It's well known that shadowing core Clojure vars can lead to unexpected bugs. In
fact, it's a common source of bugs in other languages too. In the status-mobile
repository there are, in total, 562 shadowed vars, ~500 are core vars. Excluding
the "old code" we still have 285 offenders.
In status-mobile I've already seen two bugs caused by shadowed vars, both with
the shadowed var "name". But probably other problems happened in the past, and
others will happen in the future if we don't do something about this. This PR is
also my response to my frustration trying to review PRs and checking for
shadowed vars, humans were not meant for that!
In this commit we are enabling ":shadowed-var" to lint certain (not all) core
vars as errors (not warnings). In future PRs we can gradually unshadow more
vars. For the record, name is shadowed 40 times in the new code and 130 in
total, and type is shadowed 93 times in the new code and 124 in total!
What about non-core vars, should we allow shadowing? There are ~70 non-core
shadowed vars. In my opinion, we should also lint and disallow shadowing
non-core vars, since it may cause the same kind of bugs of shadowing core vars.
But this decision can be left for another moment/issue, after we have fixed the
most prominent problem of shadowing core vars.
Which vars are unshadowed in this PR? I fixed 62 errors and unshadowed
cljs.core/iter, cljs.core/time, cljs.core/count, cljs.core/key,
clojure.core/key.
Resources:
- [clj-kondo linter: shadowed-var](https://github.com/clj-kondo/clj-kondo/blob/master/doc/linters.md#shadowed-var)
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