This feature hub defines the normative contract for **ast and hir shape contract** and links newcomer-oriented reference articles.

## Implementation anchors
- `compiler/crates/beskid_analysis/src/syntax/items/` exposes AST-like syntax node shapes.
- `compiler/crates/beskid_analysis/src/resolve/items.rs` maps parsed items into resolved structures.
- `compiler/crates/beskid_analysis/src/analysis/` consumes those shapes for semantic passes.

## Decisions
<!-- spec:generate:adr-index -->
No open decisions. Closed choices are normative ADRs under **`adr/`** (`D-COMP-FRONT-0001` … `D-COMP-FRONT-0003`); use the reader **ADRs** tab for expandable detail.
<!-- /spec:generate:adr-index -->
## Articles
<!-- spec:generate:article-index -->
- [AST and HIR shape contract - Contracts and edge cases](./articles/contracts-and-edge-cases/)
- [AST and HIR shape contract - Design model](./articles/design-model/)
- [AST and HIR shape contract - Examples](./articles/examples/)
- [AST and HIR shape contract - FAQ and troubleshooting](./articles/faq-and-troubleshooting/)
- [AST and HIR shape contract - Flow and algorithm](./articles/flow-and-algorithm/)
- [AST and HIR shape contract - Verification and traceability](./articles/verification-and-traceability/)
<!-- /spec:generate:article-index -->

## Context

Sibling articles under this feature previously restated requirements in inconsistent forms.

## Decision

This feature hub **owns** normative MUST/SHOULD contract text. Sibling articles **must not** redefine hub requirements and **should** link here for authority.

## Consequences

Contract changes start on the hub or in linked ADRs, then propagate to articles and implementation anchors.

## Verification anchors

- `site/website/src/content/docs/platform-spec/compiler/front-end/ast-hir-shape-contract/index.mdx`
- `article bundle under the same feature directory.`

## Context

Implementation crates accumulated informal notes that diverged from published contracts.

## Decision

Normative platform-spec prose and ADRs under this feature **supersede** informal comments in implementation crates until explicitly migrated into spec text.

## Consequences

Engineers file spec/ADR updates when behavior changes; crate comments are non-authoritative for conformance arguments.

## Verification anchors

- `compiler/crates/beskid_analysis/src/syntax/items/`
- `compiler/crates/beskid_analysis/src/resolve/items.rs`
- `compiler/crates/beskid_analysis/src/analysis/`

## Context

This feature hub defines the normative contract for **ast and hir shape contract** and links newcomer-oriented reference articles.

## Decision

The reference compiler **must** implement AST and HIR shape contract as documented in this feature hub and its article bundle.

## Consequences

Changes require hub/ADR updates and verification anchor extensions.

## Verification anchors

- `compiler/crates/beskid_analysis/src/syntax/items/`
- `compiler/crates/beskid_analysis/src/resolve/items.rs`
- `compiler/crates/beskid_analysis/src/analysis/`

This article documents **contracts and edge cases** for **ast and hir shape contract** in the reference compiler.

## What this covers
For newcomers, this page explains where the contract shows up in day-to-day compiler work and which code paths are most useful first reads.

## Anchored code paths
- `compiler/crates/beskid_analysis/src/syntax/items/` exposes AST-like syntax node shapes.
- `compiler/crates/beskid_analysis/src/resolve/items.rs` maps parsed items into resolved structures.
- `compiler/crates/beskid_analysis/src/analysis/` consumes those shapes for semantic passes.

## Practical notes
- Prefer tracing from CLI/test entry points into analysis/codegen crates before changing internals.
- Treat diagnostics and tests as part of the contract, not optional implementation details.
- If behavior changes, update this article and add/adjust tests in `compiler/crates/beskid_tests` or `compiler/crates/beskid_e2e_tests`.

This article documents **design model** for **ast and hir shape contract** in the reference compiler.

## What this covers
For newcomers, this page explains where the contract shows up in day-to-day compiler work and which code paths are most useful first reads.

## Anchored code paths
- `compiler/crates/beskid_analysis/src/syntax/items/` exposes AST-like syntax node shapes.
- `compiler/crates/beskid_analysis/src/resolve/items.rs` maps parsed items into resolved structures.
- `compiler/crates/beskid_analysis/src/analysis/` consumes those shapes for semantic passes.

## `extend type` and HIR

`extend type` lowers to HIR member metadata attached to the extended type symbol. Generated extensions from mod contracts follow the same lowering path as hand-authored extensions. HIR **must not** partially encode unmerged generator contributions.

## Practical notes
- Prefer tracing from CLI/test entry points into analysis/codegen crates before changing internals.
- Treat diagnostics and tests as part of the contract, not optional implementation details.
- If behavior changes, update this article and add/adjust tests in `compiler/crates/beskid_tests` or `compiler/crates/beskid_e2e_tests`.

This article documents **examples** for **ast and hir shape contract** in the reference compiler.

## What this covers
For newcomers, this page explains where the contract shows up in day-to-day compiler work and which code paths are most useful first reads.

## Anchored code paths
- `compiler/crates/beskid_analysis/src/syntax/items/` exposes AST-like syntax node shapes.
- `compiler/crates/beskid_analysis/src/resolve/items.rs` maps parsed items into resolved structures.
- `compiler/crates/beskid_analysis/src/analysis/` consumes those shapes for semantic passes.

## Practical notes
- Prefer tracing from CLI/test entry points into analysis/codegen crates before changing internals.
- Treat diagnostics and tests as part of the contract, not optional implementation details.
- If behavior changes, update this article and add/adjust tests in `compiler/crates/beskid_tests` or `compiler/crates/beskid_e2e_tests`.

This article documents **faq and troubleshooting** for **ast and hir shape contract** in the reference compiler.

## What this covers
For newcomers, this page explains where the contract shows up in day-to-day compiler work and which code paths are most useful first reads.

## Anchored code paths
- `compiler/crates/beskid_analysis/src/syntax/items/` exposes AST-like syntax node shapes.
- `compiler/crates/beskid_analysis/src/resolve/items.rs` maps parsed items into resolved structures.
- `compiler/crates/beskid_analysis/src/analysis/` consumes those shapes for semantic passes.

## Practical notes
- Prefer tracing from CLI/test entry points into analysis/codegen crates before changing internals.
- Treat diagnostics and tests as part of the contract, not optional implementation details.
- If behavior changes, update this article and add/adjust tests in `compiler/crates/beskid_tests` or `compiler/crates/beskid_e2e_tests`.

This article documents **flow and algorithm** for **ast and hir shape contract** in the reference compiler.

## What this covers
For newcomers, this page explains where the contract shows up in day-to-day compiler work and which code paths are most useful first reads.

## Anchored code paths
- `compiler/crates/beskid_analysis/src/syntax/items/` exposes AST-like syntax node shapes.
- `compiler/crates/beskid_analysis/src/resolve/items.rs` maps parsed items into resolved structures.
- `compiler/crates/beskid_analysis/src/analysis/` consumes those shapes for semantic passes.

## Practical notes
- Prefer tracing from CLI/test entry points into analysis/codegen crates before changing internals.
- Treat diagnostics and tests as part of the contract, not optional implementation details.
- If behavior changes, update this article and add/adjust tests in `compiler/crates/beskid_tests` or `compiler/crates/beskid_e2e_tests`.

This article documents **verification and traceability** for **ast and hir shape contract** in the reference compiler.

## What this covers
For newcomers, this page explains where the contract shows up in day-to-day compiler work and which code paths are most useful first reads.

## Anchored code paths
- `compiler/crates/beskid_analysis/src/syntax/items/` exposes AST-like syntax node shapes.
- `compiler/crates/beskid_analysis/src/resolve/items.rs` maps parsed items into resolved structures.
- `compiler/crates/beskid_analysis/src/analysis/` consumes those shapes for semantic passes.

## Practical notes
- Prefer tracing from CLI/test entry points into analysis/codegen crates before changing internals.
- Treat diagnostics and tests as part of the contract, not optional implementation details.
- If behavior changes, update this article and add/adjust tests in `compiler/crates/beskid_tests` or `compiler/crates/beskid_e2e_tests`.