Add support for fields that match go reserved names

Earthfile

@@ -1,8 +1,8 @@
 VERSION 0.7
 
-ARG ALPINE_VERSION=3.19
-ARG GO_VERSION=1.22
-ARG LINTER_VERSION=v1.57.2
+ARG --global ALPINE_VERSION=3.19
+ARG --global GO_VERSION=1.22
+ARG --global LINTER_VERSION=v1.57.2
 FROM golang:$GO_VERSION-alpine$ALPINE_VERSION
 WORKDIR /app
 

protoc/plugin.go

@@ -51,9 +51,6 @@ func generateFile(f *protogen.File, plugin *protogen.Plugin, seen map[string]str
 
 // generateFieldMaskPaths generates a FieldMaskPath struct for each proto message which will contain the fieldmask paths
 func generateFieldMaskPaths(g *protogen.GeneratedFile, generatedFileImportPath string, message *protogen.Message, currFieldPath string, seen map[string]struct{}, varsGenerator *varsGenerator, maxDepth uint) []generator {
-	if len(message.Fields) == 0 {
-		return nil
-	}
 	messageName := string(message.Desc.FullName())
 	if _, exists := seen[messageName]; exists {
 		return nil

protoc/struct_generator.go

@@ -1,6 +1,8 @@
 package protoc
 
 import (
+	"go/token"
+
 	"github.com/iancoleman/strcase"
 	"google.golang.org/protobuf/compiler/protogen"
 )
@@ -29,17 +31,28 @@ func (x *structGenerator) AddMessageFields(fields ...*protogen.Field) {
 	x.msgFields = append(x.msgFields, fields...)
 }
 
+// safeFieldName generates a valid go identifier for the field name
+//
+// Additionally the and underscore is appended if the field name is 'fieldPath' or 'prefix'
+func safeFieldName(field *protogen.Field) string {
+	out := strcase.ToLowerCamel(field.GoName)
+	if token.IsKeyword(out) || out == "fieldPath" || out == "prefix" {
+		return out + "_"
+	}
+	return out
+}
+
 // Generate generates a struct with all fieldmask paths functions for the given type.
 func (x *structGenerator) Generate(g *protogen.GeneratedFile) {
 	// generate struct with all fields
 	g.P("type ", x.name, " struct {")
 	g.P("fieldPath string")
 	g.P("prefix string")
 	for _, field := range x.strFields {
-		g.P(strcase.ToLowerCamel(field.GoName), " string")
+		g.P(safeFieldName(field), " string")
 	}
 	for _, field := range x.msgFields {
-		g.P(strcase.ToLowerCamel(field.GoName), " *", getStructName(field.Message))
+		g.P(safeFieldName(field), " *", getStructName(field.Message))
 	}
 	g.P("}")
 	g.P()
@@ -57,11 +70,11 @@ func (x *structGenerator) Generate(g *protogen.GeneratedFile) {
 	g.P("fieldPath: fieldPath,")
 	g.P("prefix: prefix,")
 	for _, field := range x.strFields {
-		g.P(strcase.ToLowerCamel(field.GoName), ": prefix + \"", field.Desc.Name(), "\",")
+		g.P(safeFieldName(field), ": prefix + \"", field.Desc.Name(), "\",")
 	}
 	for _, field := range x.msgFields {
 		fieldStructNewFunction := getStructNewFunction(field.Message)
-		g.P(strcase.ToLowerCamel(field.GoName), ": ", fieldStructNewFunction, "(prefix + \"", field.Desc.Name(), "\", maxDepth - 1),")
+		g.P(safeFieldName(field), ": ", fieldStructNewFunction, "(prefix + \"", field.Desc.Name(), "\", maxDepth - 1),")
 	}
 	g.P("}")
 	g.P("}")
@@ -70,10 +83,10 @@ func (x *structGenerator) Generate(g *protogen.GeneratedFile) {
 	// generate receiver methods
 	g.P("func (x *", x.name, ") String() string { return x.fieldPath }")
 	for _, field := range x.strFields {
-		g.P("func (x *", x.name, ") ", field.GoName, "() string { return x.", strcase.ToLowerCamel(field.GoName), "}")
+		g.P("func (x *", x.name, ") ", field.GoName, "() string { return x.", safeFieldName(field), "}")
 	}
 	for _, field := range x.msgFields {
-		varName := strcase.ToLowerCamel(field.GoName)
+		varName := safeFieldName(field)
 		fieldStructNewFunction := getStructNewFunction(field.Message)
 		g.P("func (x *", x.name, ") ", field.GoName, "() *", getStructName(field.Message), " {")
 		g.P("if x.", varName, "!= nil {")

protos/cases/types.proto

@@ -56,3 +56,44 @@ message Foo {
   TestNestedInternalMessage my_nested_int_msg = 25;
   YetAnotherTestNestedExternalMessage my_yet_another_test_nested_external_msg = 26;
 }
+
+message TestReservedGoFieldNames {
+  // These fields are reserved Go field names and should be escaped.
+  // copied from https://golang.org/ref/spec#Keywords
+
+  string break = 2;
+  string case = 3;
+  string chan = 4;
+  string const = 5;
+  string continue = 6;
+
+  string default = 7;
+  string defer = 8;
+  string else = 9;
+  string fallthrough = 10;
+  string for = 11;
+
+  string func = 12;
+  string go = 13;
+  string goto = 14;
+  string if = 15;
+  string import = 16;
+
+  string interface = 17;
+  string map = 18;
+  string package = 19;
+  string range = 20;
+  string return = 21;
+
+  string select = 22;
+  string struct = 23;
+  string switch = 24;
+  string type = 25;
+  string var = 26;
+}
+
+message EmptyMessage {}
+
+message TestMessageWithEmptyMessage {
+  EmptyMessage empty = 1;
+}

test/cases_test.go

@@ -36,6 +36,8 @@ func (s *TestSuite) TestTypes() {
 		"an external nested message also gets fieldmasks when it's a parent message":                       {msg: &cases.TestNestedExternalMessage{}},
 		"an internal nested message also gets fieldmasks when it's a parent message":                       {msg: &cases.Foo_TestNestedInternalMessage{}},
 		"an external nested message from another file also gets fieldmasks when it's a parent message":     {msg: &cases.YetAnotherTestNestedExternalMessage{}},
+		"a message with reserved go field names works":                                                     {msg: &cases.TestReservedGoFieldNames{}},
+		"a message with field that is an empty message works":                                              {msg: &cases.TestMessageWithEmptyMessage{}},
 		"messages with the same name and a different package get fieldmasks (a.Foo, 1/2)":                  {msg: &a.Foo{}},
 		"messages with the same name and a different package get fieldmasks (b.Foo, 2/2)":                  {msg: &b.Foo{}},
 		"messages from different proto files, in the same package can get fieldmask for 3rd-parties (1/2)": {msg: &thirdpartyimport.FooA{}},