refactor: stop probing emptiness with Object.keys(obj).length (#9548)

`Object.keys(obj).length` allocates a full key array when callers only need to know whether data exists. Replace those probes with producer-owned presence state, `undefined` for absent results, and existing API absence signals, preserving the distinction between absent and populated data without a consumer-side allocation.

A narrow `no-restricted-syntax` rule catches the pattern only in boolean/test positions, leaving genuine counts valid. Explicit exceptions remain for arbitrary user-defined keys and copy paths where separate presence tracking would change existing semantics.

Author: BridgeAR

eslint.config.mjs

@@ -107,6 +107,37 @@ const GLOBAL_RESTRICTED_REQUIRES = [
   },
 ]
 
+const SRC_RESTRICTED_SYNTAX = [
+  {
+    // Inline `.evaluate(<fn>)` callbacks (Playwright/Puppeteer) are serialized with
+    // `toString()` and run in chromium — coverage counters inside would ReferenceError.
+    selector:
+      "CallExpression[callee.property.name='evaluate']" +
+      ":matches([arguments.0.type='ArrowFunctionExpression'], [arguments.0.type='FunctionExpression'])",
+    message:
+      'Move the inline `.evaluate(...)` callback into a `*-browser-scripts.js` file ' +
+      '(NYC-excluded in nyc.config.js) and import it here.',
+  },
+  {
+    // Static-analysis bundlers (esbuild, webpack, rollup) only see literals as require
+    // arguments; once any transform (e.g. NYC) wraps them, this shape breaks bundling.
+    selector: "CallExpression[callee.name='require'][arguments.0.type='ConditionalExpression']",
+    message: 'Use `cond ? require(\'a\') : require(\'b\')` instead of `require(cond ? \'a\' : \'b\')`.',
+  },
+]
+
+// Matches only probe positions; a genuine count (`writeMapPrefix(Object.keys(x).length)`) must stay allowed.
+const OBJECT_KEYS_LENGTH_PROBE = {
+  selector:
+    ':matches(BinaryExpression[right.value=0], BinaryExpression[left.value=0], UnaryExpression[operator="!"],' +
+    ' IfStatement, ConditionalExpression, LogicalExpression, WhileStatement, DoWhileStatement)' +
+    " > MemberExpression[property.name='length']" +
+    " > CallExpression[callee.object.name='Object'][callee.property.name='keys']",
+  message: 'Do not probe emptiness with `Object.keys(obj).length`; the keys array is allocated on every call. ' +
+    'Track presence with a boolean at the assignment site, probe a known key (`obj.field !== undefined`), or ' +
+    'return `undefined` when there is nothing to report instead of an empty object.',
+}
+
 export default [
   {
     name: 'dd-trace/global-ignore',
@@ -643,21 +674,7 @@ export default [
       'eslint-rules/eslint-prefer-set-service-name': 'error',
       'eslint-rules/eslint-timer-unref': 'error',
 
-      'no-restricted-syntax': ['error', {
-        // Inline `.evaluate(<fn>)` callbacks (Playwright/Puppeteer) are serialized with
-        // `toString()` and run in chromium — coverage counters inside would ReferenceError.
-        selector:
-          "CallExpression[callee.property.name='evaluate']" +
-          ":matches([arguments.0.type='ArrowFunctionExpression'], [arguments.0.type='FunctionExpression'])",
-        message:
-          'Move the inline `.evaluate(...)` callback into a `*-browser-scripts.js` file ' +
-          '(NYC-excluded in nyc.config.js) and import it here.',
-      }, {
-        // Static-analysis bundlers (esbuild, webpack, rollup) only see literals as require
-        // arguments; once any transform (e.g. NYC) wraps them, this shape breaks bundling.
-        selector: "CallExpression[callee.name='require'][arguments.0.type='ConditionalExpression']",
-        message: 'Use `cond ? require(\'a\') : require(\'b\')` instead of `require(cond ? \'a\' : \'b\')`.',
-      }],
+      'no-restricted-syntax': ['error', ...SRC_RESTRICTED_SYNTAX],
 
       'n/no-restricted-require': ['error', [
         ...GLOBAL_RESTRICTED_REQUIRES,
@@ -793,6 +810,16 @@ export default [
       'unicorn/prefer-optional-catch-binding': 'error',
     },
   },
+  {
+    name: 'dd-trace/packages/src',
+    files: [
+      'packages/*/src/**/*.js',
+      'packages/*/src/**/*.mjs',
+    ],
+    rules: {
+      'no-restricted-syntax': ['error', ...SRC_RESTRICTED_SYNTAX, OBJECT_KEYS_LENGTH_PROBE],
+    },
+  },
   {
     name: 'dd-trace/config-sync',
     files: [

packages/datadog-instrumentations/src/cucumber.js

@@ -116,7 +116,7 @@ let pickleByFile = {}
 const pickleResultByFile = {}
 
 let skippableSuites = []
-let skippableSuitesCoverage = {}
+let skippableSuitesCoverage
 let skippedSuitesCoverage = {}
 let itrCorrelationId = ''
 let isForcedToRun = false
@@ -153,12 +153,6 @@ function isValidKnownTests (receivedKnownTests) {
   return !!receivedKnownTests.cucumber
 }
 
-function hasSkippableSuitesCoverage () {
-  return skippableSuitesCoverage &&
-    typeof skippableSuitesCoverage === 'object' &&
-    Object.keys(skippableSuitesCoverage).length > 0
-}
-
 function isTiaCoverageBackfillEnabled () {
   return isItrEnabled && isCoverageReportUploadEnabled
 }
@@ -172,7 +166,7 @@ function shouldReportCodeCoverageLinesPct (hasBackfilledCoverage) {
 }
 
 function getSkippedSuitesCoverageForRun () {
-  return isSuitesSkipped && isTiaCoverageBackfillEnabled() && hasSkippableSuitesCoverage()
+  return isSuitesSkipped && isTiaCoverageBackfillEnabled() && skippableSuitesCoverage !== undefined
     ? skippableSuitesCoverage
     : {}
 }
@@ -188,7 +182,7 @@ function getCucumberTestSessionCoverageFiles () {
 
 function resetSuiteSkippingRunState () {
   skippableSuites = []
-  skippableSuitesCoverage = {}
+  skippableSuitesCoverage = undefined
   skippedSuitesCoverage = {}
   skippedSuites = []
   isSuitesSkipped = false
@@ -1143,7 +1137,7 @@ function getWrappedStart (start, frameworkVersion, isParallel = false, isCoordin
 
       errorSkippableRequest = skippableResponse.err
       skippableSuites = skippableResponse.skippableSuites ?? []
-      skippableSuitesCoverage = skippableResponse.skippableSuitesCoverage ?? {}
+      skippableSuitesCoverage = skippableResponse.skippableSuitesCoverage
 
       if (!errorSkippableRequest) {
         const filteredPickles = isCoordinator

packages/datadog-instrumentations/src/fastify.js

@@ -146,6 +146,7 @@ function wrapHookDone (ctx, request, reply, req, name, doneCallback) {
     ctx.error = error
     publishError(ctx)
 
+    // eslint-disable-next-line no-restricted-syntax -- arbitrary cookie names; publishing {} sets a WAF address
     const hasCookies = request.cookies && Object.keys(request.cookies).length > 0
 
     if (cookieParserReadCh.hasSubscribers && hasCookies && !cookiesPublished.has(req)) {
@@ -193,6 +194,7 @@ function preHandler (request, reply, done) {
   const res = getRes(reply)
   const ctx = { req, res }
 
+  // eslint-disable-next-line no-restricted-syntax -- arbitrary body keys; publishing {} sets a WAF address
   const hasBody = request.body && Object.keys(request.body).length > 0
 
   // For multipart/form-data, the body is not available until after preValidation hook

packages/datadog-instrumentations/src/jest.js

@@ -112,7 +112,7 @@ const jestSessionState = (globalThis[JEST_SESSION_STATE] ||= {})
 const RETRY_TIMES = Symbol.for('RETRY_TIMES')
 
 let skippableSuites = []
-let skippableSuitesCoverage = {}
+let skippableSuitesCoverage
 let skippedSuitesCoverage = {}
 let knownTests = {}
 let isCodeCoverageEnabled = false
@@ -133,7 +133,7 @@ let isTestManagementTestsEnabled = false
 let testManagementTests = {}
 let testManagementAttemptToFixRetries = 0
 let isImpactedTestsEnabled = false
-let modifiedFiles = {}
+let modifiedFiles
 let repositoryRoot
 let lastCoverageMap
 let lastCoverageMapRootDir
@@ -690,8 +690,7 @@ function getWrappedEnvironment (BaseEnvironment, jestVersion) {
 
       if (this.isImpactedTestsEnabled) {
         try {
-          const hasImpactedTests = Object.keys(modifiedFiles).length > 0
-          this.modifiedFiles = hasImpactedTests ? modifiedFiles : this.testEnvironmentOptions._ddModifiedFiles
+          this.modifiedFiles = modifiedFiles ?? this.testEnvironmentOptions._ddModifiedFiles
         } catch (e) {
           log.error('Error parsing impacted tests', e)
           this.isImpactedTestsEnabled = false
@@ -2491,12 +2490,6 @@ function getRepositoryRootFromTest (test, fallbackRootDir) {
   return getRepositoryRootFromConfig(test?.context?.config, fallbackRootDir)
 }
 
-function hasSkippableSuitesCoverage () {
-  return skippableSuitesCoverage &&
-    typeof skippableSuitesCoverage === 'object' &&
-    Object.keys(skippableSuitesCoverage).length > 0
-}
-
 function shouldCollectJestCoverageForTia () {
   return shouldReportJestSuiteCoverageForTia() ||
     (isJestCoverageBackfillSupported && isItrEnabled && isCoverageReportUploadEnabled)
@@ -2607,7 +2600,7 @@ function resetLibraryConfiguration () {
   testManagementTests = {}
   testManagementAttemptToFixRetries = 0
   isImpactedTestsEnabled = false
-  modifiedFiles = {}
+  modifiedFiles = undefined
   repositoryRoot = undefined
 }
 
@@ -2629,13 +2622,14 @@ function applySuiteSkipping (originalTests, rootDir, frameworkVersion) {
 
   isSuitesSkipped ||= jestSuitesToRun.suitesToRun.length !== originalTests.length
   numSkippedSuites += jestSuitesToRun.skippedSuites.length
-  skippedSuitesCoverage = isSuitesSkipped && isTiaCoverageBackfillEnabled() && hasSkippableSuitesCoverage()
+  const hasSkippableSuitesCoverage = skippableSuitesCoverage !== undefined
+  skippedSuitesCoverage = isSuitesSkipped && isTiaCoverageBackfillEnabled() && hasSkippableSuitesCoverage
     ? skippableSuitesCoverage
     : {}
   coverageBackfillContexts = isSuitesSkipped && isTiaCoverageBackfillEnabled()
     ? getTestContexts(originalTests)
     : undefined
-  coverageBackfillFiles = isSuitesSkipped && isTiaCoverageBackfillEnabled() && hasSkippableSuitesCoverage()
+  coverageBackfillFiles = isSuitesSkipped && isTiaCoverageBackfillEnabled() && hasSkippableSuitesCoverage
     ? getCoverageBackfillFiles(skippableSuitesCoverage, repositoryRoot, getTestSuitePath)
     : undefined
 
@@ -3024,10 +3018,10 @@ function getCliWrapper (isNewJestVersion) {
             skippableSuitesCoverage: receivedSkippableSuitesCoverage,
           } = skippableSuitesResponse || await getChannelPromise(skippableSuitesCh)
           if (err) {
-            skippableSuitesCoverage = {}
+            skippableSuitesCoverage = undefined
           } else {
             skippableSuites = receivedSkippableSuites
-            skippableSuitesCoverage = receivedSkippableSuitesCoverage || {}
+            skippableSuitesCoverage = receivedSkippableSuitesCoverage
           }
           skippedSuitesCoverage = {}
         } catch (err) {

packages/datadog-instrumentations/src/mocha/main.js

@@ -92,7 +92,7 @@ let suitesToSkip = []
 let isSuitesSkipped = false
 let areAllSuitesSkipped = false
 let skippedSuites = []
-let skippableSuitesCoverage = {}
+let skippableSuitesCoverage
 let skippedSuitesCoverage = {}
 let itrCorrelationId = ''
 let isForcedToRun = false
@@ -203,12 +203,6 @@ function getFilteredSuites (originalSuites) {
   }, { suitesToRun: [], skippedSuites: new Set(), suitesToSkipForRun })
 }
 
-function hasSkippableSuitesCoverage () {
-  return skippableSuitesCoverage &&
-    typeof skippableSuitesCoverage === 'object' &&
-    Object.keys(skippableSuitesCoverage).length > 0
-}
-
 function isTiaCoverageBackfillEnabled () {
   return config.isItrEnabled && config.isCoverageReportUploadEnabled
 }
@@ -239,7 +233,7 @@ function shouldReportCodeCoverageLinesPct (hasBackfilledCoverage) {
 }
 
 function getSkippedSuitesCoverageForRun () {
-  return isSuitesSkipped && isTiaCoverageBackfillEnabled() && hasSkippableSuitesCoverage()
+  return isSuitesSkipped && isTiaCoverageBackfillEnabled() && skippableSuitesCoverage !== undefined
     ? skippableSuitesCoverage
     : {}
 }
@@ -257,7 +251,7 @@ function resetSuiteSkippingRunState () {
   isSuitesSkipped = false
   areAllSuitesSkipped = false
   skippedSuites = []
-  skippableSuitesCoverage = {}
+  skippableSuitesCoverage = undefined
   skippedSuitesCoverage = {}
   untestedCoverage = undefined
   config.repositoryRoot = undefined
@@ -927,11 +921,11 @@ function getExecutionConfiguration (runner, isParallel, frameworkVersion, onFini
     } = response || {}
     if (!response || err) {
       suitesToSkip = []
-      skippableSuitesCoverage = {}
+      skippableSuitesCoverage = undefined
     } else {
       suitesToSkip = skippableSuites
       itrCorrelationId = responseItrCorrelationId
-      skippableSuitesCoverage = responseSkippableSuitesCoverage || {}
+      skippableSuitesCoverage = responseSkippableSuitesCoverage
     }
     if (localSuites) {
       suitesToSkip = getSuitesToSkipFromPaths(localSuites)

packages/datadog-instrumentations/src/router.js

@@ -596,6 +596,7 @@ const visitedParams = new WeakSet()
 function wrapHandleRequest (original) {
   return function wrappedHandleRequest (...args) {
     const req = args[0]
+    // eslint-disable-next-line no-restricted-syntax -- arbitrary param names; publishing {} sets a WAF address
     if (routerParamStartCh.hasSubscribers && !visitedParams.has(req.params) && Object.keys(req.params).length) {
       visitedParams.add(req.params)
 
@@ -635,6 +636,7 @@ function wrapParam (original) {
     args[1] = shimmer.wrapFunction(args[1], (originalFn) => {
       return function wrappedFn (...fnArgs) {
         const req = fnArgs[0]
+        // eslint-disable-next-line no-restricted-syntax -- arbitrary param names; publishing {} sets a WAF address
         if (routerParamStartCh.hasSubscribers && Object.keys(req.params).length && !visitedParams.has(req.params)) {
           visitedParams.add(req.params)
 

packages/datadog-plugin-azure-functions/src/index.js

@@ -156,7 +156,7 @@ function setSpanLinks (triggerType, tracer, span, ctx) {
     : triggerMetadata.propertiesArray
 
   const addLinkFromProperties = (props) => {
-    if (!props || Object.keys(props).length === 0) return
+    if (!props) return
     const spanContext = tracer.extract('text_map', props)
     if (spanContext) {
       span.addLink({ context: spanContext })

packages/datadog-plugin-cypress/src/cypress-plugin.js

@@ -477,7 +477,7 @@ class CypressPlugin {
   testsToSkip = []
   skippedTests = []
   skippedTestIds = new Set()
-  skippableTestsCoverage = {}
+  skippableTestsCoverage
   testSessionCoverageMap = createCoverageMap()
   hasForcedToRunSuites = false
   hasUnskippableSuites = false
@@ -566,7 +566,7 @@ class CypressPlugin {
     this.testsToSkip = []
     this.skippedTests = []
     this.skippedTestIds = new Set()
-    this.skippableTestsCoverage = {}
+    this.skippableTestsCoverage = undefined
     this.testSessionCoverageMap = createCoverageMap()
     this.hasForcedToRunSuites = false
     this.hasUnskippableSuites = false
@@ -679,17 +679,6 @@ class CypressPlugin {
     return this.repositoryRoot || this.rootDir || process.cwd()
   }
 
-  /**
-   * Returns whether the backend supplied skipped-test coverage data.
-   *
-   * @returns {boolean}
-   */
-  hasSkippableTestsCoverage () {
-    return !!(this.skippableTestsCoverage &&
-      typeof this.skippableTestsCoverage === 'object' &&
-      Object.keys(this.skippableTestsCoverage).length > 0)
-  }
-
   /**
    * Returns whether skipped test coverage should be backfilled into the session coverage map.
    *
@@ -699,7 +688,7 @@ class CypressPlugin {
     return this.isItrEnabled &&
       this.isCoverageReportUploadEnabled &&
       this.isTestsSkipped &&
-      this.hasSkippableTestsCoverage()
+      this.skippableTestsCoverage !== undefined
   }
 
   /**
@@ -1162,7 +1151,7 @@ class CypressPlugin {
       } else {
         const { skippableTests, correlationId, skippableTestsCoverage } = skippableTestsResponse
         this.testsToSkip = skippableTests || []
-        this.skippableTestsCoverage = skippableTestsCoverage || {}
+        this.skippableTestsCoverage = skippableTestsCoverage
         this.itrCorrelationId = correlationId
         incrementCountMetric(TELEMETRY_ITR_SKIPPED, { testLevel: 'test' }, this.testsToSkip.length)
       }

packages/datadog-plugin-openai-agents/src/integration.js

@@ -498,6 +498,7 @@ class OpenAIAgentsIntegration {
 
     this.#tagger.tagTextIO(ddSpan, inputValue, outputValue)
 
+    // eslint-disable-next-line no-restricted-syntax -- agents-core builds metadata before the plugin receives it
     if (info.metadata && Object.keys(info.metadata).length > 0) {
       this.#tagger.tagMetadata(ddSpan, info.metadata)
     }