From 0c5f05ab8c9942c255035a1d027eb7c9f14afb67 Mon Sep 17 00:00:00 2001
From: Cory Lynch <cjl2625@gmail.com>
Date: Thu, 21 May 2026 09:49:50 -0700
Subject: [PATCH] Fix: Don't rewrite_casts for for subclasses like JSONCast

Signed-off-by: Cory Lynch <cjl2625@gmail.com>
---
 sqlmesh/core/dialect.py    |  3 ++-
 tests/core/test_dialect.py | 23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/sqlmesh/core/dialect.py b/sqlmesh/core/dialect.py
index 2ac15c2a5c..add30d1189 100644
--- a/sqlmesh/core/dialect.py
+++ b/sqlmesh/core/dialect.py
@@ -774,7 +774,8 @@ def format_model_expressions(
     if rewrite_casts:
 
         def cast_to_colon(node: exp.Expr) -> exp.Expr:
-            if isinstance(node, exp.Cast) and not any(
+            # Directly check type instead of isinstance to avoid rewriting subclasses of CAST, e.g. JSONCast
+            if type(node) is exp.Cast and not any(
                 # Only convert CAST into :: if it doesn't have additional args set, otherwise this
                 # conversion could alter the semantics (eg. changing SAFE_CAST in BigQuery to CAST)
                 arg
diff --git a/tests/core/test_dialect.py b/tests/core/test_dialect.py
index 02068b1c59..3b8df28f8b 100644
--- a/tests/core/test_dialect.py
+++ b/tests/core/test_dialect.py
@@ -207,6 +207,29 @@ def test_format_model_expressions():
   SAFE_CAST('bla' AS INT64) AS FOO"""
     )
 
+    x = format_model_expressions(
+        parse(
+            """
+            MODEL(name a.b, kind FULL, dialect clickhouse);
+            SELECT data.:String AS foo, CAST(1 AS INT) AS bar
+            """
+        ),
+        dialect="clickhouse",
+    )
+    # JSONCast (e.g. `.:` syntax in ClickHouse) must not be written to `::`
+    assert (
+        x
+        == """MODEL (
+  name a.b,
+  kind FULL,
+  dialect clickhouse
+);
+
+SELECT
+  data.:String AS foo,
+  1::Int32 AS bar"""
+    )
+
     x = format_model_expressions(
         parse(
             """