Add yaml::format

src/format.rs

@@ -0,0 +1,31 @@
+use std::fmt;
+
+
+/// Adds zero, one or two line breaks to make sure that there are at least two
+/// line breaks at the end of the string. Except if the buffer is completely
+/// empty, in which case it is not modified.
+pub(crate) fn add_empty_line(out: &mut String) {
+    match () {
+        () if out.is_empty() => {},
+        () if out.ends_with("\n\n") => {},
+        () if out.ends_with('\n') => out.push('\n'),
+        _ => out.push_str("\n\n"),
+    }
+}
+
+pub(crate) fn assert_single_trailing_newline(out: &mut String) {
+    while out.ends_with("\n\n") {
+        out.pop();
+    }
+}
+
+pub(crate) struct DefaultValueComment<T>(pub(crate) Option<T>);
+
+impl<T: fmt::Display> fmt::Display for DefaultValueComment<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match &self.0 {
+            None => "Required! This value must be specified.".fmt(f),
+            Some(v) => write!(f, "Default value: {}", v),
+        }
+    }
+}