feat(linter): add typescript/no-unnecessary-type-parameters rule

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

@@ -24,6 +24,7 @@
     "typescript/no-unnecessary-template-expression": "error",
     "typescript/no-unnecessary-type-arguments": "error",
     "typescript/no-unnecessary-type-assertion": "error",
+    "typescript/no-unnecessary-type-parameters": "error",
     "typescript/no-unsafe-argument": "error",
     "typescript/no-unsafe-assignment": "error",
     "typescript/no-unsafe-call": "error",

apps/oxlint/fixtures/tsgolint/no-unnecessary-type-parameters.ts

@@ -0,0 +1,5 @@
+// Examples of incorrect code for no-unnecessary-type-parameters rule
+
+function parseYAML<T>(input: string): T {
+  return input as any as T;
+}

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 71 errors.
-Finished in <variable>ms on 56 files with 55 rules using 1 threads.
+Found 0 warnings and 74 errors.
+Finished in <variable>ms on 57 files with 56 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 56 files with 1 rules using 1 threads.
+Finished in <variable>ms on 57 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 55 rules using 1 threads.
+Finished in <variable>ms on 1 file with 56 rules using 1 threads.
 ----------
 CLI result: LintFoundErrors
 ----------

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

@@ -197,6 +197,31 @@ working directory: fixtures/tsgolint
  3 | 
    `----
 
+  x typescript-eslint(no-unnecessary-type-parameters): Type parameter T is used only once in the function signature.
+   ,-[no-unnecessary-type-parameters.ts:3:20]
+ 2 | 
+ 3 | function parseYAML<T>(input: string): T {
+   :                    ^                  |
+   :                    |                  `-- This is the only usage of type parameter T in the signature.
+ 4 |   return input as any as T;
+   `----
+
+  x typescript-eslint(no-unsafe-type-assertion): Unsafe assertion to `any` detected: consider using a more specific type to ensure safety.
+   ,-[no-unnecessary-type-parameters.ts:4:10]
+ 3 | function parseYAML<T>(input: string): T {
+ 4 |   return input as any as T;
+   :          ^^^^^^^^^^^^
+ 5 | }
+   `----
+
+  x typescript-eslint(no-unsafe-type-assertion): Unsafe assertion from `any` detected: consider using type guards or a safer assertion.
+   ,-[no-unnecessary-type-parameters.ts:4:10]
+ 3 | function parseYAML<T>(input: string): T {
+ 4 |   return input as any as T;
+   :          ^^^^^^^^^^^^^^^^^
+ 5 | }
+   `----
+
   x typescript-eslint(no-unsafe-argument): Unsafe argument of type any assigned to a parameter of type string.
    ,-[no-unsafe-argument.ts:3:13]
  2 | function takesString(str: string): void {}
@@ -564,8 +589,8 @@ 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 71 errors.
-Finished in <variable>ms on 56 files with 55 rules using 1 threads.
+Found 0 warnings and 74 errors.
+Finished in <variable>ms on 57 files with 56 rules using 1 threads.
 ----------
 CLI result: LintFoundErrors
 ----------

crates/oxc_linter/src/rules.rs

@@ -268,6 +268,7 @@ pub(crate) mod typescript {
     pub mod no_unnecessary_type_arguments;
     pub mod no_unnecessary_type_assertion;
     pub mod no_unnecessary_type_constraint;
+    pub mod no_unnecessary_type_parameters;
     pub mod no_unsafe_argument;
     pub mod no_unsafe_assignment;
     pub mod no_unsafe_call;

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

@@ -0,0 +1,42 @@
+use oxc_macros::declare_oxc_lint;
+
+use crate::rule::Rule;
+
+#[derive(Debug, Default, Clone)]
+pub struct NoUnnecessaryTypeParameters;
+
+declare_oxc_lint!(
+    /// ### What it does
+    ///
+    /// Disallow type parameters that are declared but not meaningfully used.
+    ///
+    /// ### Why is this bad?
+    ///
+    /// Unnecessary type parameters make signatures noisier and harder to understand, and they
+    /// often hide opportunities to simplify APIs.
+    ///
+    /// ### Examples
+    ///
+    /// Examples of **incorrect** code for this rule:
+    /// ```ts
+    /// function parseYAML<T>(input: string): T {
+    ///   return input as any as T;
+    /// }
+    /// ```
+    ///
+    /// Examples of **correct** code for this rule:
+    /// ```ts
+    /// function parseYAML(input: string): unknown {
+    ///   return input;
+    /// }
+    ///
+    /// function identity<T>(value: T): T {
+    ///   return value;
+    /// }
+    /// ```
+    NoUnnecessaryTypeParameters(tsgolint),
+    typescript,
+    nursery,
+);
+
+impl Rule for NoUnnecessaryTypeParameters {}