feat: Add DocComments to PR (#4701)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: max-sixty

prqlc/prqlc-parser/src/error.rs

@@ -46,8 +46,12 @@ pub enum MessageKind {
 pub enum Reason {
     Simple(String),
     Expected {
+        /// Where we were
+        // (could rename to `where` / `location` / `within`?)
         who: Option<String>,
+        /// What we expected
         expected: String,
+        /// What we found
         found: String,
     },
     Unexpected {

prqlc/prqlc-parser/src/lexer/mod.rs

@@ -184,6 +184,9 @@ fn line_wrap() -> impl Parser<char, TokenKind, Error = Cheap<char>> {
 
 fn comment() -> impl Parser<char, TokenKind, Error = Cheap<char>> {
     just('#').ignore_then(choice((
+        // One option would be to check that doc comments have new lines in the
+        // lexer (we currently do in the parser); which would give better error
+        // messages?
         just('!').ignore_then(
             newline()
                 .not()

prqlc/prqlc-parser/src/parser/common.rs

@@ -5,8 +5,10 @@ use super::pr::{Annotation, Stmt, StmtKind};
 use crate::lexer::lr::TokenKind;
 use crate::span::Span;
 
-pub fn ident_part() -> impl Parser<TokenKind, String, Error = PError> + Clone {
-    return select! {
+use super::SupportsDocComment;
+
+pub(crate) fn ident_part() -> impl Parser<TokenKind, String, Error = PError> + Clone {
+    select! {
         TokenKind::Ident(ident) => ident,
         TokenKind::Keyword(ident) if &ident == "module" => ident,
     }
@@ -16,18 +18,27 @@ pub fn ident_part() -> impl Parser<TokenKind, String, Error = PError> + Clone {
             [Some(TokenKind::Ident("".to_string()))],
             e.found().cloned(),
         )
-    });
+    })
 }
 
-pub fn keyword(kw: &'static str) -> impl Parser<TokenKind, (), Error = PError> + Clone {
+pub(crate) fn keyword(kw: &'static str) -> impl Parser<TokenKind, (), Error = PError> + Clone {
     just(TokenKind::Keyword(kw.to_string())).ignored()
 }
 
+/// Our approach to new lines is each item consumes new lines _before_ itself,
+/// but not newlines after itself. This allows us to enforce new lines between
+/// some items. The only place we handle new lines after an item is in the root
+/// parser.
 pub fn new_line() -> impl Parser<TokenKind, (), Error = PError> + Clone {
-    just(TokenKind::NewLine).ignored()
+    just(TokenKind::NewLine)
+        // Start is considered a new line, so we can enforce things start on a new
+        // line while allowing them to be at the beginning of a file
+        .or(just(TokenKind::Start))
+        .ignored()
+        .labelled("new line")
 }
 
-pub fn ctrl(char: char) -> impl Parser<TokenKind, (), Error = PError> + Clone {
+pub(crate) fn ctrl(char: char) -> impl Parser<TokenKind, (), Error = PError> + Clone {
     just(TokenKind::Control(char)).ignored()
 }
 
@@ -36,5 +47,77 @@ pub fn into_stmt((annotations, kind): (Vec<Annotation>, StmtKind), span: Span) -
         kind,
         span: Some(span),
         annotations,
+        doc_comment: None,
+    }
+}
+
+pub(crate) fn doc_comment() -> impl Parser<TokenKind, String, Error = PError> + Clone {
+    // doc comments must start on a new line, so we enforce a new line (which
+    // can also be a file start) before the doc comment
+    //
+    // TODO: we currently lose any empty newlines between doc comments;
+    // eventually we want to retain them
+    (new_line().repeated().at_least(1).ignore_then(select! {
+        TokenKind::DocComment(dc) => dc,
+    }))
+    .repeated()
+    .at_least(1)
+    .collect()
+    .map(|lines: Vec<String>| lines.join("\n"))
+    .labelled("doc comment")
+}
+
+pub(crate) fn with_doc_comment<'a, P, O>(
+    parser: P,
+) -> impl Parser<TokenKind, O, Error = PError> + Clone + 'a
+where
+    P: Parser<TokenKind, O, Error = PError> + Clone + 'a,
+    O: SupportsDocComment + 'a,
+{
+    doc_comment()
+        .or_not()
+        .then(parser)
+        .map(|(doc_comment, inner)| inner.with_doc_comment(doc_comment))
+}
+
+#[cfg(test)]
+mod tests {
+    use insta::assert_debug_snapshot;
+
+    use super::*;
+    use crate::test::parse_with_parser;
+
+    #[test]
+    fn test_doc_comment() {
+        assert_debug_snapshot!(parse_with_parser(r#"
+        #! doc comment
+        #! another line
+
+        "#, doc_comment()), @r###"
+        Ok(
+            " doc comment\n another line",
+        )
+        "###);
+    }
+
+    #[test]
+    fn test_doc_comment_or_not() {
+        assert_debug_snapshot!(parse_with_parser(r#"hello"#, doc_comment().or_not()).unwrap(), @"None");
+        assert_debug_snapshot!(parse_with_parser(r#"hello"#, doc_comment().or_not().then_ignore(new_line().repeated()).then(ident_part())).unwrap(), @r###"
+        (
+            None,
+            "hello",
+        )
+        "###);
+    }
+
+    #[test]
+    fn test_no_doc_comment_in_with_doc_comment() {
+        impl SupportsDocComment for String {
+            fn with_doc_comment(self, _doc_comment: Option<String>) -> Self {
+                self
+            }
+        }
+        assert_debug_snapshot!(parse_with_parser(r#"hello"#, with_doc_comment(new_line().ignore_then(ident_part()))).unwrap(), @r###""hello""###);
     }
 }