# PBS AST Workshop 1

Status: Closed (2026-03-05)

## Purpose

Close the top-level AST contract for `11. AST Specification.md`:

- file/root model,
- minimum node-family baseline,
- mandatory attribution fields.

## Decisions To Produce

1. Root/file node contract and per-file AST boundary.
2. Mandatory attribution fields on AST nodes (`file/start/end`).
3. Which families are mandatory in v1 AST (declaration/statement/expression categories).
4. Contract status: obligations-based versus one mandatory in-memory class hierarchy.

## Candidate Decisions

### 1. Obligations-First AST Contract

- Spec defines required observable AST obligations.
- Internal object model remains implementation-defined.

### 2. Attribution Is Mandatory

- Nodes consumed by diagnostics or lowering must carry stable source attribution.
- Missing attribution on mandatory nodes is non-conformant.

### 3. Root Boundary Is Per Source File

- Parser output is one root per file.
- Root must preserve deterministic child ordering.

## Questions To Resolve

1. Which minimal node families are required immediately for v1 conformance?
2. Which optional node metadata may remain implementation-defined for now?
3. What is the minimum integrity rule for recovered AST after parse errors?

## Expected Outputs

1. Decision note on AST contract model.
2. Decision note on attribution minimums.
3. Section targets for `11. AST Specification.md`.

## Decision Outcome (2026-03-05)

Decision record: `docs/pbs/decisions/AST Contract and Root Model Decision.md`.

1. `11` standardizes AST by observable obligations, not by one mandatory Java/in-memory class hierarchy.
2. AST root boundary is one root per source file with deterministic child order.
3. Nodes consumed by diagnostics or lowering must carry `file/start/end`.
4. Mandatory v1 families are declaration/statement/expression categories for the supported source slice.
5. Unsupported forms are deterministic reject and must not be masked by permissive synthetic AST.

## Inputs

- `docs/pbs/specs/3. Core Syntax Specification.md`
- `docs/pbs/specs/11. AST Specification.md`
- `docs/pbs/specs/12. Diagnostics Specification.md`
- `docs/pbs/agendas/archive/11. AST Agenda.md`