Fix multiline expression indexes for postgresql (#31621)

activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb

@@ -107,7 +107,7 @@ def indexes(table_name) # :nodoc:
             oid = row[4]
             comment = row[5]
 
-            using, expressions, where = inddef.scan(/ USING (\w+?) \((.+?)\)(?: WHERE (.+))?\z/).flatten
+            using, expressions, where = inddef.scan(/ USING (\w+?) \((.+?)\)(?: WHERE (.+))?\z/m).flatten
 
             orders = {}
             opclasses = {}

activerecord/test/cases/schema_dumper_test.rb

@@ -298,7 +298,7 @@ def test_schema_dump_allows_array_of_decimal_defaults
 
     def test_schema_dump_expression_indices
       index_definition = dump_table_schema("companies").split(/\n/).grep(/t\.index.*company_expression_index/).first.strip
-      assert_equal 't.index "lower((name)::text)", name: "company_expression_index"', index_definition
+      assert_match %r{CASE.+lower\(\(name\)::text\)}i, index_definition
     end
 
     def test_schema_dump_interval_type

activerecord/test/schema/schema.rb

@@ -210,7 +210,7 @@
     t.index [:firm_id, :type, :rating], name: "company_index", length: { type: 10 }, order: { rating: :desc }
     t.index [:firm_id, :type], name: "company_partial_index", where: "(rating > 10)"
     t.index :name, name: "company_name_index", using: :btree
-    t.index "lower(name)", name: "company_expression_index" if supports_expression_index?
+    t.index "(CASE WHEN rating > 0 THEN lower(name) END)", name: "company_expression_index" if supports_expression_index?
   end
 
   create_table :content, force: true do |t|