68 lines
2.7 KiB
Markdown
68 lines
2.7 KiB
Markdown
# PBS AST Workshop 4
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Status: Closed (2026-03-05)
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## Purpose
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Close AST-facing diagnostics/recovery rules and Gate U evidence needed to finalize the AST contract.
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## Decisions To Produce
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1. Required diagnostics attribution behavior sourced from AST.
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2. Recovery invariants for parser output after syntax errors.
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3. Mandatory AST fixture corpus for Gate U evidence.
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4. Explicit deferred list for non-AST concerns.
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## Candidate Decisions
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### 1. AST Must Sustain Diagnostics Fidelity
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- Primary attribution for syntax diagnostics must remain stable and source-anchored.
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- Cross-file related spans are attached when required by diagnostics rules.
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### 2. Recovery Must Preserve Structural Integrity
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- Recovered AST may be partial, but must remain structurally coherent.
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- Recovery must not fabricate semantically valid shapes that hide syntax failure.
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### 3. Gate U Evidence Baseline
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- AST conformance evidence includes representative valid trees, invalid/recovery cases, and attribution assertions.
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## Questions To Resolve
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1. Which recovery behaviors are mandatory versus implementation-defined?
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2. What is the minimum fixture set to prevent AST regressions?
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3. Which AST-facing diagnostics codes must be frozen now?
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## Expected Outputs
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1. Decision note on AST diagnostics/recovery policy.
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2. Decision note on Gate U AST evidence baseline.
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3. Closure checklist for `11. AST Specification.md`.
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## Decision Outcome (2026-03-05)
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Decision record: `docs/pbs/decisions/AST Diagnostics, Recovery, and Gate Evidence Decision.md`.
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1. AST-facing syntax diagnostics must remain stable by identity (`code`, `severity`, `phase`, primary attribution).
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2. Human message text is locale-dependent and not the conformance identity key.
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3. Stable i18n identity is token/template-id based, aligned with diagnostics contract fields.
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4. Recovery is allowed for continued diagnostics, but recovered AST must stay structurally coherent with consistent attribution.
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5. Recovery must not mask real syntax failure by fabricating permissive valid AST shapes.
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6. Gate U AST evidence must include valid fixtures, malformed/recovery fixtures, diagnostics assertions, and attribution assertions.
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7. Mandatory negative fixture families include unexpected tokens, missing closers, forbidden non-associative chains, and unsupported forms with deterministic rejection.
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## Explicit Deferrals
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- IRBackend lowering details (owned by `13`),
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- backend/runtime/verifier concerns,
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- compatibility/publication policy.
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## Inputs
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- `docs/pbs/specs/11. AST Specification.md`
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- `docs/pbs/specs/12. Diagnostics Specification.md`
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- `docs/general/specs/13. Conformance Test Specification.md`
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- `docs/pbs/agendas/11.3. AST Workshop 3 - Statements and Expressions.md`
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