Adds a lookup for type files when generating the package.json

README.md

@@ -149,3 +149,9 @@ When installing locally, npm links bins into `node_modules/.bin`, which
 is in the `PATH` environ when npm runs scripts.  When
 installing globally, they are linked into `{prefix}/bin`, which is
 presumably in the `PATH` environment variable.
+
+### `types` and `flow` fields
+
+If you do not have a `types` or `flow` field, then it will check if 
+corresponding `*.d.ts` or `*.flow.js` files exist for your package
+entry file and add them to the `package.json`.

read-json.js

@@ -1,3 +1,4 @@
+/** @type {import("fs")} */
 var fs
 try {
   fs = require('graceful-fs')
@@ -25,7 +26,8 @@ readJson.extraSet = [
   readme,
   mans,
   bins,
-  githead
+  githead,
+  fillTypes
 ]
 
 var typoWarned = {}
@@ -437,6 +439,30 @@ function final (file, data, log, strict, cb) {
   })
 }
 
+function fillTypes (file, data, cb) {
+  var index = data.main ? data.main : 'index.js'
+  function switchExt (file, ext) {
+    var extless = path.join(path.dirname(file), path.dirname(file), path.basename(file, path.extname(file)))
+    return './' + extless + '.' + ext
+  }
+
+  var dts = switchExt(index, 'd.ts')
+  var dtsPath = path.join(path.dirname(file), dts)
+  var hasDTSFields = 'types' in data || 'typings' in data
+  if (!hasDTSFields && fs.existsSync(dtsPath)) {
+    data.types = dts
+  }
+
+  var flow = switchExt(index, 'flow.js')
+  var flowPath = path.join(path.dirname(file), flow)
+  var hasFlowField = 'flow' in data
+  if (!hasFlowField && fs.existsSync(flowPath)) {
+    data.flow = flow
+  }
+
+  cb(null, data)
+}
+
 function makePackageId (data) {
   var name = cleanString(data.name)
   var ver = cleanString(data.version)

test/fill-types.js

@@ -0,0 +1,57 @@
+const t = require('tap')
+const read = require('../')
+const { resolve } = require('path')
+
+t.test('adds types with a custom main field', t => {
+  const fixture = resolve(__dirname, 'fixtures/types/custom-dts/two-new-fields.json')
+  read(fixture, (er, data) => {
+    if (er) {
+      throw er
+    }
+    t.match(data, {
+      main: './custom-path.js',
+      types: './custom-path.d.ts',
+      flow: './custom-path.flow.js'
+    })
+    t.end()
+  })
+})
+
+t.test('handles the inferred index.js', t => {
+  const fixture = resolve(__dirname, 'fixtures/types/default-dts/inferred.json')
+  read(fixture, (er, data) => {
+    if (er) {
+      throw er
+    }
+    t.match(data, {
+      types: './index.d.ts'
+    })
+    t.end()
+  })
+})
+
+t.test('handles not overwriting existing fields', t => {
+  const fixture = resolve(__dirname, 'fixtures/types/with-field/has-types-field.json')
+  read(fixture, (er, data) => {
+    if (er) {
+      throw er
+    }
+    t.match(data, {
+      types: '@types/express',
+      flow: './index.flow.js'
+    })
+    t.end()
+  })
+})
+
+t.test('does not add types fields if not present', t => {
+  const fixture = resolve(__dirname, 'fixtures/readmes/package.json')
+  read(fixture, (er, data) => {
+    if (er) {
+      throw er
+    }
+    t.false(data.types, 'types field should not be added')
+    t.false(data.flow, 'flow field should not be added')
+    t.end()
+  })
+})

test/fixtures/types/custom-dts/custom-path.d.ts

@@ -0,0 +1 @@
+// Empty because implementation isn't important

test/fixtures/types/custom-dts/custom-path.flow.js

@@ -0,0 +1 @@
+// Empty because implementation isn't important

test/fixtures/types/custom-dts/two-new-fields.json

@@ -0,0 +1,5 @@
+{
+  "$schema": "https://json.schemastore.org/package",
+  "name": "two-new-fields",
+  "main": "./custom-path.js"
+}

test/fixtures/types/default-dts/index.d.ts

@@ -0,0 +1 @@
+// Empty because implementation isn't important

test/fixtures/types/default-dts/inferred.json

@@ -0,0 +1,4 @@
+{
+  "$schema": "https://json.schemastore.org/package",
+  "name": "no-main"
+}

test/fixtures/types/with-field/has-types-field.json

@@ -0,0 +1,5 @@
+{
+  "$schema": "https://json.schemastore.org/package",
+  "name": "has-types-reference",
+  "types": "@types/express"
+}

test/fixtures/types/with-field/index.flow.js

@@ -0,0 +1 @@
+// Empty because implementation isn't important