Make StructVariableInitializer an AST node

compiler/ast/src/expressions/struct_init.rs

@@ -27,10 +27,14 @@ pub struct StructVariableInitializer {
     /// The expression to initialize the field with.
     /// When `None`, a binding, in scope, with the name will be used instead.
     pub expression: Option<Expression>,
+    /// The span of the node.
+    pub span: Span,
     /// The ID of the node.
     pub id: NodeID,
 }
 
+crate::simple_node_impl!(StructVariableInitializer);
+
 impl fmt::Display for StructVariableInitializer {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         if let Some(expr) = &self.expression {

compiler/parser/src/parser/expression.rs

@@ -571,14 +571,16 @@ impl ParserContext<'_> {
             self.expect_identifier()?
         };
 
-        let expression = if self.eat(&Token::Colon) {
+        let (expression, span) = if self.eat(&Token::Colon) {
             // Parse individual struct variable declarations.
-            Some(self.parse_expression()?)
+            let expression = self.parse_expression()?;
+            let span = identifier.span + expression.span();
+            (Some(expression), span)
         } else {
-            None
+            (None, identifier.span)
         };
 
-        Ok(StructVariableInitializer { identifier, expression, id: NodeID::default() })
+        Ok(StructVariableInitializer { identifier, expression, id: NodeID::default(), span })
     }
 
     /// Returns an [`Expression`] AST node if the next tokens represent a