Variants

A variant describes files and values that a package must contain.

monoswan.config.ts

import { defineConfig } from "monoswan";

export default defineConfig({
  variants: {
    "my-library": {
      packageJson: {
        type: "module",
        scripts: { check: "tsc --noEmit" },
      },
      tsConfig: {
        compilerOptions: { strict: true },
      },
      tsConfigs: {
        "tsconfig.build.json": {
          compilerOptions: { declaration: true },
        },
      },
      additionalJsonFiles: {
        ".example.json": { enabled: true },
      },
      additionalTextFiles: {
        ".node-version": "22\n",
      },
    },
  },
});

Validation behavior

• Objects are checked recursively. Extra keys are allowed.
• Arrays and primitive values must match exactly.
• Configured files must exist.
• Text files must match exactly, including whitespace and trailing newlines.
• JSON-backed files accept JSONC comments and trailing commas.

Dynamic variants

Use a function when expected values depend on the package.

monoswan.config.ts

variants: {
  named: ({ packageName }) => ({
    packageJson: {
      description: packageName != null ? `${packageName} package` : "My package description",
    },
  }),
}

Composing variants

Packages can select multiple variants. monoswan merges them in the listed order. JSON objects are deeply merged; for text files, the last defined value wins. Unknown variant names produce an INVALID_VARIANTS error.

Variant content is only checked when a rule does so. Add enforceVariants() to validate the fields shown above.

See the variant and file reference for field types, path resolution, missing and invalid files, and initialization behavior.