Add support for DuckDB struct literal syntax (#1194)

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

src/ast/mod.rs

@@ -347,6 +347,23 @@ impl fmt::Display for StructField {
     }
 }
 
+/// A dictionary field within a dictionary.
+///
+/// [duckdb]: https://duckdb.org/docs/sql/data_types/struct#creating-structs
+#[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[cfg_attr(feature = "visitor", derive(Visit, VisitMut))]
+pub struct DictionaryField {
+    pub key: Ident,
+    pub value: Box<Expr>,
+}
+
+impl fmt::Display for DictionaryField {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}: {}", self.key, self.value)
+    }
+}
+
 /// Options for `CAST` / `TRY_CAST`
 /// BigQuery: <https://cloud.google.com/bigquery/docs/reference/standard-sql/format-elements#formatting_syntax>
 #[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
@@ -687,6 +704,14 @@ pub enum Expr {
         expr: Box<Expr>,
         name: Ident,
     },
+    /// `DuckDB` specific `Struct` literal expression [1]
+    ///
+    /// Syntax:
+    /// ```sql
+    /// syntax: {'field_name': expr1[, ... ]}
+    /// ```
+    /// [1]: https://duckdb.org/docs/sql/data_types/struct#creating-structs
+    Dictionary(Vec<DictionaryField>),
     /// An array index expression e.g. `(ARRAY[1, 2])[1]` or `(current_schemas(FALSE))[1]`
     ArrayIndex {
         obj: Box<Expr>,
@@ -1146,6 +1171,9 @@ impl fmt::Display for Expr {
             Expr::Named { expr, name } => {
                 write!(f, "{} AS {}", expr, name)
             }
+            Expr::Dictionary(fields) => {
+                write!(f, "{{{}}}", display_comma_separated(fields))
+            }
             Expr::ArrayIndex { obj, indexes } => {
                 write!(f, "{obj}")?;
                 for i in indexes {