"yarn build" fails to build in Windows 10

What?

yarn build on Windows 10 fails to build (while yarn dev runs smoothly).

How to reproduce the error

Run the following command

yarn build

Detailed Error Message

PS C:\misc\sources\Github\pr\reactjs.org> yarn build                                                                                                                                      
yarn run v1.12.1                                                                                                                                                                          
$ gatsby build                                                                                                                                                                            
success open and validate gatsby-config — 0.005 s                                                                                                                                         
success load plugins — 0.223 s                                                                                                                                                            
success onPreInit — 0.931 s                                                                                                                                                               
success delete html and css files from previous builds — 0.183 s                                                                                                                          
success initialize cache — 0.009 s                                                                                                                                                        
success copy gatsby files — 0.333 s                                                                                                                                                       
success onPreBootstrap — 0.021 s                                                                                                                                                          
success source and transform nodes — 0.663 s                                                                                                                                              
success building schema — 0.384 s                                                                                                                                                         
success createPages — 0.347 s                                                                                                                                                             
success createPagesStatefully — 0.041 s                                                                                                                                                   
success onPreExtractQueries — 0.015 s                                                                                                                                                     
success update schema — 0.171 s                                                                                                                                                           
success extract queries from components — 0.144 s                                                                                                                                         
success run graphql queries — 0.197 s — 69/69 353.97 queries/second                                                                                                                       
success write out page data — 0.031 s                                                                                                                                                     
success write out redirect data — 0.012 s                                                                                                                                                 
success onPostBootstrap — 0.001 s                                                                                                                                                         
                                                                                                                                                                                          
info bootstrap finished - 5.941 s                                                                                                                                                         
                                                                                                                                                                                          
success Building production JavaScript and CSS bundles — 5.190 s                                                                                                                          
                                                                                                                                                                                          
error Building static HTML for pages failed                                                                                                                                               
                                                                                                                                                                                          
See our docs page on debugging HTML builds for help https://goo.gl/yL9lND                                                                                                                 
                                                                                                                                                                                          
   5 |          function __webpack_require__(moduleId) {                                                                                                                                  
   6 |                                                                                                                                                                                    
>  7 |                  // Check if module is in cache                                                                                                                                    
     | ^                                                                                                                                                                                  
   8 |                  if(installedModules[moduleId]) {                                                                                                                                  
   9 |                          return installedModules[moduleId].exports;                                                                                                                
  10 |                  }                                                                                                                                                                 
                                                                                                                                                                                          
                                                                                                                                                                                          
  WebpackError: C:\misc\sources\Github\pr\reactjs.org\public\C:\misc\sources\Github\pr\reactjs.org\examples\16-3-release-blog-post\context-example contains invalid WIN32 path characters.
                                                                                                                                                                                          
  - bootstrap:7 Object.mkdirs                                                                                                                                                             
    lib/webpack/bootstrap:7:1                                                                                                                                                             
                                                                                                                                                                                          
  - universalModuleDefinition:5 Object.mkdirs                                                                                                                                             
    lib/webpack/universalModuleDefinition:5:1                                                                                                                                             
                                                                                                                                                                                          
  - bootstrap:9 pathExists                                                                                                                                                                
    lib/webpack/bootstrap:9:1                                                                                                                                                             
                                                                                                                                                                                          
  - bootstrap:12 fn.apply.then.r                                                                                                                                                          
    lib/webpack/bootstrap:12:1                                                                                                                                                            
                                                                                                                                                                                          
                                                                                                                                                                                          
error Command failed with exit code 1.                                                                                                                                                    
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.                                                                                                      

Error Demo

Following image shows that yarn dev runs without an issue while yarn build fails.

Environment

• Fork: https://github.com/dance2die/reactjs.org
• Yarn version: 1.12.1
• Node version: 10.1.0
• Git version: 2.17.1.windows.2
• OS
  

yarn build のエントリポイントから始め、Windows 10 上での Gatsby の静的 HTML ビルド中に発生する失敗を再現します。報告された無効な WIN32 パスを Webpack のビルド出力とパス処理に沿って追跡します。Windows 上で本番ビルドが正常に完了し、yarn dev が引き続き動作すれば完了です。