Enhancement: Compiler diagnostics improvements

[Chesterguan]

Summary

Potential improvements to the compiler diagnostics identified during RFC-0006 implementation review.

Proposed Enhancements

1. Transitive Unused Entity Detection

Current behavior: A signal used only by an unused trend is not flagged as unused.

Example:

signals:
  BUN:
    ref: blood_urea_nitrogen  # Not flagged as unused

trends:
  bun_unused:
    expr: sma(BUN, 24h)  # Flagged as unused

logic:
  alert:
    when: some_other_trend > 0  # Does not use bun_unused

Proposed: Add "transitively unused" warnings for signals that are only used by unused trends.

2. Expanded Diagnostic Codes

Current codes (in DiagnosticCode):

• S100: Signal not found
• T101: Trend unknown signal
• L101: Logic unknown term
• D100: DAG circular dependency
• W100: Unused signal
• W101: Unused trend

Proposed additions:

• T102: Trend uses deprecated operator
• T103: Trend window exceeds recommended maximum
• L102: Logic expression complexity warning
• W102: Transitively unused signal
• I100: Info - optimization suggestion

3. Optional Strict Schema Validation Mode

Current behavior: Parser is more permissive than JSON Schema for developer convenience.

Proposed: Add --strict flag to parser that validates against full JSON Schema (requires psdl_version, audit, outputs).

# Current (permissive)
scenario = parse_scenario(yaml)

# Proposed (strict mode)
scenario = parse_scenario(yaml, strict=True)  # Validates against spec/schema.json

Implementation Notes

• These are non-breaking enhancements
• Transitive detection requires updating _detect_unused_entities() in compile.py
• Strict mode can leverage existing _generated/validate.py

Related

• RFC-0006: Spec-Driven Compilation Architecture
• src/psdl/core/compile.py: CompilationDiagnostics
• src/psdl/_generated/validate.py: Schema validation utilities