fix indent issue when parsing tag unions

compiler/parse/src/blankspace.rs

@@ -1,7 +1,7 @@
 use crate::ast::CommentOrNewline;
 use crate::ast::Spaceable;
 use crate::parser::{
-    self, and, BadInputError, Col, Parser,
+    self, and, backtrackable, BadInputError, Col, Parser,
     Progress::{self, *},
     Row, State,
 };
@@ -28,7 +28,10 @@ where
             space0_e(min_indent, space_problem, indent_before_problem),
             and(
                 parser,
-                space0_e(min_indent, space_problem, indent_after_problem),
+                one_of![
+                    backtrackable(space0_e(min_indent, space_problem, indent_after_problem)),
+                    succeed!(&[] as &[_]),
+                ],
             ),
         ),
         move |arena: &'a Bump,

compiler/parse/src/parser.rs

@@ -1299,6 +1299,15 @@ macro_rules! collection_trailing_sep_e {
     };
 }
 
+#[macro_export]
+macro_rules! succeed {
+    ($value:expr) => {
+        move |_arena: &'a bumpalo::Bump, state: $crate::parser::State<'a>| {
+            Ok((NoProgress, $value, state))
+        }
+    };
+}
+
 #[macro_export]
 macro_rules! and {
     ($p1:expr, $p2:expr) => {