fix(lint/noUnassignedVariables): handle JSX ref attribute assignments (#7000)

Author: harxki

.changeset/five-ghosts-wave.md

@@ -0,0 +1,5 @@
+---
+"@biomejs/biome": patch
+---
+
+Fixed [#6795](https://github.com/biomejs/biome/issues/6795): `noUnassignedVariables` now correctly recognizes variables used in JSX `ref` attributes.

crates/biome_js_analyze/tests/specs/nursery/noUnassignedVariables/valid.jsx

@@ -0,0 +1,6 @@
+/* should not generate diagnostics */
+export const Component = () => {
+    let value;
+    return <div ref={value} />
+  }
+  

crates/biome_js_analyze/tests/specs/nursery/noUnassignedVariables/valid.jsx.snap

@@ -0,0 +1,13 @@
+---
+source: crates/biome_js_analyze/tests/spec_tests.rs
+expression: valid.jsx
+---
+# Input
+```jsx
+/* should not generate diagnostics */
+export const Component = () => {
+    let value;
+    return <div ref={value} />
+  }
+  
+```

crates/biome_js_semantic/src/events.rs

@@ -6,7 +6,9 @@ use biome_js_syntax::{
     AnyJsIdentifierUsage, JsDirective, JsLanguage, JsSyntaxKind, JsSyntaxNode, TextRange,
     TsTypeParameterName, inner_string_text,
 };
-use biome_js_syntax::{AnyJsImportClause, AnyJsNamedImportSpecifier, AnyTsType};
+use biome_js_syntax::{
+    AnyJsImportClause, AnyJsNamedImportSpecifier, AnyJsxAttributeName, AnyTsType, JsxAttribute,
+};
 use biome_rowan::TextSize;
 use biome_rowan::{AstNode, SyntaxNodeOptionExt, TokenText, syntax::Preorder};
 use rustc_hash::FxHashMap;
@@ -709,6 +711,18 @@ impl SemanticEventExtractor {
         }
     }
 
+    fn is_inside_jsx_ref_attribute(node: &JsSyntaxNode) -> bool {
+        node.ancestors()
+            .find_map(JsxAttribute::cast)
+            .and_then(|attr| attr.name().ok())
+            .is_some_and(|attr_name| match attr_name {
+                AnyJsxAttributeName::JsxName(jsx_name) => jsx_name
+                    .value_token()
+                    .is_ok_and(|token| token.text_trimmed() == "ref"),
+                _ => false,
+            })
+    }
+
     fn enter_identifier_usage(&mut self, node: AnyJsIdentifierUsage) {
         let range = node.syntax().text_trimmed_range();
         let Ok(name_token) = node.value_token() else {
@@ -728,6 +742,14 @@ impl SemanticEventExtractor {
                     );
                     return;
                 };
+
+                if parent.kind() == JS_IDENTIFIER_EXPRESSION
+                    && Self::is_inside_jsx_ref_attribute(&parent)
+                {
+                    self.push_reference(BindingName::Value(name), Reference::Write(range));
+                    return;
+                }
+
                 match parent.kind() {
                     JS_EXPORT_NAMED_SHORTHAND_SPECIFIER | JS_EXPORT_NAMED_SPECIFIER => {
                         self.push_reference(