From ed7b51feef6d36dda765d15a0aaad22b3227eb20 Mon Sep 17 00:00:00 2001 From: Michael Stapelberg Date: Fri, 23 Aug 2024 10:46:33 +0200 Subject: [PATCH] proto: extend documentation of GetExtension, SetExtension MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Document the type mapping and the recommended pattern for working with extensions. This documentation was Google-internal (cl/335451491), presumably because of the reference to static analysis tools that don’t exist outside. Compared to the internal version, this CL uses “should” instead of “must”. Change-Id: I9293c10b2f6f91c9546d145c94b52e84f3a7a9c9 Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/607995 LUCI-TryBot-Result: Go LUCI Reviewed-by: Damien Neil Reviewed-by: Christian Höppner --- proto/extension.go | 71 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 71 insertions(+) diff --git a/proto/extension.go b/proto/extension.go index d248f2928..78445d116 100644 --- a/proto/extension.go +++ b/proto/extension.go @@ -39,6 +39,48 @@ func ClearExtension(m Message, xt protoreflect.ExtensionType) { // If the field is unpopulated, it returns the default value for // scalars and an immutable, empty value for lists or messages. // It panics if xt does not extend m. +// +// The type of the value is dependent on the field type of the extension. +// For extensions generated by protoc-gen-go, the Go type is as follows: +// +// ╔═══════════════════╤═════════════════════════╗ +// ║ Go type │ Protobuf kind ║ +// ╠═══════════════════╪═════════════════════════╣ +// ║ bool │ bool ║ +// ║ int32 │ int32, sint32, sfixed32 ║ +// ║ int64 │ int64, sint64, sfixed64 ║ +// ║ uint32 │ uint32, fixed32 ║ +// ║ uint64 │ uint64, fixed64 ║ +// ║ float32 │ float ║ +// ║ float64 │ double ║ +// ║ string │ string ║ +// ║ []byte │ bytes ║ +// ║ protoreflect.Enum │ enum ║ +// ║ proto.Message │ message, group ║ +// ╚═══════════════════╧═════════════════════════╝ +// +// The protoreflect.Enum and proto.Message types are the concrete Go type +// associated with the named enum or message. Repeated fields are represented +// using a Go slice of the base element type. +// +// If a generated extension descriptor variable is directly passed to +// GetExtension, then the call should be followed immediately by a +// type assertion to the expected output value. For example: +// +// mm := proto.GetExtension(m, foopb.E_MyExtension).(*foopb.MyMessage) +// +// This pattern enables static analysis tools to verify that the asserted type +// matches the Go type associated with the extension field and +// also enables a possible future migration to a type-safe extension API. +// +// Since singular messages are the most common extension type, the pattern of +// calling HasExtension followed by GetExtension may be simplified to: +// +// if mm := proto.GetExtension(m, foopb.E_MyExtension).(*foopb.MyMessage); mm != nil { +// ... // make use of mm +// } +// +// The mm variable is non-nil if and only if HasExtension reports true. func GetExtension(m Message, xt protoreflect.ExtensionType) any { // Treat nil message interface as an empty message; return the default. if m == nil { @@ -51,6 +93,35 @@ func GetExtension(m Message, xt protoreflect.ExtensionType) any { // SetExtension stores the value of an extension field. // It panics if m is invalid, xt does not extend m, or if type of v // is invalid for the specified extension field. +// +// The type of the value is dependent on the field type of the extension. +// For extensions generated by protoc-gen-go, the Go type is as follows: +// +// ╔═══════════════════╤═════════════════════════╗ +// ║ Go type │ Protobuf kind ║ +// ╠═══════════════════╪═════════════════════════╣ +// ║ bool │ bool ║ +// ║ int32 │ int32, sint32, sfixed32 ║ +// ║ int64 │ int64, sint64, sfixed64 ║ +// ║ uint32 │ uint32, fixed32 ║ +// ║ uint64 │ uint64, fixed64 ║ +// ║ float32 │ float ║ +// ║ float64 │ double ║ +// ║ string │ string ║ +// ║ []byte │ bytes ║ +// ║ protoreflect.Enum │ enum ║ +// ║ proto.Message │ message, group ║ +// ╚═══════════════════╧═════════════════════════╝ +// +// The protoreflect.Enum and proto.Message types are the concrete Go type +// associated with the named enum or message. Repeated fields are represented +// using a Go slice of the base element type. +// +// If a generated extension descriptor variable is directly passed to +// SetExtension (e.g., foopb.E_MyExtension), then the value should be a +// concrete type that matches the expected Go type for the extension descriptor +// so that static analysis tools can verify type correctness. +// This also enables a possible future migration to a type-safe extension API. func SetExtension(m Message, xt protoreflect.ExtensionType, v any) { xd := xt.TypeDescriptor() pv := xt.ValueOf(v)