Rules and matching

A Rule interprets one managed or data resource instance in a plan JSON or state JSON. Its match decides eligibility; as assigns an optional Concept; emissions and composition add further architecture meaning. The Rule name alone creates no Concept or fact.

For the mental model, see Read a Rule.

Complete example

reference/dialect.rf.hcl RF

dialect "example" {
  version = "0.1.0"

  provider "hashicorp/aws" {
    version = ">= 6.0.0, < 7.0.0"
  }
}

rule "bucket" {
  match {
    type = "aws_s3_bucket"
  }

  as = rf.concept.object-storage-container

  identity {
    attributes = ["bucket"]
    scope      = "provider"
  }

  endpoint {
    attributes = ["id", "bucket", "arn"]
  }
}

The official AWS Dialect uses this shape for buckets. bucket is an instance identity attribute; id, bucket, and arn are endpoint paths that a verified saved-plan traversal may name. Neither block publishes its values. See Fact emissions for target resolution.

rule block

Property	Contract
Placement	Top level of a Dialect source root
Cardinality	Zero or more
Label	Exactly one Rule name, unique within the Dialect
Attributes	Optional as Concept reference
Nested blocks	Exactly one match; optional identity, endpoint, and composition; zero or more emissions

A Rule must have as, at least one emission, or a nonempty composition. A match-only Rule fails validation with RULE_NO_ARCHITECTURE. The Rule has no description attribute. See Member resolution for per-instance evidence and Unresolved members for what remains when one member cannot be established.

Parameters

Name	Type	Required	Default	Constraint
Label	Identifier	Yes	None	Lowercase kebab case, 1–64 bytes
as	Concept reference	No	No Concept	Local/current owner or supported rf.concept.*

Nested blocks

Block	Cardinality	Purpose
match	Exactly one	Choose eligible instances
identity	Zero or one	Name value attributes for target matching
endpoint	Zero or one	Name attributes a saved-plan traversal can pair with this instance
context, relation, contribution	Zero or more	Emit facts; see Fact emissions
composition	Zero or one	Claim ordered members

match block

Rule match RF

match {
  kind  = "resource"
  type  = "aws_s3_bucket"
  where = source.bucket == "logs"
}

Property	Contract
Placement	Exactly once inside rule or a composition member
Labels and nested blocks	Forbidden
Attributes	kind, type, and optional where

Name	Type	Required	Default	Constraint
kind	Static string	No	"resource"	"resource" or "data" for plan/state instances
type	Static string	Yes	None	Exact, nonempty resource type; case-sensitive
where	Predicate	No	Known true	Closed predicate grammar

match has no label or nested block. where reads the instance's available source.* values. An unknown or sensitive operand can make the predicate indeterminate; it cannot make a candidate false. A bare traversal such as where = source.enabled is not a Boolean predicate and produces PREDICATE_UNRESOLVED during validation.

match.kind values

The language keeps a closed 15-value set. Plan/state analysis provides only the first two populations:

Value	Construct	Plan/state instances
resource	Managed resource	Yes
data	Data source	Yes
settings, provider, ephemeral, action, module	Other infrastructure constructs	No
variable, local, output	Values declared in configuration	No
moved, removed, import, check, language	Other configuration constructs	No

The other values remain accepted language syntax, but plan and state inputs contain no instances of those kinds, so a Rule that matches one never applies. type never glob-matches or follows the Rule name.

Identity and endpoint declarations

Block	Attribute	Required	Default	Meaning
identity	attributes	Yes	None	Nonempty, distinct attribute paths eligible for an emission's match.by
identity	scope	No	"provider"	"provider" requires compatible provider address and alias; "global" permits cross-provider candidates
endpoint	attributes	Yes	None	Nonempty, distinct paths a verified traversal may use to identify the instance

These attributes are declared on a target Rule, not inferred from a Concept. A target with an unavailable provider alias remains a possible candidate, so Rootform cannot force a unique value match around it. scope = "global" changes candidate eligibility, not the meaning of an identity value. With --plan-file, a direct reference to a declared endpoint can establish the exact instance even if its evaluated value is unknown or shared. Traversals and scope gives the supported expression syntax variants.

Classification with as

as assigns one Concept to an interpreted instance. A Rule can instead emit facts or compose members without a Concept. There is no Concept inheritance or automatic classification from resource type. The built-in RF Vocabulary supplies shared Concepts; a Dialect can declare local ones.

Eligibility pipeline

For each instance, Rootform checks, in order:

1. mode (resource or data);
2. exact resource type;
3. provider source address;
4. optional where predicate.

The provider source address determines Dialect binding. A shorthand such as hashicorp/aws binds its corresponding Terraform and OpenTofu public-registry addresses; a fully qualified host binds only that host. An unbound provider is reported with PROVIDER_UNBOUND. The Dialect's provider version constraint declares its compatibility envelope, but Rule selection does not compare it with an observed exact provider version. A version constraint cannot distinguish two Rules for the same instance.

Selection precedence

Priority	Condition	Result
1	More than one Rule accepted	RULE_MATCH_AMBIGUOUS; no Rule applies
2	An eligible Rule has an indeterminate predicate	Interpretation indeterminate; no Rule selected around it
3	Exactly one Rule accepted	Apply it
4	No Rule accepted	Keep the instance without an applied Rule or Concept

If a resource type could match but no selected Dialect binds its provider address, interpretation fails with PROVIDER_UNBOUND before Rule selection. There is no priority by file order, Dialect origin, or Rule name. A managed or data instance with no matching Rule still has a Representation in the Form. It has no invented classification or emissions. Policy selection can also include an instance whose possible Rule is indeterminate or failed, producing an indeterminate policy evaluation; see Evaluation. Rule selection places this step in the analysis pipeline.

Rejected syntax

invalid/match-only.rf.hcl RF

dialect "example" {
  version = "0.1.0"

  provider "hashicorp/aws" {
    version = ">= 6.0.0"
  }
}

rule "no-architecture" {
  match {
    type = "aws_s3_bucket"
  }
}

rootform validate dialects reports RULE_NO_ARCHITECTURE. Add an as, an emission, or a nonempty composition only when it expresses intended meaning. Test and validate shows how to check a Rule against a plan fixture.