dart-public-api-docs

name: dart-public-api-docs description: > Write public `///` documentation for exported Dart APIs. Use when adding or editing public classes, methods, getters, or fields in library packages (flutter_adaptive_cards_fs, flutter_adaptive_charts_fs, flutter_adaptive_cards_host_fs, flutter_adaptive_template_fs) or when reviewing doc-comment quality on exported APIs.

Public API Documentation (`///`)

Public API comments should explain why an API exists and how callers use it. They should not reiterate the steps the code is taking.

Scope

Apply to every member exported from a package barrel file (for example lib/flutter_adaptive_cards_fs.dart, lib/flutter_adaptive_charts_fs.dart).

Lint enforcement: packages/flutter_adaptive_cards_fs sets public_member_api_docs: error in analysis_options.yaml — every public member under lib/ must have a /// summary (fvm dart analyze lib).

Internal lib/src/ helpers may use shorter docs, but follow the same principles when the helper is part of a public contract (for example callback typedefs or sealed variants).

What to write

Each public /// block should answer, in order of priority:

Purpose — What problem does this API solve for the caller?
Usage — When to call it, what to pass, what you get back, and side effects.
Constraints — Spec behavior, thread/async expectations, null semantics, or invariants that are not obvious from the signature.
Links — [OtherType] dartdoc references and markdown links to project docs when integration context matters.

Parameter and return docs ([id], [uri]) should clarify caller intent, not restated parameter types already visible in the signature.

What to avoid

Do not:

Narrate implementation ("first parses JSON, then validates, then returns…").
Duplicate the method body in prose ("loops over facts and builds widgets").
Restate obvious signatures ("Returns a [String]" when the return type is String).
Use filler ("This method is used to…", "Gets the value of…") without adding context.

Implementation details belong in private helpers, tests, or plan docs — not on public API surfaces unless callers must know them to use the API correctly (for example security policy rules or Adaptive Cards spec edge cases).

Patterns

Class or type

Lead with the caller-facing role, not the file it lives in.

/// Validates card-controlled URLs before launch or HTTP fetch.
class AdaptiveUriPolicy { ... }

Factory, preset, or constant

Explain when a caller should pick this variant.

/// Default production policy: https/http only, no private networks.
static const standard = AdaptiveUriPolicy();

/// Relaxed policy for local widget tests and dev servers.
static const development = AdaptiveUriPolicy(
  allowLoopback: true,
  allowPrivateHosts: true,
);

Method with non-obvious behavior

Document contract and caller workflow, not algorithm steps.

/// Parses an Adaptive Card [Input.Date] value from host `initData` or JSON.
///
/// Accepts `yyyy-MM-dd` (spec) and ISO-8601 datetimes. For datetimes, only
/// the calendar date portion is used; time and timezone offsets are ignored.
DateTime? parseAdaptiveDateValue(Object? raw) { ... }

Result / sealed variants

Tell the caller what to do with each outcome.

/// [url] passed policy checks; use [uri] for launch/fetch.
class AdaptiveUriAllowed extends AdaptiveUriValidationResult { ... }

/// [url] was rejected; [reason] is safe to log (no secrets).
class AdaptiveUriDenied extends AdaptiveUriValidationResult { ... }

Document notifier / overlay APIs

Explain host vs runtime state and when to call.

/// Replaces effective `"facts"` for `FactSet` [id].
///
/// Call from host refresh handlers or tests; baseline JSON is unchanged until
/// [clearFactsOverlay] is called.
void setFactsOverlay(String id, List<Fact> facts) { ... }

Good vs bad

Bad (narrates implementation):

/// Parses the raw value by trimming it, checking for T or space, splitting,
/// then calling [DateFormat.parseStrict] on the date portion.
DateTime? parseAdaptiveDateValue(Object? raw);

Good (caller contract):

/// Parses an Adaptive Card [Input.Date] value from host `initData` or JSON.
///
/// Accepts `yyyy-MM-dd` (spec) and ISO-8601 datetimes. For datetimes, only
/// the calendar date portion is used; time and timezone offsets are ignored.
DateTime? parseAdaptiveDateValue(Object? raw);

Bad (restates signature):

/// Returns the resolved element map for the given id.
Map<String, dynamic>? getResolvedElement(String id);

Good (why + how):

/// Merged element JSON for [id]: baseline card map plus runtime overlays.
///
/// Use when building submit payloads or custom host logic outside widget
/// rebuilds. Returns `null` when [id] is unknown.
Map<String, dynamic>? getResolvedElement(String id);

Review checklist

When reviewing or authoring public API docs:

Every new/changed exported member has a /// summary.
Summary states purpose or caller workflow, not algorithm steps.
Non-obvious spec, security, or async behavior is documented.
Presets/factories explain when to choose them.
No comment would become wrong if the implementation were refactored (sign of narrating "how" instead of "why/how to use").

See also code-review (Exports / public API section) and root AGENTS.md (Documentation Philosophy).

Public API Documentation (///)