feat(commands): defineCommand - typed declarative commands via an ICommand adapter (#6101)

Author: edusperoni

defining-commands.md

@@ -0,0 +1,351 @@
+Defining Commands
+=================
+
+`defineCommand` is the declarative way to add a command to the NativeScript
+CLI. A definition is a plain object: a name, an option schema, and a `run`
+function. The CLI compiles it into the command shape its registry expects, so a
+definition gets the same option parsing, hooks, analytics and help wiring as a
+hand-written command class — without a class, a constructor, or an
+`allowedParameters` array.
+
+This is purely additive. The legacy `ICommand` classes registered through
+`$injector.registerCommand` keep working exactly as before, and the two styles
+coexist in the same registry.
+
+At a glance
+-----------
+
+```ts
+import {
+	defineCommand,
+	booleanOption,
+	stringOption,
+} from "nativescript/contracts";
+
+export default defineCommand({
+	name: "widget|add",
+	description: "Adds a widget to the project",
+	options: {
+		overwrite: booleanOption({ default: false }),
+		output: stringOption({ alias: "o" }),
+	},
+	arguments: "any",
+	async run(ctx) {
+		// ctx.args    -> string[] of positional arguments
+		// ctx.options -> { overwrite: boolean; output: string | undefined }
+		if (ctx.options.output) {
+			console.log(`adding ${ctx.args.join(", ")} to ${ctx.options.output}`);
+		}
+	},
+});
+```
+
+`defineCommand` validates the definition and returns it, tagged with a marker
+symbol so that any copy of the CLI can recognise it. `isCommandDefinition(value)`
+is the exported check, and it narrows to `DefinedCommand`. The tag survives a
+spread, so `{ ...baseDefinition, name: "widget|add2" }` is still recognised.
+
+`defineCommand` does not register anything by itself — see
+[Registering a definition](#registering-a-definition).
+
+Validation happens where you can see it
+---------------------------------------
+
+A definition is checked at the moment `defineCommand` is called, not when the
+command eventually runs. A misspelled field, a missing `run`, an option
+declared with something other than the four helpers, an `arguments` value
+outside `"none" | "any"` — each throws immediately, naming the command and the
+accepted form:
+
+```
+Invalid command definition for 'widget|add': unknown field(s) 'handler'; a
+definition accepts name, description, options, arguments, canExecute,
+disableAnalytics, enableHooks, run. Accepted form: defineCommand({ name:
+"widget|add", run(ctx) { ... } }) — with the optional fields description,
+options, arguments, canExecute, disableAnalytics and enableHooks.
+```
+
+Names and the command hierarchy
+-------------------------------
+
+`name` is either a single string or an array of strings, in which case every
+entry becomes an alias for the same command.
+
+The CLI's command registry is flat; the hierarchy the user types on the command
+line is encoded in the name with a `|` separator. `"widget|add"` is the command
+invoked as `ns widget add`, and `"widget|template|list"` is `ns widget template
+list`. Registering a hierarchical name automatically synthesises the parent
+dispatcher (`widget`), which routes to the right subcommand or prints help.
+
+A leading `*` on the last segment marks a **default subcommand**: `"widget|*add"`
+runs both for `ns widget add` and for a bare `ns widget`. This is the convention
+the CLI's own commands use (`run|*all`, `debug|*all`); the encoding is
+user-visible because it feeds shell autocompletion and generated help.
+
+A parent name cannot also be a command of its own. If `widget` is already
+registered as a flat command, registering `widget|add` leaves that command in
+place, warns naming both, and creates no dispatcher — so `ns widget add` will
+not route until one of the two is renamed.
+
+Options
+-------
+
+`options` is a schema keyed by the long option name — `output` is passed as
+`--output`. Declare each entry with one of the four helpers, which fix the
+value type:
+
+| Helper          | Declared with `default` | Declared without        |
+| --------------- | ----------------------- | ----------------------- |
+| `booleanOption` | `boolean`               | `boolean \| undefined`  |
+| `stringOption`  | `string`                | `string \| undefined`   |
+| `numberOption`  | `number`                | `number \| undefined`   |
+| `arrayOption`   | `string[]`              | `string[] \| undefined` |
+
+The two columns are the whole story of the option types: a flag the user did
+not pass is absent at runtime, so only a `default` makes the value on
+`ctx.options` always present. Declare a default whenever there is a sensible
+one and the `| undefined` disappears from the type.
+
+Each helper takes an optional spec:
+
+```ts
+options: {
+	// --release, absent means false
+	release: booleanOption({ default: false }),
+	// --output <dir>, also accepted as -o <dir>
+	output: stringOption({ alias: "o", description: "Output directory" }),
+	// --retries <n>
+	retries: numberOption({ default: 3 }),
+	// --file a.ts --file b.ts
+	file: arrayOption(),
+	// kept out of analytics and logs
+	token: stringOption({ hasSensitiveValue: true }),
+}
+```
+
+- `default` — value used when the flag is absent.
+- `alias` — single-dash shorthand, or an array of them (`alias: ["o", "out"]`).
+- `hasSensitiveValue` — defaults to `false`; set it for anything that must not
+  be recorded. There is no reason not to be explicit about credentials, paths
+  containing user directories, and tokens.
+- `description` — reserved for generated help. It reaches the option parser but
+  nothing renders it yet.
+
+The schema types `ctx.options` and nothing else: `ctx.options` carries exactly
+the declared keys, and a typo is a compile error. Values that the CLI parses
+globally (`--path`, `--log`, …) are not exposed there; resolve the `options`
+service if you need them.
+
+### Sharing a schema between commands
+
+Extract the schema with `satisfies` rather than a type annotation. An
+annotation widens every entry back to the general spec type and the `default`
+information — and with it the non-optional value types — is lost:
+
+```ts
+const buildOptions = {
+	release: booleanOption({ default: false }),
+	output: stringOption({ alias: "o" }),
+} satisfies CommandOptionsSchema;
+```
+
+### Do not shadow a CLI-wide option
+
+`--verbose`, `--path`, `--log`, `--release`, `--env` and friends are declared by
+the CLI itself. Declaring one of those names in a command's schema makes the
+command's declaration win for the duration of that command, which means the
+same flag means different things depending on which command is running. The CLI
+warns at registration naming both sides of the collision; pick another name.
+
+Aliases count too, in both directions: an `alias: "p"` collides with `--path`'s
+shorthand just as `output: stringOption()` would collide with a CLI-wide
+`--output`.
+
+### How validation behaves
+
+Option validation is the CLI's existing behaviour, not something the definition
+opts into. Before a command runs, the parser is re-primed with that command's
+declared options and the command line is re-parsed:
+
+- Declared options are accepted and appear on `ctx.options`.
+- An option the CLI does not know — neither global nor declared by this command
+  — produces a warning: `The option '<name>' is not supported. This will become
+an error in a future release.` The command still runs. Set
+  `NS_STRICT_OPTIONS=error` to preview the hard failure, which is what a future
+  release will do by default.
+- The same staging applies to value-shape violations: a string option passed
+  with no value, an array option passed nothing, a single-valued option passed
+  twice.
+
+So adding an option is a matter of adding a schema entry; forgetting to declare
+one that users pass is a warning today and a failure later, never a silent
+`undefined`.
+
+Positional arguments
+--------------------
+
+`arguments` declares whether the command takes positional arguments at all:
+
+- `"none"` (the default) — the command accepts no positional arguments. Passing
+  any is rejected with `This command doesn't accept parameters.`
+- `"any"` — positional arguments are accepted and handed to `run` as
+  `ctx.args`.
+
+Anything finer than that belongs in `canExecute`.
+
+### `canExecute` refines, it does not replace
+
+```ts
+defineCommand({
+	name: "widget|add",
+	arguments: "any",
+	async canExecute(ctx) {
+		return ctx.args.length === 1;
+	},
+	async run(ctx) {
+		/* ... */
+	},
+});
+```
+
+The two fields compose. The declared `arguments` policy is enforced first, and
+`canExecute` is consulted only for command lines that already satisfy it — so a
+definition that leaves `arguments` at `"none"` still rejects stray positional
+arguments even when it supplies a `canExecute`, and a `canExecute` that only
+inspects options cannot accidentally widen what the command accepts.
+
+`canExecute` receives a context of the same shape as `run`'s — the same
+`args`, the same declared options and the same `fail` — built freshly for the
+call, and returns a boolean (or a promise of one). Returning `false` aborts the
+command and prints a bare help suggestion; `ctx.fail(message)` aborts it with
+your own message, which is usually the friendlier choice.
+
+`canExecute` runs inside a dependency-injection context, on the same terms as
+`run`: `inject()` is valid up to the first `await`.
+
+The run context
+---------------
+
+`run(ctx)` receives:
+
+- `ctx.args` — `string[]`, the positional arguments left after the command name
+  (including any subcommand segments) has been consumed.
+- `ctx.options` — the current value of each declared option, read at the moment
+  the command executes.
+- `ctx.fail(message)` — fails the command with `message` and a usage help
+  suggestion.
+
+`run` may be synchronous or `async`; the CLI awaits the result and treats a
+rejection as a command failure.
+
+### Failing a command
+
+`ctx.fail(message)` is the idiomatic way to stop a command:
+
+```ts
+defineCommand({
+	name: "widget|add",
+	arguments: "any",
+	options: { output: stringOption() },
+	async run(ctx) {
+		if (!ctx.options.output) {
+			ctx.fail("--output is required.");
+		}
+
+		/* ... */
+	},
+});
+```
+
+It is available on the `canExecute` context as well, and it returns `never`, so
+it can end a branch without a `return`. The message must be a non-empty string.
+
+Throwing is equivalent and keeps working — `ctx.fail` is sugar over the
+`errors` service's `failWithHelp`, which is what adds the "Run `ns widget add
+--help`" line. Throw when you already have an `Error` to propagate; call
+`ctx.fail` when you are writing the message.
+
+`run` starts inside a dependency-injection context, so `inject()` works
+directly:
+
+```ts
+import { defineCommand, inject } from "nativescript/contracts";
+import { DoctorService } from "nativescript/contracts";
+
+export default defineCommand({
+	name: "widget|check",
+	async run() {
+		const doctorService = inject(DoctorService);
+		await doctorService.printWarnings();
+	},
+});
+```
+
+The injection context is synchronous: `inject()` is valid up to the first
+`await` in `run`, and not after it. Capture what you need at the top of `run`,
+or inject the `Injector` itself and use `injector.get()` for late lookups. See
+`dependency-injection.md`.
+
+Other flags
+-----------
+
+- `disableAnalytics: true` — skips analytics tracking for this command.
+- `enableHooks: false` — skips the before/after hooks that normally run around
+  the command. Hooks are enabled by default.
+
+Both are simply passed through to the command the CLI executes; omitting them
+leaves the CLI's defaults in place.
+
+Registering a definition
+------------------------
+
+Inside the CLI, a definition is registered with `registerCommandDefinition`:
+
+```ts
+import { registerCommandDefinition } from "../common/services/command-definition-adapter";
+import addWidgetCommand from "./add-widget";
+
+registerCommandDefinition(addWidgetCommand);
+```
+
+It takes a `DefinedCommand` — the result of `defineCommand`, marker and all —
+and rejects a bare object of the right shape, so a definition can never reach
+the registry without having been validated. It registers under every name the
+definition declares, through the `CommandRegistry` the target injector provides;
+pass a second argument to target a different injector (tests do this). The
+command instance is built by a factory on first resolution and cached.
+
+`registerCommandDefinition` lives in
+`lib/common/services/command-definition-adapter` rather than in
+`nativescript/contracts`, because it reaches into the CLI runtime — the
+side-effect-free contracts entry point deliberately does not pull it in.
+`defineCommand`, the option helpers and all the types are exported from both
+`nativescript/contracts` and `lib/common/define-command`.
+
+Declaring commands from an extension manifest, so that an extension does not
+have to call a registration function at load time, is being added separately.
+Until then, extensions register definitions the same way the CLI does.
+
+Relationship to `ICommand`
+--------------------------
+
+A definition is compiled into an ordinary `ICommand`, so nothing downstream —
+the registry, the router, hooks, help, analytics — knows the difference. The
+mapping is:
+
+| Definition                        | `ICommand`                                         |
+| --------------------------------- | -------------------------------------------------- |
+| `options`                         | `dashedOptions`                                    |
+| `run`                             | `execute`, wrapped in an injection context         |
+| `arguments`, `canExecute`         | `canExecute`: policy enforced, then the refinement |
+| —                                 | `allowedParameters`, always `[]`                   |
+| `disableAnalytics`, `enableHooks` | passed through unchanged                           |
+
+The compiled command always exposes `canExecute`, because `CommandsService`
+stops consulting `allowedParameters` as soon as a command has one — the adapter
+therefore enforces the `arguments` policy itself.
+
+Existing command classes need no migration. Reach for a definition when a
+command is mostly "parse these flags and do this"; a class still makes sense
+when a command needs constructor-injected collaborators shared across several
+methods, custom `ICommandParameter` validators, or a `postCommandAction`.