keep indent state in fmt Buf

compiler/fmt/src/def.rs

@@ -1,7 +1,7 @@
 use crate::annotation::{Formattable, Newlines, Parens};
 use crate::pattern::fmt_pattern;
-use crate::spaces::{fmt_spaces, newline, INDENT};
-use bumpalo::collections::String;
+use crate::spaces::{fmt_spaces, INDENT};
+use crate::Buf;
 use roc_parse::ast::{Def, Expr, Pattern};
 use roc_region::all::Located;
 
@@ -27,7 +27,7 @@ impl<'a> Formattable<'a> for Def<'a> {
 
     fn format_with_options(
         &self,
-        buf: &mut String<'a>,
+        buf: &mut Buf<'a>,
         _parens: Parens,
         _newlines: Newlines,
         indent: u16,
@@ -43,7 +43,7 @@ impl<'a> Formattable<'a> for Def<'a> {
                         buf,
                         Parens::NotNeeded,
                         Newlines::Yes,
-                        indent,
+                        indent + INDENT,
                     );
                 } else {
                     buf.push_str(" : ");
@@ -56,6 +56,7 @@ impl<'a> Formattable<'a> for Def<'a> {
                 }
             }
             Alias { name, vars, ann } => {
+                buf.indent(indent);
                 buf.push_str(name.value);
 
                 if vars.is_empty() {
@@ -69,7 +70,7 @@ impl<'a> Formattable<'a> for Def<'a> {
 
                 buf.push_str(" : ");
 
-                ann.format(buf, indent)
+                ann.format(buf, indent + INDENT)
             }
             Body(loc_pattern, loc_expr) => {
                 fmt_body(buf, &loc_pattern.value, &loc_expr.value, indent);
@@ -89,7 +90,7 @@ impl<'a> Formattable<'a> for Def<'a> {
                     buf.push_str(" # ");
                     buf.push_str(comment_str.trim());
                 }
-                newline(buf, indent);
+                buf.newline();
                 fmt_body(buf, &body_pattern.value, &body_expr.value, indent);
             }
 
@@ -107,7 +108,7 @@ impl<'a> Formattable<'a> for Def<'a> {
 }
 
 fn fmt_expect<'a>(
-    buf: &mut String<'a>,
+    buf: &mut Buf<'a>,
     condition: &'a Located<Expr<'a>>,
     is_multiline: bool,
     indent: u16,
@@ -122,16 +123,11 @@ fn fmt_expect<'a>(
     condition.format(buf, return_indent);
 }
 
-pub fn fmt_def<'a>(buf: &mut String<'a>, def: &Def<'a>, indent: u16) {
+pub fn fmt_def<'a>(buf: &mut Buf<'a>, def: &Def<'a>, indent: u16) {
     def.format(buf, indent);
 }
 
-pub fn fmt_body<'a>(
-    buf: &mut String<'a>,
-    pattern: &'a Pattern<'a>,
-    body: &'a Expr<'a>,
-    indent: u16,
-) {
+pub fn fmt_body<'a>(buf: &mut Buf<'a>, pattern: &'a Pattern<'a>, body: &'a Expr<'a>, indent: u16) {
     pattern.format_with_options(buf, Parens::InApply, Newlines::No, indent);
     buf.push_str(" =");
     if body.is_multiline() {
@@ -140,7 +136,7 @@ pub fn fmt_body<'a>(
                 body.format_with_options(buf, Parens::NotNeeded, Newlines::Yes, indent + INDENT);
             }
             Expr::Record { .. } | Expr::List { .. } => {
-                newline(buf, indent + INDENT);
+                buf.newline();
                 body.format_with_options(buf, Parens::NotNeeded, Newlines::Yes, indent + INDENT);
             }
             _ => {