metosin/malli

malli.transform/-interceptor doesn’t support emptly-ish ?interceptor

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#596 opened on Dec 17, 2021

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 (2 comments) (0 reactions) (0 assignees)Clojure (1,724 stars) (237 forks)batch import
bughelp wanted

Description

https://github.com/metosin/malli/blob/152af3a3f8d59cca37a597b2403111bafbdee6ee/src/malli/transform.cljc#L36-L42

Hi,

I’m hitting a corner case with malli transform. I’m still trying to figure out why I’m hitting that corner case and what I can do to avoid that, but I think there’s also a robustness improvement that’s possible in malli.

When the keep function returns an empty list, the reduce function calls the anonymous function on line 38 with no arguments, and this fails.

One possible fix would be to make the anonymous function multi-arity and make it return nil when called with no arguments. Another possible fix would be to check the return value of keep, and only proceed with reducing it if it is a non-empty-list.

Contributor guide

Tech stack
None
Domain
backend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Clojure knowledgeBasic understanding of reduce
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Look at the file src/malli/transform.cljc lines 36-42. The anonymous function passed to reduce is called with no arguments when `keep` returns an empty list, causing a failure. Two possible fixes are suggested: make the anonymous function multi arity to return nil when called with no arguments, or check the return value of `keep` and only reduce if it is non empty. Review the surrounding code and choose the simpler approach.