Add in-place group adoption for arena-resident batches

node-graph/libraries/core-types/src/node.rs

@@ -74,6 +74,10 @@ impl<'a> RecordBatch<'a> {
 		self.layout
 	}
 
+	pub(crate) fn frames_ptr(&self) -> *const u8 {
+		self.frames
+	}
+
 	pub fn get(&self, lane: usize) -> RecordLane<'a> {
 		assert!(lane < self.len, "lane {lane} out of bounds for a batch of {}", self.len);
 		RecordLane {
@@ -214,6 +218,10 @@ impl<'a, T> List<'a, T> {
 		self.batch.is_empty()
 	}
 
+	pub fn batch(&self) -> RecordBatch<'a> {
+		self.batch
+	}
+
 	pub fn get(&self, index: usize) -> T
 	where
 		T: Copy,

node-graph/libraries/core-types/src/record.rs

@@ -1623,9 +1623,28 @@ impl GroupItem {
 		&self.layout
 	}
 
+	/// A `GroupItem` over the batch's frames, without copying.
+	///
+	/// # Safety
+	/// The frames must stay valid for the evaluation. Arena-resident batches
+	/// qualify, caller stack scratch does not.
+	pub unsafe fn from_resident(batch: crate::node::RecordBatch<'_>) -> Self {
+		let layout = batch.layout().clone();
+		assert!(!layout.element.parked || layout.element.content_hash.is_some(), "a parked element adopts only with content glue");
+		for field in &layout.fields {
+			assert!(field.repark.is_none() || field.content_hash.is_some(), "a parked field adopts only with content glue");
+		}
+		Self {
+			frames: batch.frames_ptr(),
+			len: batch.len(),
+			layout,
+		}
+	}
+
 	/// A batch view over the stored records.
 	pub fn lanes(&self) -> crate::node::RecordBatch<'_> {
-		// SAFETY: `adopt` filled `len` lanes of `layout` at the layout's stride.
+		// SAFETY: the constructors store `len` lanes of `layout` at the
+		// layout's stride.
 		unsafe { crate::node::RecordBatch::new(self.frames, self.len, &self.layout) }
 	}