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require-declaration-with-composite

Require "declaration": true whenever "composite": true is set in compilerOptions, because composite projects must emit declaration files.

Targeted pattern scopeโ€‹

The compilerOptions.composite and compilerOptions.declaration fields in any tsconfig*.json file.

What this rule reportsโ€‹

This rule reports when "composite": true is present but "declaration": true is absent (or explicitly set to false).

Why this rule existsโ€‹

TypeScript requires "declaration": true for composite projects. Without it, tsc will report an error when building the project:

Option 'composite' requires option 'declaration' to be enabled.

This rule surfaces that constraint at lint time, providing faster feedback before a build is attempted.

Additionally, composite projects exist to allow other projects to reference them. The declaration files produced by declaration: true are the mechanism by which referencing projects consume the types โ€” without them, the project reference chain is broken.

The auto-fixer adds "declaration": true to compilerOptions.

โŒ Incorrectโ€‹

{
    "compilerOptions": {
        "composite": true,
        "outDir": "./dist"
    }
}

composite is set but declaration is absent, which TypeScript will reject.

{
    "compilerOptions": {
        "composite": true,
        "declaration": false
    }
}

declaration is explicitly disabled, which is invalid for composite projects.

โœ… Correctโ€‹

{
    "compilerOptions": {
        "composite": true,
        "declaration": true,
        "outDir": "./dist"
    }
}

When not to use itโ€‹

This combination is always required by TypeScript when composite is true. Disabling this rule is not appropriate.

Package documentationโ€‹

Rule catalog ID: R016

Further readingโ€‹