From 1b3e935fdd78e80178d1491024c9413870d8d870 Mon Sep 17 00:00:00 2001
From: Samuel de Rougemont <nandan108@gmail.com>
Date: Sun, 11 Oct 2026 22:28:52 +0200
Subject: [PATCH] Fix a warning for a foreign key referencing a table with a
 shorter unique key

When looking for the unique constraint that a foreign key references, each
unique index of the referenced table is checked for having the referenced
columns as a prefix. An index with fewer columns than the foreign key was
read past its end, raising "Undefined array key" warnings.

Skip indexes that are shorter than the column list of the reference.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 ...s-wp-sqlite-information-schema-builder.php |  5 ++++
 .../WP_MySQL_On_SQLite_Metadata_Tests.php     | 29 +++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/packages/mysql-on-sqlite/src/sqlite/class-wp-sqlite-information-schema-builder.php b/packages/mysql-on-sqlite/src/sqlite/class-wp-sqlite-information-schema-builder.php
index 12b34be10..af5b73287 100644
--- a/packages/mysql-on-sqlite/src/sqlite/class-wp-sqlite-information-schema-builder.php
+++ b/packages/mysql-on-sqlite/src/sqlite/class-wp-sqlite-information-schema-builder.php
@@ -1802,6 +1802,11 @@ private function extract_referential_constraint_data( WP_Parser_Node $node, stri
 		// Find which index includes referenced column names as a prefix.
 		$unique_constraint_name = null;
 		foreach ( $index_columns_map as $index_name => $index_columns ) {
+			// An index with fewer columns than the reference can't have them as a prefix.
+			if ( count( $index_columns ) < count( $reference_parts ) ) {
+				continue;
+			}
+
 			$is_prefix = true;
 			foreach ( $reference_parts as $i => $reference_part ) {
 				if ( $index_columns[ $i ] !== $this->get_value( $reference_part ) ) {
diff --git a/packages/mysql-on-sqlite/tests/WP_MySQL_On_SQLite_Metadata_Tests.php b/packages/mysql-on-sqlite/tests/WP_MySQL_On_SQLite_Metadata_Tests.php
index e8a8f4d33..7dfb79548 100644
--- a/packages/mysql-on-sqlite/tests/WP_MySQL_On_SQLite_Metadata_Tests.php
+++ b/packages/mysql-on-sqlite/tests/WP_MySQL_On_SQLite_Metadata_Tests.php
@@ -1914,6 +1914,35 @@ public function testInformationSchemaForeignKeysWithMultipleColumns(): void {
 		);
 	}
 
+	public function testInformationSchemaForeignKeysReferencingShorterUniqueKey(): void {
+		// The referenced table also has a unique key with fewer columns than the reference.
+		$this->assertQuery(
+			'CREATE TABLE t1 (
+				id INT,
+				name VARCHAR(255),
+				UNIQUE KEY u_id (id),
+				UNIQUE KEY u_id_name (id, name)
+			)'
+		);
+		$this->assertQuery(
+			'CREATE TABLE t2 (
+				id INT,
+				name VARCHAR(255),
+				FOREIGN KEY (id, name) REFERENCES t1 (id, name)
+			)'
+		);
+
+		$result = $this->assertQuery( "SELECT unique_constraint_name FROM information_schema.referential_constraints WHERE table_name = 't2'" );
+		$this->assertEquals(
+			array(
+				(object) array(
+					'UNIQUE_CONSTRAINT_NAME' => 'u_id_name',
+				),
+			),
+			$result
+		);
+	}
+
 	public function testInformationSchemaAlterTableAddForeignKeys(): void {
 		$this->assertQuery( 'CREATE TABLE t1 (id INT PRIMARY KEY, name VARCHAR(255))' );
 		$this->assertQuery( 'CREATE TABLE t2 (id INT)' );