chore: Coverage for signal-exit handler. (#1190)

This allows us to record coverage for all code called from the
signal-exit handler.

index.js

@@ -25,9 +25,16 @@ const util = require('util')
 
 const debugLog = util.debuglog('nyc')
 
+let selfCoverageHelper
+
 /* istanbul ignore next */
 if (/self-coverage/.test(__dirname)) {
-  require('../self-coverage-helper')
+  selfCoverageHelper = require('../self-coverage-helper')
+} else {
+  // Avoid additional conditional code
+  selfCoverageHelper = {
+    onExit () {}
+  }
 }
 
 function coverageFinder () {
@@ -323,11 +330,15 @@ class NYC {
   }
 
   _wrapExit () {
+    selfCoverageHelper.registered = true
+
     // we always want to write coverage
     // regardless of how the process exits.
     onExit(
-      /* istanbul ignore next: the callback is run but coverage is not recorded */
-      () => this.writeCoverageFile(),
+      () => {
+        this.writeCoverageFile()
+        selfCoverageHelper.onExit()
+      },
       { alwaysLast: true }
     )
   }

self-coverage-helper.js

@@ -5,16 +5,25 @@ const fs = require('fs')
 const mkdirp = require('make-dir')
 const onExit = require('signal-exit')
 
-onExit(function () {
-  var coverage = global.___NYC_SELF_COVERAGE___
-  if (typeof ___NYC_SELF_COVERAGE___ === 'object') coverage = ___NYC_SELF_COVERAGE___
-  if (!coverage) return
+module.exports = {
+  registered: false,
+  onExit () {
+    const coverage = ___NYC_SELF_COVERAGE___
 
-  var selfCoverageDir = path.join(__dirname, '.self_coverage')
-  mkdirp.sync(selfCoverageDir)
-  fs.writeFileSync(
-    path.join(selfCoverageDir, process.pid + '.json'),
-    JSON.stringify(coverage),
-    'utf-8'
-  )
+    const selfCoverageDir = path.join(__dirname, '.self_coverage')
+    mkdirp.sync(selfCoverageDir)
+    fs.writeFileSync(
+      path.join(selfCoverageDir, process.pid + '.json'),
+      JSON.stringify(coverage),
+      'utf-8'
+    )
+  }
+}
+
+onExit(() => {
+  if (module.exports.registered) {
+    return
+  }
+
+  module.exports.onExit()
 })