Fix map file path creation

index.js

@@ -16,6 +16,7 @@ const reporter = require('postcss-reporter/lib/formatter')()
 
 const argv = require('./lib/args')
 const depGraph = require('./lib/depGraph')
+const getMapfile = require('./lib/getMapfile')
 
 let input = argv._
 const { dir, output } = argv
@@ -221,10 +222,7 @@ function css(css, file) {
             tasks.push(fs.outputFile(options.to, result.css))
 
             if (result.map) {
-              const mapfile = options.to.replace(
-                path.extname(options.to),
-                `${path.extname(options.to)}.map`
-              )
+              const mapfile = getMapfile(options.to)
               tasks.push(fs.outputFile(mapfile, result.map))
             }
           } else process.stdout.write(result.css, 'utf8')

lib/getMapfile.js

@@ -0,0 +1,8 @@
+'use strict'
+const path = require('path')
+
+module.exports = function getMapfile(p) {
+  const ext = path.extname(p)
+  const base = path.basename(p)
+  return p.replace(base, base.replace(ext, `${ext}.map`))
+}

test/map.js

@@ -5,6 +5,8 @@ import cli from './helpers/cli.js'
 import tmp from './helpers/tmp.js'
 import read from './helpers/read.js'
 
+import getMapfile from '../lib/getMapfile'
+
 test('inline maps are generated by default', async t => {
   const output = tmp('output.css')
 
@@ -53,3 +55,20 @@ test('--no-map disables internal sourcemaps', async t => {
 
   t.notRegex(await read(output), /\/*# sourceMappingURL=/)
 })
+
+test('mapFile path is property resolved', async t => {
+  const paths = [
+    {
+      input: '/foo/bar.css/baz/index.css',
+      want: '/foo/bar.css/baz/index.css.map'
+    },
+    {
+      input: '/foo/bar.sss/baz/index.sss',
+      want: '/foo/bar.sss/baz/index.sss.map'
+    }
+  ]
+
+  for (const p of paths) {
+    t.is(getMapfile(p.input), p.want)
+  }
+})