Support token substitution for pre-defined tokens on transformation

[gharirao]

One of the reasons for config file bloat is the addition of environment-specific transforms for config values that only differ by the environment name.

For e.g. the below config key in web.config

<add key="WebServiceUrl" value="http://devservice.example.com/ws" />

is repeated in web.systemtest.config as

<add key="WebServiceUrl" value="http://systemtestservice.example.com/ws" xdt:Locator="match(key)" xdt:Transform="Replace"  />

and in web.production.config as

<add key="WebServiceUrl" value="http://productionservice.example.com/ws" xdt:Locator="match(key)" xdt:Transform="Replace"  />

In this scenario, the config key in the base web.config can be converted to a tokenized string. The value for the token is input during the transformation process (can be a UI dialog for Preview Transform operation in VS, and command line args during the transformation process on build server) and is replaced during transformation appropriately.

So, the above e.g. would become

<add key="WebServiceUrl" value="http://{ENVIRONMENT}service.example.com/ws" />

in web.config and there would be no repetitions of this key in the environment-specific transforms. The {ENVIRONMENT} token would be replaced with the input value during transformation. The transformation process should be able to handle multiple token replacement (for e.g. with delimiter separated list of substitution values, like ENVIRONMENT:systemtest;USER:stuser; or similar).

The command-line Config Transform Tool (http://ctt.codeplex.com/) has similar functionality (http://outcoldman.com/en/archive/2010/09/09/config-transformation-tool-parameters-support/). Having this functionality in SlowCheetah would bring this to Visual Studio as well as the build process.

[sayedihashimi]

Great idea. If anyone out there want's to implement it I will provide guidance & review/merge the PR.