fix: raise on unsupported query expressions

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Changed
+
+- **Unsupported Query Expressions Raise** - An expression the adapter cannot translate now raises `Ecto.QueryError` ("unsupported expression ...") instead of being rendered as a `?` placeholder, which bound the wrong parameter in its place and silently changed the query.
+
 ## [0.9.1] - 2026-05-07
 
 ### Fixed

lib/ecto/adapters/libsql/connection.ex

@@ -1384,9 +1384,12 @@ defmodule Ecto.Adapters.LibSql.Connection do
   defp expr(false, _sources, _query), do: "0"
   defp expr(nil, _sources, _query), do: "NULL"
 
-  # Default fallback for unsupported expressions
-  defp expr(_expr, _sources, _query) do
-    "?"
+  # Unsupported expressions raise: rendering them as a placeholder would bind
+  # the next parameter in their place and silently change the query.
+  defp expr(expr, _sources, query) do
+    raise Ecto.QueryError,
+      query: query,
+      message: "unsupported expression #{inspect(expr)}"
   end
 
   defp combination(%{combinations: []}, _as_prefix), do: []

test/in_expression_comprehensive_test.exs

@@ -507,4 +507,14 @@ defmodule EctoLibSql.InExpressionComprehensiveTest do
       assert "item3" in result
     end
   end
+
+  describe "unsupported expressions" do
+    test "raise instead of being rendered as a \"?\" placeholder" do
+      query = from(t in "test_items", where: ilike(t.name, "job%"), select: t.name)
+
+      assert_raise Ecto.QueryError, ~r/unsupported expression/, fn ->
+        Ecto.Adapters.SQL.to_sql(:all, TestRepo, query)
+      end
+    end
+  end
 end