fmt: fix removal of selective imported types used in type decl (#12868)

vlib/v/fmt/fmt.v

@@ -1238,6 +1238,7 @@ pub fn (mut f Fmt) alias_type_decl(node ast.AliasTypeDecl) {
 	f.write('type $node.name = $ptype')
 
 	f.comments(node.comments, has_nl: false)
+	f.mark_types_import_as_used(node.parent_type)
 }
 
 pub fn (mut f Fmt) fn_type_decl(node ast.FnTypeDecl) {
@@ -1254,6 +1255,7 @@ pub fn (mut f Fmt) fn_type_decl(node ast.FnTypeDecl) {
 			f.write(arg.typ.share().str() + ' ')
 		}
 		f.write(arg.name)
+		f.mark_types_import_as_used(arg.typ)
 		mut s := f.no_cur_mod(f.table.type_to_str_using_aliases(arg.typ, f.mod2alias))
 		if arg.is_mut {
 			if s.starts_with('&') {
@@ -1278,6 +1280,7 @@ pub fn (mut f Fmt) fn_type_decl(node ast.FnTypeDecl) {
 	}
 	f.write(')')
 	if fn_info.return_type.idx() != ast.void_type_idx {
+		f.mark_types_import_as_used(fn_info.return_type)
 		ret_str := f.no_cur_mod(f.table.type_to_str_using_aliases(fn_info.return_type,
 			f.mod2alias))
 		f.write(' $ret_str')
@@ -1298,8 +1301,11 @@ pub fn (mut f Fmt) sum_type_decl(node ast.SumTypeDecl) {
 	f.write_generic_types(node.generic_types)
 	f.write(' = ')
 
-	mut sum_type_names := node.variants.map(f.table.type_to_str_using_aliases(it.typ,
-		f.mod2alias))
+	mut sum_type_names := []string{cap: node.variants.len}
+	for variant in node.variants {
+		sum_type_names << f.table.type_to_str_using_aliases(variant.typ, f.mod2alias)
+		f.mark_types_import_as_used(variant.typ)
+	}
 	sum_type_names.sort()
 
 	mut separator := ' | '

vlib/v/fmt/tests/import_selective_expected.vv

@@ -6,7 +6,10 @@ import os {
 	user_os,
 }
 import mod {
+	AliasTarget,
 	Enum,
+	FnAliasParam,
+	FnAliasRet,
 	FnArg,
 	FnArgGeneric,
 	FnArgTypeParam1,
@@ -29,8 +32,14 @@ import mod {
 	StructMethodRet,
 	StructMethodRetGeneric,
 	StructRefField,
+	SumVariant1,
+	SumVariant2,
 }
 
+type Alias = AliasTarget
+type SumType = SumVariant1 | SumVariant2
+type Fn = fn (FnAliasParam) FnAliasRet
+
 struct Struct {
 	StructEmbed
 	v   StructField

vlib/v/fmt/tests/import_selective_input.vv

@@ -32,9 +32,17 @@ import mod {
 	RightOfIs,
 	RightOfAs,
 
+	AliasTarget,
+	SumVariant1, SumVariant2,
+	FnAliasParam, FnAliasRet
+
 	Enum
 }
 
+type Alias = AliasTarget
+type SumType = SumVariant1 | SumVariant2
+type Fn = fn(FnAliasParam) FnAliasRet
+
 struct Struct {
 	StructEmbed
 	v StructField