Remove trailing whitespace from the output of the formatter

compiler/fmt/src/lib.rs

@@ -13,6 +13,7 @@ use bumpalo::{collections::String, Bump};
 
 pub struct Buf<'a> {
     text: String<'a>,
+    spaces_to_flush: usize,
     beginning_of_line: bool,
 }
 
@@ -20,6 +21,7 @@ impl<'a> Buf<'a> {
     pub fn new_in(arena: &'a Bump) -> Buf<'a> {
         Buf {
             text: String::new_in(arena),
+            spaces_to_flush: 0,
             beginning_of_line: true,
         }
     }
@@ -43,18 +45,49 @@ impl<'a> Buf<'a> {
 
     pub fn push(&mut self, ch: char) {
         debug_assert!(!self.beginning_of_line);
-        debug_assert!(ch != '\n');
+        debug_assert!(ch != '\n' && ch != ' ');
+
+        self.flush_spaces();
+
         self.text.push(ch);
     }
 
+    pub fn push_str_allow_spaces(&mut self, s: &str) {
+        debug_assert!(!self.beginning_of_line);
+        debug_assert!(!s.contains('\n'));
+
+        self.flush_spaces();
+
+        self.text.push_str(s);
+    }
+
     pub fn push_str(&mut self, s: &str) {
         debug_assert!(!self.beginning_of_line);
-        debug_assert!(!s.contains('\n'));
+        debug_assert!(!s.contains('\n') && !s.ends_with(' '));
+
+        if !s.is_empty() {
+            self.flush_spaces();
+        }
+
         self.text.push_str(s);
     }
 
+    pub fn spaces(&mut self, count: usize) {
+        self.spaces_to_flush += count;
+    }
+
     pub fn newline(&mut self) {
+        self.spaces_to_flush = 0;
         self.text.push('\n');
         self.beginning_of_line = true;
     }
+
+    fn flush_spaces(&mut self) {
+        if self.spaces_to_flush > 0 {
+            for _ in 0..self.spaces_to_flush {
+                self.text.push(' ');
+            }
+            self.spaces_to_flush = 0;
+        }
+    }
 }