code: function clearCache (mainCompiler) {
    const childCompiler = getChildCompiler(mainCompiler);
    // If this childCompiler was already used
    // remove the entire childCompiler from the cache
    if (childCompiler.isCompiling() || childCompiler.didCompile()) {
      childCompilerCache.delete(mainCompiler);
    }
  }
docs: Remove the childCompiler from the cache
  
  @param {WebpackCompiler} mainCompiler