Make Edge::label required instead of optional.

This involves a couple of changes outside of just changing the field type:
1. `CursorIterator` must be able to produce a label for every node now. This wasn't possible before because the root nodes of a cursor had no parent, and so could not derive a label. I've changed `Cursor` in the following ways to fix this:
    * `Cursor::parent` is a new type, `Parent<T>`, instead of `Option<Rc<PathAncestor<T>>>`. `Parent<T>` is an enum with three variants - `None`, `Open(Rc<PathAncestor<T>>)`, and `Closed(Rc<PathAncestor<T>>)`. A `Closed` parent is used when a cursor is spawned from an arbitrary non-root node, and means that the parent can be read but not traversed to. `None` is only used for the true root node.
2. `KindTypes::EdgeLabel` is given a `Default` implementation, which for now just returns the first `PredefinedLabel` variant. This is needed in order to be able to set a "concrete" `EdgeLabel` value from the `metaslang_cst` crate.
3. Added a `Root` variant to `PredefinedLabel`. This will be used when a node is the true root node. For now this will be the default value for `KindTypes::EdgeLabel`.

crates/codegen/language/definition/src/model/manifest.rs

@@ -178,6 +178,7 @@ pub struct Topic {
 )]
 #[strum(serialize_all = "snake_case")]
 pub enum PredefinedLabel {
+    Root,
     Item,
     Variant,
     Separator,

crates/codegen/runtime/cargo/crate/src/runtime/cst/edge_label.rs.jinja2

@@ -34,3 +34,9 @@ pub enum EdgeLabel {
 }
 
 impl crate::cst::EdgeLabelExtensions for EdgeLabel {}
+
+impl Default for EdgeLabel {
+    fn default() -> Self {
+        Self::{{ model.kinds.predefined_labels[0] | pascal_case }}
+    }
+}

crates/codegen/runtime/cargo/crate/src/runtime/parser/parser_support/parser_result.rs

@@ -77,13 +77,13 @@ impl ParserResult {
             label: prev_label, ..
         }) = self.significant_node_mut()
         {
-            *prev_label = Some(label);
+            *prev_label = label;
         }
         // Also allow to name a single trivia terminal node
         else if let ParserResult::Match(Match { nodes, .. }) = &mut self {
             if let [node] = nodes.as_mut_slice() {
                 if node.as_terminal().is_some_and(|tok| tok.kind.is_trivia()) {
-                    node.label = Some(label);
+                    node.label = label;
                 }
             }
         }

crates/codegen/runtime/cargo/crate/src/runtime/parser/parser_support/precedence_helper.rs

@@ -174,7 +174,7 @@ impl PrecedenceHelper {
                 let left_nodes = match left {
                     Some(Expression { nodes }) => {
                         vec![Edge {
-                            label: Some(left_label),
+                            label: left_label,
                             node: Node::nonterminal(child_kind, nodes),
                         }]
                     }
@@ -185,7 +185,7 @@ impl PrecedenceHelper {
                 let right_nodes = match right {
                     Some(Expression { nodes }) => {
                         vec![Edge {
-                            label: Some(right_label),
+                            label: right_label,
                             node: Node::nonterminal(child_kind, nodes),
                         }]
                     }
@@ -197,7 +197,7 @@ impl PrecedenceHelper {
 
                 Expression {
                     nodes: vec![Edge {
-                        label: Some(EdgeLabel::Variant),
+                        label: EdgeLabel::Variant,
                         node: Node::nonterminal(kind, children),
                     }],
                 }

crates/codegen/runtime/cargo/wasm/src/runtime/interface/cst.wit.jinja2

@@ -142,7 +142,7 @@ interface cst {
     /// Represents a connection between nodes in the syntax tree.
     record edge {
         /// Optional label describing the relationship between nodes.
-        label: option<edge-label>,
+        label: edge-label,
         /// The target node of this edge.
         node: node,
     }
@@ -167,7 +167,7 @@ interface cst {
         /// Returns the current node under the cursor.
         node: func() -> node;
         /// Returns the label of the edge from the parent to the current node, if any.
-        label: func() -> option<edge-label>;
+        label: func() -> edge-label;
 
         /// Returns the current text offset of the cursor.
         text-offset: func() -> text-index;

crates/codegen/runtime/cargo/wasm/src/runtime/wrappers/ast/selectors.rs.jinja2

@@ -162,15 +162,15 @@ impl Helper {
             let Edge { label, node } = self.node.children.get(self.index)?;
 
             match label {
-                // Skip unlabeled nodes:
-                | None
+                // Skip root nodes:
+                | EdgeLabel::Root
                 // Skip trivia:
-                | Some(EdgeLabel::LeadingTrivia | EdgeLabel::TrailingTrivia) => {
+                | EdgeLabel::LeadingTrivia | EdgeLabel::TrailingTrivia => {
                     self.index += 1;
                     continue;
                 }
                 // Otherwise, return the edge:
-                Some(other_label) => {
+                other_label => {
                     return Some((*other_label, node.clone()));
                 }
             }

crates/codegen/runtime/cargo/wasm/src/runtime/wrappers/cst/mod.rs

@@ -182,7 +182,7 @@ impl IntoFFI<ffi::Edge> for rust::Edge {
     #[inline]
     fn _into_ffi(self) -> ffi::Edge {
         ffi::Edge {
-            label: self.label.map(IntoFFI::_into_ffi),
+            label: IntoFFI::_into_ffi(self.label),
             node: self.node._into_ffi(),
         }
     }
@@ -219,8 +219,8 @@ define_refcell_wrapper! { Cursor {
         self._borrow_ffi().node()._into_ffi()
     }
 
-    fn label(&self) -> Option<ffi::EdgeLabel> {
-        self._borrow_ffi().label().map(IntoFFI::_into_ffi)
+    fn label(&self) -> ffi::EdgeLabel {
+        IntoFFI::_into_ffi(self._borrow_ffi().label())
     }
 
     fn text_offset(&self) -> ffi::TextIndex {

crates/metaslang/cst/src/cursor.rs

@@ -6,10 +6,34 @@ use crate::kinds::KindTypes;
 use crate::nodes::{Edge, Node, NonterminalNode};
 use crate::text_index::{TextIndex, TextRange};
 
+#[derive(Clone, Debug, PartialEq, Eq)]
+enum Parent<T: KindTypes> {
+    None,
+    Open(Rc<PathAncestor<T>>),
+    Closed(Rc<PathAncestor<T>>),
+}
+
+impl<T: KindTypes> Parent<T> {
+    fn as_closed(&self) -> Parent<T> {
+        match self {
+            Parent::Open(ancestor) => Parent::Closed(ancestor.to_owned()),
+            _ => self.clone(),
+        }
+    }
+
+    fn get_readable(&self) -> Option<&Rc<PathAncestor<T>>> {
+        match self {
+            Parent::Open(ancestor) => Some(ancestor),
+            Parent::Closed(ancestor) => Some(ancestor),
+            Parent::None => None,
+        }
+    }
+}
+
 /// A node in the ancestor path of a [`Cursor`].
 #[derive(Clone, Debug, PartialEq, Eq)]
 struct PathAncestor<T: KindTypes> {
-    parent: Option<Rc<PathAncestor<T>>>,
+    parent: Parent<T>,
     nonterminal_node: Rc<NonterminalNode<T>>,
     child_number: usize,
     text_offset: TextIndex,
@@ -21,7 +45,7 @@ struct PathAncestor<T: KindTypes> {
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct Cursor<T: KindTypes> {
     /// The parent path of this cursor
-    parent: Option<Rc<PathAncestor<T>>>,
+    parent: Parent<T>,
     /// The node the cursor is currently pointing to.
     node: Node<T>,
     /// The index of the current child node in the parent's children.
@@ -59,7 +83,7 @@ impl<T: KindTypes> Cursor<T> {
 impl<T: KindTypes> Cursor<T> {
     pub(crate) fn new(node: Node<T>, text_offset: TextIndex) -> Self {
         Self {
-            parent: None,
+            parent: Parent::None,
             node,
             child_number: 0,
             text_offset,
@@ -75,9 +99,9 @@ impl<T: KindTypes> Cursor<T> {
 
     /// Completes the cursor, setting it to the root node.
     pub fn complete(&mut self) {
-        if let Some(parent) = &self.parent.clone() {
+        if let Parent::Open(parent) = &self.parent.clone() {
             let mut parent = parent;
-            while let Some(grandparent) = &parent.parent {
+            while let Parent::Open(grandparent) = &parent.parent {
                 parent = grandparent;
             }
             self.set_from_ancestor_node(parent);
@@ -92,7 +116,7 @@ impl<T: KindTypes> Cursor<T> {
     pub fn spawn(&self) -> Self {
         Self {
             is_completed: false,
-            parent: None,
+            parent: self.parent.as_closed(),
             node: self.node.clone(),
             child_number: 0,
             text_offset: self.text_offset,
@@ -109,12 +133,13 @@ impl<T: KindTypes> Cursor<T> {
         self.node.clone()
     }
 
-    pub fn label(&self) -> Option<T::EdgeLabel> {
-        self.parent.as_ref().and_then(|parent| {
+    pub fn label(&self) -> T::EdgeLabel {
+        if let Some(parent) = self.parent.get_readable() {
             let this = &parent.nonterminal_node.children[self.child_number];
-
             this.label
-        })
+        } else {
+            T::EdgeLabel::default()
+        }
     }
 
     /// Returns the text offset that corresponds to the beginning of the currently pointed to node.
@@ -132,10 +157,10 @@ impl<T: KindTypes> Cursor<T> {
     /// Returns the depth of the current node in the CST, i.e. the number of ancestors.
     pub fn depth(&self) -> usize {
         let mut depth = 0;
-        if let Some(parent) = &self.parent {
+        if let Parent::Open(parent) = &self.parent {
             let mut parent = parent;
             depth += 1;
-            while let Some(grandparent) = &parent.parent {
+            while let Parent::Open(grandparent) = &parent.parent {
                 depth += 1;
                 parent = grandparent;
             }
@@ -224,7 +249,7 @@ impl<T: KindTypes> Cursor<T> {
     ///
     /// Returns `false` if the cursor is finished and at the root.
     pub fn go_to_parent(&mut self) -> bool {
-        if let Some(parent) = &self.parent.clone() {
+        if let Parent::Open(parent) = &self.parent.clone() {
             self.set_from_ancestor_node(parent);
 
             true
@@ -246,7 +271,7 @@ impl<T: KindTypes> Cursor<T> {
         // If the current cursor is a node and it has children, go to first children
         if let Some(new_parent) = self.as_ancestor_node() {
             if let Some(new_child) = new_parent.nonterminal_node.children.first().cloned() {
-                self.parent = Some(new_parent);
+                self.parent = Parent::Open(new_parent);
                 self.node = new_child.node;
                 self.child_number = 0;
 
@@ -273,7 +298,7 @@ impl<T: KindTypes> Cursor<T> {
                 for sibling in &new_parent.nonterminal_node.children[..self.child_number] {
                     self.text_offset += sibling.text_len();
                 }
-                self.parent = Some(new_parent);
+                self.parent = Parent::Open(new_parent);
 
                 return true;
             }
@@ -303,7 +328,7 @@ impl<T: KindTypes> Cursor<T> {
                 for sibling in &new_parent.nonterminal_node.children[..self.child_number] {
                     self.text_offset += sibling.text_len();
                 }
-                self.parent = Some(new_parent);
+                self.parent = Parent::Open(new_parent);
 
                 return true;
             }
@@ -320,7 +345,7 @@ impl<T: KindTypes> Cursor<T> {
             return false;
         }
 
-        if let Some(parent) = &self.parent {
+        if let Parent::Open(parent) = &self.parent {
             let new_child_number = self.child_number + 1;
             if let Some(new_child) = parent.nonterminal_node.children.get(new_child_number) {
                 self.text_offset += self.node.text_len();
@@ -342,7 +367,7 @@ impl<T: KindTypes> Cursor<T> {
             return false;
         }
 
-        if let Some(parent) = &self.parent {
+        if let Parent::Open(parent) = &self.parent {
             if self.child_number > 0 {
                 let new_child_number = self.child_number - 1;
                 let new_child = &parent.nonterminal_node.children[new_child_number];
@@ -438,14 +463,15 @@ impl<T: KindTypes> Iterator for CursorIterator<T> {
 }
 
 pub struct AncestorsIterator<T: KindTypes> {
-    current: Option<Rc<PathAncestor<T>>>,
+    current: Parent<T>,
 }
 
 impl<T: KindTypes> Iterator for AncestorsIterator<T> {
     type Item = Rc<NonterminalNode<T>>;
 
     fn next(&mut self) -> Option<Self::Item> {
-        if let Some(current) = self.current.take() {
+        // if let Some(current) = self.current.take() {
+        if let Parent::Open(current) = self.current.clone() {
             self.current = current.parent.clone();
             Some(Rc::clone(&current.nonterminal_node))
         } else {

crates/metaslang/cst/src/kinds.rs

@@ -41,7 +41,7 @@ pub trait TerminalKindExtensions: BaseKind {
 
 pub trait NonterminalKindExtensions: BaseKind {}
 
-pub trait EdgeLabelExtensions: BaseKind {}
+pub trait EdgeLabelExtensions: BaseKind + Default {}
 
 pub trait KindTypes: std::fmt::Debug + Clone + PartialEq {
     type NonterminalKind: NonterminalKindExtensions;

crates/metaslang/cst/src/nodes.rs

@@ -60,14 +60,17 @@ pub enum Node<T: KindTypes> {
 
 #[derive(Clone, Debug, PartialEq, Eq, Serialize)]
 pub struct Edge<T: KindTypes> {
-    pub label: Option<T::EdgeLabel>,
+    pub label: T::EdgeLabel,
     pub node: Node<T>,
 }
 
 impl<T: KindTypes> Edge<T> {
     /// Creates an anonymous node (without a label).
     pub fn anonymous(node: Node<T>) -> Self {
-        Self { label: None, node }
+        Self {
+            label: T::EdgeLabel::default(),
+            node,
+        }
     }
 }
 

crates/metaslang/cst/src/query/engine.rs

@@ -35,12 +35,12 @@ impl<T: KindTypes + 'static> Cursor<T> {
                     NodeKind::Nonterminal(nonterminal.kind) == *node_kind
                 }
                 NodeSelector::NodeText { .. } => false,
-                NodeSelector::EdgeLabel { edge_label } => Some(*edge_label) == self.label(),
+                NodeSelector::EdgeLabel { edge_label } => *edge_label == self.label(),
                 NodeSelector::EdgeLabelAndNodeKind {
                     edge_label,
                     node_kind,
                 } => {
-                    Some(*edge_label) == self.label()
+                    *edge_label == self.label()
                         && NodeKind::Nonterminal(nonterminal.kind) == *node_kind
                 }
                 NodeSelector::EdgeLabelAndNodeText { .. } => false,
@@ -54,18 +54,15 @@ impl<T: KindTypes + 'static> Cursor<T> {
                     NodeKind::Terminal(terminal.kind) == *node_kind
                 }
                 NodeSelector::NodeText { node_text } => terminal.text == *node_text,
-                NodeSelector::EdgeLabel { edge_label } => Some(*edge_label) == self.label(),
+                NodeSelector::EdgeLabel { edge_label } => *edge_label == self.label(),
                 NodeSelector::EdgeLabelAndNodeKind {
                     edge_label,
                     node_kind,
-                } => {
-                    Some(*edge_label) == self.label()
-                        && NodeKind::Terminal(terminal.kind) == *node_kind
-                }
+                } => *edge_label == self.label() && NodeKind::Terminal(terminal.kind) == *node_kind,
                 NodeSelector::EdgeLabelAndNodeText {
                     edge_label,
                     node_text,
-                } => Some(*edge_label) == self.label() && terminal.text == *node_text,
+                } => *edge_label == self.label() && terminal.text == *node_text,
             },
         }
     }

crates/metaslang/graph_builder/src/functions.rs

@@ -283,7 +283,6 @@ pub mod stdlib {
                 let index = parent
                     .children()
                     .iter()
-                    .filter(|edge| edge.label.is_some())
                     .position(|edge| edge.node == node)
                     .ok_or(ExecutionError::FunctionFailed(
                         "named-child-index".into(),
@@ -403,11 +402,7 @@ pub mod stdlib {
             ) -> Result<Value, ExecutionError> {
                 let cursor = &graph[parameters.param()?.into_syntax_node_ref()?];
                 parameters.finish()?;
-                let named_child_count = cursor
-                    .children()
-                    .iter()
-                    .filter(|edge| edge.label.is_some())
-                    .count();
+                let named_child_count = cursor.children().len();
                 Ok(Value::Integer(named_child_count as u32))
             }
         }

crates/metaslang/graph_builder/tests/functions.rs

@@ -17,13 +17,15 @@ use {log as _, regex as _, serde_json as _, smallvec as _, string_interner as _,
     Clone,
     Copy,
     Debug,
+    Default,
     Eq,
     PartialEq,
     serde::Serialize,
     strum_macros::IntoStaticStr,
     strum_macros::EnumString,
 )]
 pub enum DummyKind {
+    #[default]
     Module,
 }
 impl metaslang_cst::kinds::TerminalKindExtensions for DummyKind {}