Do not add parens around exprs if they are not needed in formatting

compiler/fmt/src/annotation.rs

@@ -18,7 +18,7 @@ use roc_region::all::Located;
 ///     Just (Just a)
 ///     List (List a)
 ///     reverse (reverse l)
-#[derive(PartialEq, Eq, Clone, Copy)]
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
 pub enum Parens {
     NotNeeded,
     InFunctionType,

compiler/fmt/src/expr.rs

@@ -133,10 +133,14 @@ impl<'a> Formattable<'a> for Expr<'a> {
                 }
             }
             ParensAround(sub_expr) => {
+                if parens == Parens::NotNeeded {
+                    sub_expr.format_with_options(buf, Parens::NotNeeded, Newlines::Yes, indent);
+                } else {
                     buf.push('(');
                     sub_expr.format_with_options(buf, Parens::NotNeeded, Newlines::Yes, indent);
                     buf.push(')');
                 }
+            }
             Str(literal) => {
                 use roc_parse::ast::StrLiteral::*;
 

compiler/fmt/tests/test_fmt.rs

@@ -362,6 +362,31 @@ mod test_fmt {
         );
     }
 
+    #[test]
+    fn excess_parens() {
+        expr_formats_to(
+            indoc!(
+                r#"
+                x = (5)
+    
+    
+                y = ((10))
+    
+                42
+                "#
+            ),
+            indoc!(
+                r#"
+                x = 5
+    
+                y = 10
+    
+                42
+                "#
+            ),
+        );
+    }
+
     // #[test]
     // fn defs_with_defs() {
     //     expr_formats_to(