preserve comment spacing in autofmt

ci/release/changelogs/next.md

@@ -5,6 +5,9 @@
 
 #### Improvements 🧹
 
+- Fmt now preserves leading comment spacing.
+  [#400](https://github.com/terrastruct/d2/issues/400)
+
 #### Bugfixes ⛑️
 
 - Fixed crash when sequence diagrams had no messages.

d2format/format.go

@@ -81,7 +81,7 @@ func (p *printer) comment(c *d2ast.Comment) {
 	lines := strings.Split(c.Value, "\n")
 	for i, line := range lines {
 		p.sb.WriteString("#")
-		if line != "" && !strings.HasPrefix(line, " ") {
+		if line != "" {
 			p.sb.WriteByte(' ')
 		}
 		p.sb.WriteString(line)

d2format/format_test.go

@@ -592,6 +592,23 @@ hi # Fraud is the homage that force pays to reason.
 			in: `x: {}
 `,
 			exp: `x
+`,
+		},
+		{
+			name: "leading_space_comments",
+			in: `# foo
+#   foobar
+#     baz
+x  ->  y
+#foo
+y
+`,
+			exp: `# foo
+#   foobar
+#     baz
+x -> y
+# foo
+y
 `,
 		},
 	}