[spec] Generic spec walking for clojure.spec

Problem

To do runtime coercion, specs need to be walked twice to strip away the branching information: s/conform + s/unform. This introduced extra latency (see the sample below).

Proposal

New versatile s/walk* to support generic spec walking.

Current status

• s/valid? allows us to do quickly check if a value conforms to a spec

  • https://dev.clojure.org/jira/browse/CLJ-2115 could help to return the errors in a single sweep.

• for coercion, we do s/conform + s/unform / s/explain

  • https://dev.clojure.org/jira/browse/CLJ-2116 would separate conforming from specs

Still, when running s/conform + s/unform, we walk the specs twice - which is performance-wise suboptimal. Below is a sample, with Late 2013 MacBook Pro with 2,5 GHz i7, with JVM running as -server.

Despite s/conform is relatively fast, we triple the latency in the sample when running also s/unform. As we know already that we are not interested in the branching info, we could just not emit those.

Suggestion

s/walk* to replace both s/confrom* and s/unform*, maybe even s/explain*. It would take extra mode argument, which would be a Keyword of one of the following:

• :validate - return false on first failing spec

• :conform - like the current s/conform*, maybe also return s/explain results?

• :unform - like the current s/unform*

• :coerce - s/conform* + s/unform*, could be optimized (e.g. if no branching info, just return the value)

The public apis could be remain the same (+ optional extra argument with CLJ-2116), and a new s/coerce to call the s/walk* with :coerce.

Results

Single sweep validation & coercion. Happy runtime.