withastro · openscript · Jan 15, 2026 · Jan 15, 2026
diff --git a/.changeset/orange-lands-search.md b/.changeset/orange-lands-search.md
@@ -0,0 +1,5 @@
+---
+"@astrojs/compiler": patch
+---
+
+Fix slot attribute stripped inside expression
diff --git a/internal/printer/__printer_js__/Preserve_slot_attribute_at_root_level_in_expression.snap b/internal/printer/__printer_js__/Preserve_slot_attribute_at_root_level_in_expression.snap
@@ -0,0 +1,41 @@
+
+[TestPrinter/Preserve_slot_attribute_at_root_level_in_expression - 1]
+## Input
+
+```
+{!href ? <button slot={slotName}>Button</button> : <a href={href} slot={slotName}>Link</a>}
+```
+
+## Output
+
+```js
+import {
+  Fragment,
+  render as $$render,
+  createAstro as $$createAstro,
+  createComponent as $$createComponent,
+  renderComponent as $$renderComponent,
+  renderHead as $$renderHead,
+  maybeRenderHead as $$maybeRenderHead,
+  unescapeHTML as $$unescapeHTML,
+  renderSlot as $$renderSlot,
+  mergeSlots as $$mergeSlots,
+  addAttribute as $$addAttribute,
+  spreadAttributes as $$spreadAttributes,
+  defineStyleVars as $$defineStyleVars,
+  defineScriptVars as $$defineScriptVars,
+  renderTransition as $$renderTransition,
+  createTransitionScope as $$createTransitionScope,
+  renderScript as $$renderScript,
+  createMetadata as $$createMetadata
+} from "http://localhost:3000/";
+
+export const $$metadata = $$createMetadata(import.meta.url, { modules: [], hydratedComponents: [], clientOnlyComponents: [], hydrationDirectives: new Set([]), hoisted: [] });
+
+const $$Component = $$createComponent(($$result, $$props, $$slots) => {
+
+return $$render`${!href ? $$render`${$$maybeRenderHead($$result)}<button${$$addAttribute(slotName, "slot")}>Button</button>` : $$render`<a${$$addAttribute(href, "href")}${$$addAttribute(slotName, "slot")}>Link</a>`}`;
+}, undefined, undefined);
+export default $$Component;
+```
+---
diff --git a/.../__printer_js__/Preserve_slot_attribute_in_conditional_expression_for_custom_element.snap b/.../__printer_js__/Preserve_slot_attribute_in_conditional_expression_for_custom_element.snap
@@ -0,0 +1,41 @@
+
+[TestPrinter/Preserve_slot_attribute_in_conditional_expression_for_custom_element - 1]
+## Input
+
+```
+<body><my-element>{show && <div slot="content">Content</div>}</my-element></body>
+```
+
+## Output
+
+```js
+import {
+  Fragment,
+  render as $$render,
+  createAstro as $$createAstro,
+  createComponent as $$createComponent,
+  renderComponent as $$renderComponent,
+  renderHead as $$renderHead,
+  maybeRenderHead as $$maybeRenderHead,
+  unescapeHTML as $$unescapeHTML,
+  renderSlot as $$renderSlot,
+  mergeSlots as $$mergeSlots,
+  addAttribute as $$addAttribute,
+  spreadAttributes as $$spreadAttributes,
+  defineStyleVars as $$defineStyleVars,
+  defineScriptVars as $$defineScriptVars,
+  renderTransition as $$renderTransition,
+  createTransitionScope as $$createTransitionScope,
+  renderScript as $$renderScript,
+  createMetadata as $$createMetadata
+} from "http://localhost:3000/";
+
+export const $$metadata = $$createMetadata(import.meta.url, { modules: [], hydratedComponents: [], clientOnlyComponents: [], hydrationDirectives: new Set([]), hoisted: [] });
+
+const $$Component = $$createComponent(($$result, $$props, $$slots) => {
+
+return $$render`${$$maybeRenderHead($$result)}<body>${$$renderComponent($$result,'my-element','my-element',{},{"default": () => $$render`${show && $$render`<div slot="content">Content</div>`}`,})}</body>`;
+}, undefined, undefined);
+export default $$Component;
+```
+---
diff --git a/...rnal/printer/__printer_js__/Preserve_slot_attribute_in_expression_for_custom_element.snap b/...rnal/printer/__printer_js__/Preserve_slot_attribute_in_expression_for_custom_element.snap
@@ -0,0 +1,41 @@
+
+[TestPrinter/Preserve_slot_attribute_in_expression_for_custom_element - 1]
+## Input
+
+```
+<body><my-element>{!href ? <button slot={slotName}>Button</button> : <a href={href} slot={slotName}>Link</a>}</my-element></body>
+```
+
+## Output
+
+```js
+import {
+  Fragment,
+  render as $$render,
+  createAstro as $$createAstro,
+  createComponent as $$createComponent,
+  renderComponent as $$renderComponent,
+  renderHead as $$renderHead,
+  maybeRenderHead as $$maybeRenderHead,
+  unescapeHTML as $$unescapeHTML,
+  renderSlot as $$renderSlot,
+  mergeSlots as $$mergeSlots,
+  addAttribute as $$addAttribute,
+  spreadAttributes as $$spreadAttributes,
+  defineStyleVars as $$defineStyleVars,
+  defineScriptVars as $$defineScriptVars,
+  renderTransition as $$renderTransition,
+  createTransitionScope as $$createTransitionScope,
+  renderScript as $$renderScript,
+  createMetadata as $$createMetadata
+} from "http://localhost:3000/";
+
+export const $$metadata = $$createMetadata(import.meta.url, { modules: [], hydratedComponents: [], clientOnlyComponents: [], hydrationDirectives: new Set([]), hoisted: [] });
+
+const $$Component = $$createComponent(($$result, $$props, $$slots) => {
+
+return $$render`${$$maybeRenderHead($$result)}<body>${$$renderComponent($$result,'my-element','my-element',{},{"default": () => $$render`${!href ? $$render`<button${$$addAttribute(slotName, "slot")}>Button</button>` : $$render`<a${$$addAttribute(href, "href")}${$$addAttribute(slotName, "slot")}>Link</a>`}`,})}</body>`;
+}, undefined, undefined);
+export default $$Component;
+```
+---
diff --git a/internal/printer/print-to-js.go b/internal/printer/print-to-js.go
@@ -482,11 +482,18 @@ func render1(p *printer, n *Node, opts RenderOptions) {
 			}
 
 			if a.Key == "slot" {
-				if n.Parent.Component || n.Parent.Expression {
+				// Walk up the tree to find the nearest non-Expression ancestor
+				// to determine if we're inside an Astro Component (slot should be stripped)
+				// or a CustomElement/regular HTML (slot should be preserved)
+				parent := n.Parent
+				for parent != nil && parent.Expression {
+					parent = parent.Parent
+				}
+				if parent != nil && parent.Component {
 					continue
 				}
 				// Note: if we encounter "slot" NOT inside a component, that's fine
-				// These should be preserved in the output
+				// These should be preserved in the output (e.g., for web components)
 				p.printAttribute(a, n)
 			} else if a.Key == "data-astro-source-file" {
 				p.printAttribute(a, n)

diff --git a/internal/printer/printer_test.go b/internal/printer/printer_test.go
@@ -1208,25 +1208,37 @@ import { Container, Col, Row } from 'react-bootstrap';
 			source: `<body><Component><Fragment slot=named><div>Default</div><div>Named</div></Fragment></Component></body>`,
 		},
 		{
-			name:  "Fragment with await",
+			name:   "Fragment with await",
 			source: `<body><Fragment> { await Promise.resolve("Awaited") } </Fragment></body>`,
 		},
 		{
-			name:  "Fragment shorthand with await",
+			name:   "Fragment shorthand with await",
 			source: `<body><> { await Promise.resolve("Awaited") } </></body>`,
 		},
 		{
-			name:  "Fragment wrapping link with awaited href",
+			name:   "Fragment wrapping link with awaited href",
 			source: `<head><Fragment><link rel="preload" href={(await import('../fonts/some-font.woff2')).default} as="font" crossorigin /></Fragment></head>`,
 		},
 		{
-			name:  "Component with await",
+			name:   "Component with await",
 			source: `<body><Component> { await Promise.resolve("Awaited") } </Component></body>`,
 		},
 		{
 			name:   "Preserve slots inside custom-element",
 			source: `<body><my-element><div slot=name>Name</div><div>Default</div></my-element></body>`,
 		},
+		{
+			name:   "Preserve slot attribute in expression for custom element",
+			source: `<body><my-element>{!href ? <button slot={slotName}>Button</button> : <a href={href} slot={slotName}>Link</a>}</my-element></body>`,
+		},
+		{
+			name:   "Preserve slot attribute in conditional expression for custom element",
+			source: `<body><my-element>{show && <div slot="content">Content</div>}</my-element></body>`,
+		},
+		{
+			name:   "Preserve slot attribute at root level in expression",
+			source: `{!href ? <button slot={slotName}>Button</button> : <a href={href} slot={slotName}>Link</a>}`,
+		},
 		{
 			name:   "Preserve namespaces",
 			source: `<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"><rect xlink:href="#id"></svg>`,