

diff --git a/packages/eventsourcing-store-filesystem/package.json b/packages/eventsourcing-store-filesystem/package.json
@@ -71,7 +71,7 @@
     "@effect/platform-bun": "0.91.2",
     "@types/node": "24.19.0",
     "effect": "3.22.2",
-    "eslint": "9.39.5",
+    "eslint": "10.11.0",
     "typescript": "5.9.3"
   },
   "publishConfig": {

diff --git a/packages/eventsourcing-store-inmemory/package.json b/packages/eventsourcing-store-inmemory/package.json
@@ -71,7 +71,7 @@
     "@types/node": "24.19.0",
     "effect": "3.22.2",
     "typescript": "5.9.3",
-    "eslint": "9.39.5"
+    "eslint": "10.11.0"
   },
   "publishConfig": {
     "access": "public"

diff --git a/packages/eventsourcing-store-postgres/package.json b/packages/eventsourcing-store-postgres/package.json
@@ -78,7 +78,7 @@
     "@effect/platform-bun": "0.91.2",
     "@types/node": "24.19.0",
     "effect": "3.22.2",
-    "eslint": "9.39.5",
+    "eslint": "10.11.0",
     "typescript": "5.9.3"
   },
   "publishConfig": {

diff --git a/packages/eventsourcing-store/package.json b/packages/eventsourcing-store/package.json
@@ -71,7 +71,7 @@
     "@codeforbreakfast/bun-test-effect": "workspace:*",
     "effect": "3.22.2",
     "typescript": "5.9.3",
-    "eslint": "9.39.5"
+    "eslint": "10.11.0"
   },
   "publishConfig": {
     "access": "public"

diff --git a/packages/eventsourcing-testing-contracts/package.json b/packages/eventsourcing-testing-contracts/package.json
@@ -74,7 +74,7 @@
     "@types/node": "24.19.0",
     "effect": "3.22.2",
     "typescript": "5.9.3",
-    "eslint": "9.39.5"
+    "eslint": "10.11.0"
   },
   "publishConfig": {
     "access": "public"

diff --git a/packages/eventsourcing-transport-inmemory/package.json b/packages/eventsourcing-transport-inmemory/package.json
@@ -71,7 +71,7 @@
     "@codeforbreakfast/bun-test-effect": "workspace:*",
     "@types/node": "24.19.0",
     "effect": "3.22.2",
-    "eslint": "9.39.5",
+    "eslint": "10.11.0",
     "typescript": "5.9.3"
   },
   "publishConfig": {

diff --git a/packages/eventsourcing-transport-websocket/package.json b/packages/eventsourcing-transport-websocket/package.json
@@ -72,7 +72,7 @@
     "@types/node": "24.19.0",
     "bun-types": "1.4.2",
     "effect": "3.22.2",
-    "eslint": "9.39.5",
+    "eslint": "10.11.0",
     "typescript": "5.9.3"
   },
   "publishConfig": {

diff --git a/packages/eventsourcing-transport-websocket/src/lib/websocket-server.ts b/packages/eventsourcing-transport-websocket/src/lib/websocket-server.ts
@@ -242,7 +242,7 @@ const buildClientState =
     clientId: Server.ClientId,
     connectedAt: ReadonlyDeep<Date>,
     ws: ReadonlyDeep<ServerWebSocket<WebSocketData>>,
-    authMetadata: Record<string, unknown>
+    authMetadata: Readonly<Record<string, unknown>>
   ) =>
   (resources: {
     readonly connectionStateQueue: Queue.Queue<ConnectionState>;
@@ -262,7 +262,7 @@ const createClientStateResources = (
   clientId: Server.ClientId,
   connectedAt: ReadonlyDeep<Date>,
   ws: ReadonlyDeep<ServerWebSocket<WebSocketData>>,
-  authMetadata: Record<string, unknown>
+  authMetadata: Readonly<Record<string, unknown>>
 ): Effect.Effect<ClientState, never, never> =>
   pipe(
     createClientResources(),

diff --git a/packages/eventsourcing-transport/package.json b/packages/eventsourcing-transport/package.json
@@ -66,7 +66,7 @@
     "@types/node": "24.19.0",
     "effect": "3.22.2",
     "typescript": "5.9.3",
-    "eslint": "9.39.5"
+    "eslint": "10.11.0"
   },
   "publishConfig": {
     "access": "public"

diff --git a/packages/eventsourcing-websocket/package.json b/packages/eventsourcing-websocket/package.json
@@ -74,7 +74,7 @@
     "@types/node": "24.19.0",
     "effect": "3.22.2",
     "typescript": "5.9.3",
-    "eslint": "9.39.5"
+    "eslint": "10.11.0"
   },
   "publishConfig": {
     "access": "public"

diff --git a/scripts/validate-changesets.ts b/scripts/validate-changesets.ts
@@ -270,8 +270,9 @@ const getChangesets = pipe(
 
 // Wrapper provides type safety for JSON.parse (returns any)
 // eslint-disable-next-line effect/no-eta-expansion -- JSON.parse is external and cannot be inlined
-const parsePackageDependencyOutput = (output: string): Record<string, readonly string[]> =>
-  JSON.parse(output);
+const parsePackageDependencyOutput = (
+  output: string
+): Readonly<Record<string, readonly string[]>> => JSON.parse(output);
 
 const handleDependencyCheckFailure = (terminal: Terminal.Terminal) => () =>
   pipe(
@@ -293,7 +294,7 @@ const getPackageDependencyMap = pipe(Terminal.Terminal, Effect.flatMap(runDepend
 
 const getBaseBranch = (): string => {
   const envVar = 'GITHUB_BASE_REF';
-  const proc: Record<string, unknown> = globalThis as never;
+  const proc: Readonly<Record<string, unknown>> = globalThis as never;
   const env = (proc['process'] as Record<string, Record<string, string>> | undefined)?.['env'];
   return (env?.[envVar] as string | undefined) ?? 'origin/main';
 };
@@ -349,7 +350,7 @@ const parseJsonSafely = (content: string): unknown => {
   }
 };
 
-const extractDependencies = (pkg: unknown, key: string): Record<string, string> => {
+const extractDependencies = (pkg: unknown, key: string): Readonly<Record<string, string>> => {
   const record = pkg as Record<string, unknown> | null;
   const deps = record?.[key];
   return (deps as Record<string, string> | undefined) || {};
@@ -749,7 +750,10 @@ const showDependencyValidationFailure = (
   );
 
 const buildDependencyError =
-  (changedPackages: ReadonlySet<string>, packageDependencyMap: Record<string, readonly string[]>) =>
+  (
+    changedPackages: ReadonlySet<string>,
+    packageDependencyMap: Readonly<Record<string, readonly string[]>>
+  ) =>
   (
     errors: readonly MissingDependentError[],
     changedPackage: string
@@ -769,7 +773,10 @@ const buildDependencyError =
   };
 
 const checkDependencyErrors =
-  (changedPackages: ReadonlySet<string>, packageDependencyMap: Record<string, readonly string[]>) =>
+  (
+    changedPackages: ReadonlySet<string>,
+    packageDependencyMap: Readonly<Record<string, readonly string[]>>
+  ) =>
   (terminal: Terminal.Terminal) => {
     const dependencyErrors = Array.from(changedPackages).reduce<readonly MissingDependentError[]>(
       buildDependencyError(changedPackages, packageDependencyMap),
@@ -799,7 +806,7 @@ const displaySuccess = (changesets: readonly ChangesetInfoInternal[]) =>
 
 const validateDependencies =
   (changedPackages: ReadonlySet<string>) =>
-  (packageDependencyMap: Record<string, readonly string[]>) =>
+  (packageDependencyMap: Readonly<Record<string, readonly string[]>>) =>
     pipe(
       Terminal.Terminal,
       Effect.flatMap(checkDependencyErrors(changedPackages, packageDependencyMap))