fix extra spaces in if-expr with bool negation (#24)

Currently, verusfmt adds a space for each 'condition' node. However, the
grammar is set up so that this has _two_ negation nodes:

```
if !b {
}
```

so it ends up formatted as:

```
if !b  {
}
```

See the expansion has two 'condition' nodes:

```
if_expr {
                  if_str {}
                  condition {
                    bang_str {}
                    condition {
                      expr_no_struct {
                        path_expr_no_generics {
                          path_no_generics {
                            path_segment_no_generics {
                              name_ref {
                                identifier {}
                              }
                            }
                          }
                        }
                      }
                    }
                  }
```

The PR changes the handling of the space to be with an 'if' expression
or 'while' expression, rather than having it handled with the
'condition' node.

Co-authored-by: Travis Hance <tjhance7@gmail.com>

src/lib.rs

@@ -434,6 +434,20 @@ fn unsupported(pair: Pair<Rule>) -> DocBuilder<Arena> {
     todo!()
 }
 
+fn if_expr_to_doc<'a>(
+    ctx: &Context,
+    arena: &'a Arena<'a, ()>,
+    pair: Pair<'a, Rule>,
+) -> DocBuilder<'a, Arena<'a>> {
+    arena.concat(pair.into_inner().map(|p| {
+        if p.as_rule() == Rule::condition {
+            to_doc(ctx, p, arena).append(arena.space())
+        } else {
+            to_doc(ctx, p, arena)
+        }
+    }))
+}
+
 fn loop_to_doc<'a>(
     ctx: &Context,
     arena: &'a Arena<'a, ()>,
@@ -450,7 +464,9 @@ fn loop_to_doc<'a>(
         _ => (),
     });
     arena.concat(pair.into_inner().map(|p| {
-        if let Some(c) = last_clause {
+        if p.as_rule() == Rule::condition {
+            to_doc(ctx, p, arena).append(arena.space())
+        } else if let Some(c) = last_clause {
             if p.as_rule() == c {
                 to_doc(ctx, p, arena).append(arena.line())
             } else {
@@ -1026,8 +1042,8 @@ fn to_doc<'a>(
                 }))
                 .group()
         }
-        Rule::condition => map_to_doc(ctx, arena, pair).append(arena.space()),
-        Rule::if_expr => map_to_doc(ctx, arena, pair),
+        Rule::condition => map_to_doc(ctx, arena, pair),
+        Rule::if_expr => if_expr_to_doc(ctx, arena, pair),
         Rule::loop_expr => loop_to_doc(ctx, arena, pair),
         Rule::for_expr => arena.concat(pair.into_inner().map(|p| match p.as_rule() {
             Rule::in_str => arena.space().append(to_doc(ctx, p, arena)),

tests/rustfmt-matching.rs

@@ -282,6 +282,9 @@ fn test_function() {
     if arg.len() < 12 {
         return 5;
     }
+    if !b {
+        return 5;
+    }
     extend_vec_u8();
     if y {
         1