ide: show function comment on hover

PLAN.md

@@ -194,6 +194,10 @@ sql for benchmarks maybe?
 
   https://github.com/earendil-works/absurd/blob/56500e5a23beca5e976f329475063f24692d99cc/sql/absurd.sql
 
+- pg_6502
+
+  https://github.com/lasect/pg_6502
+
 ### CLI
 
 from `deno`

crates/squawk_ide/src/comments.rs

@@ -0,0 +1,143 @@
+use rowan::{Direction, NodeOrToken};
+use squawk_syntax::{
+    SyntaxNode,
+    ast::{self, AstToken},
+};
+
+pub(crate) fn preceding_comment(node: &SyntaxNode) -> Option<String> {
+    let mut comments = vec![];
+
+    for element in node.siblings_with_tokens(Direction::Prev).skip(1) {
+        let NodeOrToken::Token(token) = element else {
+            break;
+        };
+
+        if let Some(comment) = ast::Comment::cast(token.clone()) {
+            let comment = normalize_comment(comment.text());
+            if !comment.is_empty() {
+                comments.push(comment);
+            }
+            continue;
+        }
+
+        // In the following case, we would skip the `-- foo` since it's not
+        // connected to the function:
+        //
+        // -- foo
+        //
+        // create function foo() returns void
+        //   as 'select 1' language sql;
+        if let Some(ws) = ast::Whitespace::cast(token)
+            && !ws.text().contains("\n\n")
+        {
+            continue;
+        }
+
+        break;
+    }
+
+    if comments.is_empty() {
+        None
+    } else {
+        comments.reverse();
+        Some(comments.join("\n"))
+    }
+}
+
+fn normalize_comment(comment: &str) -> String {
+    if let Some(comment) = comment.strip_prefix("--") {
+        return comment.trim().to_string();
+    }
+
+    if let Some(comment) = comment
+        .strip_prefix("/*")
+        .and_then(|comment| comment.strip_suffix("*/"))
+    {
+        let normalized = comment
+            .lines()
+            .map(|line| line.trim_start().trim_start_matches('*').trim_start())
+            .collect::<Vec<_>>()
+            .join("\n");
+
+        return normalized.trim().to_string();
+    }
+
+    comment.trim().to_string()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::db::{Database, File, parse};
+
+    use insta::assert_snapshot;
+    use squawk_syntax::ast::AstNode;
+
+    #[must_use]
+    fn preceding_comment(sql: &str) -> String {
+        let db = Database::default();
+        let file = File::new(&db, sql.to_string().into());
+        let parse = parse(&db, file);
+        assert_eq!(parse.errors(), vec![]);
+
+        let stmt = parse.tree().stmts().next().unwrap();
+        super::preceding_comment(stmt.syntax()).unwrap()
+    }
+
+    fn no_comment(sql: &str) {
+        let db = Database::default();
+        let file = File::new(&db, sql.to_string().into());
+        let parse = parse(&db, file);
+        assert_eq!(parse.errors(), vec![]);
+
+        let stmt = parse.tree().stmts().next().unwrap();
+        assert!(
+            super::preceding_comment(stmt.syntax()).is_none(),
+            "We shouldn't find a comment, if that's expected, use the preceding_comment instead"
+        );
+    }
+
+    #[test]
+    fn not_preceding_func() {
+        no_comment(
+            "
+-- whitespace between so we don't count this
+
+create function foo() returns int as $$ select 1 $$ language sql;
+",
+        );
+    }
+
+    #[test]
+    fn preceding_func_line() {
+        let comment = preceding_comment(
+            "
+-- whitespace between this and the following, so skip it
+
+-- this is a doc comment
+-- for foo
+create function foo() returns int as $$ select 1 $$ language sql;
+",
+        );
+
+        assert_snapshot!(comment, @r"
+        this is a doc comment
+        for foo
+        ");
+    }
+
+    #[test]
+    fn preceding_func_block() {
+        let comment = preceding_comment(
+            "
+/** line 1 */
+/* line 2 */
+create function foo() returns int as $$ select 1 $$ language sql;
+",
+        );
+
+        assert_snapshot!(comment, @"
+        line 1
+        line 2
+        ");
+    }
+}