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Consider Git's `-C` option: git -C /path/to/repo checkout <TAB> When you hit `Tab`, Git completes branch names from `/path/to/repo`, not your current directory. The completion is context-aware—it depends on the value of another option. Most CLI parsers can't do this. They treat each option in isolation, so completion for `--branch` has no way of knowing the `--repo` value. You end up with two unpleasant choices: either show completions for _all_ possible branches across all repositories (useless), or give up on completion entirely for these options. Optique 0.10.0 introduces a dependency system that solves this problem while preserving full type safety. ## Static dependencies with `or()` Optique already handles certain kinds of dependent options via the `or()` combinator: import { flag, object, option, or, string } from "@optique/core"; const outputOptions = or( object({ json: flag("--json"), pretty: flag("--pretty"), }), object({ csv: flag("--csv"), delimiter: option("--delimiter", string()), }), ); TypeScript knows that if `json` is `true`, you'll have a `pretty` field, and if `csv` is `true`, you'll have a `delimiter` field. The parser enforces this at runtime, and shell completion will suggest `--pretty` only when `--json` is present. This works well when the valid combinations are known at definition time. But it can't handle cases where valid values depend on _runtime input_ —like branch names that vary by repository. ## Runtime dependencies Common scenarios include: * A deployment CLI where `--environment` affects which services are available * A database tool where `--connection` affects which tables can be completed * A cloud CLI where `--project` affects which resources are shown In each case, you can't know the valid values until you know what the user typed for the dependency option. Optique 0.10.0 introduces `dependency()` and `derive()` to handle exactly this. ## The dependency system The core idea is simple: mark one option as a _dependency source_ , then create _derived parsers_ that use its value. import { choice, dependency, message, object, option, string, } from "@optique/core"; function getRefsFromRepo(repoPath: string): string[] { // In real code, this would read from the Git repository return ["main", "develop", "feature/login"]; } // Mark as a dependency source const repoParser = dependency(string()); // Create a derived parser const refParser = repoParser.derive({ metavar: "REF", factory: (repoPath) => { const refs = getRefsFromRepo(repoPath); return choice(refs); }, defaultValue: () => ".", }); const parser = object({ repo: option("--repo", repoParser, { description: message`Path to the repository`, }), ref: option("--ref", refParser, { description: message`Git reference`, }), }); The `factory` function is where the dependency gets resolved. It receives the actual value the user provided for `--repo` and returns a parser that validates against refs from that specific repository. Under the hood, Optique uses a three-phase parsing strategy: 1. Parse all options in a first pass, collecting dependency values 2. Call factory functions with the collected values to create concrete parsers 3. Re-parse derived options using those dynamically created parsers This means both validation and completion work correctly—if the user has already typed `--repo /some/path`, the `--ref` completion will show refs from that path. ## Repository-aware completion with `@optique/git` The `@optique/git` package provides async value parsers that read from Git repositories. Combined with the dependency system, you can build CLIs with repository-aware completion: import { command, dependency, message, object, option, string, } from "@optique/core"; import { gitBranch } from "@optique/git"; const repoParser = dependency(string()); const branchParser = repoParser.deriveAsync({ metavar: "BRANCH", factory: (repoPath) => gitBranch({ dir: repoPath }), defaultValue: () => ".", }); const checkout = command( "checkout", object({ repo: option("--repo", repoParser, { description: message`Path to the repository`, }), branch: option("--branch", branchParser, { description: message`Branch to checkout`, }), }), ); Now when you type `my-cli checkout --repo /path/to/project --branch <TAB>`, the completion will show branches from `/path/to/project`. The `defaultValue` of `"."` means that if `--repo` isn't specified, it falls back to the current directory. ## Multiple dependencies Sometimes a parser needs values from multiple options. The `deriveFrom()` function handles this: import { choice, dependency, deriveFrom, message, object, option, } from "@optique/core"; function getAvailableServices(env: string, region: string): string[] { return [`${env}-api-${region}`, `${env}-web-${region}`]; } const envParser = dependency(choice(["dev", "staging", "prod"] as const)); const regionParser = dependency(choice(["us-east", "eu-west"] as const)); const serviceParser = deriveFrom({ dependencies: [envParser, regionParser] as const, metavar: "SERVICE", factory: (env, region) => { const services = getAvailableServices(env, region); return choice(services); }, defaultValues: () => ["dev", "us-east"] as const, }); const parser = object({ env: option("--env", envParser, { description: message`Deployment environment`, }), region: option("--region", regionParser, { description: message`Cloud region`, }), service: option("--service", serviceParser, { description: message`Service to deploy`, }), }); The `factory` receives values in the same order as the dependency array. If some dependencies aren't provided, Optique uses the `defaultValues`. ## Async support Real-world dependency resolution often involves I/O—reading from Git repositories, querying APIs, accessing databases. Optique provides async variants for these cases: import { dependency, string } from "@optique/core"; import { gitBranch } from "@optique/git"; const repoParser = dependency(string()); const branchParser = repoParser.deriveAsync({ metavar: "BRANCH", factory: (repoPath) => gitBranch({ dir: repoPath }), defaultValue: () => ".", }); The `@optique/git` package uses isomorphic-git under the hood, so `gitBranch()`, `gitTag()`, and `gitRef()` all work in both Node.js and Deno. There's also `deriveSync()` for when you need to be explicit about synchronous behavior, and `deriveFromAsync()` for multiple async dependencies. ## Wrapping up The dependency system lets you build CLIs where options are aware of each other—not just for validation, but for shell completion too. You get type safety throughout: TypeScript knows the relationship between your dependency sources and derived parsers, and invalid combinations are caught at compile time. This is particularly useful for tools that interact with external systems where the set of valid values isn't known until runtime. Git repositories, cloud providers, databases, container registries—anywhere the completion choices depend on context the user has already provided. This feature will be available in Optique 0.10.0. To try the pre-release: deno add jsr:@optique/[email protected] Or with npm: npm install @optique/[email protected] See the documentation for more details.