feat(rvm): add context/metadata support, new instructions, and serial…

[anakrish]

…ization v6

Extend the RVM infrastructure with evaluation context, program metadata, and several new instructions needed by language frontends beyond Rego.

VM & instructions:

• Add LoadContext / LoadMetadata instructions for accessing evaluation context and program metadata from within RVM programs
• Add ArrayPushDefined (skip-undefined variant of ArrayPush) for wildcard alias collection where absent properties should be excluded
• Add ReturnUndefinedIfNotTrue for early-return semantics without triggering VM assertion failures
• Add CoalesceUndefinedToNull for languages where missing fields are null rather than undefined
• Support IterationState::Single in loops and comprehensions for iterating over scalar values alongside collections

Program metadata:

• Extend ProgramMetadata with language identifier, typed annotations (BTreeMap<String, MetadataValue>), and to_value() conversion
• Add MetadataValue enum (String, Bool, Integer, Float, Array, Object) with full serde support
• Add has_host_await flag to Program with recompute_host_await_presence()

Serialization:

• Bump binary format version to 6
• Add JSON serialization for ProgramMetadata including annotations

Compiler:

• Track has_host_await during compilation
• Minor import cleanups

Test infrastructure:

• Extend VM test harness with context, metadata_language, and metadata_annotations fields
• Add instruction parser support for new instructions
• Add assembly listing support (readable, tabular, compact formats)
• Add 3 new YAML test suites: load_context_metadata, coalesce_undefined_to_null, return_undefined_if_not_true

[Copilot]

Pull request overview

This PR extends the RVM to support additional runtime/environment inputs (evaluation context + program metadata) and introduces several Azure Policy–oriented instruction/semantic additions (guard-style early return, undefined→null coalescing, skip-undefined array push, and scalar/non-collection iteration behavior), along with expanded VM YAML test coverage and tooling support (parser + assembly listing).

Changes:

• Add LoadContext / LoadMetadata instructions and VM plumbing to supply host context and cached program metadata at runtime.
• Add new instructions: ArrayPushDefined, ReturnUndefinedIfNotTrue, and CoalesceUndefinedToNull, plus IterationState::Single for scalar/non-collection loop iteration.
• Extend VM test harness + add new YAML suites covering new instructions and context/metadata behavior; update instruction parser and program listing formatting.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/rvm/vm/suites/type_errors.yaml	Updates a NOT type-error test description for clarified semantics.
tests/rvm/vm/suites/return_undefined_if_not_true.yaml	New YAML suite validating ReturnUndefinedIfNotTrue (including HostAwait interactions).
tests/rvm/vm/suites/load_context_metadata.yaml	New YAML suite for LoadContext/LoadMetadata behaviors and interactions with Input/Data.
tests/rvm/vm/suites/coalesce_undefined_to_null.yaml	New YAML suite validating undefined→null coalescing and interactions with guards/HostAwait.
tests/rvm/vm/suites/array_push_defined.yaml	New YAML suite validating skip-undefined array push semantics and error behavior.
src/rvm/vm/machine.rs	Adds VM context, metadata caching, Azure Policy loop semantic flag; refactors timer + memory-check paths.
src/rvm/vm/loops.rs	Adds Azure Policy “virtual element” iteration path via IterationState::Single.
src/rvm/vm/dispatch.rs	Implements new instruction dispatch for context/metadata loads and the new Azure Policy instructions.
src/rvm/vm/context.rs	Adds IterationState::Single and advance behavior.
src/rvm/vm/comprehension.rs	Updates comprehension iteration handling to tolerate IterationState::Single.
src/rvm/tests/vm.rs	Extends YAML harness to accept context + metadata inputs and recompute derived program flags.
src/rvm/tests/instruction_parser.rs	Adds parser support for newly introduced instructions.
src/rvm/program/listing.rs	Adds assembly listing support for new instructions and names.
src/rvm/instructions/mod.rs	Adds new instruction variants to the core instruction enum.
src/rvm/instructions/display.rs	Adds Display formatting for newly introduced instructions.

Comments suppressed due to low confidence (1)

src/rvm/vm/machine.rs:426

• execution_timer_tick() now calls monotonic_now() whenever a timer config is present, which likely means a clock read per instruction (this function is invoked each dispatch step). That defeats the check-interval amortization that ExecutionTimer::accumulate was designed for. Consider accumulating work units first and only reading the clock when a check is due (or provide a helper that preserves the interval behavior without requiring now every call).

        if self.execution_timer.limit().is_none() {
            return Ok(());
        }

        let Some(now) = monotonic_now() else {

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[Copilot]

In load_context_independent_of_input, the steps labeled “reuse … for comparison” never actually perform a comparison, and the loaded input value (r5) is never asserted/returned. This makes the test pass even if LoadInput/LoadContext interaction were broken, and also leaves an unused Load (dest: 6). Consider returning both values (e.g., as an array/object) or adding an Eq/And chain so the test truly validates independence.

[Copilot]

Pull request overview

Copilot reviewed 15 out of 15 changed files in this pull request and generated 3 comments.

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[Copilot]

Pull request overview

Copilot reviewed 15 out of 15 changed files in this pull request and generated 2 comments.

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[Copilot]

Pull request overview

Copilot reviewed 15 out of 15 changed files in this pull request and generated 1 comment.

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[Copilot]

The comment above virtual_element_on_non_collection initialization is misleading: enabling this flag doesn’t make Every over a non-collection always evaluate to false; it changes Every to iterate once over a virtual Null element (so the result depends on the loop body, and is just no longer vacuously true). Consider rewording the comment to describe the virtual-element behavior rather than a fixed boolean outcome.