Refactor disk index build structure

[wuw92]

Why

This is a follow-up to #1254. Removing checkpoint and continuation support eliminated the workflow state that previously justified much of the disk-build indirection, allowing the remaining build path to be simplified and its module ownership clarified.

Module changes

1. Rename core.rs to merged_index.rs; the renamed module retains the merged-build implementation and RAM estimation.
2. Move shared builder fixtures and end-to-end disk-build tests from the renamed module to tests.rs.
3. Move IndexBuildStrategy and determine_build_strategy from the renamed module to build.rs, where the one-shot versus merged decision is made.
4. Move the single in-memory graph construction pipeline from build.rs to inmem_builder.rs.

build.rs
├── one-shot ────────────────> inmem_builder.rs
└── merged ──> merged_index.rs ──> inmem_builder.rs

[Copilot]

Pull request overview

This PR refactors the diskann-disk disk index build path to clarify module ownership: merged-index building logic is separated from top-level orchestration, and the in-memory single-graph build pipeline is consolidated behind an internal entry point, while keeping behavior unchanged.

Changes:

• Extract merged-index build implementation (partition/shard build/merge/cleanup) into a dedicated merged_index module.
• Move the in-memory build pipeline into inmem_builder and call it from the top-level disk builder.
• Centralize builder test fixtures under build::builder::tests and update test imports accordingly.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
diskann-disk/src/search/provider/disk_provider.rs	Updates test fixture import path to the new builder test module location.
diskann-disk/src/build/builder/tests.rs	Introduces centralized builder test fixtures and helpers under build::builder::tests.
diskann-disk/src/build/builder/quantizer.rs	Updates documentation wording for build quantizer types.
diskann-disk/src/build/builder/mod.rs	Adjusts module layout (adds merged_index, exposes tests as pub(crate) under cfg(test)).
diskann-disk/src/build/builder/merged_index.rs	New module containing merged-index build implementation and RAM estimation tests.
diskann-disk/src/build/builder/inmem_builder.rs	Consolidates the one-shot in-memory build pipeline behind an internal entry point.
diskann-disk/src/build/builder/build.rs	Keeps top-level orchestration and policy; wires in merged_index + inmem_builder entry points.
diskann-disk/src/build/builder/core.rs	Deletes the previous combined “core” module after refactor.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated no new comments.