fix(analyze): check if a fragment has only one child element using tokens.

CHANGELOG.md

@@ -52,7 +52,7 @@ our [guidelines for writing a good changelog entry](https://github.com/biomejs/b
   - `--log-prefix-name`: a prefix that's added to the file name of the logs. It defaults to `server.log`. The commands also accepts the environment variable `BIOME_LOG_PREFIX_NAME`.
 
   @Contributed by @ematipico
-   
+
 
 #### Enhancements
 
@@ -87,6 +87,7 @@ our [guidelines for writing a good changelog entry](https://github.com/biomejs/b
 
 - `biome lint --write` now takes `--only` and `--skip` into account ([#3470](https://github.com/biomejs/biome/issues/3470)). Contributed by @Conaclos
 - Fix [#3368](https://github.com/biomejs/biome/issues/3368), now the reporter `github` tracks the diagnostics that belong to formatting and organize imports. Contributed by @ematipico
+- Fix [#3545](https://github.com/biomejs/biome/issues/3545), display a warning, 'Avoid using unnecessary Fragment,' when a Fragment contains only one child element that is placed on a new line. Contributed by @satojin219
 
 ### Configuration
 

crates/biome_js_analyze/src/lint/complexity/no_useless_fragments.rs

@@ -161,14 +161,48 @@ impl Rule for NoUselessFragments {
                 let child_list = fragment.children();
 
                 if !parents_where_fragments_must_be_preserved {
-                    match child_list.first() {
-                        Some(first) if child_list.len() == 1 => {
-                            if JsxText::can_cast(first.syntax().kind()) && in_jsx_attr_expr {
-                                return None;
+                    let mut significant_children = 0;
+                    let mut first_significant_child = None;
+
+                    for child in child_list.iter() {
+                        match child.syntax().kind() {
+                            JsSyntaxKind::JSX_SELF_CLOSING_ELEMENT
+                            | JsSyntaxKind::JSX_ELEMENT
+                            | JsSyntaxKind::JSX_EXPRESSION_CHILD
+                            | JsSyntaxKind::JSX_FRAGMENT => {
+                                significant_children += 1;
+                                if first_significant_child.is_none() {
+                                    first_significant_child = Some(child);
+                                }
+                            }
+                            JsSyntaxKind::JSX_TEXT => {
+                                if !child.syntax().text().to_string().trim().is_empty() {
+                                    significant_children += 1;
+                                    if first_significant_child.is_none() {
+                                        first_significant_child = Some(child);
+                                    }
+                                }
+                            }
+                            _ => {}
+                        }
+                        if significant_children > 1 {
+                            break;
+                        }
+                    }
+
+                    match significant_children {
+                        0 => Some(NoUselessFragmentsState::Empty),
+                        1 => {
+                            if let Some(first) = first_significant_child {
+                                if JsxText::can_cast(first.syntax().kind()) && in_jsx_attr_expr {
+                                    None
+                                } else {
+                                    Some(NoUselessFragmentsState::Child(first))
+                                }
+                            } else {
+                                None
                             }
-                            Some(NoUselessFragmentsState::Child(first))
                         }
-                        None => Some(NoUselessFragmentsState::Empty),
                         _ => None,
                     }
                 } else {
@@ -254,7 +288,18 @@ impl Rule for NoUselessFragments {
                 None => parent.into_syntax(),
             };
 
-            let child = node.children().first();
+            let child = node
+                .children()
+                .iter()
+                .find(|child| match child.syntax().kind() {
+                    JsSyntaxKind::JSX_SELF_CLOSING_ELEMENT
+                    | JsSyntaxKind::JSX_ELEMENT
+                    | JsSyntaxKind::JSX_EXPRESSION_CHILD
+                    | JsSyntaxKind::JSX_FRAGMENT => true,
+                    JsSyntaxKind::JSX_TEXT => !child.syntax().text().to_string().trim().is_empty(),
+                    _ => false,
+                });
+
             if let Some(child) = child {
                 let new_node = match child {
                     AnyJsxChild::JsxElement(node) => {

crates/biome_js_analyze/tests/specs/complexity/noUselessFragments/fromImportNamespaceInvalid.jsx.snap

@@ -1,5 +1,6 @@
 ---
 source: crates/biome_js_analyze/tests/spec_tests.rs
+assertion_line: 84
 expression: fromImportNamespaceInvalid.jsx
 ---
 # Input
@@ -13,6 +14,35 @@ import * as AwesomeReact from "react";
 ```
 
 # Diagnostics
+```
+fromImportNamespaceInvalid.jsx:3:1 lint/complexity/noUselessFragments  FIXABLE  ━━━━━━━━━━━━━━━━━━━━
+
+  ! Avoid using unnecessary Fragment.
+
+    1 │ import * as AwesomeReact from "react";
+    2 │ 
+  > 3 │ <>
+      │ ^^
+  > 4 │     <AwesomeReact.Fragment>foo</AwesomeReact.Fragment>
+  > 5 │ </>
+      │ ^^^
+    6 │ 
+
+  i A fragment is redundant if it contains only one child, or if it is the child of a html element, and is not a keyed fragment.
+
+  i Unsafe fix: Remove the Fragment
+
+    1 1 │   import * as AwesomeReact from "react";
+    2 2 │   
+    3   │ - <>
+    4   │ - ····<AwesomeReact.Fragment>foo</AwesomeReact.Fragment>
+    5   │ - </>
+      3 │ + <AwesomeReact.Fragment>foo</AwesomeReact.Fragment>
+    6 4 │   
+
+
+```
+
 ```
 fromImportNamespaceInvalid.jsx:4:5 lint/complexity/noUselessFragments  FIXABLE  ━━━━━━━━━━━━━━━━━━━━
 
@@ -32,5 +62,3 @@ fromImportNamespaceInvalid.jsx:4:5 lint/complexity/noUselessFragments  FIXABLE
       │     -----------------------   ------------------------
 
 ```
-
-

crates/biome_js_analyze/tests/specs/complexity/noUselessFragments/issue_3545.jsx

@@ -0,0 +1,4 @@
+// https://github.com/biomejs/biome/issues/3545
+<>
+	<Component />
+</>;

crates/biome_js_analyze/tests/specs/complexity/noUselessFragments/issue_3545.jsx.snap

@@ -0,0 +1,41 @@
+---
+source: crates/biome_js_analyze/tests/spec_tests.rs
+assertion_line: 84
+expression: issue_3545.jsx
+---
+# Input
+```jsx
+// https://github.com/biomejs/biome/issues/3545
+<>
+	<Component />
+</>;
+
+```
+
+# Diagnostics
+```
+issue_3545.jsx:2:1 lint/complexity/noUselessFragments  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+  ! Avoid using unnecessary Fragment.
+
+    1 │ // https://github.com/biomejs/biome/issues/3545
+  > 2 │ <>
+      │ ^^
+  > 3 │ 	<Component />
+  > 4 │ </>;
+      │ ^^^
+    5 │ 
+
+  i A fragment is redundant if it contains only one child, or if it is the child of a html element, and is not a keyed fragment.
+
+  i Unsafe fix: Remove the Fragment
+
+    1 1 │   // https://github.com/biomejs/biome/issues/3545
+    2   │ - <>
+    3   │ - → <Component·/>
+    4   │ - </>;
+      2 │ + <Component·/>;
+    5 3 │   
+
+
+```