feat(linter): support direct const assertions in useExplicitFunctionR…

…eturnType rule (#4027)

crates/biome_js_analyze/src/lint/nursery/use_explicit_function_return_type.rs

@@ -3,7 +3,7 @@ use biome_analyze::{
 };
 use biome_console::markup;
 use biome_js_semantic::HasClosureAstNode;
-use biome_js_syntax::AnyJsBinding;
+use biome_js_syntax::{AnyJsBinding, AnyJsExpression, AnyJsFunctionBody, AnyTsType};
 use biome_js_syntax::{
  AnyJsFunction, JsGetterClassMember, JsGetterObjectMember, JsMethodClassMember,
  JsMethodObjectMember,
@@ -61,6 +61,11 @@ declare_lint_rule! {
  /// }
  /// ```
  ///
+ /// ```ts,expect_diagnostic
+ /// // Should use const assertions
+ /// const func = (value: number) => ({ type: 'X', value }) as any;
+ /// ```
+ ///
  /// ### Valid
  /// ```ts
  /// // No return value should be expected (void)
@@ -90,6 +95,10 @@ declare_lint_rule! {
  /// }
  /// ```
  ///
+ /// ```ts
+ /// const func = (value: number) => ({ foo: 'bar', value }) as const;
+ /// ```
+ ///
  pub UseExplicitFunctionReturnType {
  version: "next",
  name: "useExplicitFunctionReturnType",
@@ -117,6 +126,10 @@ impl Rule for UseExplicitFunctionReturnType {
  return None;
  }
 
+ if is_direct_const_assertion_in_arrow_functions(func) {
+ return None;
+ }
+
  let func_range = func.syntax().text_range();
  if let Ok(Some(AnyJsBinding::JsIdentifierBinding(id))) = func.id() {
  return Some(TextRange::new(
@@ -176,3 +189,28 @@ impl Rule for UseExplicitFunctionReturnType {
  )
  }
 }
+
+/**
+ * Checks if an arrow function immediately returns a `as const` value.
+ * const func = (value: number) => ({ foo: 'bar', value }) as const;
+ * const func = () => x as const;
+ */
+fn is_direct_const_assertion_in_arrow_functions(func: &AnyJsFunction) -> bool {
+ let AnyJsFunction::JsArrowFunctionExpression(arrow_func) = func else {
+ return false;
+ };
+
+ let Ok(AnyJsFunctionBody::AnyJsExpression(expr)) = arrow_func.body() else {
+ return false;
+ };
+
+ let AnyJsExpression::TsAsExpression(ts_expr) = expr else {
+ return false;
+ };
+
+ let Ok(AnyTsType::TsReferenceType(ts_ref)) = ts_expr.ty() else {
+ return false;
+ };
+
+ ts_ref.text() == "const"
+}

crates/biome_js_analyze/tests/specs/nursery/useExplicitFunctionReturnType/invalid.ts

@@ -38,3 +38,6 @@ const obj = {
  return "test"
  },
 };
+
+const func = (value: number) => ({ type: 'X', value }) as any;
+const func = (value: number) => ({ type: 'X', value }) as Action;

crates/biome_js_analyze/tests/specs/nursery/useExplicitFunctionReturnType/invalid.ts.snap

@@ -45,6 +45,8 @@ const obj = {
  },
 };
 
+const func = (value: number) => ({ type: 'X', value }) as any;
+const func = (value: number) => ({ type: 'X', value }) as Action;
 ```
 
 # Diagnostics
@@ -254,3 +256,37 @@ invalid.ts:37:3 lint/nursery/useExplicitFunctionReturnType ━━━━━━━
  
 
 ```
+
+```
+invalid.ts:42:14 lint/nursery/useExplicitFunctionReturnType ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+ ! Missing return type on function.
+ 
+ 40 │ };
+ 41 │ 
+ > 42 │ const func = (value: number) => ({ type: 'X', value }) as any;
+ │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ 43 │ const func = (value: number) => ({ type: 'X', value }) as Action;
+ 
+ i Declaring the return type makes the code self-documenting and can speed up TypeScript type checking.
+ 
+ i Add a return type annotation.
+ 
+
+```
+
+```
+invalid.ts:43:14 lint/nursery/useExplicitFunctionReturnType ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+ ! Missing return type on function.
+ 
+ 42 │ const func = (value: number) => ({ type: 'X', value }) as any;
+ > 43 │ const func = (value: number) => ({ type: 'X', value }) as Action;
+ │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ 
+ i Declaring the return type makes the code self-documenting and can speed up TypeScript type checking.
+ 
+ i Add a return type annotation.
+ 
+
+```

crates/biome_js_analyze/tests/specs/nursery/useExplicitFunctionReturnType/valid.ts

@@ -32,3 +32,6 @@ const obj = {
  return "test"
  },
 };
+
+const func = (value: number) => ({ foo: 'bar', value }) as const;
+const func = () => x as const;

crates/biome_js_analyze/tests/specs/nursery/useExplicitFunctionReturnType/valid.ts.snap

@@ -39,4 +39,6 @@ const obj = {
  },
 };
 
+const func = (value: number) => ({ foo: 'bar', value }) as const;
+const func = () => x as const;
 ```