fix: binop associativity formatting

it seems we can fix this by changing which side
gets subtracted by 1 depending on the op associativity.
BinOp::Or & BinOp::And are right associative while the
other bin ops are left associative.

closes #893

Co-authored-by: Kasey White <kwhitemsg@gmail.com>

crates/aiken-lang/src/format.rs

@@ -1219,11 +1219,27 @@ impl<'comments> Formatter<'comments> {
         let left = self.expr(left, false);
         let right = self.expr(right, false);
 
-        self.operator_side(left, precedence, left_precedence)
+        self.operator_side(
-            .append(" ")
+            left,
-            .append(name)
+            precedence,
-            .append(" ")
+            if matches!(name, BinOp::Or | BinOp::And) {
-            .append(self.operator_side(right, precedence, right_precedence.saturating_sub(1)))
+                left_precedence.saturating_sub(1)
+            } else {
+                left_precedence
+            },
+        )
+        .append(" ")
+        .append(name)
+        .append(" ")
+        .append(self.operator_side(
+            right,
+            precedence,
+            if matches!(name, BinOp::Or | BinOp::And) {
+                right_precedence
+            } else {
+                right_precedence.saturating_sub(1)
+            },
+        ))
     }
 
     pub fn operator_side<'a>(&mut self, doc: Document<'a>, op: u8, side: u8) -> Document<'a> {

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

@@ -755,3 +755,25 @@ fn fuzzer_annotations() {
         "#
     );
 }
+
+#[test]
+fn preserve_associativity_parens_in_binop() {
+    assert_format!(
+        r#"
+        pub fn bar() {
+          ( a || b ) || c
+        }
+        "#
+    );
+}
+
+#[test]
+fn superfluous_parens_in_binop() {
+    assert_format!(
+        r#"
+        pub fn bar() {
+          a && ( b && c )
+        }
+        "#
+    );
+}

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

@@ -11,5 +11,5 @@ fn bar() {
 }
 
 fn baz() {
-  a || ( b && c || d )
+  a || b && c || d
 }

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

@@ -0,0 +1,7 @@
+---
+source: crates/aiken-lang/src/tests/format.rs
+description: "Code:\n\npub fn bar() {\n  ( a || b ) || c\n}\n"
+---
+pub fn bar() {
+  ( a || b ) || c
+}

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

@@ -0,0 +1,7 @@
+---
+source: crates/aiken-lang/src/tests/format.rs
+description: "Code:\n\npub fn bar() {\n  a && ( b && c )\n}\n"
+---
+pub fn bar() {
+  a && b && c
+}