Start pretty printing comments

src/pretty/basic.rs

@@ -0,0 +1,86 @@
+use std::mem;
+
+use pretty::{DocAllocator, DocBuilder, Pretty, RcAllocator, RcDoc};
+
+use crate::ast::{Ident, Line, Space};
+
+pub enum Group<'a> {
+    EmptyLine,
+    CommentBlock(Vec<&'a str>),
+}
+
+/// Group comments and deduplicate empty lines
+fn group_comments(lines: &[Line]) -> Vec<Group> {
+    let mut result = vec![];
+
+    let mut current_block = vec![];
+    let mut last_line_was_empty = false;
+    for line in lines {
+        match line {
+            Line::Empty if last_line_was_empty => {}
+            Line::Empty => {
+                last_line_was_empty = true;
+                if !current_block.is_empty() {
+                    result.push(Group::CommentBlock(mem::take(&mut current_block)));
+                }
+                result.push(Group::EmptyLine);
+            }
+            Line::Comment(comment) => {
+                last_line_was_empty = false;
+                current_block.push(comment);
+            }
+        }
+    }
+
+    if !current_block.is_empty() {
+        result.push(Group::CommentBlock(current_block));
+    }
+
+    result
+}
+
+fn remove_leading_empty_line(groups: &mut Vec<Group>) {
+    if let Some(Group::EmptyLine) = groups.first() {
+        groups.remove(0);
+    }
+}
+
+fn remove_trailing_empty_line(groups: &mut Vec<Group>) {
+    if let Some(Group::EmptyLine) = groups.last() {
+        groups.pop();
+    }
+}
+
+fn comment_group_to_doc(comment: Vec<&str>) -> RcDoc {
+    RcAllocator
+        .concat(comment.into_iter().map(|c| {
+            RcDoc::text("# ")
+                .append(RcDoc::text(c))
+                .append(RcDoc::hardline())
+        }))
+        .indent(0)
+        .into_doc()
+}
+
+impl Space {
+    /// Format as document for inline use, prefering nil if possible.
+    pub fn to_doc_inline_nospace(&self) -> RcDoc {
+        RcDoc::nil()
+    }
+
+    /// Format as document, prefering a single space if possible.
+    pub fn to_doc_inline_space(&self) -> RcDoc {
+        RcDoc::space()
+    }
+
+    /// Format as document, prefering a newline if possible.
+    pub fn to_doc_newline(&self) -> RcDoc {
+        RcDoc::line()
+    }
+}
+
+impl Ident {
+    pub fn to_doc(&self) -> RcDoc {
+        RcDoc::text(&self.name)
+    }
+}