internal: Add SyntaxFactory to ease generating nodes with syntax mappings

crates/syntax/src/ast/syntax_factory.rs

@@ -0,0 +1,45 @@
+//! Builds upon [`crate::ast::make`] constructors to create ast fragments with
+//! optional syntax mappings.
+//!
+//! Instead of forcing make constructors to perform syntax mapping, we instead
+//! let [`SyntaxFactory`] handle constructing the mappings. Care must be taken
+//! to remember to feed the syntax mappings into a [`SyntaxEditor`](crate::syntax_editor::SyntaxEditor),
+//! if applicable.
+
+mod constructors;
+
+use std::cell::{RefCell, RefMut};
+
+use crate::syntax_editor::SyntaxMapping;
+
+pub struct SyntaxFactory {
+    // Stored in a refcell so that the factory methods can be &self
+    mappings: Option<RefCell<SyntaxMapping>>,
+}
+
+impl SyntaxFactory {
+    /// Creates a new [`SyntaxFactory`], generating mappings between input nodes and generated nodes.
+    pub fn new() -> Self {
+        Self { mappings: Some(RefCell::new(SyntaxMapping::new())) }
+    }
+
+    /// Creates a [`SyntaxFactory`] without generating mappings.
+    pub fn without_mappings() -> Self {
+        Self { mappings: None }
+    }
+
+    /// Gets all of the tracked syntax mappings, if any.
+    pub fn finish_with_mappings(self) -> SyntaxMapping {
+        self.mappings.unwrap_or_default().into_inner()
+    }
+
+    fn mappings(&self) -> Option<RefMut<'_, SyntaxMapping>> {
+        self.mappings.as_ref().map(|it| it.borrow_mut())
+    }
+}
+
+impl Default for SyntaxFactory {
+    fn default() -> Self {
+        Self::without_mappings()
+    }
+}