prometeu-studio/docs/pbs/agendas/11.4. AST Workshop 4 - Diagnostics, Recovery, and Gate Evidence.md

PBS AST Workshop 4

Status: Active

Purpose

Close AST-facing diagnostics/recovery rules and Gate U evidence needed to finalize the AST contract.

Decisions To Produce

1. Required diagnostics attribution behavior sourced from AST.
2. Recovery invariants for parser output after syntax errors.
3. Mandatory AST fixture corpus for Gate U evidence.
4. Explicit deferred list for non-AST concerns.

Candidate Decisions

1. AST Must Sustain Diagnostics Fidelity

• Primary attribution for syntax diagnostics must remain stable and source-anchored.
• Cross-file related spans are attached when required by diagnostics rules.

2. Recovery Must Preserve Structural Integrity

• Recovered AST may be partial, but must remain structurally coherent.
• Recovery must not fabricate semantically valid shapes that hide syntax failure.

3. Gate U Evidence Baseline

• AST conformance evidence includes representative valid trees, invalid/recovery cases, and attribution assertions.

Questions To Resolve

1. Which recovery behaviors are mandatory versus implementation-defined?
2. What is the minimum fixture set to prevent AST regressions?
3. Which AST-facing diagnostics codes must be frozen now?

Expected Outputs

1. Decision note on AST diagnostics/recovery policy.
2. Decision note on Gate U AST evidence baseline.
3. Closure checklist for 11. AST Specification.md.

Explicit Deferrals

• IRBackend lowering details (owned by 13),
• backend/runtime/verifier concerns,
• compatibility/publication policy.

Inputs

• docs/pbs/specs/11. AST Specification.md
• docs/pbs/specs/12. Diagnostics Specification.md
• docs/general/specs/13. Conformance Test Specification.md
• docs/pbs/agendas/11.3. AST Workshop 3 - Statements and Expressions.md