[APPS] Add @datadog/eslint-plugin-apps with valid-connections-file rule by sdkennedy2 · Pull Request #332 · DataDog/build-plugins

sdkennedy2 · 2026-04-29T15:17:28Z

Motivation

Stacked on top of #331. That PR introduced the build-time extract-connections.ts extractor that fails the build when a project's connections.ts is malformed. PR #331 explicitly defers an ESLint rule for the same shape to a follow-up — this is that follow-up.

The rule mirrors the extractor's failure cases one-for-one so customers see violations in their editor instead of as a build error. Living in the same repo as the extractor means the two stay in lockstep — extractor contract changes land in the same PR as the rule that mirrors them.

Changes

New publishable npm package @datadog/eslint-plugin-apps at packages/published/eslint-plugin-apps/. Builds with rollup (custom config — getDefaultBuildConfigs is bundler-plugin specific and would mis-parse the package name), emits dual ESM (.mjs) + CJS (.js) + .d.ts to dist/src/. Versioned in lockstep with the rest of the @datadog/* packages (3.1.4) so yarn version:all keeps everything aligned.

Customers wire it up with either flat config or legacy .eslintrc:

// eslint.config.js (flat config, ESLint v9)
import apps from '@datadog/eslint-plugin-apps';
import tsParser from '@typescript-eslint/parser';

export default [
    ...apps.configs.recommended,
    {
        files: ['connections.{ts,tsx,js,jsx}'],
        languageOptions: { parser: tsParser },
    },
];

// .eslintrc.json (legacy)
{
    "extends": ["plugin:@datadog/apps/recommended-legacy"],
    "parser": "@typescript-eslint/parser"
}

The package is structured to grow: more rules can be added under src/rules/<name>.ts and registered in src/index.ts.

Initial rule: `valid-connections-file`

Mirrors the extractor at packages/plugins/apps/src/backend/extract-connections.ts. Auto-scopes by basename — only runs on files matching connections.{ts,tsx,js,jsx}. Reports:

Violation	Message ID
Missing top-level `export const CONNECTIONS = {…}`	`missingExport`
Initializer not an object literal (after unwrapping `as const` etc.)	`notObjectLiteral`
Two top-level `export const CONNECTIONS`	`duplicateExport`
Spread element inside the object	`spreadElement`
Computed key	`computedKey`
Non-string-literal value	`valueNotStaticString`
Template literal with interpolation	`templateInterpolation`

Only CONNECTIONS (uppercase) is accepted, matching the extractor. The rule unwraps TSAsExpression / TSTypeAssertion / TSSatisfiesExpression / TSNonNullExpression before structural checks since @typescript-eslint/parser preserves those as AST nodes.

Notable build details

format: 'cjs' output, external: ['eslint', 'node:path', 'path'] — eslint plugins must be require()-loadable for legacy .eslintrc. Rollup's CJS emit for an export default source already produces module.exports = plugin directly, so no module.exports.default footer trick is needed (that workaround is only required when the bundler is esbuild).
Three rollup configs (ESM, CJS, DTS via rollup-plugin-dts).
buildPlugin.hideFromRootReadme: true keeps yarn cli integrity's root-README plugin table from gaining a row that doesn't fit (it's wired for bundler plugins).
The rule uses named @types/estree types internally for traversal (real type-checking on field access) and casts as unknown as Rule.Node only at the few context.report call sites. The reason for the casts: @types/eslint@9.6.1 ships a nested copy of @types/estree@1.0.7, while the rest of the repo (rollup, webpack, @dd/apps-plugin) pins 1.0.8. The two physical type modules are structurally identical but TypeScript treats them as distinct identities, so a VariableDeclarator from our top-level estree doesn't satisfy Rule.Node (which references @types/eslint's nested copy). Pinning our package to 1.0.7 doesn't help either — Node's module resolution still finds a different physical install path adjacent to our package vs. the one nested under @types/eslint. A small, localized cast at the report boundary is the cleanest fix; an asRuleNode helper documents the intent in one place.

QA Instructions

yarn workspace @datadog/eslint-plugin-apps build — emits dist/src/index.{js,mjs,d.ts}.
yarn workspace @dd/tests jest packages/published/eslint-plugin-apps/src/rules/valid-connections-file.test.ts — 13 RuleTester cases pass (4 valid + 9 invalid, including a "lowercase connections is not accepted" assertion).
yarn lint, yarn typecheck:all — clean.
yarn cli integrity — clean (no required updates).
End-to-end against a scaffolded customer app:
- yarn pack --out /tmp/eslint-plugin-apps.tgz from packages/published/eslint-plugin-apps/.
- npm install --no-save /tmp/eslint-plugin-apps.tgz @typescript-eslint/parser eslint@9 in the test app.
- Walk each violation case in connections.ts (missing export, lowercase connections, non-object init, duplicate, spread, computed key, identifier value, template interpolation). Each fires its corresponding messageId at the offending line:col.
- CJS smoke test: node -e "console.log(Object.keys(require('@datadog/eslint-plugin-apps').rules))" → [ 'valid-connections-file' ].

Blast Radius

Adds a new published-package directory; nothing in the existing build pipeline depends on it.
Not yet published to npm — until a release ships, no customer can install it.
New @datadog/* package picks up the existing version:all and release workflow automatically.
yarn cli integrity doesn't auto-add a row to the root README's plugin table thanks to buildPlugin.hideFromRootReadme: true. Future contributors browsing the table won't be misled into thinking this is a bundler plugin.

sdkennedy2 · 2026-04-29T15:17:42Z

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[APPS] Add @datadog/eslint-plugin-apps with valid-connections-file rule #332 👈 (View in Graphite)
[APPS] Add backend function connection support #331
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sdkennedy2 · 2026-04-29T15:18:33Z

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chatgpt-codex-connector · 2026-04-29T15:26:02Z

+    "peerDependencies": {
+        "eslint": ">=8.57.0"
+    },


Declare the TypeScript parser for consumers

For the documented connections.ts setup, both README configs require @typescript-eslint/parser, but this package only declares eslint as a peer and keeps the parser in devDependencies. In a fresh app that follows npm install --save-dev @datadog/eslint-plugin-apps, the consumer won't get this package's dev dependency, so the flat-config import or legacy parser resolution fails before the rule can run. Add the parser to the consumer-facing install path (for example a peer/optional peer plus docs) or remove the requirement.

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chatgpt-codex-connector · 2026-04-29T15:26:02Z

+        const basename = path.basename(context.filename);
+        if (!CONNECTIONS_BASENAME_RE.test(basename)) {


Scope the rule to the root connections file

Because the recommended config enables this rule globally, checking only path.basename(context.filename) makes any nested src/connections.ts or packages/foo/connections.js subject to the Apps root-file contract. The Vite plugin finder only reads connections.{ts,tsx,js,jsx} directly under buildRoot, so nested files are ignored at build time but now fail lint with missingExport or shape errors. Scope the recommended config/rule to the configured root file to avoid these false positives.

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chatgpt-codex-connector · 2026-04-29T15:26:02Z

+import validConnectionsFile from './rules/valid-connections-file';
+
+const PLUGIN_NAME = 'apps';
+const PLUGIN_PACKAGE = '@datadog/eslint-plugin-apps';


Derive plugin metadata version from package.json

This hard-coded version will not be updated by the repo's yarn version:all workflow, which only bumps package manifests, so the published plugin metadata becomes stale after the next release even though ESLint expects plugin meta.version to match the package. That can make --print-config misleading and can keep --cache from noticing plugin updates; derive it from package.json like the other published packages do.

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sdkennedy2 · 2026-05-04T14:47:03Z

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chatgpt-codex-connector · 2026-05-04T14:53:37Z

+## Install
+
+```bash
+npm install --save-dev @datadog/eslint-plugin-apps


Install the parser used by the documented configs

In a fresh consumer project following this install command, both documented configs immediately reference @typescript-eslint/parser (the flat config imports it and the legacy config names it), but this package only declares that parser as a devDependency, so it is not installed or peer-checked for consumers. This makes the README setup fail with a missing parser as soon as users lint a TypeScript connections.ts; include the parser in the install instructions or declare an appropriate peer/optional peer.

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sdkennedy2 mentioned this pull request Apr 29, 2026

[APPS] Add backend function connection support #331

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sdkennedy2 force-pushed the sdkennedy2/eslint-plugin-apps branch from 735769b to 9362c60 Compare April 30, 2026 13:53

sdkennedy2 force-pushed the sdkennedy2/apps-emit-connections-manifest branch from 6f12a4e to b64302d Compare April 30, 2026 13:53

sdkennedy2 added 2 commits May 4, 2026 10:46

[APPS] Add @datadog/eslint-plugin-apps with valid-connections-file rule

5577541

Use named estree types and declare @types/estree as a direct dep

0e68960

sdkennedy2 force-pushed the sdkennedy2/eslint-plugin-apps branch from 9362c60 to 0e68960 Compare May 4, 2026 14:46

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[APPS] Add @datadog/eslint-plugin-apps with valid-connections-file rule#332

[APPS] Add @datadog/eslint-plugin-apps with valid-connections-file rule#332
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sdkennedy2 commented Apr 29, 2026 •

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		const basename = path.basename(context.filename);
		if (!CONNECTIONS_BASENAME_RE.test(basename)) {

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Motivation

Changes

Initial rule: valid-connections-file

Notable build details

QA Instructions

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sdkennedy2 commented Apr 29, 2026 •

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Initial rule: `valid-connections-file`