fix: translate exists/1 subqueries

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]
+
+### Fixed
+
+- **`exists/1` Subqueries** - `exists(subquery)` had no `expr/3` clause and fell through to the catch-all, which rendered it as a bare `?` placeholder. The next bound parameter then stood in for the whole condition, so the filter silently matched every row or none depending on its value (for example, the policies Ash Framework expresses with `exists(...)` let every actor through). It is now translated to `exists(SELECT ...)`, as in the `ecto_sqlite3` adapter.
+
 ## [0.9.1] - 2026-05-07
 
 ### Fixed

lib/ecto/adapters/libsql/connection.ex

@@ -1359,6 +1359,11 @@ defmodule Ecto.Adapters.LibSql.Connection do
     expr(value, sources, query)
   end
 
+  # EXISTS subquery: exists(subquery) -> exists(SELECT ...)
+  defp expr({:exists, _, [subquery]}, sources, query) do
+    ["exists", expr(subquery, sources, query)]
+  end
+
   # SubQuery expression - generates inline SQL subquery
   defp expr(%Ecto.SubQuery{query: query}, sources, parent_query) do
     combinations =

test/in_expression_comprehensive_test.exs

@@ -507,4 +507,61 @@ defmodule EctoLibSql.InExpressionComprehensiveTest do
       assert "item3" in result
     end
   end
+
+  describe "exists/1" do
+    test "keeps every row when the subquery matches, none otherwise" do
+      Ecto.Adapters.SQL.query!(TestRepo, """
+      INSERT INTO test_items (id, state, name, inserted_at, updated_at)
+      VALUES (1, 'scheduled', 'job1', datetime('now'), datetime('now')),
+             (2, 'completed', 'job2', datetime('now'), datetime('now'))
+      """)
+
+      Ecto.Adapters.SQL.query!(TestRepo, """
+      INSERT INTO archived_items (item_id, state, name, inserted_at, updated_at)
+      VALUES (1, 'archived', 'job1_archived', datetime('now'), datetime('now'))
+      """)
+
+      # BEFORE FIX: exists/1 fell through to the catch-all expr clause, so the
+      # whole condition became "WHERE (?)": the parameter bound in its place
+      # matched every row or none depending on its value.
+      query = fn state ->
+        from(t in "test_items",
+          where: exists(from(a in "archived_items", where: a.state == ^state, select: 1)),
+          select: t.name,
+          order_by: t.name
+        )
+      end
+
+      {sql, _params} = Ecto.Adapters.SQL.to_sql(:all, TestRepo, query.("archived"))
+      assert sql =~ "WHERE (exists(SELECT "
+
+      assert TestRepo.all(query.("archived")) == ["job1", "job2"]
+      # "1" alone would have been read as true.
+      assert TestRepo.all(query.("1")) == []
+    end
+
+    test "negated" do
+      Ecto.Adapters.SQL.query!(TestRepo, """
+      INSERT INTO test_items (id, state, name, inserted_at, updated_at)
+      VALUES (1, 'scheduled', 'job1', datetime('now'), datetime('now')),
+             (2, 'completed', 'job2', datetime('now'), datetime('now'))
+      """)
+
+      Ecto.Adapters.SQL.query!(TestRepo, """
+      INSERT INTO archived_items (item_id, state, name, inserted_at, updated_at)
+      VALUES (1, 'archived', 'job1_archived', datetime('now'), datetime('now'))
+      """)
+
+      query = fn state ->
+        from(t in "test_items",
+          where: not exists(from(a in "archived_items", where: a.state == ^state, select: 1)),
+          select: t.name,
+          order_by: t.name
+        )
+      end
+
+      assert TestRepo.all(query.("archived")) == []
+      assert TestRepo.all(query.("deleted")) == ["job1", "job2"]
+    end
+  end
 end