make the formatter remove double negations

Author: giacomocavalieri

CHANGELOG.md

@@ -107,6 +107,27 @@
 
 ### Formatter
 
+- The formatter now removes needless multiple negations that are safe to remove.
+  For example, this snippet of code:
+
+  ```gleam
+  pub fn useless_negations() {
+    let lucky_number = --11
+    let lucy_is_a_star = !!!False
+  }
+  ```
+
+  Is rewritten as:
+
+  ```gleam
+  pub fn useless_negations() {
+    let lucky_number = 11
+    let lucy_is_a_star = !False
+  }
+  ```
+
+  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))
+
 ### Bug fixes
 
 - Fixed a bug where `echo` could crash on JavaScript if the module contains

compiler-core/src/format.rs

@@ -2521,16 +2521,17 @@ impl<'comments> Formatter<'comments> {
 
     fn negate_bool<'a>(&mut self, expr: &'a UntypedExpr) -> Document<'a> {
         match expr {
+            UntypedExpr::NegateBool { value, .. } => self.expr(value),
             UntypedExpr::BinOp { .. } => "!".to_doc().append(wrap_block(self.expr(expr))),
             _ => docvec!["!", self.expr(expr)],
         }
     }
 
     fn negate_int<'a>(&mut self, expr: &'a UntypedExpr) -> Document<'a> {
         match expr {
-            UntypedExpr::BinOp { .. } | UntypedExpr::NegateInt { .. } => {
-                "- ".to_doc().append(self.expr(expr))
-            }
+            UntypedExpr::NegateInt { value, .. } => self.expr(value),
+            UntypedExpr::Int { value, .. } if value.starts_with('-') => self.int(value),
+            UntypedExpr::BinOp { .. } => "- ".to_doc().append(self.expr(expr)),
 
             _ => docvec!["-", self.expr(expr)],
         }

compiler-core/src/format/tests.rs

@@ -4902,7 +4902,7 @@ fn double_negate() {
 "#,
         r#"pub fn main() {
   let a = 3
-  let b = - -a
+  let b = a
 }
 "#
     );
@@ -4918,7 +4918,7 @@ fn triple_negate() {
 "#,
         r#"pub fn main() {
   let a = 3
-  let b = - - -a
+  let b = -a
 }
 "#
     );
@@ -4950,14 +4950,32 @@ fn binary_double_negate() {
 "#,
         r#"pub fn main() {
   let a = 3
-  let b = - -{ a + 3 }
+  let b = { a + 3 }
 }
 "#
     );
 }
 
 #[test]
-fn repeated_negate_after_subtract() {
+fn even_repeated_negate_after_subtract() {
+    assert_format_rewrite!(
+        r#"pub fn main() {
+  let a = 3
+  let b = 4
+  let c = a-------b
+}
+"#,
+        r#"pub fn main() {
+  let a = 3
+  let b = 4
+  let c = a - b
+}
+"#
+    );
+}
+
+#[test]
+fn odd_repeated_negate_after_subtract() {
     assert_format_rewrite!(
         r#"pub fn main() {
   let a = 3
@@ -4968,12 +4986,26 @@ fn repeated_negate_after_subtract() {
         r#"pub fn main() {
   let a = 3
   let b = 4
-  let c = a - - - - - - - -b
+  let c = a - -b
 }
 "#
     );
 }
 
+#[test]
+fn double_negation_on_bools_is_removed() {
+    assert_format_rewrite!(
+        r#"pub fn main() {
+  !!True
+}
+"#,
+        "pub fn main() {
+  True
+}
+"
+    );
+}
+
 #[test]
 fn wrap_long_line_with_int_negation() {
     assert_format_rewrite!(