add unflatten trait

substrate/src/types/layout.rs

@@ -2,6 +2,7 @@
 
 use super::{
     FlatLen, Flatten, HasBundleKind, HasNameTree, NameBuf, NameFragment, NameTree, Signal,
+    Unflatten,
 };
 use crate::error::Result;
 use crate::layout::element::NamedPorts;
@@ -67,7 +68,12 @@ impl<L> Bbox for PortGeometry<L> {
 ///
 /// An instance of a [`BundleKind`].
 pub trait LayoutBundle<S: Schema>:
-    super::HasBundleKind + Flatten<PortGeometry<S::Layer>> + TransformRef + Send + Sync
+    super::HasBundleKind
+    + Flatten<PortGeometry<S::Layer>>
+    + Unflatten<Self::BundleKind, PortGeometry<S::Layer>>
+    + TransformRef
+    + Send
+    + Sync
 {
 }
 
@@ -77,6 +83,7 @@ where
     T: super::HasBundleKind
         + FlatLen
         + Flatten<PortGeometry<S::Layer>>
+        + Unflatten<Self::BundleKind, PortGeometry<S::Layer>>
         + TransformRef
         + Send
         + Sync,

substrate/src/types/mod.rs

@@ -60,6 +60,19 @@ pub trait Flatten<T>: FlatLen {
     }
 }
 
+/// Unflatten a structure from an iterator.
+pub trait Unflatten<D, T>: FlatLen + Sized {
+    /// Unflatten a structure from an iterator.
+    ///
+    /// A correct implementation must only return [`None`]
+    /// if the iterator has insufficient elements.
+    /// Returning None for any other reason is a logic error.
+    /// Unsafe code should not rely on implementations of this method being correct.
+    fn unflatten<I>(data: &D, source: &mut I) -> Option<Self>
+    where
+        I: Iterator<Item = T>;
+}
+
 impl<S, T: Flatten<S>> Flatten<S> for &T {
     fn flatten<E>(&self, output: &mut E)
     where