fix(prefer-const): Use additionalProperties instead of ignoreReadonly to match the ESLint core rule option name (#1239)

Author: baseballyama

.changeset/good-carrots-notice.md

@@ -0,0 +1,5 @@
+---
+'eslint-plugin-svelte': patch
+---
+
+fix(prefer-const): Use `additionalProperties` instead of `ignoreReadonly` to match the ESLint core rule option name.

docs/rules/prefer-const.md

@@ -46,22 +46,22 @@ This rule reports the same as the base ESLint `prefer-const` rule, except that i
     "error",
     {
       "destructuring": "any",
-      "ignoreReadonly": true,
+      "additionalProperties": false,
       "excludedRunes": ["$props", "$derived"]
     }
   ]
 }
 ```
 
 - `destructuring`: The kind of the way to address variables in destructuring. There are 2 values:
-  - `any` (default): if any variables in destructuring should be const, this rule warns for those variables.
-  - `all`: if all variables in destructuring should be const, this rule warns the variables. Otherwise, ignores them.
-- `ignoreReadonly`: If `true`, this rule will ignore variables that are read between the declaration and the _first_ assignment.
+  - `any` (default) - If any variables in destructuring should be const, this rule warns for those variables.
+  - `all`: If all variables in destructuring should be const, this rule warns the variables. Otherwise, ignores them.
+- `ignoreReadBeforeAssign`: This is an option to avoid conflicting with `no-use-before-define` rule (without "nofunc" option). If `true` is specified, this rule will ignore variables that are read between the declaration and the first assignment. Default is `false`.
 - `excludedRunes`: An array of rune names that should be ignored. Even if a rune is declared with `let`, it will still be ignored.
 
 ## :books: Further Reading
 
-- See [ESLint `prefer-const` rule](https://eslint.org/docs/latest/rules/prefer-const) for more information about the base rule.
+- See [ESLint prefer-const rule](https://eslint.org/docs/latest/rules/prefer-const) for more information about the base rule.
 
 ## :rocket: Version
 

packages/eslint-plugin-svelte/src/rule-types.ts

@@ -573,6 +573,7 @@ type SveltePreferConst = []|[{
   destructuring?: ("any" | "all")
   ignoreReadBeforeAssign?: boolean
   excludedRunes?: string[]
+  [k: string]: unknown | undefined
 }]
 // ----- svelte/require-event-prefix -----
 type SvelteRequireEventPrefix = []|[{

packages/eslint-plugin-svelte/src/rules/prefer-const.ts

@@ -68,7 +68,8 @@ export default createRule('prefer-const', {
 						}
 					}
 				},
-				additionalProperties: false
+				// Allow ESLint core rule properties in case new options are added in the future.
+				additionalProperties: true
 			}
 		]
 	},

packages/eslint-plugin-svelte/tests/fixtures/rules/prefer-const/valid/1238/_config.json

@@ -0,0 +1,8 @@
+{
+	"options": [
+		{
+			"destructuring": "all",
+			"additionalProperties": true
+		}
+	]
+}

packages/eslint-plugin-svelte/tests/fixtures/rules/prefer-const/valid/1238/input.svelte

@@ -0,0 +1 @@
+123