Implement space_after_not option

Configurations.md

@@ -2546,6 +2546,30 @@ fn lorem<T : Eq>(t : T) {
 
 See also: [`space_after_colon`](#space_after_colon).
 
+## `space_after_not`
+
+Leave a space after the `!` operator.
+
+- **Default value**: `false`
+- **Possible values**: `true`, `false`
+- **Stable**: No
+
+#### `false` (default):
+
+```rust
+fn not(b: bool) -> bool {
+    return !b;
+}
+```
+
+#### `true`:
+
+```rust
+fn not(b: bool) -> bool {
+    return ! b;
+}
+```
+
 ## `spaces_around_ranges`
 
 Put spaces around the .., ..=, and ... range operators

src/config/mod.rs

@@ -107,6 +107,7 @@ create_config! {
         "Determines if '+' or '=' are wrapped in spaces in the punctuation of types";
     space_before_colon: bool, false, false, "Leave a space before the colon";
     space_after_colon: bool, true, false, "Leave a space after the colon";
+    space_after_not: bool, false, false, "Leave a space after the `!` operator";
     spaces_around_ranges: bool, false, false, "Put spaces around the  .. and ..= range operators";
     binop_separator: SeparatorPlace, SeparatorPlace::Front, false,
         "Where to put a binary operator when a binary expression goes multiline";
@@ -659,6 +660,7 @@ reorder_impl_items = false
 type_punctuation_density = "Wide"
 space_before_colon = false
 space_after_colon = true
+space_after_not = false
 spaces_around_ranges = false
 binop_separator = "Front"
 remove_nested_parens = true

src/expr.rs

@@ -1943,7 +1943,12 @@ fn rewrite_unary_op(
     shape: Shape,
 ) -> Option<String> {
     // For some reason, an UnOp is not spanned like BinOp!
-    rewrite_unary_prefix(context, op.as_str(), expr, shape)
+    match op {
+        ast::UnOp::Not if context.config.space_after_not() => {
+            rewrite_unary_prefix(context, format!("{} ", op.as_str()).as_str(), expr, shape)
+        }
+        _ => rewrite_unary_prefix(context, op.as_str(), expr, shape),
+    }
 }
 
 pub(crate) enum RhsAssignKind<'ast> {