From d95d0dd792aa4f081773a56423f5c5f81b6e4a00 Mon Sep 17 00:00:00 2001
From: sravan27 <sridharsravan@live.com>
Date: Thu, 21 May 2026 09:56:46 +0530
Subject: [PATCH] Fix Sync Streams iif arity validation

---
 .changeset/fix-sync-streams-iif-arity.md         |  5 +++++
 packages/sync-rules/src/sync_plan/expression.ts  |  2 +-
 .../sync-rules/test/src/compiler/sqlite.test.ts  | 16 ++++++++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/fix-sync-streams-iif-arity.md

diff --git a/.changeset/fix-sync-streams-iif-arity.md b/.changeset/fix-sync-streams-iif-arity.md
new file mode 100644
index 000000000..6b5e48cc6
--- /dev/null
+++ b/.changeset/fix-sync-streams-iif-arity.md
@@ -0,0 +1,5 @@
+---
+'@powersync/service-sync-rules': patch
+---
+
+Validate `iif()` calls with the same three-argument arity used by the sync stream evaluator.
diff --git a/packages/sync-rules/src/sync_plan/expression.ts b/packages/sync-rules/src/sync_plan/expression.ts
index 9997bf5aa..ddce6db1d 100644
--- a/packages/sync-rules/src/sync_plan/expression.ts
+++ b/packages/sync-rules/src/sync_plan/expression.ts
@@ -143,7 +143,7 @@ export const supportedFunctions: Record<string, ArgumentCount> = {
   hex: 1,
   ifnull: { min: 2 },
   //if: { min: 2 },
-  iif: { min: 2 },
+  iif: 3,
   instr: 2,
   length: 1,
   // TODO: Establish defaults for case sensitivity, changing escape characters, ICU support.
diff --git a/packages/sync-rules/test/src/compiler/sqlite.test.ts b/packages/sync-rules/test/src/compiler/sqlite.test.ts
index 8c873d3d1..8f7eea9f0 100644
--- a/packages/sync-rules/test/src/compiler/sqlite.test.ts
+++ b/packages/sync-rules/test/src/compiler/sqlite.test.ts
@@ -85,6 +85,22 @@ describe('sqlite conversion', () => {
         ]);
       });
 
+      test('iif requires exactly three args', () => {
+        expect(translate('iif(1, 2)')[1]).toStrictEqual([
+          {
+            message: 'Expected at least 3 arguments',
+            source: 'iif(1, 2)'
+          }
+        ]);
+
+        expect(translate('iif(1, 2, 3, 4)')[1]).toStrictEqual([
+          {
+            message: 'Expected at most 3 arguments',
+            source: 'iif(1, 2, 3, 4)'
+          }
+        ]);
+      });
+
       test.skip('must be even', () => {
         expect(translate("json_object('foo')")[1]).toStrictEqual([
           {