feat: generates trailing comments of message field

close gogo#764

Author: hitzhangjie

protoc-gen-gogo/generator/generator.go

@@ -35,9 +35,9 @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 /*
-	The code generator for the plugin for the Google protocol buffer compiler.
-	It generates Go code from the protocol buffer description files read by the
-	main routine.
+The code generator for the plugin for the Google protocol buffer compiler.
+It generates Go code from the protocol buffer description files read by the
+main routine.
 */
 package generator
 
@@ -1321,15 +1321,30 @@ func (g *Generator) PrintComments(path string) bool {
 	if !g.writeOutput {
 		return false
 	}
-	if c, ok := g.makeComments(path); ok {
+	if c, ok := g.makeLeadingComments(path); ok {
 		g.P(c)
 		return true
 	}
 	return false
 }
 
-// makeComments generates the comment string for the field, no "\n" at the end
-func (g *Generator) makeComments(path string) (string, bool) {
+// makeLeadingComments generates the comment string for the field, no "\n" at the end
+func (g *Generator) makeLeadingComments(path string) (string, bool) {
+	loc, ok := g.file.comments[path]
+	if !ok {
+		return "", false
+	}
+	w := new(bytes.Buffer)
+	nl := ""
+	for _, line := range strings.Split(strings.TrimSuffix(loc.GetLeadingComments(), "\n"), "\n") {
+		fmt.Fprintf(w, "%s//%s", nl, line)
+		nl = "\n"
+	}
+	return w.String(), true
+}
+
+// makeTrailingComments generates the trailing comment string for the field, no "\n" at the end
+func (g *Generator) makeTrailingComments(path string) (string, bool) {
 	loc, ok := g.file.comments[path]
 	if !ok {
 		return "", false
@@ -1605,6 +1620,7 @@ func (g *Generator) generateEnum(enum *EnumDescriptor) {
 // The tag is a string like "varint,2,opt,name=fieldname,def=7" that
 // identifies details of the field for the protocol buffer marshaling and unmarshaling
 // code.  The fields are:
+//
 //	wire encoding
 //	protocol tag number
 //	opt,req,rep for optional, required, or repeated
@@ -1613,6 +1629,7 @@ func (g *Generator) generateEnum(enum *EnumDescriptor) {
 //	enum= the name of the enum type if it is an enum-typed field.
 //	proto3 if this field is in a proto3 message
 //	def= string representation of the default value, if any.
+//
 // The default value must be in a representation that can be used at run-time
 // to generate the default value. Thus bools become 0 and 1, for instance.
 func (g *Generator) goTag(message *Descriptor, field *descriptor.FieldDescriptorProto, wiretype string) string {
@@ -2179,17 +2196,18 @@ func (f *fieldCommon) getGoType() string {
 // simpleField is not weak, not a oneof, not an extension. Can be required, optional or repeated.
 type simpleField struct {
 	fieldCommon
-	protoTypeName string                               // Proto type name, empty if primitive, e.g. ".google.protobuf.Duration"
-	protoType     descriptor.FieldDescriptorProto_Type // Actual type enum value, e.g. descriptor.FieldDescriptorProto_TYPE_FIXED64
-	deprecated    string                               // Deprecation comment, if any, e.g. "// Deprecated: Do not use."
-	getterDef     string                               // Default for getters, e.g. "nil", `""` or "Default_MessageType_FieldName"
-	protoDef      string                               // Default value as defined in the proto file, e.g "yoshi" or "5"
-	comment       string                               // The full comment for the field, e.g. "// Useful information"
+	protoTypeName   string                               // Proto type name, empty if primitive, e.g. ".google.protobuf.Duration"
+	protoType       descriptor.FieldDescriptorProto_Type // Actual type enum value, e.g. descriptor.FieldDescriptorProto_TYPE_FIXED64
+	deprecated      string                               // Deprecation comment, if any, e.g. "// Deprecated: Do not use."
+	getterDef       string                               // Default for getters, e.g. "nil", `""` or "Default_MessageType_FieldName"
+	protoDef        string                               // Default value as defined in the proto file, e.g "yoshi" or "5"
+	comment         string                               // The full comment for the field, e.g. "// Useful information"
+	trailingComment string                               // The trailing comment for the field, e.g. "fieldName fieldType // Useful information"
 }
 
 // decl prints the declaration of the field in the struct (if any).
 func (f *simpleField) decl(g *Generator, mc *msgCtx) {
-	g.P(f.comment, Annotate(mc.message.file, f.fullPath, f.goName), "\t", f.goType, "\t`", f.tags, "`", f.deprecated)
+	g.P(f.comment, Annotate(mc.message.file, f.fullPath, f.goName), "\t", f.goType, "\t`", f.tags, "`", f.deprecated, f.trailingComment)
 }
 
 // getter prints the getter for the field.
@@ -2870,7 +2888,7 @@ func (g *Generator) generateMessage(message *Descriptor) {
 			// This is the first field of a oneof we haven't seen before.
 			// Generate the union field.
 			oneofFullPath := fmt.Sprintf("%s,%d,%d", message.path, messageOneofPath, *field.OneofIndex)
-			c, ok := g.makeComments(oneofFullPath)
+			c, ok := g.makeLeadingComments(oneofFullPath)
 			if ok {
 				c += "\n//\n"
 			}
@@ -2965,10 +2983,15 @@ func (g *Generator) generateMessage(message *Descriptor) {
 		}
 
 		fieldFullPath := fmt.Sprintf("%s,%d,%d", message.path, messageFieldPath, i)
-		c, ok := g.makeComments(fieldFullPath)
+		c, ok := g.makeLeadingComments(fieldFullPath)
 		if ok {
 			c += "\n"
 		}
+		tc, ok := g.makeTrailingComments(fieldFullPath)
+		if ok {
+			tc += "\n"
+		}
+
 		rf := simpleField{
 			fieldCommon: fieldCommon{
 				goName:     fieldName,
@@ -2979,12 +3002,13 @@ func (g *Generator) generateMessage(message *Descriptor) {
 				fullPath:   fieldFullPath,
 				protoField: field,
 			},
-			protoTypeName: field.GetTypeName(),
-			protoType:     *field.Type,
-			deprecated:    fieldDeprecated,
-			getterDef:     dvalue,
-			protoDef:      field.GetDefaultValue(),
-			comment:       c,
+			protoTypeName:   field.GetTypeName(),
+			protoType:       *field.Type,
+			deprecated:      fieldDeprecated,
+			getterDef:       dvalue,
+			protoDef:        field.GetDefaultValue(),
+			comment:         c,
+			trailingComment: tc,
 		}
 		var pf topLevelField = &rf