feat(transformer): implement jsx spread child

crates/oxc_transformer/src/jsx/diagnostics.rs

@@ -30,7 +30,3 @@ pub fn valueless_key(span: Span) -> OxcDiagnostic {
     OxcDiagnostic::warn("Please provide an explicit key value. Using \"key\" as a shorthand for \"key={true}\" is not allowed.")
         .with_label(span)
 }
-
-pub fn spread_children_are_not_supported(span: Span) -> OxcDiagnostic {
-    OxcDiagnostic::warn("Spread children are not supported in React.").with_label(span)
-}

crates/oxc_transformer/src/jsx/jsx_impl.rs

@@ -625,7 +625,7 @@ impl<'a> JsxImpl<'a, '_> {
         // Append children to object properties in automatic mode
         if is_automatic {
             let mut children = ctx.ast.vec_from_iter(
-                children.iter().filter_map(|child| self.transform_jsx_child(child, ctx)),
+                children.iter().filter_map(|child| self.transform_jsx_child_automatic(child, ctx)),
             );
             children_len = children.len();
             if children_len != 0 {
@@ -750,10 +750,7 @@ impl<'a> JsxImpl<'a, '_> {
             // React.createElement(type, arguments, ...children)
             //                                      ^^^^^^^^^^^
             arguments.extend(
-                children
-                    .iter()
-                    .filter_map(|child| self.transform_jsx_child(child, ctx))
-                    .map(Argument::from),
+                children.iter().filter_map(|child| self.transform_jsx_child_classic(child, ctx)),
             );
         }
 
@@ -883,6 +880,40 @@ impl<'a> JsxImpl<'a, '_> {
         }
     }
 
+    fn transform_jsx_child_automatic(
+        &mut self,
+        child: &JSXChild<'a>,
+        ctx: &mut TraverseCtx<'a>,
+    ) -> Option<Expression<'a>> {
+        // Align spread child behavior with esbuild.
+        // Instead of Babel throwing `Spread children are not supported in React.`
+        // `<>{...foo}</>` -> `jsxs(Fragment, { children: [ ...foo ] })`
+        if let JSXChild::Spread(e) = child {
+            // SAFETY: `ast.copy` is unsound! We need to fix.
+            let argument = unsafe { ctx.ast.copy(&e.expression) };
+            let spread_element = ctx.ast.array_expression_element_spread_element(e.span, argument);
+            let elements = ctx.ast.vec1(spread_element);
+            return Some(ctx.ast.expression_array(e.span, elements, None));
+        }
+        self.transform_jsx_child(child, ctx)
+    }
+
+    fn transform_jsx_child_classic(
+        &mut self,
+        child: &JSXChild<'a>,
+        ctx: &mut TraverseCtx<'a>,
+    ) -> Option<Argument<'a>> {
+        // Align spread child behavior with esbuild.
+        // Instead of Babel throwing `Spread children are not supported in React.`
+        // `<>{...foo}</>` -> `React.createElement(React.Fragment, null, ...foo)`
+        if let JSXChild::Spread(e) = child {
+            // SAFETY: `ast.copy` is unsound! We need to fix.
+            let argument = unsafe { ctx.ast.copy(&e.expression) };
+            return Some(ctx.ast.argument_spread_element(e.span, argument));
+        }
+        self.transform_jsx_child(child, ctx).map(Argument::from)
+    }
+
     fn transform_jsx_child(
         &mut self,
         child: &JSXChild<'a>,
@@ -903,10 +934,7 @@ impl<'a> JsxImpl<'a, '_> {
             JSXChild::Fragment(e) => {
                 Some(self.transform_jsx(&JSXElementOrFragment::Fragment(e), ctx))
             }
-            JSXChild::Spread(e) => {
-                self.ctx.error(diagnostics::spread_children_are_not_supported(e.span));
-                None
-            }
+            JSXChild::Spread(_) => unreachable!(),
         }
     }
 

tasks/coverage/snapshots/semantic_typescript.snap

@@ -39578,11 +39578,20 @@ after transform: ScopeId(0): [ScopeId(1), ScopeId(2)]
 rebuilt        : ScopeId(0): [ScopeId(1)]
 
 tasks/coverage/typescript/tests/cases/conformance/jsx/tsxSpreadChildren.tsx
-semantic error: Spread children are not supported in React.
+semantic error: Bindings mismatch:
+after transform: ScopeId(0): ["JSX", "React", "Todo", "TodoList", "_jsxFileName", "_objectSpread", "_reactJsxRuntime", "x"]
+rebuilt        : ScopeId(0): ["Todo", "TodoList", "_jsxFileName", "_objectSpread", "_reactJsxRuntime", "x"]
+Scope children mismatch:
+after transform: ScopeId(0): [ScopeId(1), ScopeId(4), ScopeId(5), ScopeId(6), ScopeId(7)]
+rebuilt        : ScopeId(0): [ScopeId(1), ScopeId(2)]
 
 tasks/coverage/typescript/tests/cases/conformance/jsx/tsxSpreadChildrenInvalidType.tsx
-semantic error: Spread children are not supported in React.
-Spread children are not supported in React.
+semantic error: Bindings mismatch:
+after transform: ScopeId(0): ["JSX", "React", "Todo", "TodoList", "TodoListNoError", "_jsxFileName", "_objectSpread", "_reactJsxRuntime", "x"]
+rebuilt        : ScopeId(0): ["Todo", "TodoList", "TodoListNoError", "_jsxFileName", "_objectSpread", "_reactJsxRuntime", "x"]
+Scope children mismatch:
+after transform: ScopeId(0): [ScopeId(1), ScopeId(4), ScopeId(5), ScopeId(6), ScopeId(7), ScopeId(8)]
+rebuilt        : ScopeId(0): [ScopeId(1), ScopeId(2), ScopeId(3)]
 
 tasks/coverage/typescript/tests/cases/conformance/jsx/tsxStatelessFunctionComponentOverload2.tsx
 semantic error: Scope children mismatch:

tasks/transform_conformance/snapshots/oxc.snap.md

@@ -1,6 +1,6 @@
 commit: acbc09a8
 
-Passed: 133/155
+Passed: 135/157
 
 # All Passed:
 * babel-plugin-transform-class-static-block
@@ -308,7 +308,7 @@ rebuilt        : SymbolId(2): []
 x Output mismatch
 
 
-# babel-plugin-transform-react-jsx (35/38)
+# babel-plugin-transform-react-jsx (37/40)
 * refresh/does-not-transform-it-because-it-is-not-used-in-the-AST/input.jsx
 x Output mismatch
 

tasks/transform_conformance/tests/babel-plugin-transform-react-jsx/test/fixtures/spread-children-automatic/input.jsx

@@ -0,0 +1 @@
+<>{...foo}</>

tasks/transform_conformance/tests/babel-plugin-transform-react-jsx/test/fixtures/spread-children-automatic/options.json

@@ -0,0 +1,10 @@
+{
+  "plugins": [
+    [
+      "transform-react-jsx",
+      {
+        "runtime": "automatic"
+      }
+    ]
+  ]
+}

tasks/transform_conformance/tests/babel-plugin-transform-react-jsx/test/fixtures/spread-children-automatic/output.js

@@ -0,0 +1,2 @@
+var _reactJsxRuntime = require("react/jsx-runtime");
+_reactJsxRuntime.jsx(_reactJsxRuntime.Fragment, { children: [...foo] });

tasks/transform_conformance/tests/babel-plugin-transform-react-jsx/test/fixtures/spread-children-classic/input.jsx

@@ -0,0 +1 @@
+<>{...foo}</>

tasks/transform_conformance/tests/babel-plugin-transform-react-jsx/test/fixtures/spread-children-classic/options.json

@@ -0,0 +1,10 @@
+{
+  "plugins": [
+    [
+      "transform-react-jsx",
+      {
+        "runtime": "classic"
+      }
+    ]
+  ]
+}

tasks/transform_conformance/tests/babel-plugin-transform-react-jsx/test/fixtures/spread-children-classic/output.js

@@ -0,0 +1 @@
+React.createElement(React.Fragment, null, ...foo);