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wtf is 11.19.20-kotlin-1.4.20-bug?

skevy/11.19.20-kotlin-1.4.20-bug — explained in plain English

Analysis updated 2026-07-17 · repo last pushed 2020-11-19

★ 2KotlinAudience · developerComplexity · 1/5DormantSetup · easy

TL;DR

A minimal reproduction repo documenting a type-inference bug in Kotlin 1.4.20, created to help the Kotlin team diagnose and fix the compiler issue.

Mindmap

mindmap
  root((repo))
    What it does
      Reproduces a bug
      Isolates the problem
    Tech stack
      Kotlin
    Use cases
      Report compiler bug
      Check known issues
      Find a workaround
    Audience
      Kotlin maintainers
      Kotlin developers
    Bug details
      Type inference
      Kotlin 1.4.20
    Fix
      Upgrade Kotlin
      Restructure code

Code map

Detail Auto

An interactive map of this repo's files and how they connect — its source is parsed live in your browser. Click Visualize to build it.

filefunction / class

Why would anyone build with this?

REASON 1

Check whether a confusing Kotlin 1.4.20 compile error matches this known type-inference bug.

REASON 2

Reference this minimal example when reporting or discussing the bug with the Kotlin team.

REASON 3

Find a workaround by seeing exactly what code pattern triggers the incorrect type inference.

What's in the stack?

Kotlin

How it stacks up

skevy/11.19.20-kotlin-1.4.20-bugyingwang/filmicad-chd/decloud
Stars223
LanguageKotlinKotlinKotlin
Last pushed2020-11-192026-04-26—
MaintenanceDormantMaintained—
Setup difficultyeasymoderateeasy
Complexity1/53/53/5
Audiencedevelopergeneralgeneral

Figures from each repo's GitHub metadata at analysis time.

How do you spin it up?

Difficulty · easy Time to first run · 5min

Not a library, a minimal bug reproduction case for the Kotlin compiler.

Yoink these prompts

Prompt 1
Explain what type-inference bug this Kotlin 1.4.20 reproduction is demonstrating.
Prompt 2
Help me rewrite this code to avoid triggering the Kotlin 1.4.20 type-inference bug.
Prompt 3
Show me whether this bug still exists in newer versions of Kotlin.
Prompt 4
Walk me through how Kotlin's type inference is supposed to work versus what goes wrong here.

Frequently asked questions

wtf is 11.19.20-kotlin-1.4.20-bug?

A minimal reproduction repo documenting a type-inference bug in Kotlin 1.4.20, created to help the Kotlin team diagnose and fix the compiler issue.

What language is 11.19.20-kotlin-1.4.20-bug written in?

Mainly Kotlin. The stack also includes Kotlin.

Is 11.19.20-kotlin-1.4.20-bug actively maintained?

Dormant — no commits in 2+ years (last push 2020-11-19).

How hard is 11.19.20-kotlin-1.4.20-bug to set up?

Setup difficulty is rated easy, with roughly 5min to a first successful run.

Who is 11.19.20-kotlin-1.4.20-bug for?

Mainly developer.

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