prometeu-studio/docs/pbs/pull-requests/PR-019-pbs-non-unit-fallthrough-diagnostics.md

PR-019 - PBS Non-Unit Fallthrough Diagnostics

Briefing

The frontend does not currently reject fallthrough of plain non-unit functions and result functions at end-of-body paths. This PR adds control-flow completion checks.

Motivation

Return-surface obligations are normative and must be statically enforced.

Target

• Callable body completion validation for function/method/ctor contexts.

Scope

• Reject plain non-unit callable bodies that may complete without explicit return.
• Reject result<E> callable bodies that may complete without explicit return.
• Preserve existing unit and optional fallthrough behavior.

Method

• Add path-completion analysis over statement/block graph.
• Integrate with existing flow body analyzer.
• Emit deterministic diagnostics with stable code/phase.

Acceptance Criteria

• Possible fallthrough on plain non-unit callable is rejected.
• Possible fallthrough on result<E> callable is rejected.
• void and optional callable fallthrough behavior remains valid.

Tests

• Add positive/negative control-flow completion fixtures.
• Cover nested if/switch/loop interactions.
• Run full flow semantics suite.

Non-Goals

• Dataflow-based optimization.
• Runtime control-flow instrumentation.