Developer specific app.config/web.config files in Visual Studio

Here a solution for web.config files and Visual Studio 2010:

1) Edit manually your web application .csproj file to add an AfterBuild Target like this:

  <Project>
   ...
    <Target Name="AfterBuild">
      <Copy SourceFiles="web.config" DestinationFiles="obj\$(Configuration)\tempweb.config" />
      <TransformXml Source="obj\$(Configuration)\tempweb.config"
                  Transform="web.$(USERNAME).config"
                  Destination="obj\$(Configuration)\tempweb2.config" />
      <ReadLinesFromFile File="obj\$(Configuration)\tempweb2.config"><Output TaskParameter="Lines" ItemName="TransformedWebConfig"/></ReadLinesFromFile>
      <ReadLinesFromFile File="web.config"><Output TaskParameter="Lines" ItemName="UnTransformedWebConfig"/></ReadLinesFromFile>
      <Copy Condition=" @(UnTransformedWebConfig) != @(TransformedWebConfig) " SourceFiles="obj\$(Configuration)\tempweb2.config" DestinationFiles="web.config" OverwriteReadOnlyFiles="True" />
    </Target>
  </Project>

This target will transform the Web.config file corresponding to the current developer logged in - hence the $(USERNAME) variable -, with the corresponding file created in 1). It will replace the local Web.config only if the content has changed (to avoid restart) at each build, even if the local Web.config is source controlled, that's why there is the OverwriteReadOnlyFiles is set to True. This point in fact is arguable.

2) Create a file named Web.[developer windows login].config for each developer in the project. (for example in the following screenshots I have two developers named smo and smo2):

These files (1 per developer) can/should be source-controlled. They should not be marked as dependent on the main Web.config beca

How about ignoring the file, so it never gets checked in? I've run into a similar issue and have added web.config to the ignore list in Subversion.

In TFS though, it's a little bit harder, see this post on how to do it.