fmt: mark types import as used in interface (#9718)

vlib/v/fmt/fmt.v

@@ -1164,6 +1164,7 @@ pub fn (mut f Fmt) interface_decl(node ast.InterfaceDecl) {
 			ft = f.short_module(ft)
 		}
 		f.writeln('\t$field.name $ft')
+		f.mark_types_import_as_used(field.typ)
 	}
 	for method in node.methods {
 		f.write('\t')
@@ -1171,6 +1172,10 @@ pub fn (mut f Fmt) interface_decl(node ast.InterfaceDecl) {
 		f.comments(method.comments, inline: true, has_nl: false, level: .indent)
 		f.writeln('')
 		f.comments(method.next_comments, inline: false, has_nl: true, level: .indent)
+		for param in method.params {
+			f.mark_types_import_as_used(param.typ)
+		}
+		f.mark_types_import_as_used(method.return_type)
 	}
 	f.writeln('}\n')
 }

vlib/v/fmt/tests/import_selective_expected.vv

@@ -5,6 +5,37 @@ import os {
 	file_ext,
 	user_os,
 }
+import mod {
+	FnArg,
+	FnRet,
+	InterfaceField,
+	InterfaceMethodArg,
+	InterfaceMethodRet,
+	StructEmbed,
+	StructField,
+	StructMethodArg,
+	StructMethodRet,
+	StructRefField,
+}
+
+struct Struct {
+	StructEmbed
+	v   StructField
+	ref &StructRefField
+}
+
+fn (s Struct) method(v StructMethodArg) StructMethodRet {
+	return {}
+}
+
+interface Interface {
+	v InterfaceField
+	f(InterfaceMethodArg) InterfaceMethodRet
+}
+
+fn f(v FnArg) FnRet {
+	return {}
+}
 
 struct App {
 	command &Command

vlib/v/fmt/tests/import_selective_input.vv

@@ -7,6 +7,39 @@ import math.complex { complex, Complex }
 import os {
 	input, user_os, file_ext }
 
+import mod {
+	Unused,
+	StructEmbed, StructField, StructRefField
+	StructMethodArg,
+	StructMethodRet
+
+	InterfaceField,
+	InterfaceMethodArg,
+	InterfaceMethodRet,
+
+	FnArg,
+	FnRet,
+}
+
+struct Struct {
+	StructEmbed
+	v StructField
+	ref &StructRefField
+}
+
+fn (s Struct) method(v StructMethodArg) StructMethodRet {
+	return {}
+}
+
+interface Interface {
+	v InterfaceField
+	f(InterfaceMethodArg) InterfaceMethodRet
+}
+
+fn f(v FnArg) FnRet {
+	return {}
+}
+
 struct App {
 	command &Command
 }
@@ -26,3 +59,4 @@ fn main() {
 	println(file_ext('main.v'))
 	println(imaginary(1))
 }
+