Code analysis

These ARCCHR#### Roslyn diagnostics belong to Arc’s Chronicle integration, not to standalone Arc or every project that references pure Chronicle. They catch integration mistakes while you build, so a misplaced key, ambiguous identity, or unsupported handler shape is visible before a request reaches production.

Rules overview

Rule	Severity	What it checks
ARCCHR0001	Error	Recognized aggregate event-handler candidates have supported signatures.
ARCCHR0002	Warning	Multiple candidate command identities without an explicit provider/recognized return exemption.
ARCCHR0003	Warning	Reactor access to the default event log instead of returned side effects.
ARCCHR0004	Warning	Redundant explicit id on [EventType]: empty, or equal to the type name.
ARCCHR0005	Warning	Chronicle usage and AddCratisArc appear in one project without integration setup.
ARCCHR0006	Warning	Manual reactor command execution without method- or class-level [OnceOnly].
ARCCHR0007	Warning	A command Handle() or Provide() parameter is IEventLog or an implementing type.
ARCCHR0008	Warning	Data annotations [Key] used where Chronicle key resolution applies.
ARCCHR0009	Warning	Likely secret command values lack audit exclusion metadata.
ARCCHR0010	Warning	A keyless command returns a raw Guid beside statically identifiable untargeted events.
ARCCHR0011	Info	Under Off, plain read-model parameters or IReadModels.GetInstanceById calls in event-producing command or validator code.
ARCCHR0012	Info / Warning under On	Immediate appends beside protected decisions or under On.
ARCCHR0013	Info	A command or aggregate root names an event source with [EventSourceType] and a definition with that name exists in the compilation.
ARCCHR0014	Warning	A reactor or reducer is filtered with [FromEventSource<T>(stream)] to a stream the definition does not declare.
ARCCHR0015	Warning	A model-bound command handler declares a nullable event, directly or in a supported awaitable/union branch.
ARCCHR0016	Warning	concurrency: true on a stream-metadata attribute of a command whose Handle() returns EventsWithConcurrencyScopes.
ARCCHR0017	Error	An [EventStreamId] template on a command names an unusable property or has malformed braces.
ARCCHR0018	Warning	An [EventStreamId] template on a reactor, where it is used literally.
ARCCHR0019	Warning	A conventional query resembling a read-model fold; discovery is unchanged.
ARCCHR0020	Warning	A literal wrapper route names a stream its known definition does not declare.
ARCCHR0021	Info	Legacy wrapper strings name a declared stream but drop its definition.
ARCCHR0022	Warning	A command-key aggregate accompanies returned or appended events targeting a generated parameter.
ARCCHR0023	Warning / Info	Distinguishing read-model keys with several or no matching command properties; repeated lookup keys.
ARCCHR0024	Warning	Statically refused read shapes in Measure or On.
ARCCHR0025	Warning / Info	Read-model or explicit Chronicle service dependencies in keyless event-producing commands.
ARCCHR0026	Info / Warning under On	MongoDB collection parameters containing recognizable Chronicle-backed models.
ARCCHR0027	Warning	A visible OnRefused callback returns a statically invalid refusal production.
ARCCHR0028	Warning	Raw Chronicle reads and explicit read bypasses under On.
ARCCHR0029	Error	Conflicting protected and advisory declarations.
ARCCHR0031	Error	Invalid explicit LookUpBy property or non-model parameter.
ARCCHR0032	Info	Inert or redundant declarations.
ARCCHR0033	Warning	Aggregate and protected plain read on the same key under On.
ARCCHR0034	Info	Method-level advisory does not cover read parameters.
ARCCHR0035	Warning	Early aggregate commit under On.
ARCCHR0036	Warning	Exact scope coverage of a protected read is not proven, including validator-first stream reads.
ARCCHR0037	Error	Per-stream model parameter does not match the command route, or uses LookUpBy.
ARCCHR0038	Info	Per-stream model guard widens through another read or declared concurrency.
ARCCHR0040	Info	Prefer a read-model parameter over a direct decision-reader or token parameter.

ARCCHR0039 was removed and its ID is retired; it is never reused. A command’s Handle() may take any dependency, including IDecisionReads and DecisionRead<T>. ARCCHR0040 offers Info-only guidance for those two direct parameters; it imposes no dependency restriction and can be suppressed with a reason for an acquisition gap.

A command that has [EventStreamId(value)] and also implements ICanProvideEventStreamId is reported by Chronicle’s own analyzer as CHR0027, not by an Arc rule. [EventStreamId("")] and [EventStreamId(null)] declare no id, so ARCCHR0017 stays silent for them.

Quick fixes

Rule	Fix
ARCCHR0008	Rewrite to the fully qualified Chronicle Key attribute.
ARCCHR0010	Compiler-checked local replacement with EventSourceId<Guid> for supported direct tuple syntax.
ARCCHR0013	Replace matching source/stream attributes with a typed event source definition.
ARCCHR0031	Use nameof for a nearby command lookup property.
ARCCHR0021	Replace legacy wrapper route strings with the matching definition and stream.
ARCCHR0015	Compiler-checked replacement of a nullable event with an explicit event-or-validation result and rejection placeholders.
ARCCHR0016	Remove concurrency: true from the attribute.
ARCCHR0019	Preview whole-type explicit query selection, retaining intended endpoints.

The other rules have no automatic fix. A fix can change behavior: in particular ARCCHR0010 changes the persistence target when the Guid was an ordinary response.

Installation

Install the optional Arc integration package:

dotnet add package Cratis.Arc.Chronicle

It brings in Cratis.Arc.Chronicle.CodeAnalysis, which supplies these analyzers and code fixes. Complete the integration setup to connect Arc’s command pipeline to Chronicle.

Pure Cratis.Chronicle provides event sourcing without Arc; referencing it alone does not install Arc’s integration diagnostics. If a diagnostic is missing, check that your application’s resolved dependencies include Cratis.Arc.Chronicle.CodeAnalysis.