feat: JSX opening and self-closing elements with a single string attribute should not go multi-line

Closes #293

Author: dsherret

src/parsing/parser.rs

@@ -3256,7 +3256,14 @@ fn parse_jsx_opening_element<'a>(node: &'a JSXOpeningElement, context: &mut Cont
     items.extend(parse_node(type_args.into(), context));
   }
 
-  if !node.attrs.is_empty() {
+  let single_line_space_at_end = node.self_closing() && space_before_self_closing_tag_slash;
+  if node.attrs.len() == 1 && node.type_args.is_none() && is_jsx_attr_with_string(&node.attrs[0]) {
+    items.push_str(" ");
+    items.extend(parse_node(node.attrs[0].into(), context));
+    if single_line_space_at_end {
+      items.push_str(" ");
+    }
+  } else if !node.attrs.is_empty() {
     items.extend(parse_separated_values(
       ParseSeparatedValuesParams {
         nodes: node.attrs.iter().map(|p| NodeOrSeparator::Node(p.into())).collect(),
@@ -3265,7 +3272,7 @@ fn parse_jsx_opening_element<'a>(node: &'a JSXOpeningElement, context: &mut Cont
         allow_blank_lines: false,
         separator: Separator::none(),
         single_line_space_at_start: true,
-        single_line_space_at_end: node.self_closing() && space_before_self_closing_tag_slash,
+        single_line_space_at_end,
         custom_single_line_separator: None,
         multi_line_options: parser_helpers::MultiLineOptions::surround_newlines_indented(),
         force_possible_newline_at_start: false,
@@ -3312,6 +3319,15 @@ fn parse_jsx_opening_element<'a>(node: &'a JSXOpeningElement, context: &mut Cont
       false
     }
   }
+
+  fn is_jsx_attr_with_string(node: &JSXAttrOrSpread) -> bool {
+    if let JSXAttrOrSpread::JSXAttr(attrib) = node {
+      if let Some(value) = attrib.value {
+        return value.kind() == NodeKind::Str;
+      }
+    }
+    return false;
+  }
 }
 
 fn parse_jsx_opening_fragment<'a>(_: &'a JSXOpeningFragment, _: &mut Context<'a>) -> PrintItems {

tests/specs/jsx/JsxElement/JsxElement_All.txt

@@ -220,3 +220,39 @@ return <E>Test: {type}</E>;
 return <E>Test: {type}</E>;
 return <E>{type} test</E>;
 return <E>{type} test</E>;
+
+== should keep multi-line jsx element with single string attribute on same line ==
+const t = (
+    <Element test="testing this out with some string that is long">
+        Test
+    </Element>
+);
+const u = (
+    <Element test="testing this out with some string that is long" />
+);
+
+[expect]
+const t = (
+    <Element test="testing this out with some string that is long">
+        Test
+    </Element>
+);
+const u = (
+    <Element test="testing this out with some string that is long" />
+);
+
+== should not keep long multi-line jsx element with single string attribute on same line when has type arg ==
+const t = (
+    <Element<arg> test="testing this out with some string that is long">
+        Test
+    </Element>
+);
+
+[expect]
+const t = (
+    <Element<arg>
+        test="testing this out with some string that is long"
+    >
+        Test
+    </Element>
+);