feat(linter): add typescript/prefer-readonly rule

apps/oxlint/fixtures/tsgolint/.oxlintrc.json

@@ -38,6 +38,7 @@
     "typescript/prefer-nullish-coalescing": "error",
     "typescript/prefer-optional-chain": "error",
     "typescript/prefer-promise-reject-errors": "error",
+    "typescript/prefer-readonly": "error",
     "typescript/prefer-readonly-parameter-types": "error",
     "typescript/prefer-reduce-type-parameter": "error",
     "typescript/prefer-return-this-type": "error",

apps/oxlint/fixtures/tsgolint/prefer-readonly.ts

@@ -0,0 +1,12 @@
+class Example {
+  private value = 1;
+  private readonly ok = 2;
+
+  constructor() {
+    this.value = 2;
+  }
+
+  mutate() {
+    return this.ok;
+  }
+}

apps/oxlint/fixtures/tsgolint_rule_options/.oxlintrc.json

@@ -74,6 +74,12 @@
         "treatMethodsAsReadonly": true
       }
     ],
+    "typescript/prefer-readonly": [
+      "error",
+      {
+        "onlyInlineLambdas": true
+      }
+    ],
     "typescript/only-throw-error": [
       "error",
       {

apps/oxlint/fixtures/tsgolint_rule_options/test.ts

@@ -102,6 +102,14 @@ function takesMutableParameter(input: MutableParameter): void {
   console.log(input.value);
 }
 
+// Test prefer-readonly with onlyInlineLambdas option
+class PreferReadonlyOptionExample {
+  private handler = () => 1;
+  getValue() {
+    return this.handler();
+  }
+}
+
 // Test only-throw-error with allowRethrowing option
 // When allowRethrowing is false, rethrowing a caught error SHOULD error
 try {

apps/oxlint/src/snapshots/fixtures__tsgolint_--type-aware --silent@oxlint.snap

@@ -6,8 +6,8 @@ arguments: --type-aware --silent
 working directory: fixtures/tsgolint
 ----------
 
-Found 0 warnings and 63 errors.
-Finished in <variable>ms on 52 files with 51 rules using 1 threads.
+Found 0 warnings and 64 errors.
+Finished in <variable>ms on 53 files with 52 rules using 1 threads.
 ----------
 CLI result: LintFoundErrors
 ----------

apps/oxlint/src/snapshots/fixtures__tsgolint_--type-aware -c config-test.json@oxlint.snap

@@ -40,7 +40,7 @@ working directory: fixtures/tsgolint
   help: Remove the debugger statement
 
 Found 2 warnings and 2 errors.
-Finished in <variable>ms on 52 files with 1 rules using 1 threads.
+Finished in <variable>ms on 53 files with 1 rules using 1 threads.
 ----------
 CLI result: LintFoundErrors
 ----------

apps/oxlint/src/snapshots/fixtures__tsgolint_--type-aware test.svelte@oxlint.snap

@@ -16,7 +16,7 @@ working directory: fixtures/tsgolint
   help: Remove the debugger statement
 
 Found 0 warnings and 1 error.
-Finished in <variable>ms on 1 file with 51 rules using 1 threads.
+Finished in <variable>ms on 1 file with 52 rules using 1 threads.
 ----------
 CLI result: LintFoundErrors
 ----------

apps/oxlint/src/snapshots/fixtures__tsgolint_--type-aware@oxlint.snap

@@ -367,6 +367,14 @@ working directory: fixtures/tsgolint
  6 |   input.value = input.value.trim();
    `----
 
+  x typescript-eslint(prefer-readonly): Member 'value' is never reassigned; mark it as `readonly`.
+   ,-[prefer-readonly.ts:2:3]
+ 1 | class Example {
+ 2 |   private value = 1;
+   :   ^^^^^^^^^^^^^
+ 3 |   private readonly ok = 2;
+   `----
+
   x typescript-eslint(no-unnecessary-type-assertion): This assertion is unnecessary since it does not change the type of the expression.
    ,-[prefer-reduce-type-parameter.ts:2:13]
  1 | const numbers = [1, 2, 3];
@@ -494,8 +502,8 @@ working directory: fixtures/tsgolint
    `----
   help: If your function does not access `this`, you can annotate it with `this: void`, or consider using an arrow function instead.
 
-Found 0 warnings and 63 errors.
-Finished in <variable>ms on 52 files with 51 rules using 1 threads.
+Found 0 warnings and 64 errors.
+Finished in <variable>ms on 53 files with 52 rules using 1 threads.
 ----------
 CLI result: LintFoundErrors
 ----------

apps/oxlint/src/snapshots/fixtures__tsgolint_rule_options_--type-aware@oxlint.snap

@@ -80,8 +80,16 @@ working directory: fixtures/tsgolint_rule_options
  102 |   console.log(input.value);
      `----
 
-Found 0 warnings and 9 errors.
-Finished in <variable>ms on 1 file with 11 rules using 1 threads.
+  x typescript-eslint(prefer-readonly): Member 'handler' is never reassigned; mark it as `readonly`.
+     ,-[test.ts:107:3]
+ 106 | class PreferReadonlyOptionExample {
+ 107 |   private handler = () => 1;
+     :   ^^^^^^^^^^^^^^^
+ 108 |   getValue() {
+     `----
+
+Found 0 warnings and 10 errors.
+Finished in <variable>ms on 1 file with 12 rules using 1 threads.
 ----------
 CLI result: LintFoundErrors
 ----------

crates/oxc_linter/src/rules.rs

@@ -295,6 +295,7 @@ pub(crate) mod typescript {
     pub mod prefer_nullish_coalescing;
     pub mod prefer_optional_chain;
     pub mod prefer_promise_reject_errors;
+    pub mod prefer_readonly;
     pub mod prefer_readonly_parameter_types;
     pub mod prefer_reduce_type_parameter;
     pub mod prefer_return_this_type;

crates/oxc_linter/src/rules/typescript/prefer_readonly.rs

@@ -0,0 +1,64 @@
+use oxc_macros::declare_oxc_lint;
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
+
+use crate::rule::{DefaultRuleConfig, Rule};
+
+#[derive(Debug, Default, Clone, Deserialize)]
+pub struct PreferReadonly(Box<PreferReadonlyConfig>);
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, JsonSchema, Default)]
+#[serde(rename_all = "camelCase", default, deny_unknown_fields)]
+pub struct PreferReadonlyConfig {
+    /// Restrict checks to members immediately initialized with inline lambda values.
+    pub only_inline_lambdas: bool,
+}
+
+declare_oxc_lint!(
+    /// ### What it does
+    ///
+    /// Require class members that are never reassigned to be marked `readonly`.
+    ///
+    /// ### Why is this bad?
+    ///
+    /// Members that never change should be declared `readonly` to make class invariants explicit
+    /// and prevent accidental mutation.
+    ///
+    /// ### Examples
+    ///
+    /// Examples of **incorrect** code for this rule:
+    /// ```ts
+    /// class Counter {
+    ///   private value = 0;
+    ///
+    ///   getValue() {
+    ///     return this.value;
+    ///   }
+    /// }
+    /// ```
+    ///
+    /// Examples of **correct** code for this rule:
+    /// ```ts
+    /// class Counter {
+    ///   private readonly value = 0;
+    ///
+    ///   getValue() {
+    ///     return this.value;
+    ///   }
+    /// }
+    /// ```
+    PreferReadonly(tsgolint),
+    typescript,
+    nursery,
+    config = PreferReadonlyConfig,
+);
+
+impl Rule for PreferReadonly {
+    fn from_configuration(value: serde_json::Value) -> Result<Self, serde_json::error::Error> {
+        serde_json::from_value::<DefaultRuleConfig<Self>>(value).map(DefaultRuleConfig::into_inner)
+    }
+
+    fn to_configuration(&self) -> Option<Result<serde_json::Value, serde_json::Error>> {
+        Some(serde_json::to_value(&*self.0))
+    }
+}