alignment in pattern match on single element tag union

compiler/gen/tests/gen_tags.rs

@@ -760,7 +760,7 @@ mod gen_tags {
     }
 
     #[test]
-    fn alignment_in_single_tag() {
+    fn alignment_in_single_tag_construction() {
         assert_evals_to!(indoc!("Three (1 == 1) 32"), (32i64, true), (i64, bool));
 
         assert_evals_to!(
@@ -769,4 +769,35 @@ mod gen_tags {
             (i64, bool, u8)
         );
     }
+
+    #[test]
+    fn alignment_in_single_tag_pattern_match() {
+        assert_evals_to!(
+            indoc!(
+                r"#
+                x = Three (1 == 1) 32
+
+                when x is
+                    Three bool int -> 
+                        { bool, int }
+                #"
+            ),
+            (32i64, true),
+            (i64, bool)
+        );
+
+        assert_evals_to!(
+            indoc!(
+                r"#
+                x = Three (1 == 1) (if True then Red else if True then Green else Blue) 32
+
+                when x is
+                    Three bool color int -> 
+                        { bool, color, int }
+                #"
+            ),
+            (32i64, true, 2u8),
+            (i64, bool, u8)
+        );
+    }
 }

compiler/mono/src/ir.rs

@@ -5313,6 +5313,20 @@ pub fn from_can_pattern<'a>(
                         }],
                     };
 
+                    let mut arguments = arguments.clone();
+
+                    arguments.sort_by(|arg1, arg2| {
+                        let ptr_bytes = 8;
+
+                        let layout1 = layout_cache.from_var(env.arena, arg1.0, env.subs).unwrap();
+                        let layout2 = layout_cache.from_var(env.arena, arg2.0, env.subs).unwrap();
+
+                        let size1 = layout1.alignment_bytes(ptr_bytes);
+                        let size2 = layout2.alignment_bytes(ptr_bytes);
+
+                        size2.cmp(&size1)
+                    });
+
                     let mut mono_args = Vec::with_capacity_in(arguments.len(), env.arena);
                     for ((_, loc_pat), layout) in arguments.iter().zip(field_layouts.iter()) {
                         mono_args.push((