sql: properly report information_schema functions in metadata

Prior to this patch, the `information_schema` functions were listed
with the `information_schema.` prefix in the pg_catalog namespace.
This was incorrect and caused confusion during tab completion.

Release note (bug fix): The compatibility scalar functions in
`information_schema` are now listed in the proper namespace in
`pg_catalog.pg_proc`.

pkg/cli/clisqlshell/testdata/complete/composite_names

@@ -63,3 +63,12 @@ select "PG_CATALOG".@
 complete 0 20
 msg: ""
 (no completions generated)
+
+complete
+select information_schema . _pg_index@
+----
+complete 0 37
+msg: ""
+completions:
+- "functions":
+  "information_schema._pg_index_position(" (Not usable; exposed only for compatibility with PostgreSQL) -> "information_schema._pg_index_position(" (0, 30)

pkg/cli/clisqlshell/testdata/complete/sql

@@ -19,7 +19,7 @@ completions:
   "\"extract_duration\"(" ((from schema pg_catalog) Extracts `element` from `input`) -> "\"extract_duration\"(" (0, 0)
   "\"family\"(" ((from schema pg_catalog) Extracts the IP family of the value; 4 for IPv4, 6 for IPv6) -> "\"family\"(" (0, 0)
   "\"greatest\"(" ((from schema pg_catalog) Returns the element with the greatest value) -> "\"greatest\"(" (0, 0)
-  "\"information_schema._pg_char_max_length\"(" ((from schema pg_catalog) Not usable; exposed only for compatibility with PostgreSQL) -> "\"information_schema._pg_char_max_length\"(" (0, 0)
+  "\"least\"(" ((from schema pg_catalog) Returns the element with the lowest value) -> "\"least\"(" (0, 0)
   ... entries omitted ...
 - "keyword":
   "ABORT" (unreserved) -> "ABORT" (0, 0)

pkg/sql/crdb_internal.go

@@ -2753,9 +2753,13 @@ CREATE TABLE crdb_internal.builtin_functions (
 			props, overloads := builtinsregistry.GetBuiltinProperties(name)
 			schema := catconstants.PgCatalogName
 			const crdbInternal = catconstants.CRDBInternalSchemaName + "."
+			const infoSchema = catconstants.InformationSchemaName + "."
 			if strings.HasPrefix(name, crdbInternal) {
 				name = name[len(crdbInternal):]
 				schema = catconstants.CRDBInternalSchemaName
+			} else if strings.HasPrefix(name, infoSchema) {
+				name = name[len(infoSchema):]
+				schema = catconstants.InformationSchemaName
 			}
 			for _, f := range overloads {
 				if err := addRow(

pkg/sql/pg_catalog.go

@@ -2357,9 +2357,13 @@ func addPgProcBuiltinRow(name string, addRow func(...tree.Datum) error) error {
 	_, overloads := builtinsregistry.GetBuiltinProperties(name)
 	nspOid := tree.NewDOid(catconstants.PgCatalogID)
 	const crdbInternal = catconstants.CRDBInternalSchemaName + "."
+	const infoSchema = catconstants.InformationSchemaName + "."
 	if strings.HasPrefix(name, crdbInternal) {
 		nspOid = tree.NewDOid(catconstants.CrdbInternalID)
 		name = name[len(crdbInternal):]
+	} else if strings.HasPrefix(name, infoSchema) {
+		nspOid = tree.NewDOid(catconstants.InformationSchemaID)
+		name = name[len(infoSchema):]
 	}
 
 	for _, builtin := range overloads {