[Version 5.0.0] Error: true is not a PostCSS plugin

[wang1212]

When I upgraded from v4.2.1 to v5.0.0, the following error occurred:

Error: true is not a PostCSS plugin

When I rolled back to v4.2.1, the error disappeared.

---

I use webpack and use postcss-loader to load the plugin:

• webpack ^4.44.2
• postcss-loader ^4.0.4
• postcss-flexbugs-fixes ^5.0.0

{
	loader: 'postcss-loader',
	options: {
		sourceMap: isEnvDevelopment,
		postcssOptions: {
			// Necessary for external CSS imports to work
			// https://github.com/facebook/create-react-app/issues/2677
			ident: 'postcss',
			plugins: [
				require('cssnano')({
					preset: 'default',
				}),
				require('postcss-flexbugs-fixes'),
				require('postcss-preset-env')({
					autoprefixer: {
						flexbox: 'no-2009',
					},
					stage: 3,
				}),
				// Adds PostCSS Normalize as the reset css with default options,
				// so that it honors browserslist config in package.json
				// which in turn let's users customize the target behavior as per their needs.
				postcssNormalize(),
			],
		},
	},
},

---

I checked the postcss-loader version changlelog, v4.0.4 supports loading postcss V8 api plugins, but I currently don’t understand why the above-mentioned error occurs?

---

I guess it may be related to the webpack version, I use webpack V5.4.0 and everything is normal.

[s100]

It may or may not be relevant that although postcss-flexbugs-fixes@5.0.0 uses postcss at run time, it does not specify a production dependency on any particular version of postcss. It does specify a development dependency on postcss@8, but a consumer running npm install postcss-flexbugs-fixes@5 will not see any particular version of postcss installed - and if there is a version of postcss already installed, postcss@7, say, it will stay where it is, and postcss-flexbugs-fixes@5 will try to use it, possibly leading to strange errors.

[luisrudge]

fixed in #74 - version 5.0.1