Use relative imports for same-package pb2 modules

protoc-gen-twirpy/generator/generator.go

@@ -71,7 +71,7 @@ func buildTwirpServiceDescription(messagesToFiles map[string]string, fd *descrip
 		FileName: name,
 	}
 
-	imports := newImportBuilder(messagesToFiles)
+	imports := newImportBuilder(messagesToFiles, name)
 
 	for _, service := range fd.GetService() {
 		serviceURL := fmt.Sprintf("%s.%s", fd.GetPackage(), service.GetName())

protoc-gen-twirpy/generator/generator_test.go

@@ -9,13 +9,14 @@ import (
 )
 
 func TestImportBuilder(t *testing.T) {
+	// The current file being generated is in twirp/twitch/example/
 	testImportBuilder := newImportBuilder(map[string]string{
 		"twirp.twitch.example.Hat":   "twirp/twitch/example/haberdasher.proto",
 		"twirp.twitch.example.Price": "twirp/twitch/example/haberdasher.proto",
 		"twirp.twitch.example.Color": "twirp/twitch/example_folder/haberdasher.proto",
 		"twirp.twitch.example.Size":  "twirp/twitch/example/haberdasher_extension.proto",
 		"google.protobuf.Empty":      "google/protobuf/empty.proto",
-	})
+	}, "twirp/twitch/example/service.proto")
 
 	testCases := []struct {
 		typeToImport    string
@@ -24,26 +25,29 @@ func TestImportBuilder(t *testing.T) {
 		expectedImport  *TwirpImport
 	}{
 		{
+			// Same package → relative import
 			typeToImport:    "twirp.twitch.example.Hat",
 			importKey:       "twirp.twitch.example.haberdasher_pb2",
 			qualifiedImport: "_haberdasher_pb2.Hat",
 			expectedImport: &TwirpImport{
-				From:   "twirp.twitch.example",
+				From:   ".",
 				Import: "haberdasher_pb2",
 				Alias:  "_haberdasher_pb2",
 			},
 		},
 		{
+			// Same package, same file → reuses existing import
 			typeToImport:    "twirp.twitch.example.Price",
 			importKey:       "twirp.twitch.example.haberdasher_pb2",
 			qualifiedImport: "_haberdasher_pb2.Price",
 			expectedImport: &TwirpImport{
-				From:   "twirp.twitch.example",
+				From:   ".",
 				Import: "haberdasher_pb2",
 				Alias:  "_haberdasher_pb2",
 			},
 		},
 		{
+			// Different package → absolute import
 			typeToImport:    "twirp.twitch.example.Color",
 			importKey:       "twirp.twitch.example_folder.haberdasher_pb2",
 			qualifiedImport: "_haberdasher_pb2_1.Color",
@@ -54,16 +58,18 @@ func TestImportBuilder(t *testing.T) {
 			},
 		},
 		{
+			// Same package, different file → relative import
 			typeToImport:    "twirp.twitch.example.Size",
 			importKey:       "twirp.twitch.example.haberdasher_extension_pb2",
 			qualifiedImport: "_haberdasher_extension_pb2.Size",
 			expectedImport: &TwirpImport{
-				From:   "twirp.twitch.example",
+				From:   ".",
 				Import: "haberdasher_extension_pb2",
 				Alias:  "_haberdasher_extension_pb2",
 			},
 		},
 		{
+			// External package → absolute import
 			typeToImport:    "google.protobuf.Empty",
 			importKey:       "google.protobuf.empty_pb2",
 			qualifiedImport: "_empty_pb2.Empty",

protoc-gen-twirpy/generator/import_builder.go

@@ -9,13 +9,25 @@ type importBuilder struct {
 	seenAliases    map[string]struct{}
 	imports        map[string]*TwirpImport
 	messagesToFile map[string]string
+	currentFileDir string
 }
 
-func newImportBuilder(messagesToFile map[string]string) *importBuilder {
+func newImportBuilder(messagesToFile map[string]string, currentFileName string) *importBuilder {
+	// Extract directory from proto filename: "crypto/v1.proto" -> "crypto"
+	dir := ""
+	parts := strings.Split(currentFileName, "/")
+	if len(parts) > 1 {
+		dirParts := parts[:len(parts)-1]
+		for i, p := range dirParts {
+			dirParts[i] = strings.ReplaceAll(p, "-", "_")
+		}
+		dir = strings.Join(dirParts, ".")
+	}
 	return &importBuilder{
 		messagesToFile: messagesToFile,
 		seenAliases:    make(map[string]struct{}),
 		imports:        make(map[string]*TwirpImport),
+		currentFileDir: dir,
 	}
 }
 
@@ -34,6 +46,10 @@ func (ib *importBuilder) addImportAndQualify(typeToImport string) (string, error
 			moduleNameSlice := strings.Split(moduleName, ".")
 			strippedModuleName := moduleNameSlice[len(moduleNameSlice)-1]
 			modulePath := strings.Join(moduleNameSlice[:len(moduleNameSlice)-1], ".")
+			// Use relative import when the module is in the same package as the file being generated
+			if modulePath == ib.currentFileDir {
+				modulePath = "."
+			}
 			alias := ib.generateAlias(strippedModuleName)
 			ib.imports[moduleName] = &TwirpImport{
 				From:   modulePath,