prune-feature-flags.clj

This is a little babashka utility script to remove conditionals based on static mappings to their test forms.

• This blogpost explains the basic idea in a bit more detail.
• Take a look at prune-feature-flags.clj, there are less than 100 lines of code and about 30 of them are docstrings.
• Clone the repo and run ./prune-feature-flags.clj to see how the file in the example directory is transformed. (Contributions to make the example more interesting very welcome!)

From the prune-conditionals docstring:

With no test-lookup supplied this will transform code in the following way:

(prune-conditionals "(if true :a :b)")

the entire if form will get replaced by just :a since the else branch is effectively dead.

When supplying a test-lookup map this becomes more useful with real world code, in particular for removing code has become dead due to feature flags being changed. Example:

(prune-conditionals "(if (flag-one?) :a :b)"
                    {'(flag-one?) true})

In this example the transformation code will behave as if all instances of '(flag-one?) have been replaced by true.

Limitations

• it only works with if, when and their -not variants
• extra forms like and, not, or etc. are not detected and therefore conditionals using them are left untouched (unless one of you test-lookup forms has them)
• inconsistent namespace aliases could make specifying the test-lookup map a bit more cumbersome
• :refer-clojure :exclude [if when] and similar configurations could lead to unwanted results"