Error: The "fileName" or "name" properties of emitted files must be strings that are neither absolute nor relative paths and do not contain invalid characters

I’m getting an error when I try to define a filename for the extract option.

postcss({
  extract: 'dist/test.css',
  …
})

v2.4.0:

[!] (plugin postcss) Error: The “fileName” or “name” properties of emitted files must be strings that are neither absolute nor relative paths and do not contain invalid characters, received “…/test.css”.

Works on v2.3.0.

[entenity]

It has not been fix this issue for 100 years

[halostatue]

This comment by @lukastaegert provides the full solution. What I had to do was:

13c05ebd 2020-04-29 | Fix issues with rollup-plugin-postcss (HEAD -> charge-purchase-history) [Austin Ziegler]

diff --git a/assets/rollup.config.js b/assets/rollup.config.js
index 1e976e0f..f1a365a1 100644
--- a/assets/rollup.config.js
+++ b/assets/rollup.config.js
@@ -60,13 +60,14 @@ const plugins = [
 ]
 
 function postcssPlugin(appType) {
-  return postcss({ extract: `${destination}/css/${appType}-app.css`, plugins: [autoprefixer] })
+  return postcss({ extract: `css/${appType}-app.css`, plugins: [autoprefixer] })
 }
 
 const employee = {
   input: 'src/employee-app.js',
   output: {
-    dir: `${destination}/js`,
+    dir: destination,
+    entryFileNames: 'js/[name].js',
     format: 'iife',
     sourcemap: !isProduction ? 'inline' : false,
   },
@@ -76,7 +77,8 @@ const employee = {
 const customer = {
   input: 'src/customer-app.js',
   output: {
-    dir: `${destination}/js`,
+    dir: destination,
+    entryFileNames: 'js/[name].js',
     format: 'iife',
     sourcemap: !isProduction ? 'inline' : false,
   },

This works perfectly.