Generated js files have SyntaxError when enabling source map in webpack config

• I confirm that this is a issue rather than a question.

Bug report

When enabling source map in the configureWebpack option, the generated js files have SyntaxErrors. Comment the devtool: "source-map" line solves the problem.

Version

1.0.0-alpha.40

Steps to reproduce

git clone https://github.com/jjyyxx/vuepress-1367-repro.git
cd vuepress-1367-repro
npm run build

What is expected?

Generate valid code.

What is actually happening?

Uncaught SyntaxError: Unexpected token } happens in app.xxx.js.

Other relevant information

• Your OS: Windows 10 1809
• Node.js version: v11.4.0
• Browser version: Google Chrome v72.0.3626.119
• Is this a global or local install? local
• Which package manager did you use for the install? npm
• Does this issue occur when all plugins are disabled? yes

[jjyyxx]

@sinchang You misused lambda.

In

() => {
    devtool: 'source-map'
    // "devtool:" is an unused label
    // 'source-map' is an unused string literal expression
}

It is pretty valid javascript but may not be what you what to achieve. The correct way is

() => ({
  devtool: 'source-map'
})

which returns an object and fails as exprected.

[jjyyxx]

I found that the function workaroundEmptyStyleChunk caused this problem. https://github.com/vuejs/vuepress/blob/1850be7f343e54575c64d82c4f0cedc25a9aa91c/packages/%40vuepress/core/lib/build.js#L174-L190

The hack was introduced to address this issue. This snippet prepends styleChunkContent to appChunkContent and writes it back to app.[hash].js. When building chunks without sourcemap, each chunk ends with a semicolon (always?). So the prepending operation generates valid code.

BUT, if sourcemap is configured to be generated, webpack will append a comment line to the end of each js chunk, which breaks the precondition of each chunk ends with a semicolon, leading to invalid code after prepending.