feat: transform nullish coalescing default parameter

j4k0xb · Dec 29, 2023 · e54edca · e54edca
1 parent aa262c0
commit e54edca
Show file tree

Hide file tree

Showing 4 changed files with 37 additions and 13 deletions.
diff --git a/apps/docs/src/concepts/transpile.md b/apps/docs/src/concepts/transpile.md
@@ -30,6 +30,11 @@ var _a$b; // [!code --]
 a.b ?? c; // [!code ++]
 ```
 
+```js
+function foo(foo, qux = (_foo$bar => (_foo$bar = foo.bar) !== null && _foo$bar !== undefined ? _foo$bar : "qux")()) {} // [!code --]
+function foo(foo, qux = foo.bar ?? "qux") {} // [!code ++]
+```
+
 ## nullish-coalescing-assignment
 
 ```js

diff --git a/packages/webcrack/src/ast-utils/matcher.ts b/packages/webcrack/src/ast-utils/matcher.ts
@@ -179,12 +179,14 @@ export function isReadonlyObject(
 export function isTemporaryVariable(
   binding: Binding | undefined,
   references: number,
+  kind: 'var' | 'param' = 'var',
 ): binding is Binding {
   return (
     binding !== undefined &&
     binding.references === references &&
     binding.constantViolations.length === 1 &&
-    binding.path.isVariableDeclarator() &&
-    binding.path.node.init === null
+    (kind === 'var'
+      ? binding.path.isVariableDeclarator() && binding.path.node.init === null
+      : binding.path.listKey === 'params' && binding.path.isIdentifier())
   );
 }
diff --git a/packages/webcrack/src/transpile/test/nullish-coalescing.test.ts b/packages/webcrack/src/transpile/test/nullish-coalescing.test.ts
@@ -49,15 +49,14 @@ test.todo('member expression (esbuild)', () =>
   `),
 );
 
-test.todo('default param (Babel)', () =>
+test('default param (Babel)', () =>
   expectJS(`
-    function foo(foo, qux = (_foo$bar => (_foo$bar = foo.bar) !== null && _foo$bar !== void 0 ? _foo$bar : "qux")()) {}
-    function bar(bar, qux = bar !== null && bar !== void 0 ? bar : "qux") {}
+    function foo(foo, qux = (_foo$bar => (_foo$bar = foo.bar) !== null && _foo$bar !== undefined ? _foo$bar : "qux")()) {}
+    function bar(bar, qux = bar !== null && bar !== undefined ? bar : "qux") {}
   `).toMatchInlineSnapshot(`
     function foo(foo, qux = foo.bar ?? "qux") {}
     function bar(bar, qux = bar ?? "qux") {}
-  `),
-);
+  `));
 
 // TODO: add unminify transform or different matchers?
 test.todo('flipped', () =>

diff --git a/packages/webcrack/src/transpile/transforms/nullish-coalescing.ts b/packages/webcrack/src/transpile/transforms/nullish-coalescing.ts
@@ -58,18 +58,36 @@ export default {
       right,
     );
 
+    const iifeMatcher = m.callExpression(
+      m.arrowFunctionExpression(
+        [m.fromCapture(tmpVar)],
+        m.anyExpression(),
+        false,
+      ),
+      [],
+    );
+
     return {
       ConditionalExpression: {
         exit(path) {
           if (idMatcher.match(path.node)) {
             const binding = path.scope.getBinding(tmpVar.current!.name);
-            if (!isTemporaryVariable(binding, 2)) return;
 
-            binding.path.remove();
-            path.replaceWith(
-              t.logicalExpression('??', left.current!, right.current!),
-            );
-            this.changes++;
+            if (
+              iifeMatcher.match(path.parentPath.parent) &&
+              isTemporaryVariable(binding, 2, 'param')
+            ) {
+              path.parentPath.parentPath!.replaceWith(
+                t.logicalExpression('??', left.current!, right.current!),
+              );
+              this.changes++;
+            } else if (isTemporaryVariable(binding, 2, 'var')) {
+              binding.path.remove();
+              path.replaceWith(
+                t.logicalExpression('??', left.current!, right.current!),
+              );
+              this.changes++;
+            }
           } else if (idLooseMatcher.match(path.node)) {
             const binding = path.scope.getBinding(tmpVar.current!.name);
             if (!isTemporaryVariable(binding, 1)) return;