vercel/next.js · error

Invalid file type {:?}

Error message

Invalid file type {:?}

What it means

JsonSource::content() loads a JSON file (typically package.json) and extracts a specific sub-key (e.g. the 'postcss' field). When the requested key is not present in the parsed JSON object, it bails with 'Invalid file type {:?}'. Note the message text is misleading — file_type is always File at this point; the real condition is a missing JSON key. A second occurrence (line 336) fires for genuinely non-file entry types (directories, symlinks).

Source

Thrown at turbopack/crates/turbopack-node/src/transforms/postcss.rs:323

    }
}

#[turbo_tasks::value_impl]
impl Asset for JsonSource {
    #[turbo_tasks::function]
    async fn content(&self) -> Result<Vc<AssetContent>> {
        let file_type = &*self.path.get_type().await?;
        match file_type {
            FileSystemEntryType::File => {
                let json = if self.allow_json5 {
                    self.path.read_json5().content().await?
                } else {
                    self.path.read_json().content().await?
                };
                let value = match &*self.key.await? {
                    Some(key) => {
                        let Some(value) = json.get(&**key) else {
                            anyhow::bail!("Invalid file type {:?}", file_type)
                        };
                        value
                    }
                    None => &*json,
                };
                Ok(AssetContent::file(
                    FileContent::Content(File::from(value.to_string())).cell(),
                ))
            }
            FileSystemEntryType::NotFound => {
                Ok(AssetContent::File(FileContent::NotFound.resolved_cell()).cell())
            }
            _ => bail!("Invalid file type {:?}", file_type),
        }
    }
}

#[turbo_tasks::function]

View on GitHub (pinned to 0ae8c72462)

Solutions

1. Add the expected key (e.g. "postcss": {}) to package.json, or point the config search at a dedicated postcss.config.js.
2. Verify the configured PostCSS config path resolves to a regular file, not a directory.
3. If the key is intentionally absent, remove the package.json from the config-search candidates.

Example fix

// before: package.json has no postcss field
{ "name": "app", "dependencies": {} }

// after
{ "name": "app", "postcss": {}, "dependencies": {} }

// Before pointing the PostCSS loader at package.json, confirm the key exists.
const fs = require('fs');
function ensureJsonKey(file, key) {
  const json = JSON.parse(fs.readFileSync(file, 'utf8'));
  if (!(key in json)) throw new Error(`${file} is missing required key "${key}"`);
}
ensureJsonKey('./package.json', 'postcss');

When it happens

Trigger: A package.json is selected as a PostCSS config source and a key (e.g. 'postcss') is requested, but that key does not exist in the JSON object. Also when the resolved path is a directory or symlink rather than a regular file.

Common situations: A monorepo where package.json exists but lacks a 'postcss' field yet is still picked up by the config search; renaming or removing the postcss config key while the loader still targets package.json; a config path resolving to a directory.

Related errors

• `forbidden()` is experimental and only allowed to be enabled
• `unauthorized()` is experimental and only allowed to be used
• NEXT_EXPORT_ERROR
• Failed to resolve pattern "${patterns.join(',')}": ${error.m
• The key "${key}" under "env" in ${config.configFileName || '

AI-assisted analysis of vercel/next.js@0ae8c72462 (2026-08-06). Data as JSON: /api/errors/0395285e64c32cd1. Report an issue: GitHub.