Flow and algorithm

Platform spec article

Flow and algorithm

Back to Runtime feature flags ◎ Open feature in platform map

Spec standingStandard

Owner

Piotr Mikstacki pmikstacki@cybernomad.it

Submitter

Piotr Mikstacki pmikstacki@cybernomad.it

Current document

ADRs (2)

1. 0014-cargo-features-not-abi-version Cargo features are separate from ABI version Accepted

   Optional runtime capabilities toggle code paths without bumping BESKID_RUNTIME_ABI_VERSION.

   Context

   CI and VSIX builds enable different beskid_runtime features. Confusing feature gates with ABI bumps breaks compatibility checks.

   Decision

   Concept	Rule
   BESKID_RUNTIME_ABI_VERSION	Changes only on breaking layout/signature per D-EXEC-ABI-0002
   Cargo features	metrics, arrays_backing, sched — build-time toggles
   Additive exports	New feature-gated symbols may ship without ABI bump if old artifacts never import them
   Shipped binaries	Must document enabled features in release notes
   Tests	Compiler tests enable features explicitly when validating optional paths

   Consequences

   Mismatch (test expects arrays_backing, default runtime does not) fails logically without ABI version inequality.

   Verification anchors

   beskid_runtime/Cargo.toml; design model feature table.

   Open full ADR page

2. 0015-arrays-backing-feature arrays_backing gates array element storage Accepted

   Without the feature, array_new may emit header-only arrays with null backing.

   Context

   Array lowering depends on whether the linked runtime allocates element storage behind BeskidArray headers.

   Decision

   arrays_backing	Behavior
   Enabled	array_new allocates element storage; ptr non-null when length > 0
   Disabled	Header-only arrays; ptr may be null
   ABI	Symbol list unchanged; semantics differ by build — document in release matrices
   Alignment	Shipped CLI/VSIX should enable arrays_backing for reference user workflows

   Consequences

   Conformance and doc tests must pin feature set when asserting array behavior.

   Verification anchors

   beskid_runtime array_new; runtime JIT tests with feature flags.

   Open full ADR page

Articles

• Contracts and edge cases MUST/SHOULD rules for optional runtime features and toolchain alignment. article Standard Reviewed Fri May 22
• Design model Cargo feature gates, runtime build capabilities, and compiler alignment expectations. article Standard Reviewed Fri May 22
• Examples Building runtime with features, array backing expectations, and engine extern_dlopen. article Standard Reviewed Fri May 22
• FAQ and troubleshooting Optional runtime features vs ABI version, array backing surprises, and CI alignment. article Standard Reviewed Fri May 22
• Flow and algorithm Selecting runtime features at build time and validating behavior at run time. article Standard Reviewed Fri May 22
• Verification and traceability Cargo feature definitions, conditional compilation gates, and CI matrix expectations. article Standard Reviewed Fri May 22

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Completeness

OKfeature · 2 SpecSection(s) · 1 H2 heading(s)

Section id	Required	Found
what-this-feature-specifies	yes	yes
implementation-anchors	yes	yes

Full tree: run pnpm verify:platform-spec-layout (writes src/generated/platform-spec-layout-report.json).

Related spec docs

• Feature
  Runtime feature flags

  Parent feature hub

Purpose

How optional features propagate from Cargo to runtime behavior. Build alignment diagram: design model.

Build-time selection

1. CI or local cargo build -p beskid_runtime --features … enables cfg gates in builtins/arrays.rs, metrics module, etc.
2. beskid_engine / CLI link the same feature-enabled runtime artifact (workspace dependency features must match).
3. BESKID_RUNTIME_ABI_VERSION stays constant unless symbol/signatures change (ABI-005).

arrays_backing runtime path

1. Lowering always emits array_new(elem_size, len).
2. Without feature: runtime writes BeskidArray { ptr: null, len, cap: len }.
3. With feature: runtime allocates elem_size * len bytes via alloc for ptr.
4. array_len returns logical len in both modes.

metrics export path

1. When enabled, builtins/metrics.rs registers additional rt_metrics_* symbols.
2. JIT must only declare imports if codegen emits calls—baseline programs ignore them.
3. Hosts read counters for profiling dashboards; not part of user Beskid language.

Engine extern_dlopen (related)

1. Separate from runtime crate: enable on beskid_engine for dynamic extern tests.
2. Does not alter beskid_runtime_abi_version.
3. Failure modes documented under Extern dispatch.

Release verification flow

1. Read release manifest / CI matrix for enabled features.
2. Run conformance tests compiled with the same feature set.
3. Compare array_new behavior in integration tests (backing vs header-only).

Related topics

• Contracts and edge cases
• compiler/crates/beskid_runtime/Cargo.toml