refactor(ssz): review tree views

[wemeetagain]

Summary

The tree view refactor in #139 correctly killed the heap-allocated BaseTreeView indirection, but it overcorrected — it scattered five fields (allocator, pool, root, children_nodes, changed) into every view type and recovered sharing through ChildNodes, a set of free functions that take anytype and duck-type their way to the right field names.

This PR fixes the abstraction:

• TreeViewState — a concrete struct embedded by value in each chunk-based view (BasicPackedChunks, CompositeChunks, BitArray). Not a pointer, not a trait — just a struct with typed methods. When you see state: TreeViewState, you know what state it carries and what operations exist. The compiler gives real errors at the call site, not inside a generic utility that reconstructs the interface from field names.

• StaticBitSet for ContainerTreeView.changed — the field count is comptime-known, so the dirty-tracking hashmap (AutoArrayHashMapUnmanaged(usize, void)) becomes a zero-allocation bitset. No hashmap init, no hashmap deinit, no allocator needed for dirty tracking.

ContainerTreeView does not use TreeViewState — its comptime tuple + fixed arrays are a genuinely different storage shape, and the bitset is the right dirty tracker for it. The split is now explicit in the type system rather than implicit in "which types happen to have the right field names."

What changed

Before	After
ChildNodes.getChildNode(self, gindex) — anytype dispatch	self.state.getChildNode(gindex) — concrete method on TreeViewState
ChildNodes.Change.commit(self) — anytype dispatch	self.state.commitNodes() — concrete method
CompositeChunks.commit() duplicated sort/setNodesGrouped/ref/unref	Flushes child views into children_nodes, delegates to commitNodes()
getLength/setLength on generic TreeViewState	Inlined into BasicPackedChunks/CompositeChunks (list-specific)
changed: AutoArrayHashMapUnmanaged(usize, void) in ContainerTreeView	changed: StaticBitSet(N) — zero allocation

Test plan

• zig build test:ssz — all 194 tests pass
• zig build test:spec_tests -Dpreset=minimal

🤖 Generated with Claude Code

[gemini-code-assist]

Summary of Changes

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This pull request significantly refactors the internal architecture of tree views within the SSZ library. The primary goal was to improve abstraction and efficiency by centralizing common state management and optimizing dirty-tracking mechanisms. This change enhances type safety, reduces boilerplate, and eliminates unnecessary heap allocations, leading to a more robust and performant implementation of tree view operations.

Highlights

• TreeViewState Introduction: Introduced a concrete TreeViewState struct to encapsulate common fields (allocator, pool, root, children_nodes, changed) for chunk-based tree views, replacing scattered fields and ChildNodes utility functions with typed methods.
• StaticBitSet for ContainerTreeView: Replaced the heap-allocated AutoArrayHashMapUnmanaged(usize, void) for dirty tracking in ContainerTreeView.changed with a zero-allocation StaticBitSet(N), leveraging comptime-known field counts.
• Method Dispatch Refactor: Converted ChildNodes.getChildNode(self, gindex) and ChildNodes.Change.commit(self) to concrete methods like self.state.getChildNode(gindex) and self.state.commitNodes().
• List-Specific Length Management: Inlined getLength and setLength methods, previously generic on TreeViewState, directly into BasicPackedChunks and CompositeChunks as they are list-specific operations.
• CompositeChunks Commit Logic Streamlined: Refactored CompositeChunks.commit() to flush child views into children_nodes and delegate to commitNodes(), removing duplicated sort/setNodesGrouped/ref/unref logic.

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Changelog

• src/ssz/tree_view/array_basic.zig
  • Updated references to self.chunks.root, self.chunks.pool, and self.chunks.children_nodes to use the new self.chunks.state member for accessing tree view state.
• src/ssz/tree_view/array_composite.zig
  • Adjusted access paths for root, pool, and children_nodes to point to the state field within self.chunks.
• src/ssz/tree_view/bit_array.zig
  • Replaced direct fields (allocator, pool, root, children_nodes, changed) with a single state: TreeViewState member.
  • Migrated init, clone, deinit, commit, and clearCache logic to delegate to the new state struct.
  • Updated getChildNode and setChildNode calls to use self.state.
• src/ssz/tree_view/bit_list.zig
  • Modified references to self.data.root, self.data.pool, and self.data.children_nodes to correctly access them via self.data.state.
• src/ssz/tree_view/bit_vector.zig
  • Changed property access from self.data.root, self.data.pool, and self.data.children_nodes to self.data.state.
• src/ssz/tree_view/chunks.zig
  • Replaced direct fields (allocator, pool, root, children_nodes, changed) with state: TreeViewState in BasicPackedChunks and CompositeChunks.
  • Updated init, clone, deinit, commit, and clearCache methods to use the state struct.
  • Moved getLength and setLength implementations from generic ChildNodes into BasicPackedChunks and CompositeChunks.
  • Refactored CompositeChunks.commit to iterate over self.state.changed keys and update self.state.children_nodes before calling self.state.commitNodes().
• src/ssz/tree_view/container.zig
  • Replaced changed: std.AutoArrayHashMapUnmanaged(usize, void) with changed: std.StaticBitSet(ST.chunk_count).
  • Updated initialization of changed from .empty to std.StaticBitSet(ST.chunk_count).initEmpty().
  • Modified changed.contains(i) to changed.isSet(i) and changed.put(allocator, field_index, {}) to changed.set(field_index).
  • Changed changed.clearRetainingCapacity() to changed = std.StaticBitSet(ST.chunk_count).initEmpty().
• src/ssz/tree_view/list_basic.zig
  • Adjusted property access for root, pool, and children_nodes to use self.chunks.state.
• src/ssz/tree_view/list_composite.zig
  • Updated references to root, pool, and children_nodes to use self.chunks.state.
• src/ssz/tree_view/utils/child_nodes.zig
  • Removed the child_nodes.zig utility file, as its functionality has been absorbed into TreeViewState.
• src/ssz/tree_view/utils/tree_view_state.zig
  • Added a new file defining the TreeViewState struct, which centralizes common state and methods for tree views.

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[gemini-code-assist]

Code Review

This pull request is a significant refactoring that improves the abstraction and type safety of the tree view implementations. The introduction of TreeViewState successfully encapsulates common state and logic, removing the need for anytype and duck-typing, which makes the code easier to understand and maintain. The switch to StaticBitSet for ContainerTreeView is also a great performance optimization, eliminating heap allocations for dirty tracking. The changes are well-structured and align with the stated goals. I've added a few suggestions to further improve safety by adding assertions, in line with the repository's style guide.

[twoeths]

looks good to me
the use of std.StaticBitSet is awesome!