Add build tag to skip default PG type registration

https://github.com/jackc/pgx/issues/1273#issuecomment-1207338136

pgtype/doc.go

@@ -139,5 +139,13 @@ implementing NumericScanner and passes that to the Codec.
 Map.Scan and Map.Encode are convenience methods that wrap Map.PlanScan and Map.PlanEncode.  Determining how to scan or
 encode a particular type may be a time consuming operation. Hence the planning and execution steps of a conversion are
 internally separated.
+
+Reducing Compiled Binary Size
+
+pgx.QueryExecModeExec and pgx.QueryExecModeSimpleProtocol require the default PostgreSQL type to be registered for each
+Go type used as a query parameter. By default pgx does this for all supported types and their array variants. If an
+application does not use those query execution modes or manually registers the default PostgreSQL type for the types it
+uses as query parameters it can use the build tag nopgxregisterdefaulttypes. This omits the default type registration
+and reduces the compiled binary size by ~2MB.
 */
 package pgtype

pgtype/pgtype.go

@@ -410,38 +410,6 @@ func NewMap() *Map {
 	return m
 }
 
-func registerDefaultPgTypeVariants[T any](m *Map, name string) {
-	arrayName := "_" + name
-
-	var value T
-	m.RegisterDefaultPgType(value, name)  // T
-	m.RegisterDefaultPgType(&value, name) // *T
-
-	var sliceT []T
-	m.RegisterDefaultPgType(sliceT, arrayName)  // []T
-	m.RegisterDefaultPgType(&sliceT, arrayName) // *[]T
-
-	var slicePtrT []*T
-	m.RegisterDefaultPgType(slicePtrT, arrayName)  // []*T
-	m.RegisterDefaultPgType(&slicePtrT, arrayName) // *[]*T
-
-	var arrayOfT Array[T]
-	m.RegisterDefaultPgType(arrayOfT, arrayName)  // Array[T]
-	m.RegisterDefaultPgType(&arrayOfT, arrayName) // *Array[T]
-
-	var arrayOfPtrT Array[*T]
-	m.RegisterDefaultPgType(arrayOfPtrT, arrayName)  // Array[*T]
-	m.RegisterDefaultPgType(&arrayOfPtrT, arrayName) // *Array[*T]
-
-	var flatArrayOfT FlatArray[T]
-	m.RegisterDefaultPgType(flatArrayOfT, arrayName)  // FlatArray[T]
-	m.RegisterDefaultPgType(&flatArrayOfT, arrayName) // *FlatArray[T]
-
-	var flatArrayOfPtrT FlatArray[*T]
-	m.RegisterDefaultPgType(flatArrayOfPtrT, arrayName)  // FlatArray[*T]
-	m.RegisterDefaultPgType(&flatArrayOfPtrT, arrayName) // *FlatArray[*T]
-}
-
 func (m *Map) RegisterType(t *Type) {
 	m.oidToType[t.OID] = t
 	m.nameToType[t.Name] = t

pgtype/register_default_pg_types.go

@@ -0,0 +1,35 @@
+//go:build !nopgxregisterdefaulttypes
+
+package pgtype
+
+func registerDefaultPgTypeVariants[T any](m *Map, name string) {
+	arrayName := "_" + name
+
+	var value T
+	m.RegisterDefaultPgType(value, name)  // T
+	m.RegisterDefaultPgType(&value, name) // *T
+
+	var sliceT []T
+	m.RegisterDefaultPgType(sliceT, arrayName)  // []T
+	m.RegisterDefaultPgType(&sliceT, arrayName) // *[]T
+
+	var slicePtrT []*T
+	m.RegisterDefaultPgType(slicePtrT, arrayName)  // []*T
+	m.RegisterDefaultPgType(&slicePtrT, arrayName) // *[]*T
+
+	var arrayOfT Array[T]
+	m.RegisterDefaultPgType(arrayOfT, arrayName)  // Array[T]
+	m.RegisterDefaultPgType(&arrayOfT, arrayName) // *Array[T]
+
+	var arrayOfPtrT Array[*T]
+	m.RegisterDefaultPgType(arrayOfPtrT, arrayName)  // Array[*T]
+	m.RegisterDefaultPgType(&arrayOfPtrT, arrayName) // *Array[*T]
+
+	var flatArrayOfT FlatArray[T]
+	m.RegisterDefaultPgType(flatArrayOfT, arrayName)  // FlatArray[T]
+	m.RegisterDefaultPgType(&flatArrayOfT, arrayName) // *FlatArray[T]
+
+	var flatArrayOfPtrT FlatArray[*T]
+	m.RegisterDefaultPgType(flatArrayOfPtrT, arrayName)  // FlatArray[*T]
+	m.RegisterDefaultPgType(&flatArrayOfPtrT, arrayName) // *FlatArray[*T]
+}

pgtype/register_default_pg_types_disabled.go

@@ -0,0 +1,6 @@
+//go:build nopgxregisterdefaulttypes
+
+package pgtype
+
+func registerDefaultPgTypeVariants[T any](m *Map, name string) {
+}