fix: false positives for builtin $$ vars in svelte/no-immutable-reactive-statements (#465)

Author: ota-meshi

.changeset/empty-badgers-learn.md

@@ -0,0 +1,5 @@
+---
+"eslint-plugin-svelte": patch
+---
+
+fix: false positives for builtin `$$` vars in `svelte/no-immutable-reactive-statements`

src/rules/no-immutable-reactive-statements.ts

@@ -136,15 +136,19 @@ export default createRule("no-immutable-reactive-statements", {
             return
           }
         }
-        if (
-          globalScope.through.some(
-            (reference) =>
-              node.range[0] <= reference.identifier.range[0] &&
-              reference.identifier.range[1] <= node.range[1],
-          )
-        ) {
-          // Do not report if there are missing references.
-          return
+        for (const through of toplevelScope.through.filter(
+          (reference) =>
+            node.range[0] <= reference.identifier.range[0] &&
+            reference.identifier.range[1] <= node.range[1],
+        )) {
+          if (through.identifier.name.startsWith("$$")) {
+            // Builtin `$$` vars
+            return
+          }
+          if (through.resolved == null) {
+            // Do not report if there are missing references.
+            return
+          }
         }
 
         context.report({

tests/fixtures/rules/no-immutable-reactive-statements/valid/builtin-vars01-input.svelte

@@ -0,0 +1,11 @@
+<script>
+  $: desc = $$slots.description
+</script>
+
+<div>
+  <slot name="title" />
+  {#if desc}
+    <hr />
+    <slot name="description" />
+  {/if}
+</div>

tests/fixtures/rules/no-immutable-reactive-statements/valid/builtin-vars02-input.svelte

@@ -0,0 +1,7 @@
+<script>
+  $: prop = $$props.prop
+  $: type = $$restProps.type
+</script>
+
+<Widget {prop} />
+<input {type} />