feat: Implement ORDER BY ... USING <operator> feature

crates/gitql-core/src/lib.rs

@@ -1,9 +1,9 @@
 pub mod combinations_generator;
 pub mod dynamic_types;
 pub mod environment;
+pub mod name_generator;
 pub mod object;
 pub mod schema;
 pub mod signature;
 pub mod types;
 pub mod value;
-pub mod name_generator;

crates/gitql-engine/src/lib.rs

@@ -5,4 +5,4 @@ pub mod engine_evaluator;
 pub mod engine_executor;
 pub mod engine_filter;
 pub mod engine_group;
-pub mod engine_join;
+pub mod engine_join;

crates/gitql-parser/src/lib.rs

@@ -3,4 +3,4 @@ pub mod diagnostic;
 pub mod format_checker;
 pub mod parser;
 pub mod tokenizer;
-pub mod type_checker;
+pub mod type_checker;

crates/gitql-parser/src/parser.rs

@@ -1152,20 +1152,9 @@ fn parse_order_by_statement(
     let mut sorting_orders: Vec<SortingOrder> = vec![];
 
     loop {
-        let argument = parse_expression(context, env, tokens, position)?;
-        arguments.push(argument);
+        arguments.push(parse_expression(context, env, tokens, position)?);
+        sorting_orders.push(parse_sorting_order(tokens, position)?);
 
-        let mut order = SortingOrder::Ascending;
-        if *position < tokens.len() && is_asc_or_desc(&tokens[*position]) {
-            if tokens[*position].kind == TokenKind::Descending {
-                order = SortingOrder::Descending;
-            }
-
-            // Consume `ASC or DESC` keyword
-            *position += 1;
-        }
-
-        sorting_orders.push(order);
         if *position < tokens.len() && tokens[*position].kind == TokenKind::Comma {
             // Consume `,` keyword
             *position += 1;
@@ -1180,6 +1169,50 @@ fn parse_order_by_statement(
     }))
 }
 
+fn parse_sorting_order(
+    tokens: &[Token],
+    position: &mut usize,
+) -> Result<SortingOrder, Box<Diagnostic>> {
+    let mut sorting_order = SortingOrder::Ascending;
+    if *position >= tokens.len() {
+        return Ok(sorting_order);
+    }
+
+    // Parse `ASC` or `DESC`
+    if is_asc_or_desc(&tokens[*position]) {
+        if tokens[*position].kind == TokenKind::Descending {
+            sorting_order = SortingOrder::Descending;
+        }
+
+        // Consume `ASC or DESC` keyword
+        *position += 1;
+        return Ok(sorting_order);
+    }
+
+    // Parse `USING <Operator>`
+    if tokens[*position].kind == TokenKind::Using {
+        // Consume `USING` keyword
+        *position += 1;
+
+        if *position < tokens.len() && is_order_by_using_operator(&tokens[*position]) {
+            if tokens[*position].kind == TokenKind::Greater {
+                sorting_order = SortingOrder::Descending;
+            }
+
+            // Consume `> or <` keyword
+            *position += 1;
+            return Ok(sorting_order);
+        }
+
+        return Err(Diagnostic::error("Expect `>` or `<` after `USING` keyword")
+            .with_location(tokens[*position - 1].location)
+            .as_boxed());
+    }
+
+    // Return default sorting order
+    Ok(sorting_order)
+}
+
 fn parse_into_statement(
     tokens: &[Token],
     position: &mut usize,
@@ -3247,6 +3280,11 @@ fn is_factor_operator(token: &Token) -> bool {
         || token.kind == TokenKind::Caret
 }
 
+#[inline(always)]
+fn is_order_by_using_operator(token: &Token) -> bool {
+    token.kind == TokenKind::Greater || token.kind == TokenKind::Less
+}
+
 #[inline(always)]
 fn is_join_token(token: &Token) -> bool {
     token.kind == TokenKind::Join

crates/gitql-parser/src/tokenizer.rs

@@ -11,6 +11,7 @@ pub enum TokenKind {
     Limit,
     Offset,
     Order,
+    Using,
     By,
     In,
     Is,
@@ -1141,6 +1142,7 @@ fn resolve_symbol_kind(literal: String) -> TokenKind {
         "limit" => TokenKind::Limit,
         "offset" => TokenKind::Offset,
         "order" => TokenKind::Order,
+        "using" => TokenKind::Using,
         "case" => TokenKind::Case,
         "when" => TokenKind::When,
         "then" => TokenKind::Then,

docs/statement/order_by.md

@@ -7,3 +7,10 @@ SELECT author_name, author_email FROM commits ORDER BY author_email, commit_id A
 SELECT author_name, author_email FROM commits ORDER BY author_name DESC
 SELECT author_name, author_email FROM commits ORDER BY author_name, LEN(author_name)
 ```
+
+The `ORDER BY` Statement with `USING <operator>` syntax inspired by PostgreSQL
+
+```sql
+SELECT author_name, author_email FROM commits ORDER BY author_email, commit_id USING <
+SELECT author_name, author_email FROM commits ORDER BY author_name USING >
+```