From c52e9827a6893f034fc259f66530071795bd97dd Mon Sep 17 00:00:00 2001
From: paoloricciuti <ricciutipaolo@gmail.com>
Date: Mon, 21 Oct 2024 22:04:13 +0200
Subject: [PATCH] fix: migrate default slots to children snippet

---
 .changeset/five-dingos-push.md                         |  5 +++++
 packages/svelte/src/compiler/migrate/index.js          |  4 ++++
 .../tests/migrate/samples/slot-usages/input.svelte     |  8 ++++++++
 .../tests/migrate/samples/slot-usages/output.svelte    | 10 ++++++++++
 4 files changed, 27 insertions(+)
 create mode 100644 .changeset/five-dingos-push.md

diff --git a/.changeset/five-dingos-push.md b/.changeset/five-dingos-push.md
new file mode 100644
index 000000000000..f359f0a9fee3
--- /dev/null
+++ b/.changeset/five-dingos-push.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: migrate default slots to children snippet
diff --git a/packages/svelte/src/compiler/migrate/index.js b/packages/svelte/src/compiler/migrate/index.js
index 33a369b8c83a..c95b0734f97a 100644
--- a/packages/svelte/src/compiler/migrate/index.js
+++ b/packages/svelte/src/compiler/migrate/index.js
@@ -1152,6 +1152,10 @@ function migrate_slot_usage(node, path, state) {
 			is_text_attribute(attribute)
 		) {
 			snippet_name = attribute.value[0].data;
+			// the default slot in svelte 4 if what the children slot is for svelte 5
+			if (snippet_name === 'default') {
+				snippet_name = 'children';
+			}
 			if (!regex_is_valid_identifier.test(snippet_name)) {
 				has_migration_task = true;
 				state.str.appendLeft(
diff --git a/packages/svelte/tests/migrate/samples/slot-usages/input.svelte b/packages/svelte/tests/migrate/samples/slot-usages/input.svelte
index 5646174c4c64..248ff0ac1312 100644
--- a/packages/svelte/tests/migrate/samples/slot-usages/input.svelte
+++ b/packages/svelte/tests/migrate/samples/slot-usages/input.svelte
@@ -77,6 +77,14 @@
     <div slot="bar">bar</div>
 </Component>
 
+<Component>
+	<span slot="default">should be children</span>
+</Component>
+
+<Component>
+	<span slot="default" let:with_prop>should be children {with_prop} too</span>
+</Component>
+
 <c-e>
     <div slot="named">unchanged</div>
 </c-e>
diff --git a/packages/svelte/tests/migrate/samples/slot-usages/output.svelte b/packages/svelte/tests/migrate/samples/slot-usages/output.svelte
index 42e219a567f8..d2aea33c83ec 100644
--- a/packages/svelte/tests/migrate/samples/slot-usages/output.svelte
+++ b/packages/svelte/tests/migrate/samples/slot-usages/output.svelte
@@ -121,6 +121,16 @@
     {/snippet}
 </Component>
 
+<Component>
+	<span >should be children</span>
+</Component>
+
+<Component>
+	<span  >{#snippet children({ with_prop })}
+                should be children {with_prop} too            {/snippet}
+        </span>
+</Component>
+
 <c-e>
     <div slot="named">unchanged</div>
 </c-e>
\ No newline at end of file