Expand clj-depend beyond cross-layer dependency analysis

[fabiodomingues]

clj-depend was initially created to be a namespace analyzer for the Clojure community, being a tool to help control dependencies between namespaces, which can be separate namespaces or namespaces belonging to a layer.

By priority, layer dependency analysis was the first feature, and it's working fine.

However, the delay in releasing other functionalities for layer-independent namespace analysis is causing people to look for alternative ways in tools other than clj-depend, which is a risk for the project in the long term.

[fabiodomingues]

Option 1)

{:source-paths #{,,,}
 :layers {,,,}
 :rules [{:doc                  "An integration test should not depend on ..."
          :defined-by           "integration\\..*"
          :should-not-depend-on #{'matcher-combinators.test
                                  "(?!integration).*-test"}}

         {:doc                  "An unit test should not depend on state-flow"
          :defined-by           "(?!integration).*-test"
          :should-not-depend-on #{"state-flow.*"}}

         {:doc                  "Specific namespace should not depend on ..."
          :namespaces           #{'foo.x}
          :should-not-depend-on #{'bar.x}}]}

• Does it make sense to make the should-not-depend-on attribute accept a single value, collection, or set?
• Is should-not-depend-on the best name for this attribute? Or is not-allowed better?

Assumptions:

• Namespace if it's a symbol
• Regex if it's a string

---

Option 2)

{:source-paths #{,,,}
 :layers {,,,}
 :rules [{:doc  "An integration test should not depend on...."
          :rule ["integration\\..*" :should-not-depend-on "matcher-combinators.test"]}]}

Compose the parts of the rule into a vector.

---

Option 3)

{:source-paths #{,,,}
 :layers {,,,}
 :rules [{:doc        "An integration test should not depend on...."
          :left       "integration\\..*"
          :condition  :should-not-depend-on
          :right      'matcher-combinators.test}]}

For lack of better names, I am representing left and right, as parts of an equation: x (left) should not depend on y (right).

---

Regardless of the option, clj-depend currently generates messages in the following format:
"foo.x" should not depend on "bar.x" (layer ":a" on ":b")

In this case where we don't have layers, the message will probably look like this (without the layer information at the end):
"foo.x" should not depend on "bar.x"

We also have the option of including text from the doc attribute to give more context:
"foo.x" should not depend on "bar.x" (An unit test should not depend on state-flow)

It may soon be interesting to address a way for people to be able to customize their own violation messages, so I created an issue #52 to discuss this issue separately.