Ignore dependencies for namespaces that use/require themselves.

[ragnard]

This commit prevents a StackOverflowError that will occur when computing
transitive dependencies for a namespace that depends on itself.

Clojure currently allows namespace declarations that use/require itself:

(ns x
  (:require [x]))

ns-tracker adds these as dependencies in its graph but blows up with a StackOverflowError when calculating transitive dependencies.

This proposed fix simply ignores such dependencies, much like the clojure ns macro does.

Having self-referential namespaces is obviously wrong, but since the problem is not caught by the ns macro it is very hard to debug when it blows up in ns-tracker.

[ragnard]

This was problem was encountered again in the wild by a colleague of mine. Any chance of considering the patch?

[weavejester]

Rather than ignore the self-referential dependency, it might be better just to add a check to the precondition. This would make the system fail in a way that's easier to debug.

The change would also need a test.

[ragnard]

Thanks for the feedback. I've updated the patch to use a pre-condition and added tests.

I can't say I'm extremely fond of using pre-conditions in this case, since all the user of this library will see is:

java.lang.AssertionError: Assert failed: (not (= dep x))

which doesn't tell them anything about what they've done wrong and requires intimate knowledge of the ns-tracker library to understand.

[weavejester]

What about changing the preconditions into asserts with messages, e.g.

(assert (not (depends? graph dep x)) "circular dependency")
(assert (not (= x dep)) "self-referential dependency")

[ragnard]

I was very close to doing exactly that, but I didn't want to change too much. I think that's a slightly more user friendly solution. Pull request updated.

[weavejester]

Excellent, thanks

[ragnard]

Thank you for taking the time!