Fix list-pattern formatting

CHANGELOG.md

@@ -9,6 +9,7 @@
 ### Changed
 
 - **aiken-lang**: Fix underflow in error message reported by the validator arity. See [#1013](https://github.com/aiken-lang/aiken/issues/1013) @KtorZ.
+- **aiken-lang**: Fix list-pattern needlessly formatting over multiple lines. @KtorZ
 
 ### Removed
 

crates/aiken-lang/src/format.rs

@@ -1878,12 +1878,16 @@ impl<'comments> Formatter<'comments> {
                 ..
             }
             | UntypedExpr::Sequence { .. }
-            | UntypedExpr::Assignment { .. } => " {"
+            | UntypedExpr::Assignment { .. } => Document::Str(" {")
-                .to_doc()
+                .append(break_("", " ").nest(INDENT))
-                .append(line().append(self.expr(expr, true)).nest(INDENT).group())
+                .append(
-                .append(line())
+                    self.expr(expr, true)
-                .append("}")
+                        .nest(INDENT)
-                .force_break(),
+                        .group()
+                        .append(line())
+                        .append("}")
+                        .force_break(),
+                ),
 
             UntypedExpr::Fn { .. } | UntypedExpr::List { .. } => {
                 line().append(self.expr(expr, false)).nest(INDENT).group()

crates/aiken-lang/src/tests/format.rs

@@ -1247,3 +1247,21 @@ fn format_validator_exhaustive_handlers_extra_non_default_fallback() {
         "#
     );
 }
+
+#[test]
+fn list_pattern() {
+    assert_format!(
+        r#"
+        fn foo() {
+          when xs is {
+            [_] -> True
+            [1, 2] -> False
+            [_, x] -> {
+               let y = x
+               y == 42
+            }
+          }
+        }
+        "#
+    );
+}

crates/aiken-lang/src/tests/snapshots/list_pattern.snap

@@ -0,0 +1,14 @@
+---
+source: crates/aiken-lang/src/tests/format.rs
+description: "Code:\n\nfn foo() {\n  when xs is {\n    [_] -> True\n    [1, 2] -> False\n    [_, x] -> {\n       let y = x\n       y == 42\n    }\n  }\n}\n"
+---
+fn foo() {
+  when xs is {
+    [_] -> True
+    [1, 2] -> False
+    [_, x] -> {
+      let y = x
+      y == 42
+    }
+  }
+}