Add Expression Indexes and Operator Classes support for PostgreSQL

Example:

    create_table :users do |t|
      t.string :name
      t.index 'lower(name) varchar_pattern_ops'
    end

Fixes #19090.
Fixes #21765.
Fixes #21819.
Fixes #24359.

Signed-off-by: Jeremy Daer <jeremydaer@gmail.com>

4 files changed, 46 insertions, 18 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index f65dc4ed5a..99a3e99bdc 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -1110,15 +1110,19 @@ module ActiveRecord
         Table.new(table_name, base)
       end
 
-      def add_index_options(table_name, column_name, comment: nil, **options) #:nodoc:
-        column_names = Array(column_name)
+      def add_index_options(table_name, column_name, comment: nil, **options) # :nodoc:
+        if column_name.is_a?(String) && /\W/ === column_name
+          column_names = column_name
+        else
+          column_names = Array(column_name)
+        end
 
         options.assert_valid_keys(:unique, :order, :name, :where, :length, :internal, :using, :algorithm, :type)
 
         index_type = options[:type].to_s if options.key?(:type)
         index_type ||= options[:unique] ? "UNIQUE" : ""
         index_name = options[:name].to_s if options.key?(:name)
-        index_name ||= index_name(table_name, column: column_names)
+        index_name ||= index_name(table_name, index_name_options(column_names))
         max_index_length = options.fetch(:internal, false) ? index_name_length : allowed_index_name_length
 
         if options.key?(:algorithm)
@@ -1174,6 +1178,8 @@ module ActiveRecord
 
         # Overridden by the MySQL adapter for supporting index lengths
         def quoted_columns_for_index(column_names, options = {})
+          return [column_names] if column_names.is_a?(String)
+
           option_strings = Hash[column_names.map {|name| [name, '']}]
 
           # add index sort order if supported
@@ -1249,6 +1255,14 @@ module ActiveRecord
         AlterTable.new create_table_definition(name)
       end
 
+      def index_name_options(column_names) # :nodoc:
+        if column_names.is_a?(String)
+          column_names = column_names.scan(/\w+/).join('_')
+        end
+
+        { column: column_names }
+      end
+
       def foreign_key_name(table_name, options) # :nodoc:
         identifier = "#{table_name}_#{options.fetch(:column)}_fk"
         hashed_identifier = Digest::SHA256.hexdigest(identifier).first(10)
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 130c03dd1d..86de8f1ca0 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -248,6 +248,11 @@ module ActiveRecord
         false
       end
 
+      # Does this adapter support expression indices?
+      def supports_expression_index?
+        false
+      end
+
       # Does this adapter support explain?
       def supports_explain?
         false
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
index 272e6293ab..074ebb90a5 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -175,7 +175,10 @@ module ActiveRecord
 
           result = query(<<-SQL, 'SCHEMA')
             SELECT distinct i.relname, d.indisunique, d.indkey, pg_get_indexdef(d.indexrelid), t.oid,
-                            pg_catalog.obj_description(i.oid, 'pg_class') AS comment
+                            pg_catalog.obj_description(i.oid, 'pg_class') AS comment,
+            (SELECT COUNT(*) FROM pg_opclass o
+               JOIN (SELECT unnest(string_to_array(d.indclass::text, ' '))::int oid) c
+                 ON o.oid = c.oid WHERE o.opcdefault = 'f')
             FROM pg_class t
             INNER JOIN pg_index d ON t.oid = d.indrelid
             INNER JOIN pg_class i ON d.indexrelid = i.oid
@@ -194,25 +197,27 @@ module ActiveRecord
             inddef = row[3]
             oid = row[4]
             comment = row[5]
+            opclass = row[6]
 
-            columns = Hash[query(<<-SQL, "SCHEMA")]
-            SELECT a.attnum, a.attname
-            FROM pg_attribute a
-            WHERE a.attrelid = #{oid}
-            AND a.attnum IN (#{indkey.join(",")})
-            SQL
+            using, expressions, where = inddef.scan(/ USING (\w+?) \((.+?)\)(?: WHERE (.+))?\z/).flatten
 
-            column_names = columns.values_at(*indkey).compact
+            if indkey.include?(0) || opclass > 0
+              columns = expressions
+            else
+              columns = Hash[query(<<-SQL.strip_heredoc, "SCHEMA")].values_at(*indkey).compact
+                SELECT a.attnum, a.attname
+                FROM pg_attribute a
+                WHERE a.attrelid = #{oid}
+                AND a.attnum IN (#{indkey.join(",")})
+              SQL
 
-            unless column_names.empty?
               # add info on sort order for columns (only desc order is explicitly specified, asc is the default)
-              desc_order_columns = inddef.scan(/(\w+) DESC/).flatten
-              orders = desc_order_columns.any? ? Hash[desc_order_columns.map {|order_column| [order_column, :desc]}] : {}
-              where = inddef.scan(/WHERE (.+)$/).flatten[0]
-              using = inddef.scan(/USING (.+?) /).flatten[0].to_sym
-
-              IndexDefinition.new(table_name, index_name, unique, column_names, [], orders, where, nil, using, comment)
+              orders = Hash[
+                expressions.scan(/(\w+) DESC/).flatten.map { |order_column| [order_column, :desc] }
+              ]
             end
+
+            IndexDefinition.new(table_name, index_name, unique, columns, [], orders, where, nil, using.to_sym, comment)
           end.compact
         end
 
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index e397a28cac..39a2cbbda7 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -140,6 +140,10 @@ module ActiveRecord
         true
       end
 
+      def supports_expression_index?
+        true
+      end
+
       def supports_transaction_isolation?
         true
       end