From 011a0179d953e3970a1d56c833c3b20503ad2db5 Mon Sep 17 00:00:00 2001
From: Cameron Clark <cameron.clark@hey.com>
Date: Mon, 2 Dec 2024 17:17:13 +0000
Subject: [PATCH] fix(linter): no-unused-expressions false positive with arrow
 fn expressions

---
 .../rules/typescript/no_unused_expressions.rs | 20 ++++++++++++++++++-
 .../typescript_no_unused_expressions.snap     |  7 +++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/crates/oxc_linter/src/rules/typescript/no_unused_expressions.rs b/crates/oxc_linter/src/rules/typescript/no_unused_expressions.rs
index ad293e5a94bff..374b4e30e4185 100644
--- a/crates/oxc_linter/src/rules/typescript/no_unused_expressions.rs
+++ b/crates/oxc_linter/src/rules/typescript/no_unused_expressions.rs
@@ -58,7 +58,9 @@ impl Rule for NoUnusedExpressions {
             return;
         };
 
-        if self.is_disallowed(&expression_stmt.expression) {
+        if self.is_disallowed(&expression_stmt.expression)
+            && !is_parent_arrow_function_expression(node, ctx)
+        {
             ctx.diagnostic(no_unused_expressions_diagnostic(expression_stmt.span));
         }
     }
@@ -89,6 +91,20 @@ impl Rule for NoUnusedExpressions {
     }
 }
 
+fn is_parent_arrow_function_expression<'a>(node: &AstNode<'a>, ctx: &LintContext<'a>) -> bool {
+    let Some(parent) = ctx.nodes().parent_node(node.id()) else { return false };
+
+    let AstKind::FunctionBody(_) = parent.kind() else { return false };
+
+    let Some(grand_parent) = ctx.nodes().parent_node(parent.id()) else { return false };
+
+    let AstKind::ArrowFunctionExpression(arrow_function_expression) = grand_parent.kind() else {
+        return false;
+    };
+
+    arrow_function_expression.expression
+}
+
 impl NoUnusedExpressions {
     fn is_disallowed(&self, expr: &Expression) -> bool {
         match expr {
@@ -265,6 +281,7 @@ fn test() {
             "foo ? import('./foo') : import('./bar');",
             Some(serde_json::json!([{ "allowTernary": true }])),
         ),
+        ("const _func = (value: number) => value + 1;", None),
     ];
 
     let fail = vec![
@@ -411,6 +428,7 @@ fn test() {
 			      ",
             None,
         ),
+        ("const _func = (value: number) => { value + 1; }", None),
     ];
 
     Tester::new(NoUnusedExpressions::NAME, NoUnusedExpressions::CATEGORY, pass, fail)
diff --git a/crates/oxc_linter/src/snapshots/typescript_no_unused_expressions.snap b/crates/oxc_linter/src/snapshots/typescript_no_unused_expressions.snap
index 99a941bac194a..d06ee11f31264 100644
--- a/crates/oxc_linter/src/snapshots/typescript_no_unused_expressions.snap
+++ b/crates/oxc_linter/src/snapshots/typescript_no_unused_expressions.snap
@@ -200,3 +200,10 @@ source: crates/oxc_linter/src/tester.rs
  4 │                   
    ╰────
   help: Consider removing this expression
+
+  ⚠ typescript-eslint(no-unused-expressions): Disallow unused expressions
+   ╭─[no_unused_expressions.tsx:1:36]
+ 1 │ const _func = (value: number) => { value + 1; }
+   ·                                    ──────────
+   ╰────
+  help: Consider removing this expression