impl(generator): support all scalar field types

I introduced a new attribute to indicate if a scalar field is optional. I am
planning to capture this attribute from the proto source in a future PR.

generator/internal/genclient/language/internal/rust/rust.go

@@ -15,6 +15,7 @@
 package rust
 
 import (
+	"fmt"
 	"log/slog"
 
 	"github.com/googleapis/google-cloud-rust/generator/internal/genclient"
@@ -40,20 +41,52 @@ func (c *Codec) LoadWellKnownTypes(s *genclient.APIState) {
 	s.MessageByID[duration.ID] = duration
 }
 
-func (c *Codec) FieldType(f *genclient.Field, state *genclient.APIState) string {
+func ScalarFieldType(f *genclient.Field) string {
 	var out string
 	switch f.Typez {
-	case genclient.STRING_TYPE:
-		out = "String"
+	case genclient.DOUBLE_TYPE:
+		out = "f64"
+	case genclient.FLOAT_TYPE:
+		out = "f32"
 	case genclient.INT64_TYPE:
 		out = "i64"
+	case genclient.UINT64_TYPE:
+		out = "u64"
 	case genclient.INT32_TYPE:
 		out = "i32"
+	case genclient.FIXED64_TYPE:
+		out = "u64"
+	case genclient.FIXED32_TYPE:
+		out = "u32"
 	case genclient.BOOL_TYPE:
 		out = "bool"
+	case genclient.STRING_TYPE:
+		out = "String"
 	case genclient.BYTES_TYPE:
 		out = "bytes::Bytes"
-	case genclient.MESSAGE_TYPE:
+	case genclient.UINT32_TYPE:
+		out = "u32"
+	case genclient.SFIXED32_TYPE:
+		out = "i32"
+	case genclient.SFIXED64_TYPE:
+		out = "i64"
+	case genclient.SINT32_TYPE:
+		out = "i32"
+	case genclient.SINT64_TYPE:
+		out = "i64"
+
+	default:
+		slog.Error("Unexpected field type", "field", *f)
+		return ""
+	}
+	if f.Optional {
+		return fmt.Sprintf("Option<%s>", out)
+	}
+	return out
+}
+
+func (c *Codec) FieldType(f *genclient.Field, state *genclient.APIState) string {
+	if f.Typez == genclient.MESSAGE_TYPE {
 		m, ok := state.MessageByID[f.TypezID]
 		if !ok {
 			slog.Error("unable to lookup type", "id", f.TypezID)
@@ -62,21 +95,21 @@ func (c *Codec) FieldType(f *genclient.Field, state *genclient.APIState) string
 		if m.IsMap {
 			key := c.FieldType(m.Fields[0], state)
 			val := c.FieldType(m.Fields[1], state)
-			out = "Option<std::collections::HashMap<" + key + "," + val + ">>"
-			break
+			return "Option<std::collections::HashMap<" + key + "," + val + ">>"
 		}
-		out = "Option<" + c.MessageName(m, state) + ">"
-	case genclient.ENUM_TYPE:
+		return "Option<" + c.MessageName(m, state) + ">"
+	} else if f.Typez == genclient.ENUM_TYPE {
 		e, ok := state.EnumByID[f.TypezID]
 		if !ok {
 			slog.Error("unable to lookup type", "id", f.TypezID)
 			return ""
 		}
-		out = c.EnumName(e, state)
-	default:
-		slog.Error("unhandled fieldType", "type", f.Typez, "id", f.TypezID)
+		return c.EnumName(e, state)
+	} else if f.Typez == genclient.GROUP_TYPE {
+		slog.Error("TODO(#39) - better handling of `oneof` fields")
+		return ""
 	}
-	return out
+	return ScalarFieldType(f)
 }
 
 func (c *Codec) TemplateDir() string {

generator/internal/genclient/language/internal/rust/rust_test.go

@@ -0,0 +1,46 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package rust
+
+import (
+	"testing"
+
+	"github.com/googleapis/google-cloud-rust/generator/internal/genclient"
+)
+
+type ScalarFieldTest struct {
+	Typez    genclient.Typez
+	Optional bool
+	Expected string
+}
+
+var scalarFieldTests = []ScalarFieldTest{
+	{genclient.INT32_TYPE, false, "i32"},
+	{genclient.INT64_TYPE, false, "i64"},
+	{genclient.UINT32_TYPE, true, "Option<u32>"},
+	{genclient.UINT64_TYPE, true, "Option<u64>"},
+	{genclient.BOOL_TYPE, true, "Option<bool>"},
+	{genclient.STRING_TYPE, true, "Option<String>"},
+	{genclient.BYTES_TYPE, true, "Option<bytes::Bytes>"},
+}
+
+func TestScalarFields(t *testing.T) {
+	for _, test := range scalarFieldTests {
+		field := genclient.Field{Typez: test.Typez, Optional: test.Optional}
+		if output := ScalarFieldType(&field); output != test.Expected {
+			t.Errorf("Output %q not equal to expected %q", output, test.Expected)
+		}
+	}
+}

generator/internal/genclient/model.go

@@ -228,6 +228,8 @@ type Field struct {
 	// JSONName is the name of the field as it appears in JSON. Useful for
 	// serializing to JSON.
 	JSONName string
+	// Optional indicates that the field is marked as optional in proto3.
+	Optional bool
 }
 
 // Pair is a key-value pair.